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Craseoschema Ravara & Aguado gen. nov. urn:lsid:zoobank.org:act: 28EA7F9D-30BF-408B-A133-2B2F38EA924E Type species Craseoschema thyasiricola gen. et sp. nov., by present designation and monotypy. Diagnosis Body long, tapering posteriorly, arched dorsally and flattened ventrally. Prostomium short, with one pair of cirriform antennae with basal swelling and one pair of pad-like palps, without eyes. First segment fused with prostomium, with dorsal and ventral cirri, neuroacicula and neuropodial chaetae. Anterior parapodia with dorsal and ventral cirri and compound neurochaetae. Median and posterior parapodia subbiramous, with dorsal and ventral cirri, simple notochaetae and compound neurochaetae. All chaetae with modified tips. Pygidium cylindrical, without appendages. Etymology The genus name is a combination of the Greek words ‘ krasis ’, meaning ‘mixture’ or ‘combination’, and ‘ schema ’, meaning ‘characteristic’ or ‘figure’, in an allusion to the mixed characteristics from the symbiont and free-living forms. Remarks The subfamily Calamyzinae includes symbiont and free-living forms, the majority of which are associated with chemosynthetic environments. These forms have different morphological characteristics in a clear adaptation to their life style. The new genus is based on a specimen found inside a thyasirid bivalve and presents all the characteristics of a symbiont form (arched body, poorly developed notopodia with short dorsal cirri, neurochaetae with modified tips, absence of pygidial cirri), but also some characteristics of the free-living forms (presence of pad-like palps, notochaetae and compound neurochaetae). This particular combination of characteristics makes it different from all other genera within Calamyzinae except for a recently described new genus, Spathochaeta Jimi et al., 2019, found on the body surface of an octopus from the Kumano Sea, Japan (Jimi et al. 2019). Spathochaeta and Craseoschema gen. nov. present a similar composition of characters: arched body, a pair of ventrally placed palps, notochaetae with modified tips, compound neurochaetae and pygidial cirri absent. However, they differ by the presence in Spathochaeta of a well-developed dorsal lobe in the notopodia and spinigerous neurochaetae, rather than falcigerous with modified tips. The genus Calamyzas, parasites of ampharetid polychaetes, also possesses compound neurochaetae but notochaetae are absent and the parapodia of the first chaetiger are reduced to a pair of ventral cirri. Craseoschema gen. nov. is similar to the freeliving genera (Vigtorniella Kiseleva, 1996, Boudemos Watson et al., 2016 and Micospina Watson et al., 2016) in the possession of notochaetae and compound neurochaetae, but differs in details of noto- and neurochaetal morphology and in lacking tentacular and anal cirri. The separation of Craseoschema gen. nov. from the other Calamyzinae is also evident in the phylogenetic analysis presented (Fig. 2). Craseoschema gen. nov. is placed together with the symbiont forms of Calamyzinae in a monophyletic group, although this is not strongly supported (Fig. 2).

Craseoschema Ravara & Aguado gen. nov. urn:lsid:zoobank.org:act: 28EA7F9D-30BF-408B-A133-2B2F38EA924E Type species Craseoschema thyasiricola gen. et sp. nov., by present designation and monotypy. Diagnosis Body long, tapering posteriorly, arched dorsally and flattened ventrally. Prostomium short, with one pair of cirriform antennae with basal swelling and one pair of pad-like palps, without eyes. First segment fused with prostomium, with dorsal and ventral cirri, neuroacicula and neuropodial chaetae. Anterior parapodia with dorsal and ventral cirri and compound neurochaetae. Median and posterior parapodia subbiramous, with dorsal and ventral cirri, simple notochaetae and compound neurochaetae. All chaetae with modified tips. Pygidium cylindrical, without appendages. Etymology The genus name is a combination of the Greek words ‘ krasis ’, meaning ‘mixture’ or ‘combination’, and ‘ schema ’, meaning ‘characteristic’ or ‘figure’, in an allusion to the mixed characteristics from the symbiont and free-living forms. Remarks The subfamily Calamyzinae includes symbiont and free-living forms, the majority of which are associated with chemosynthetic environments. These forms have different morphological characteristics in a clear adaptation to their life style. The new genus is based on a specimen found inside a thyasirid bivalve and presents all the characteristics of a symbiont form (arched body, poorly developed notopodia with short dorsal cirri, neurochaetae with modified tips, absence of pygidial cirri), but also some characteristics of the free-living forms (presence of pad-like palps, notochaetae and compound neurochaetae). This particular combination of characteristics makes it different from all other genera within Calamyzinae except for a recently described new genus, Spathochaeta Jimi et al., 2019, found on the body surface of an octopus from the Kumano Sea, Japan (Jimi et al. 2019). Spathochaeta and Craseoschema gen. nov. present a similar composition of characters: arched body, a pair of ventrally placed palps, notochaetae with modified tips, compound neurochaetae and pygidial cirri absent. However, they differ by the presence in Spathochaeta of a well-developed dorsal lobe in the notopodia and spinigerous neurochaetae, rather than falcigerous with modified tips. The genus Calamyzas, parasites of ampharetid polychaetes, also possesses compound neurochaetae but notochaetae are absent and the parapodia of the first chaetiger are reduced to a pair of ventral cirri. Craseoschema gen. nov. is similar to the freeliving genera (Vigtorniella Kiseleva, 1996, Boudemos Watson et al., 2016 and Micospina Watson et al., 2016) in the possession of notochaetae and compound neurochaetae, but differs in details of noto- and neurochaetal morphology and in lacking tentacular and anal cirri. The separation