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The fossil record shows that the two clavagelloid or watering pot families evolved at different times, the Clavagellidae first in the late Mesozoic (100–66 mya), the Penicillidae later in the Cenozoic (33–23 mya)—the former originally with, thus, a near-global Tethyan distribution, the latter restricted to the Indo-West Pacific. Representatives of the two clavagelloid families, moreover, have wholly different adventitious tube/crypt structures and, thus, methods of formation suggesting that evolutionary experiments have been undertaken to achieve such radical architectural novelties. This has resulted in one of the most surprising examples of convergent evolution in the Bivalvia. But, what were the ancestors of the Clavagelloidea? The shell and internal morphology of representatives of the three recognized genera of the Lyonsiidae, that is, Lyonsia, Entodesma and Mytilimeria, are described. Species of the latter two genera are highly specialized epibenthic, byssate, nestlers and embedded symbionts of ascidian colonies and sponges, respectively. Species of Lyonsia, however, are mostly shallow endobenthic burrowers. On the basis of these studies, it is concluded that species of Lyonsia can be regarded as representative of the ancestral watering pot (Clavagelloidea) condition. Evidence for this conclusion include the mineralogy, characteristics and ligament structure of the shell and features of the anatomy, importantly the modification of the vestigial pedal retractor muscles to form simple (Clavagellidae) and more complex (Penicillidae) proprioreceptors. Such an anatomy-based conclusion is supported to some extent by DNA analyses of representatives of the Lyonsiidae and the two constituent families of the Clavagelloidea. To some extent because all clavagelloids are exceedingly rare hindering such analyses. Such rarity, however, also argues for the strict conservation of all the species of the Clavagelloidea.

Mitogenomic trees for Bivalvia have proved problematic in the past, but several highly divergent lineages were missing from these analyses and increased representation of these groups may yet improve resolution. Here, we add seven new sequences from the Anomalodesmata and one unidentified semelid species ( Bryopa lata, Euciroa cf. queenslandica, Laternula elliptica, Laternula truncata, Lyonsia norwegica, Myadora brevis, Tropidomya abbreviata, “Abra” sp.). We show that relationships in a mitogenomic tree for the Class are improved by the addition of seven anomalodesmatans from this highly divergent clade, but are still not completely consistent with relationships recovered in studies of nuclear genes. We suggest that some anomalous relationships (for instance the non-monophyly of Bivalvia) may be partially explained by compositional heterogeneity in the mitogenome and suggest that the addition of more taxa may help resolve both this effect and possible instances of long branch attraction. We also identify several curious features about anomalodesmatan mitogenomes. For example, many protein-coding gene boundaries are poorly defined in marine bivalves, but particularly so in anomalodesmatans, primarily due to non-conserved boundary sequences. The use of transcriptomic and genomic data together enabled better definition of gene boundaries, the identification of possible pseudogenes and suggests that most genes are translated monocistronically, which contrasts with many other studies. We also identified a possible case of gene duplication of ND5 in Myadora brevis (Myochamidae) . Mitogenome size in the Anomalodesmata ranges from very small compact molecules, with the smallest for Laternula elliptica (Laternulidae) only 14,622 bp, to Bryopa lata (Clavagellidae) which is at least 31,969 bp long and may be >40,000 bp. Finally, sampled species show a high degree of sequence divergence and variable gene order, although intraspecific variation in Laternula elliptica is very low.

The only extant, preserved and complete specimen of Stirpulina ramosa has been discovered in the collections of the late Emperor Shōwa (Hirohito) and is described herein. Hitherto, only shells and the adventitious tubes of this species have been described. This study of the anatomy complements previous ones and adds further information as to how the adventitious tube is formed: that is, by the laying down of an organic, periostracum-like, template that is then biomineralized internally to form the tube and is externally plastered with the clasts that constitute the enclosing burrow wall. Such secretions are produced by pallial lobes that unite on the right side to create the characteristic sutured pleat in this region of the tube. The periostracum enclosing the so-interred animal is then secreted against the internal template of the tube. The shell of S. ramosa and, as a consequence, the musculature, is greatly disfigured as a result of the incorporation of the left valve into the fabric of the adventitious tube. This valve can, however, continue to grow within the tube, especially posteriorly. The right valve remains free inside the tube but grows only a little more anteriorly. The anterior mantle, with a minute pedal gape, is greatly thickened and secretes the watering pot component of the tube. In many anatomical respects, for example simultaneous hermaphroditism, S. ramosa still reflects the basic anomalodesmatan plan and such modifications as there are from the clavagellid form relate principally to the structure, formation and thus functioning of the adventitious tube. This study of S. ramosa has allowed the full spectrum of clavagellid adaptive radiation to be analysed and an evolutionary picture created which suggests that species of Clavagella/Dacosta and Stirpulina are Mesozoic (Late Cretaceous) remnants. Conversely, species of Bryopa and Dianadema are more modern, Late Oligocene and Palaeocene (Cenozoic), respectively, and possibly evolved in association with the emergence of the Indo-West Pacific centre of coral diversity, with a postulated average age of just 30 Myr. © 2013 The Linnean Society of London