of Craseoschema gen. nov. from the other Calamyzinae is also evident in the phylogenetic analysis presented (Fig. 2). Craseoschema gen. nov. is placed together with the symbiont forms of Calamyzinae in a monophyletic group, although this is not strongly supported (Fig. 2)., Published as part of Ravara, Ascensão, Aguado, M. Teresa, Rodrigues, Clara F., Génio, Luciana & Cunha, Marina R., 2019, Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species, pp. 1-21 in European Journal of Taxonomy 539 on page 12, DOI: 10.5852/ejt.2019.539, http://zenodo.org/record/3353542, {"references":["Jimi N., Moritaki T. & Kajihara H. 2019. Polychaete meets octopus: symbiotic relationship between Spathochaeta octopodis gen. et sp. nov. (Annelida: Chrysopetalidae) and Octopus sp. (Mollusca: Octopodidae). Systematics and Biodiversity 17 (1): 1 - 6. https: // doi. org / 10.1080 / 14772000.2018.1520753","Watson C., Carvajal J. I., Sergeeva N. G., Pleijel F. & Rouse G. W. 2016. Free-living calamyzin chrysopetalids (Annelida) from methane seeps, anoxic basins, and whale falls. Zoological Journal of the Linnaen Society 177 (4): 700 - 719. https: // doi. org / 10.1111 / zoj. 12390"]}

Craseoschema thyasiricola Ravara & Aguado sp. nov. urn:lsid:zoobank.org:act: 146CA9DD-11B3-46F0-81A8-2E6B085458C0 Figs 3–5 Diagnosis Chaetous neuropodia and dorsal and ventral cirri present on the first segment. Notopodial lobes poorly developed. Notochaetae stick-like, with denticulated tips. Neurochaetae compound, with serrated blades and denticulated tips. Etymology The species name is derived from the host bivalve genus Thyasira, with the Latin suffix -cola denoting ‘inhabiting’. Material examined Holotype PORTUGAL • 1 af, 1 pf, several mf; Gulf of Cadiz, Carlos Ribeiro mud volcano; 35°47.238′ N, 08°25.272′ W; 2200 m; specimen found inside mantle cavity of Thyasira vulcolutre (Bivalvia, Thyasiridae); St TTR16_AT615; ANEA NHMUK 2019.7339 • 2 mf; same locality; 1 slide and 1 SEM stub; DBUA 0002275. Description Only one fragmented specimen was found, inside the mantle cavity of a bivalve of the species Thyasira vulcolutre Rodrigues & Oliver, 2008. The anterior fragment has three chaetigers, the posterior nine chaetigers; largest median fragment with seventeen chaetigers, 5.82 mm long. Body elongate, tapering at anterior and posterior ends, arched dorsally and flattened ventrally, rectangular in crosssection (Fig. 5A). Colour in ethanol white. Prostomium very short, broadly rounded anteriorly, fused to first chaetiger (Figs 3A, 4A). Eyes absent. Paired antennae cirriform, with basal swelling, inserted dorsolaterally (Figs 3A, 4A). Palps as low mound structures, inserted ventrally just anterior to mouth (Fig. 3B). Pharynx strongly muscularised; jaws not examined (specimen not dissected in order to keep its integrity as holotype). Parapodia much shorter on first segment than on following ones (Fig. 3A–B). Dorsal and ventral cirri digitiform, present from first chaetiger. Notopodia clearly present from segment 4, rounded, with straight notoacicula and dorsal cirri inserted distally; neuropodia much longer and conical, neuroacicula with bent tips (Fig. 4D), ventral cirri inserted close to base (Figs 3 C–D, 4B, 5B). Notochaetae simple, stick-like, laddered basally, with a few rows of small spines subdistally, and ending in blunt and slightly curved tips with several denticles (only visible in SEM; Figs 3E, 5 C–D); absent in first three segments, up to 15 present in median and posterior segments; a single notochaeta in last segments. Neurochaetae compound falcigers, with long, laddered shafts and short, finely serrated blades (Figs 3 F–G, 4E, 5E–H). Neurochaetae longer in dorsalmost position, gradually shortening ventrally, and present in greater numbers than notochaetae in all segments. Blades of dorsalmost neurochaetae with two rows of longitudinal spines and numerous denticles distally, with a worn appearance under compound microscope (Fig. 5 E–F); blades of ventralmost neurochaetae with longer spines arranged in two longitudinal rows that are wider apart distally, resembling a spaghetti-spoon (Fig. 5 G–H). Pygidium button-like, with terminal anus and no appendages (Fig. 4C). Remarks Carlos Ribeiro is the deepest and most active mud volcano among the five mud volcanoes from where chrysopetalid specimens are recorded in this study. Two species of thyasirid bivalves, Thyasira vulcolutre (3 specimens) and T. obsoleta (Verrill & Bush, 1898) (1 specimen), were collected in the crater of this mud volcano (Rodrigues et al. 2008), but only one large specimen of T. vulcolutre was infested. This thyasirid species was also reported to occur in higher abundance on Captain Arutyunov MV (37 spms) and Sagres MV (32 spms). These mud volcanoes were also reported as active cold seeps in the deepwater field, but none of the small-sized specimens collected from them (at depths of 1321 m and 1562 m, respectively) were infested. In the Gulf of Cadiz, Thyasiridae are represented by nine species collected from 10 different mud volcanoes, but only two are recognized as chemosymbiotic and both occur in MVs of the Deep Field: Thyasira vulcolutre (Captain Arutyunov, Sagres and Carlos Ribeiro MVs) and Spinaxinus sentosus Oliver & Holmes, 2006 (Captain Arutyunov MV) (Rodrigues et al. 2013). Another two species are mixotrophic and occur across a wider bathymetric range: Axinulus croulinensis (Jeffreys, 1847) (Mercator, Meknès, Captain Arutyunov, Bonjardim and Porto MVs; 350–3900 m) and Thyasira granulosa (Monterosato, 1874) (Mercator, Meknès, Chechaouen, Darwin and Captain Arutyunov MVs; 350–1321 m) (Rodrigues et al. 2013 and unpublished data). Except for the large specimen of T. vulcolutre from Carlos Ribeiro MV, all the other thyasirid specimens were not infested. Ecology and distribution NE Atlantic (Gulf of Cadiz), on Carlos Ribeiro MV, at a depth of 2200 m. Found in the mantle cavity of the chemosynthesis-based bivalve Thyasira vulcolutre Rodrigues & Oliver, 2008.