The purpose of this application, under Article 23.9.3 and Recommendation 23A of the Code, is to conserve the genus name Stirpulina Stoliczka, 1870 for a group of watering pot shells. The genus name Stirpulina is in widespread and current use. This name is threatened by the little-used senior subjective synonym Tubolana Bivona Bernardi, 1832. It is proposed that the name Stirpulina be conserved by the suppression of Tubolana.

The endobenthic ‘watering pot shell’ Clavagella maxwelli n. sp. is described from the Early Miocene, and the similarly endobenthic species Stirpulina cf. pallinupensis Morton, identified hitherto only from the Late Eocene (Priabonian) of Western Australia, is recorded from the late Early Oligocene, both from Otago, New Zealand. Previously, only Clavagella oamarutica Maxwell (Early Miocene) has been recorded from New Zealand. Although the holotypes of Clavagella maxwelli and C. oamarutica have similar tube lengths (c. 80 mm), the two species differ from each other in several important respects. C. maxwelli was a vertically (or nearly so) burrowing endobenthic species whereas C. oamarutica was a cryptic, nestling, possibly cemented species. This is the first record of Stirpulina from New Zealand. The adventitious tube of Clavagella maxwelli was secreted by the mantle from four foci, progressively enclosing the right shell valve and creating an irregular suture on its right side within the array of ...

Two small cemented, cryptic, species of Dianadema (Bivalvia: Anomalodesmata: Clavagellidae) have been recorded from shallow waters of the Indian Ocean. These are Dianadema minima and Dianadema mascarensis. A study of their shells and adventitious crypt morphologies, however, suggests that the two species are conspecific, the former name taking precedence. This re-description of D. minima suggests that on settlement, the larva develops a juvenile shell that continues to grow until a length of ∼9.0 mm is reached, when it secretes around itself a primary calcareous crypt and cements itself ventrally into a concavity in coral rubble. Subsequently, a crown of tubules is secreted from the dorsal surface of the exposed mantle and an adventitious siphonal tube is formed, which is characteristically oriented at ∼45° from the horizontal. In the absence of preserved internal tissues and pre-adult life history stages, there is no possibility of fully comprehending exactly how such a remarkable adventitious structure is produced. Dianadema minima does, however, provide us with another example of the remarkable adaptive radiation of the Clavagelloidea and, in particular, the pattern of convergent evolution expressed not just between D. minima (Clavagellidae) and Humphreyia strangei (Penicillidae), but also between the two families that have independently evolved “watering pot” shells and tubes.

Stirpulina pallinupense sp. nov. (Clavagellidae) is described from the late Eocene Pallinup Formation of the Bremer Basin, southern Western Australia. The Tehyan Stirpulina is hitherto unrecorded from the southern hemisphere. During the late Eocene, elements of a Tethyan — Southwest Pacific fauna and other, more cosmopolitan, groups of molluscs extended their ranges to southern Australia, joining endemic species to form the distinctive, blended, fauna of the Pallinip Formation.