Craseoschema thyasiricola Ravara & Aguado sp. nov. urn:lsid:zoobank.org:act: 146CA9DD-11B3-46F0-81A8-2E6B085458C0 Figs 3–5 Diagnosis Chaetous neuropodia and dorsal and ventral cirri present on the first segment. Notopodial lobes poorly developed. Notochaetae stick-like, with denticulated tips. Neurochaetae compound, with serrated blades and denticulated tips. Etymology The species name is derived from the host bivalve genus Thyasira, with the Latin suffix -cola denoting ‘inhabiting’. Material examined Holotype PORTUGAL • 1 af, 1 pf, several mf; Gulf of Cadiz, Carlos Ribeiro mud volcano; 35°47.238′ N, 08°25.272′ W; 2200 m; specimen found inside mantle cavity of Thyasira vulcolutre (Bivalvia, Thyasiridae); St TTR16_AT615; ANEA NHMUK 2019.7339 • 2 mf; same locality; 1 slide and 1 SEM stub; DBUA 0002275. Description Only one fragmented specimen was found, inside the mantle cavity of a bivalve of the species Thyasira vulcolutre Rodrigues & Oliver, 2008. The anterior fragment has three chaetigers, the posterior nine chaetigers; largest median fragment with seventeen chaetigers, 5.82 mm long. Body elongate, tapering at anterior and posterior ends, arched dorsally and flattened ventrally, rectangular in crosssection (Fig. 5A). Colour in ethanol white. Prostomium very short, broadly rounded anteriorly, fused to first chaetiger (Figs 3A, 4A). Eyes absent. Paired antennae cirriform, with basal swelling, inserted dorsolaterally (Figs 3A, 4A). Palps as low mound structures, inserted ventrally just anterior to mouth (Fig. 3B). Pharynx strongly muscularised; jaws not examined (specimen not dissected in order to keep its integrity as holotype). Parapodia much shorter on first segment than on following ones (Fig. 3A–B). Dorsal and ventral cirri digitiform, present from first chaetiger. Notopodia clearly present from segment 4, rounded, with straight notoacicula and dorsal cirri inserted distally; neuropodia much longer and conical, neuroacicula with bent tips (Fig. 4D), ventral cirri inserted close to base (Figs 3 C–D, 4B, 5B). Notochaetae simple, stick-like, laddered basally, with a few rows of small spines subdistally, and ending in blunt and slightly curved tips with several denticles (only visible in SEM; Figs 3E, 5 C–D); absent in first three segments, up to 15 present in median and posterior segments; a single notochaeta in last segments. Neurochaetae compound falcigers, with long, laddered shafts and short, finely serrated blades (Figs 3 F–G, 4E, 5E–H). Neurochaetae longer in dorsalmost position, gradually shortening ventrally, and present in greater numbers than notochaetae in all segments. Blades of dorsalmost neurochaetae with two rows of longitudinal spines and numerous denticles distally, with a worn appearance under compound microscope (Fig. 5 E–F); blades of ventralmost neurochaetae with longer spines arranged in two longitudinal rows that are wider apart distally, resembling a spaghetti-spoon (Fig. 5 G–H). Pygidium button-like, with terminal anus and no appendages (Fig. 4C). Remarks Carlos Ribeiro is the deepest and most active mud volcano among the five mud volcanoes from where chrysopetalid specimens are recorded in this study. Two species of thyasirid bivalves, Thyasira vulcolutre (3 specimens) and T. obsoleta (Verrill & Bush, 1898) (1 specimen), were collected in the crater of this mud volcano (Rodrigues et al. 2008), but only one large specimen of T. vulcolutre was infested. This thyasirid species was also reported to occur in higher abundance on Captain Arutyunov MV (37 spms) and Sagres MV (32 spms). These mud volcanoes were also reported as active cold seeps in the deepwater field, but none of the small-sized specimens collected from them (at depths of 1321 m and 1562 m, respectively) were infested. In the Gulf of Cadiz, Thyasiridae are represented by nine species collected from 10 different mud volcanoes, but only two are recognized as chemosymbiotic and both occur in MVs of the Deep Field: Thyasira vulcolutre (Captain Arutyunov, Sagres and Carlos Ribeiro MVs) and Spinaxinus sentosus Oliver & Holmes, 2006 (Captain Arutyunov MV) (Rodrigues et al. 2013). Another two species are mixotrophic and occur across a wider bathymetric range: Axinulus croulinensis (Jeffreys, 1847) (Mercator, Meknès, Captain Arutyunov, Bonjardim and Porto MVs; 350–3900 m) and Thyasira granulosa (Monterosato, 1874) (Mercator, Meknès, Chechaouen, Darwin and Captain Arutyunov MVs; 350–1321 m) (Rodrigues et al. 2013 and unpublished data). Except for the large specimen of T. vulcolutre from Carlos Ribeiro MV, all the other thyasirid specimens were not infested. Ecology and distribution NE Atlantic (Gulf of Cadiz), on Carlos Ribeiro MV, at a depth of 2200 m. Found in the mantle cavity of the chemosynthesis-based bivalve Thyasira vulcolutre Rodrigues & Oliver, 2008., Published as part of Ravara, Ascensão, Aguado, M. Teresa, Rodrigues, Clara F., Génio, Luciana & Cunha, Marina R., 2019, Description of a new genus and species of Chrysopetalidae (Annelida: Polychaeta) from the NE Atlantic, with some further records of related species, pp. 1-21 in European Journal of Taxonomy 539 on pages 13-16, DOI: 10.5852/ejt.2019.539, http://zenodo.org/record/3353542, {"references":["Rodrigues C. F., Oliver P. G. & Cunha M. R. 2008. Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic). Zootaxa 1752: 41 - 56. Available from https: // www. mapress. com / j / zt / article / view / 4731 [accessed 5 Jul. 2019].","Rodrigues C. F., Hilario A. & Cunha M. R. 2013. Chemosymbiotic species from the Gulf of Cadiz (NE Atlantic): distribution, life styles and nutritional patterns. Biogeosciences 10: 2569 - 2581. https: // doi. org / 10.5194 / bg- 10 - 2569 - 2013"]}

Thyasira tortuosa (Jeffreys, 1881) (Fig. 27) Material examined. One live-collected specimen, TTR 16 cruise, station AT 622 Gr, Porto mud volcano, Gulf of Cadiz, 35 �� 33.773 N, 09�� 30.416 W, 3902 m, 3 June 2006 (DBUA 00830.01). Remarks. The only specimen examined is provisionally identified as Thyasira tortuosa and has the characteristically compressed and anteriorly expanded outline noted by Payne and Allen (1991). The shell from Gulf of Cadiz (5.5 mm) is much larger than any of the shells described by these authors (3.2 mm) and comes from a greater depth: 3902m whilst the maximum given by Payne & Allen (1991) was 2359 m. Dufour (2005) did not examine this species but the Gulf of Cadiz specimen has a Type 2 gill with both demibranchs. The gills are rather thick and have the same appearance as the ones that exhibit strong bacterial symbiosis such as T. flexu osa and T. gouldi., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 50, DOI: 10.5281/zenodo.274249, {"references":["Jeffreys, J. G. (1881) On the Mollusca procured during the H. M. S. \" Lightning \" and \" Porcupine \" expedition (Part 3). Proceedings of the Zoological Society of London (1881), 693 - 724.","Payne, C. M. & Allen, J. A. (1991) The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London B, 334, 481 - 562.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}