A new species of Clavagellidae, Bryopa aligamenta, from Okinawa, Japan, is described. The species is endolithic in living corals, with the left valve cemented to the crypt wall, as in all clavagellids. The free right valve exhibits an unusual growth pattern, with commarginal lines seemingly arising from the posterior valve margin and extending towards the anterior. This results from: (i) progressive anterior erosion of the umbones, probably as a consequence of the boring process; (ii) the apparent migration posteriorly, as the umbones are eroded, of the dorso-ventral growth axis of the shell; and (iii) enhanced posterior inter-commarginal growth. Unlike other clavagellid genera and species, however, there is no discernible primary ligament, at least in the adult. It is possible, however, that if a juvenile ligament were present (as in B. lata), it too would be lost as a consequence of antero-dorsal erosion during boring. To retain valve alignment in the absence of a primary ligament, and possibly upon reaching an adult size, the mantle lays down alternating layers of calcium carbonate and proteinaceous periostracum onto the interior surface of the shell to thicken it, most noticeably marginally and, especially, posteriorly. The two valves are united dorsally, therefore, by thin layers of periostracum that probably exert a minimal opening force. B. aligamenta is, however, further characterised by large adductor, pallial, and siphonal retractor muscles so that the entire animal is encased tightly within an internally strengthened shell within a crypt. Movement must be minimal, blood being pumped into pallial haemocoels to push open the valves and extend the siphons. Despite a suggestion to the contrary, Bryopa is retained in the Clavagellidae, its unusual growth processes resulting from an endolithic life style within living corals. The fossil clavagellid Stirpulina bacillus, from the Pliocene/Pleistocene of Palermo, Sicily, Italy, was, unlike Bryopa aligamenta and other clavagellids, endobenthic, with a long adventitious tube and anterior watering pot superficially similar to species of Penicillidae, another family of the Clavagelloidea. Furthermore, as in all clavagellids only the left valve is fused into the fabric of the tube, the right being free within it. In all penicillids, both valves are fused into the fabric of their tubes. The watering pots of the fossil S. coronata, S. vicentina, and S. bacillus, moreover, are formed in a different manner to that of penicillids, by progressive encasement of the right valve inside the tube. In penicillids, the tube is secreted in a single event from the general mantle surface and the incorporation of both valves into its fabric. The constituent genera of the Clavagellidae thus constitute an example of parallel evolution with members of the Penicillidae.

This paper describes a number of new taxa in the Arcidae, Philobryidae, Mytilidae, Galeommatidae, Kelliidae, Cyamiidae, Carditidae, Thraciidae and Clavagellidae. A further 17 species are included as new to the malacofauna of Rodrigues. Most of the species included came from cryptic habitats, of which the most interesting are apparently cavernicolous and similar to those described from southern Japan. Other species were described from crevice or algal turf communities. The most understudied group is the Galeommatoidea with four species described as new and a further five with as yet unresolved taxonomy.

The anomalodesmatan Clavagellidae can be separated from the Penicillidae on the basis of ligament and adventitious tube or crypt structure. The Clavagellidae includes species of Clavagella (and Dacosta), Bryopa and Stirpulina. Two species, first described as Clavagella torresi Smith, 1885 and Aspergillum multangularis Tate, 1887, have consistently been placed in the genus Clavagella, but both are herein located in the new genus Dianadema. Because more material is available, this is primarily a study of Dianadema multangularis (Tate) which is designated as the type species of the new genus. Dianadema multangularis is unlike Clavagella, Bryopa and Stirpulina which are, respectively, recessing, boring and endobenthic representatives of the Clavagellidae, in that it is cemented and possesses a crown of dorsal tubules, in addition to anterior and ventral ones. As in all clavagellids (sensu stricto) the left valve is cemented into the fabric of an adventitious crypt while the right valve is free inside it. There is also a posterior multi-angular siphonal tube. The anatomy of D. multangularis is described and it is, in most respects, a typical clavagellid. The species differs from other clavagellids in the inferred aeration of the crypt via patterns of water flow, the crown of crypt tubules, and its unique cemented lifestyle. There are three (known) genera of clavagelloids endemic to southern and eastern Australia, i.e. Dacosta and, now, Dianadema (Clavagellidae) and to which the third, Humphreyia (Penicillidae), is similar in that the latter two are both cemented, albeit convergently. They also provide a surprising picture of convergent evolution of the cemented lifestyle even to the extent that both possess a unique pair of pericardial proprioreceptors, each derived differently, to monitor body tonus. Moreover, two other anomalodesmatan genera are also cemented, i.e. Cleidothaerus (Cleidothaeridae) and Myochama (Myochamidae), and these too are restricted to eastern Australia (and New Zealand). What forces promoted cementation in these four antipodean anomalodesmatan families are unknown.