Thyasira (Parathyasira) granulosa (Monterosato, 1874) (Figs 24 & 25) Material examined. All from Gulf of Cadiz; two live-collected specimens, MSM01-03, stn 241 GKG 12, Mercator mud volcano, 35 �� 17.918 'N, 06�� 38.717 'W, 353 m, 6 May 2006 (DBUA 00828.01); one live-collected specimen MSM01-03, stn 242 GKG 13, same locality, 35 �� 17.870 'N, 06�� 38.810 'W, 350 m, 6 May 2006 (DBUA 00828.02); one live-collected specimen, MSM01-03, stn 321 GKG 22, Mekn��s mud volcano, 34 �� 58.796 'N, 07��04.394'W, 732 m, 14 May 2006 (DBUA 00828.03); one live-collected specimen, TTR 16 cruise, station AT 610 Gr, Chechaouen mud volcano, 35 �� 28.468 N, 07�� 15.477 W, 1177 m, 30 May 2006 (DBUA 00829.01). Remarks. This species is readily identified by the radially arranged granular striations on the shell surface. It is widely distributed in the Mediterranean and northeastern Atlantic from 100 to 1800 m (Oliver & Killeen 2002). Dufour (2005) classified this as having Type 2 gills with both demibranchs present but lacking bacterial symbionts., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 49, DOI: 10.5281/zenodo.274249, {"references":["Monterosato, T. A. (1874) Recherches conchyliologiques, effectuees au Cap Santo Vito, en Sicile. (Traduz. dall'italiano di H. Crosse). Journal de Conchyliologie, 22 (3), 243 - 282.","Oliver, P. G. & Killeen, I. J. (2002) The Thyasiridae (Mollusca: Bivalvia) of the British Continental Shelf and North Sea Oilfields. An Identification Manual. Studies in Marine Biodiversity and Systematics from the National Museum of Wales, BIOMOR Reports, 3, 1 - 73.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}

Leptaxinus minutus Verrill & Bush, 1898 (Fig. 30) Material examined. All from Gulf of Cadiz; two live-collected specimens, MSM01-03, stn 242 GKG 13, Mercator mud volcano, 35 �� 17.870 'N, 06�� 38.810 'W, 350 m, 6 May 2006 (DBUA 00835.01); one live-collected specimen, TTR 16, stn AT 608 Gr, Darwin mud volcano, 35 �� 23.531 N, 07�� 11.475 W, 1115 m, 30 May 2006 (DBUA 00836.01); two live-collected specimens, TTR 16, stn AT 604 Gr, Yuma mud volcano, 35 �� 25.820 N, 07�� 06.330W, 1030 m, 29 May 2006 (DBUA 00836.02). PLATE 4. Figures 24���25: Thyasira (Parathyasira) granulosa (Monterosato, 1874), Fig. 24 stn 321 GKG 22, Mekn��s mud volcano, 732 m (DBUA 00828.03), Fig. 25 stn 242 GKG 13, Mercator mud volcano, 350 m (DBUA 00828.02); Fig. 26 Thyasira obsoleta (Verrill & Bush, 1898) stn 190 MUC 8, Captain Arutyunov mud volcano, 1322 m, (DBUA 00831.02); Fig. 27 Thyasira tortuosa (Jeffreys, 1881) AT 622 Gr, Porto mud volcano, 3902 m (DBUA 00830.01); Fig. 28 Axinulus croulinensis (Jeffreys, 1847) stn 242 GKG 13, Mercator mud volcano, 350 m (DBUA 00832.02); Fig. 29 Mendicula ferruginosa (Forbes, 1844) stn AT 575 B, Mercator mud volcano, 355 m (DBUA 000834.01); Fig. 30 Leptaxinus minutus Verrill & Bush, 1898, stn AT 608 Gr, Darwin mud volcano, 1115 m (DBUA 00836.01). Remarks. Leptaxinus minutus is rather tumid with a distinctly angular posterior outline but lacking a posterior sinus. The hinge is well developed with weak lateral folds and a tubercular cardinal. It was described from the northwest Atlantic and has been recorded from Norway and Iceland (Ockelmann in Oliver & Killeen 2002). The Gulf of Cadiz specimens agree well with the shell figured by Oliver and Killeen (2002, Pl. 25 C, D) but comes from a much greater depth. Dufour (2005) did not examine this species but the Gulf of Cadiz specimens have a Type 2 gill with a single demibranch and according to similar forms described by this author, it will doubtfully be symbiotic., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on pages 50-52, DOI: 10.5281/zenodo.274249, {"references":["Verrill, A. E. & Bush K. J. (1898) Revision of the deep-water Mollusca of the Atlantic coast of North America, with descriptions of new genera and species. Proceedings of the United States National Museum, 20, 775 - 901.","Monterosato, T. A. (1874) Recherches conchyliologiques, effectuees au Cap Santo Vito, en Sicile. (Traduz. dall'italiano di H. Crosse). Journal de Conchyliologie, 22 (3), 243 - 282.","Jeffreys, J. G. (1881) On the Mollusca procured during the H. M. S. \" Lightning \" and \" Porcupine \" expedition (Part 3). Proceedings of the Zoological Society of London (1881), 693 - 724.","Jeffreys, J. G. (1847) Additional notices on British shells. Annals and Magazine of Natural History, 20, 16 - 19.","Forbes, E. (1844) Report on the Mollusca and Radiata of the Aegean sea, and on their distribution, considered as bearing on geology. Reports of the British Association for the Advancement of Science (1843), 130 - 193.","Oliver, P. G. & Killeen, I. J. (2002) The Thyasiridae (Mollusca: Bivalvia) of the British Continental Shelf and North Sea Oilfields. An Identification Manual. Studies in Marine Biodiversity and Systematics from the National Museum of Wales, BIOMOR Reports, 3, 1 - 73.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}

Genus Thyasira Leach ms in Lamarck, 1818 Type species. Tellina flexuosa Montagu, 1803 Generic Definition. Fragile shells, subcircular, ovate to ovate-polygonal in outline with a posterior sulcus; escutcheon variably expressed, absent to deep, with or without an auricle producing a submarginal sulcus. Hinge teeth lacking or as a single ���cardinal��� tubercle, ligament sunken. Anterior adductor scar elongate, posterior adductor scar ovate, pallial line entire. Ctenidium with two demibranchs, lateral body pouches large and multilobed, foot vermiform, heel obsolete, toe developed., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 43, DOI: 10.5281/zenodo.274249

Thyasira vulcolutre sp. nov. Rodrigues CF & Oliver PG (Figs 2���23) Material examined. Holotype: one live-collected specimen, MSM01-03 stn 217 GKG 10, Captain Arutyunov mud volcano, Gulf of Cadiz, 35 �� 39.643 'N, 07�� 20.046 'W, 1321 m, 30 April 2006, M.R. Cunha (NMW.Z.2007.3.1). Paratypes: 24 live-collected specimens as holotype. (NMW.Z.2007.3.2- 3; USNM 1110226, DBUA 00826.01). Other material: All from Gulf of Cadiz; nine live-collected specimens, MSM01-03, stn 246 / 274 BIGO 3, Captain Arutyunov mud volcano, 35 �� 39.738 'N, 07�� 20.010 'W, 1321 m, 10 May 2006 (NMW.Z.2007.3.4- 6, DBUA 00826.02); one live-collected specimen, TTR 10, stn AT 243 G, Carlos Ribeiro mud volcano, 35 �� 47.217 'N, 08�� 25.313 'W, 2200 m, 26 July 2000 (DBUA 00827.01); one shell, TTR 16, stn AT 615 Gr, Carlos Ribeiro mud volcano, 35 �� 47.238,N, 08�� 25.272 ���W, 2200 m (NMW.Z.2007.3.7). Description. Measurements: Holotype, length 17.0 mm, height 16.5 mm, tumidity 10.4 mm. Summary statistics of morphometric ratios are presented in Table 1. Shell (Figs 2���11): To 17.2 mm in length; thin shelled; equivalve; subequilateral, beaks slightly in front of the midline, pointed prosogyrate. Relatively tumid but variable, (Length:Tumidity ratio 1.3: 1 to 1.9: 1, mean 1.6: 1). Outline typically subcircular, with length similar to height, some specimens with length greater than height (see variation below). Lunule margin incurved, long. Anterior dorsal margin narrowly curved, ventral margin broadly curved. Posterior sinus distinct but shallow, submarginal sinus distinct. Posterior dorsal margin more or less straight. Posterior sulcus shallow but distinct, submarginal sulcus shallow but with a sharp, well-defined margin. Auricle elevated but low and very long almost filling the entire escutcheon. Ligament visible for most of the length of the auricle (Escutcheon:auricle ratio 1.1: 1 to 1.5: 1, mean 1.3: 1). Lunule shallowly sunken, cordate, broad. Hinge plate narrow, lacking clearly defined teeth. Ligament long, sunken. Sculpture concentric, of lines and relatively regular narrow ridges. Radial lines visible in some, but are not surface features but are reflected inside the shell by numerous radial striations. Pallial line entire. Anterior adductor scar long; posterior adductor scar oval. Periostracum very thin, pale, greyish brown. Va r ia ti on: The outline is variable (Figs 8���10), this variability generally increases with the size of shell, and is reflected mostly in the disproportionate increase in tumidity in the largest size classes. The expression of the lunule is highly variable and is probably related to the variation in shell tumidity. Anatomy: Mantle edge fused posteriorly between termination of gill axis and posterior adductor; exhalant siphonal opening simple, margins smooth (Fig. 13). Labial palps small, with indistinct sorting ridges. Posterior ventral mantle edge with a glandular area on its inner side (Fig. 16). Ventral mantle edge with a distinct median fold (Fig. 17). Anterior inhalant aperture with an elongate glandular area on its inner side (Fig. 14); ventral side of anterior adductor muscle with a digitate sensory papilla (Figs 14, 15). Ctenidium large, of outer and inner demibranchs, both as thick fleshy lamellae (Fig. 12). Outer demibranchs about 2 / 3 size of inner demibranchs. Foot elongate, vermiform (Fig. 12), with a muscular ring at the junction with the visceral mass; heel indistinct. Visceral mass, lateral body pouches large, extensively lobed (Figs 12, 18). Lobes flat-ended, roughly cuboidal. Lobes arise from large, single orifice at base of stomach (Figs 19, 20). Stomach cylindrical in a transverse longitudinal orientation; midgut a simple tight loop and lies over stomach before looping posteriorly into the straight hindgut and rectum (Fig. 20). Kidneys large (Fig. 19), with dense aggregations of crystalline granules and a yellow/white fibrous mass in the lumen. Note. Dissection of the holotype revealed an identical gross structure to that described above but the ctenidia were thin and semi-transparent and the lateral body pouches were greatly contracted (Fig. 21). The kidney was extensively stained dark brown and was massively infested with a fibrous mass and crystalline granules (Figs 22, 23). PLATE 1. Thyasira vulcolutre sp. nov.; Figs 2���5 Holotype, NMW.Z.2007.3.1; Figs 6 & 7 Juvenile shells, NMW.Z.2007.3.2- 3; Figs 8���10 variations in shells form, NMW.Z.2007.3.4- 6; Fig. 11 large shell, NMW.Z.2007.3.7. PLATE 2. Thyasira vulcolutre sp. nov., NMW.Z.2007.3.4- 6. Gross anatomy after removal of the right shell and mantle. Fig. 12 whole view; Fig. 13 enlarged view of area A, the posterior exhalant aperture; Fig. 14 enlarged view of area B, the anterior inhalant aperture; Fig. 15 detail of the sensory papilla; Fig. 16 enlarged view of area C, the posterior ventral area; Fig. 17 enlarged view of area D, the median ventral mantle edge. PLATE 3. Figures 18���20: Thyasira vulcolutre sp. nov., NMW.Z.2007.3.4- 6. Fig. 18 Gross anatomy after removal of right shell, mantle and ctenidium; Fig. 19 Gross anatomy after removal of right mantle, ctenidium and lateral body pouch; Fig 20 Dissection of the alimentary system; Figures 21���23. Thyasira vulcolutre sp. nov. Holotype, NMW.Z.2007.3.1; Fig. 21 Gross anatomy after removal of right shell and mantle; Fig. 22 kidney as viewed through the epithelial tissues; Fig. 23 Kidney dissected showing crystalline granules and fibrous mass in lumen. Distribution. Most of the specimens were collected on the Captain Arutyunov mud volcano, some specimens were also collected on Carlos Ribeiro mud volcano; depth range between 1300 and 2200 m. Etymology. Vulcolutre, Latin combination of vulcano from ���volcano���, lutum from ���mud���; suffix tre denoting ���belonging to���. Remarks. Species comparisons: This new species is morphologically similar to Thyasira sarsi (Philippi, 1845), T. southwardae Oliver & Holmes, 2006, T. oleophila Clarke, 1989 and T. methanophila Oliver & Sellanes, 2005 all known to be associated with chemosynthetic sites. Thyasira striata Sturany, 1896 has also been recorded from mud volcanoes in the eastern Mediterranean (Olu-Le Roy et al. 2004) but that species has a very distinct posterior sulcus and is more similar to the T. flexuosa group than to the above taxa. Thyasira sarsi has been reported from methane seeps in the North Sea (Dando et al. 1994) but is also known from vegetation-derived organic-rich environments in Norwegian fjords (Southward 1986). Thyasira sarsi differs by having a weakly developed posterior sulcus, a submarginal sulcus without a sharp, clearly defined margin and the lunule not so depressed and heart-shaped. Thyasira sarsi also possesses shell sculpture without concentric ridges and with a distinctly granular surface (see Oliver & Holmes 2006). Thyasira southwardae has been reported only from the Logatchev hydrothermal vent in association with Bathymodiolus and Calyptogena. Only two shells and one valve of this species have been collected, making comparisons difficult but it is clear that the shells of T. vulcolutre and T. southwardae are similar. The shells of T. southwardae (see Oliver & Holmes 2006) are thinner and have irregular sculpture of concentric lines and corrugations and never display the regular concentric ridges typical of T. vulcolutre. The definition of the submarginal sulcus is not so sharp in T. southwardae and the submarginal sinus and posterior sinus are not so pronounced. From the anatomy, the gills of T. southwardae were pink in contrast to the light brown in T. vulcolutre. Thyasira oleophila was described from the Louisiana oil and gas seeps at depths around 500 m. It is a large species reaching 22.0 mm in length and is almost devoid of a posterior sulcus, is not expanded anteriorly and has a strongly granular surface (see Oliver & Holmes 2006). Thyasira methanophila Oliver & Sellanes, 2005 was described from a methane seepage area off Concepcion, Chile at bathyal depths. Thyasira methanophila differs from T. vulcolutre in that the lunule is not sunken, and the escutcheon is less defined. From morphology alone, a new genus could be proposed for the group of species similar to T. vulcolutre, including T. methanophila, T. southwardae, T. sarsi and T. oleophila but this is not wholly supported by the molecular data. An 18 S rRNA gene Neighbour Joining tree (not shown) combining an unpublished sequence from Thyasira vulcolutre with previously published sequences from thyasirids analyzed by Taylor, Williams and Glover (2007) shows that T. vulcolutre is clustered with T. perplicata Salas, 1996 and is distant from T. methanophila and T. sarsi. (S Williams and JD Taylor pers. comm.). Payne and Allen (1991) described T. perplicata under the name T. excavata plicata (Verrill, 1885) as having a shell with a strong posterior carina and thus most similar to shells of the genus Conchocele. Anatomically T. perplicata is also similar to Conchocele with a bulbous tipped foot, large fleshy gills and prominent anterior mantle edge folds (Nakazima, 1958; Kamenev et al. 2001). The lack of congruence between morphology and molecular data may be clarified once a larger set of taxa are included but until this study is completed the genus Thyasira is retained for the majority of species with sulcate shells, with two demibranchs and that are chemoautotrophic. Functional morphology: The functional morphology is essentially similar to other thyasirids that are primarily chemosymbiotic and strongly associated with chemosynthetic settings (Oliver & Sellanes 2005). The gills are thick and fleshy and of Dufour Type 3 (Dufour 2005). The foot is vermiform and the lateral body pouches are large and multilobed. Stable isotopic ratios are in the range of other symbiotic chemosyntheticbased bivalves hosting sulfide-oxydizing symbionts (CF Rodrigues unpublished results). The presence of a sensory papilla situated on the anterior ventral face of the anterior adductor muscle was first reported by Payne and Allen (1991) for the members of genus Axinus. A similar papilla is present in A. cascadiensis, and it was also reported on the dorsal surface of the adductor muscle in T. sarsi, T. flexuosa, T. obsoleta and Axinulus croulinensis (Oliver & Holmes in press). In Thyasira vulcolutre the papilla (Figs 14, 15) is situated in the inhalant flow and it probably functions in a sensory manner to monitor flow or water chemistry of the inhalant current. An obvious feature of Thyasira vulcolutre is the extensive staining of the kidneys by both crystalline granules and fibrous material in the lumen. Similar deposits were seen in T. methanophila and could be related to metabolism in a mineral-rich environment or to the bacterial source of nutrition. The unusual condition of the holotype suggests that the bacteria were lost from the gills and that digestion had slowed or ceased resulting in morbidity. The mortality of bivalves has been already studied and sulphide deprivation, sulphide toxicity, and disease were indicated as possible agents of mortality on the system (Mills et al. 2005)., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on pages 43-49, DOI: 10.5281/zenodo.274249, {"references":["Oliver, P. G. & Holmes, A. M. (2006) New species of Thyasiridae (Bivalvia) from chemosynthetic communities in the Atlantic Ocean. Journal of Conchology, 39 (2), 175 - 184.","Clarke, A. H. (1989) New mollusks from undersea oil seep sites off Louisiana. Malacology Data Net, 2, 122 - 134.","Oliver, P. G. & Sellanes, J. (2005) New species of Thyasiridae from a methane seepage area off Concepcion, Chile. Zootaxa, 1092, 1 - 20.","Olu-Le Roy, K., Sibuet, M., Fiala-Medioni, A., Gofas, S., Salas, C., Mariotti, A., Foucher, J-P & Woodside, J. (2004) Cold seep communities in the deep eastern Mediterranean Sea: composition, symbiosis and spatial distribution on mud volcanoes. Deep-Sea Research I, 51, 1915 - 1936.","Dando, P. R., Bussman, I., Niven, S. J., O'Hara, S. C. M., Schaljohann, R. & Taylor L. J. (1994) A methane seep in the Skagerrak, the habitat of the pogonophore Siboglinum poseidoni and the bivalve mollusk Thyasira sarsi. Marine Ecology Progress Series, 107, 157 - 167.","Southward, E. C. (1986) Gill symbionts in thyasirids and other bivalve molluscs. Journal of the Marine Biological Asso Sturany, R. (1896) Zoologische Ergebnisse VII. Mollusken I (Prosobranchier und Opisthobranchier; Scaphopoden; Lamellibranchier) gesammelt von S. M. Schiff \" Pola \" 1890 - 1894, Denkschriften der Kaiserlichen Akademie der Wissenschaften, 1 - 36 ciation of the United Kingdom, 66, 889 - 914.","Taylor, J. D., Williams, S. T. & Glover, E. A. (2007) Evolutionary relationships of the bivalve family Thyasiridae (Mollusca: Bivalvia), monophyly and superfamily status. Journal of the Marine Biological Association of the United Kingdom, 87, 5440 / 1 - 10.","Salas, C. 1996 Marine bivalves from off the Southern Iberian Peninsula collected by the Balgim and Fauna 1 expeditions. Haliotis, 25, 33 - 100.","Payne, C. M. & Allen, J. A. (1991) The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London B, 334, 481 - 562.","Verrill, A. E. (1885) Third catalogue of Mollusca recently added to the fauna of the New England Coast and the adjacent parts of the Atlantic, consisting mostly of deep sea species, with notes on others previously recorded. Transactions of the Connecticut Academy of Arts and Sciences, 6, 395 - 452.","Nakazima, M. (1958) Notes on gross anatomy of Conchocele disjuncta. Venus, 20, 186 - 197.","Kamenev, M. K., Nadtochy, V. A. & Kuznetsov, A. P. (2001) Conchocele disjuncta (Conrad, 1849) (Bivalvia: Thyasiridae) from cold water methane-rich areas of the Sea of Okhotsk. The Veliger, 44, 84 - 94.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212.","Mills, A. M., Ward, M. E., Heyl, T. P., Van Dover, C. L. (2005) Parasitism as a potential contributor to massive clam mortality at the Blake Ridge Diapir methane-hydrate seep. Journal of the Marine Biological Association of the United Kingdom, 85, 1489 - 1497."]}

Axinulus croulinensis (Jeffreys, 1847) (Fig. 28) Material examined. All from Gulf of Cadiz; twelve live-collected specimens, MSM01-03, stn 241 GKG 12, Mercator mud volcano, 35 �� 17.918 'N, 06�� 38.717 'W, 353 m, 6 May 2006 (DBUA 00832.01); four live-collected specimens, MSM01-03, stn 242 GKG 13, same locality, 35 �� 17.870 'N, 06�� 38.810 'W, 350 m, 6 May 2006 (DBUA 00832.02); one live-collected specimen, TTR 15, stn AT 576 B, same locality, 35 �� 17.657 N, 06�� 39.129 W, 428 m, 26 July 2005 (DBUA 00833.01). Remarks. Axinulus croulinensis is recognised by the almost symmetrical oval outline and weak to absent posterior sulcus. It is widely distributed throughout the Atlantic Ocean. It has been recorded from 40 to 3800 m and has not been associated with any specific reducing environment (Payne & Allen 1991). Dufour (2005) classified this as having Type 2 gills with single demibranchs and showing weak bacterial symbiosis., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 50, DOI: 10.5281/zenodo.274249, {"references":["Jeffreys, J. G. (1847) Additional notices on British shells. Annals and Magazine of Natural History, 20, 16 - 19.","Payne, C. M. & Allen, J. A. (1991) The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London B, 334, 481 - 562.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}

Thyasira vulcolutre sp. nov. Rodrigues CF & Oliver PG (Figs 2–23) Material examined. Holotype: one live-collected specimen, MSM01-03 stn 217 GKG 10, Captain Arutyunov mud volcano, Gulf of Cadiz, 35 º 39.643 'N, 07º 20.046 'W, 1321 m, 30 April 2006, M.R. Cunha (NMW.Z.2007.3.1). Paratypes: 24 live-collected specimens as holotype. (NMW.Z.2007.3.2- 3; USNM 1110226, DBUA 00826.01). Other material: All from Gulf of Cadiz; nine live-collected specimens, MSM01-03, stn 246 / 274 BIGO 3, Captain Arutyunov mud volcano, 35 º 39.738 'N, 07º 20.010 'W, 1321 m, 10 May 2006 (NMW.Z.2007.3.4- 6, DBUA 00826.02); one live-collected specimen, TTR 10, stn AT 243 G, Carlos Ribeiro mud volcano, 35 º 47.217 'N, 08º 25.313 'W, 2200 m, 26 July 2000 (DBUA 00827.01); one shell, TTR 16, stn AT 615 Gr, Carlos Ribeiro mud volcano, 35 º 47.238,N, 08º 25.272 ’W, 2200 m (NMW.Z.2007.3.7). Description. Measurements: Holotype, length 17.0 mm, height 16.5 mm, tumidity 10.4 mm. Summary statistics of morphometric ratios are presented in Table 1. Shell (Figs 2–11): To 17.2 mm in length; thin shelled; equivalve; subequilateral, beaks slightly in front of the midline, pointed prosogyrate. Relatively tumid but variable, (Length:Tumidity ratio 1.3: 1 to 1.9: 1, mean 1.6: 1). Outline typically subcircular, with length similar to height, some specimens with length greater than height (see variation below). Lunule margin incurved, long. Anterior dorsal margin narrowly curved, ventral margin broadly curved. Posterior sinus distinct but shallow, submarginal sinus distinct. Posterior dorsal margin more or less straight. Posterior sulcus shallow but distinct, submarginal sulcus shallow but with a sharp, well-defined margin. Auricle elevated but low and very long almost filling the entire escutcheon. Ligament visible for most of the length of the auricle (Escutcheon:auricle ratio 1.1: 1 to 1.5: 1, mean 1.3: 1). Lunule shallowly sunken, cordate, broad. Hinge plate narrow, lacking clearly defined teeth. Ligament long, sunken. Sculpture concentric, of lines and relatively regular narrow ridges. Radial lines visible in some, but are not surface features but are reflected inside the shell by numerous radial striations. Pallial line entire. Anterior adductor scar long; posterior adductor scar oval. Periostracum very thin, pale, greyish brown. Va r ia ti on: The outline is variable (Figs 8–10), this variability generally increases with the size of shell, and is reflected mostly in the disproportionate increase in tumidity in the largest size classes. The expression of the lunule is highly variable and is probably related to the variation in shell tumidity. Anatomy: Mantle edge fused posteriorly between termination of gill axis and posterior adductor; exhalant siphonal opening simple, margins smooth (Fig. 13). Labial palps small, with indistinct sorting ridges. Posterior ventral mantle edge with a glandular area on its inner side (Fig. 16). Ventral mantle edge with a distinct median fold (Fig. 17). Anterior inhalant aperture with an elongate glandular area on its inner side (Fig. 14); ventral side of anterior adductor muscle with a digitate sensory papilla (Figs 14, 15). Ctenidium large, of outer and inner demibranchs, both as thick fleshy lamellae (Fig. 12). Outer demibranchs about 2 / 3 size of inner demibranchs. Foot elongate, vermiform (Fig. 12), with a muscular ring at the junction with the visceral mass; heel indistinct. Visceral mass, lateral body pouches large, extensively lobed (Figs 12, 18). Lobes flat-ended, roughly cuboidal. Lobes arise from large, single orifice at base of stomach (Figs 19, 20). Stomach cylindrical in a transverse longitudinal orientation; midgut a simple tight loop and lies over stomach before looping posteriorly into the straight hindgut and rectum (Fig. 20). Kidneys large (Fig. 19), with dense aggregations of crystalline granules and a yellow/white fibrous mass in the lumen. Note. Dissection of the holotype revealed an identical gross structure to that described above but the ctenidia were thin and semi-transparent and the lateral body pouches were greatly contracted (Fig. 21). The kidney was extensively stained dark brown and was massively infested with a fibrous mass and crystalline granules (Figs 22, 23). PLATE 1. Thyasira vulcolutre sp. nov.; Figs 2–5 Holotype, NMW.Z.2007.3.1; Figs 6 & 7 Juvenile shells, NMW.Z.2007.3.2- 3; Figs 8–10 variations in shells form, NMW.Z.2007.3.4- 6; Fig. 11 large shell, NMW.Z.2007.3.7. PLATE 2. Thyasira vulcolutre sp. nov., NMW.Z.2007.3.4- 6. Gross anatomy after removal of the right shell and mantle. Fig. 12 whole view; Fig. 13 enlarged view of area A, the posterior exhalant aperture; Fig. 14 enlarged view of area B, the anterior inhalant aperture; Fig. 15 detail of the sensory papilla; Fig. 16 enlarged view of area C, the posterior ventral area; Fig. 17 enlarged view of area D, the median ventral mantle edge. PLATE 3. Figures 18–20: Thyasira vulcolutre sp. nov., NMW.Z.2007.3.4- 6. Fig. 18 Gross anatomy after removal of right shell, mantle and ctenidium; Fig. 19 Gross anatomy after removal of right mantle, ctenidium and lateral body pouch; Fig 20 Dissection of the alimentary system; Figures 21–23. Thyasira vulcolutre sp. nov. Holotype, NMW.Z.2007.3.1; Fig. 21 Gross anatomy after removal of right shell and mantle; Fig. 22 kidney as viewed through the epithelial tissues; Fig. 23 Kidney dissected showing crystalline granules and fibrous mass in lumen. Distribution. Most of the specimens were collected on the Captain Arutyunov mud volcano, some specimens were also collected on Carlos Ribeiro mud volcano; depth range between 1300 and 2200 m. Etymology. Vulcolutre, Latin combination of vulcano from “volcano”, lutum from “mud”; suffix tre denoting “belonging to”. Remarks. Species comparisons: This new species is morphologically similar to Thyasira sarsi (Philippi, 1845), T. southwardae Oliver & Holmes, 2006, T. oleophila Clarke, 1989 and T. methanophila Oliver & Sellanes, 2005 all known to be associated with chemosynthetic sites. Thyasira striata Sturany, 1896 has also been recorded from mud volcanoes in the eastern Mediterranean (Olu-Le Roy et al. 2004) but that species has a very distinct posterior sulcus and is more similar to the T. flexuosa group than to the above taxa. Thyasira sarsi has been reported from methane seeps in the North Sea (Dando et al. 1994) but is also known from vegetation-derived organic-rich environments in Norwegian fjords (Southward 1986). Thyasira sarsi differs by having a weakly developed posterior sulcus, a submarginal sulcus without a sharp, clearly defined margin and the lunule not so depressed and heart-shaped. Thyasira sarsi also possesses shell sculpture without concentric ridges and with a distinctly granular surface (see Oliver & Holmes 2006). Thyasira southwardae has been reported only from the Logatchev hydrothermal vent in association with Bathymodiolus and Calyptogena. Only two shells and one valve of this species have been collected, making comparisons difficult but it is clear that the shells of T. vulcolutre and T. southwardae are similar. The shells of T. southwardae (see Oliver & Holmes 2006) are thinner and have irregular sculpture of concentric lines and corrugations and never display the regular concentric ridges typical of T. vulcolutre. The definition of the submarginal sulcus is not so sharp in T. southwardae and the submarginal sinus and posterior sinus are not so pronounced. From the anatomy, the gills of T. southwardae were pink in contrast to the light brown in T. vulcolutre. Thyasira oleophila was described from the Louisiana oil and gas seeps at depths around 500 m. It is a large species reaching 22.0 mm in length and is almost devoid of a posterior sulcus, is not expanded anteriorly and has a strongly granular surface (see Oliver & Holmes 2006). Thyasira methanophila Oliver & Sellanes, 2005 was described from a methane seepage area off Concepcion, Chile at bathyal depths. Thyasira methanophila differs from T. vulcolutre in that the lunule is not sunken, and the escutcheon is less defined. From morphology alone, a new genus could be proposed for the group of species similar to T. vulcolutre, including T. methanophila, T. southwardae, T. sarsi and T. oleophila but this is not wholly supported by the molecular data. An 18 S rRNA gene Neighbour Joining tree (not shown) combining an unpublished sequence from Thyasira vulcolutre with previously published sequences from thyasirids analyzed by Taylor, Williams and Glover (2007) shows that T. vulcolutre is clustered with T. perplicata Salas, 1996 and is distant from T. methanophila and T. sarsi. (S Williams and JD Taylor pers. comm.). Payne and Allen (1991) described T. perplicata under the name T. excavata plicata (Verrill, 1885) as having a shell with a strong posterior carina and thus most similar to shells of the genus Conchocele. Anatomically T. perplicata is also similar to Conchocele with a bulbous tipped foot, large fleshy gills and prominent anterior mantle edge folds (Nakazima, 1958; Kamenev et al. 2001). The lack of congruence between morphology and molecular data may be clarified once a larger set of taxa are included but until this study is completed the genus Thyasira is retained for the majority of species with sulcate shells, with two demibranchs and that are chemoautotrophic. Functional morphology: The functional morphology is essentially similar to other thyasirids that are primarily chemosymbiotic and strongly associated with chemosynthetic settings (Oliver & Sellanes 2005). The gills are thick and fleshy and of Dufour Type 3 (Dufour 2005). The foot is vermiform and the lateral body pouches are large and multilobed. Stable isotopic ratios are in the range of other symbiotic chemosyntheticbased bivalves hosting sulfide-oxydizing symbionts (CF Rodrigues unpublished results). The presence of a sensory papilla situated on the anterior ventral face of the anterior adductor muscle was first reported by Payne and Allen (1991) for the members of genus Axinus. A similar papilla is present in A. cascadiensis, and it was also reported on the dorsal surface of the adductor muscle in T. sarsi, T. flexuosa, T. obsoleta and Axinulus croulinensis (Oliver & Holmes in press). In Thyasira vulcolutre the papilla (Figs 14, 15) is situated in the inhalant flow and it probably functions in a sensory manner to monitor flow or water chemistry of the inhalant current. An obvious feature of Thyasira vulcolutre is the extensive staining of the kidneys by both crystalline granules and fibrous material in the lumen. Similar deposits were seen in T. methanophila and could be related to metabolism in a mineral-rich environment or to the bacterial source of nutrition. The unusual condition of the holotype suggests that the bacteria were lost from the gills and that digestion had slowed or ceased resulting in morbidity. The mortality of bivalves has been already studied and sulphide deprivation, sulphide toxicity, and disease were indicated as possible agents of mortality on the system (Mills et al. 2005).

Mendicula ferruginosa (Forbes, 1844) (Fig. 29) Material examined. Nine live-collected specimens, TTR 15, stn AT 575 B, Mercator mud volcano, Gulf of Cadiz, 35 �� 17.903 N, 06�� 38.715 W, 355 m, 26 July 2005 (DBUA 000834.01). Remarks. The heavily encrusted ferruginous deposit and subovate outline are characteristic of this ubiquitous species. It has been recorded from many parts of the Atlantic and Mediterranean in depths from 50 to 4825 m and has not been associated with any specific reducing environment (Payne & Allen 1991). Dufour (2005) classified this as having Type 2 gills with a single demibranch and showing no evidence of bacterial symbiosis., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 50, DOI: 10.5281/zenodo.274249, {"references":["Forbes, E. (1844) Report on the Mollusca and Radiata of the Aegean sea, and on their distribution, considered as bearing on geology. Reports of the British Association for the Advancement of Science (1843), 130 - 193.","Payne, C. M. & Allen, J. A. (1991) The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London B, 334, 481 - 562.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}

Thyasira obsoleta (Verrill & Bush, 1898) (Fig. 26) Material examined. All from Gulf of Cadiz; two live-collected specimens, MSM01-03, stn 145 GKG 3, Porto mud volcano, 35 �� 33.699 'N, 09�� 30.437 'W, 3860 m, 21 April 2006 (DBUA 00831.01); one live-collected specimen MSM01-03, stn 190 MUC 8, Captain Arutyunov mud volcano, 35 �� 39.665 'N, 07�� 19.970 'W, 1322 m, 28 April 2006 (DBUA 00831.02); one live-collected specimen, MSM01-03, stn 241 GKG 12, Mercator mud volcano, 35 �� 17.918 'N, 06�� 38.717 'W, 353 m, 6 May 2006 (DBUA 00831.03); one live-collected specimen MSM01-03, stn 169 MUC 7, Carlos Ribeiro mud volcano, 35 �� 47.256 'N, 08�� 25.361 'W, 2199 m, 25 April 2006 (DBUA 00831.04). Remarks. All specimens are very small (not exceeding 2.0 mm) but exhibit the characteristically weakly sulcate posterior and angular outline. This is a common and widespread species recorded from across the Atlantic Ocean in depths from 24 to 2900 m (Payne & Allen 1991). It has not been associated with any particular reducing environment. Dufour (2005) classified this as having Type 2 gills with both demibranchs but showing no evidence of bacterial symbiosis., Published as part of Rodrigues, Clara F., Oliver, Graham & Cunha, Marina R., 2008, Thyasiroidea (Mollusca: Bivalvia) from the mud volcanoes of the Gulf of Cadiz (NE Atlantic), pp. 41-56 in Zootaxa 1752 on page 49, DOI: 10.5281/zenodo.274249, {"references":["Verrill, A. E. & Bush K. J. (1898) Revision of the deep-water Mollusca of the Atlantic coast of North America, with descriptions of new genera and species. Proceedings of the United States National Museum, 20, 775 - 901.","Payne, C. M. & Allen, J. A. (1991) The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London B, 334, 481 - 562.","Dufour, S. (2005) Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin, 208, 200 - 212."]}