Amongst the watering pot shells of the Clavagellidae (Anomalodesmata), the least well known is Humphreyia, with a single species H. strangei. Unlike representatives of the other extant clavagellid genera, i.e. Clavagella and Brechites, however, where juveniles are unknown, there is a single juvenile (plus adult specimens) of H. strangei available for study. The Clavagellidae contains the weirdest of all bivalves, encased in a huge (in proportion to the tiny juvenile shell) adventitious tube with an anterior ‘watering pot’. The juvenile H. strangei is dimyarian with a large foot and byssal groove, and a large pedal gape; the entire body is enclosed within a bag-like periostracum-covered mantle cavity. Upon permanent residence, however, the anterior watering pot component of the adventitious tube is cemented to the chosen substratum, the adductor muscles are lost and the foot and pedal gape greatly reduced; the fourth pallial aperture closes and the pedal gape and the tubules of the watering pot are similarly occluded. Once cementation is achieved, further growth anteriorly is impossible and the adventitious tube is secreted posteriorly, to house the long siphons, and subsequently can be added to as growth increments. Anatomically, H. strangei has a typical anomalodesmatan arrangement of mantle cavity and digestive organs so that it is, probably, a suspension feeder. Inside the pericardium, however, is a pair of unique proprioreceptors which probably serve to monitor rectal tonus and thus control defecation, co-ordinated with siphonal retraction and extension. They probably also prevent over-filling of the capacious rectum. It is believed that cementation and adventitious tube formation occur at the time of sexual maturity and this change in lifestyle between juvenile and adult represents a form of metamorphosis – quite distinct from that which occurs in all bivalves between the pediveliger and juvenile stages – and seems to be unique to Humphreyia and probably Brechites. This family of anomalodesmatan bivalves is thus actually stranger than the already aberrant watering pot would suggest.

Living individuals of the bivalve ‘watering pot’ superfamily Clavagelloidea were collected from Withnell Bay, Burrup Peninsula, Dampier Archipelago, Western Australia. Details of the anatomy suggest that, in most respects, Brechites vaginiferus is a typical filter-feeding bivalve, albeit encased in a tube of its own secretion. The true shell is tiny (∼ 4 mm long) and surrounded by a ‘saddle’ of initially-secreted adult shell. To this is fused, by an internally produced layer of calcium carbonate, the adventitious tube which comprises a single layer, confirming that it is produced only once. Posteriorly, however, it can be added to internally as ‘plaited ruffles’ creating a multi-layered structure. The anterior watering pot comprises a perforated plate fringed by tubules, with a small pedal aperture. Brechites vaginiferus pumps interstitial water into the mantle cavity via the watering pot, at least principally, not out of it as previously thought. In this way, the animal is either tapping an interstitial source of accessory food, or aerating the anterior end of its burrow (or both). It has also been demonstrated, however, that pumping interstitial water into the mantle cavity via the pedal gape results in hydraulic pressures being built up that extend the siphons. The pedal disc pump, therefore, acts in this amyarian bivalve in the same way as the adductor muscles do in more typical species. The ctenidia collect suspended material in the usual way from seawater and from interstitial water: they do not, however, possess chemoautotrophic sulphur-oxidizing bacteria, and the species is thus not using sulphur as an energy source. Pedal gape feeding is considered to be the ancestral condition not only in the earliest anomalodesmatans, e.g. the Pholadomyidae, but also the autobranchs in general. This has been refined in the Clavagelloidea to create the unique form of the adventitious tube, its watering pot and a wholly surprising lifestyle. Tube form in B. vaginiferus varies in relation to habitat occupied. Its major habitat on Withnell Bay, however, is the riffles of a high-salinity stream draining down the mangrove-fringed shore from the semi-arid land behind. Although much more is now known about B. vaginiferus and ‘watering pot’ shells, no pre-tube juvenile is known and awaits discovery to confirm hypothesized life-history details.

Oliver, P. Graham, Holmes, Anna, Killeen, Ian, Light, Janice, Wood, Harriet (2004): Annotated checklist of the marine Bivalvia of Rodrigues. Journal of Natural History 38 (23): 3229-3272, DOI: 10.1080/00222930410001695097, URL: http://www.informaworld.com/openurl?genre=article&doi=10.1080/00222930410001695097&magic=crossref||D404A21C5BB053405B1A640AFFD44AE3

The biology and functional morphology of the unusual boring anomalodesmatan bivalve Clavagella (Dacosta) australis (Clavagellacea) is described. The animal occupies a borehole in calcareous (including coral) rocks to which it cements itself by the left shell valve. Radial mantle glands developed in the middle folds of the siphonal tip produce the glue but also stick sand grains to the periostracum to camouflage the siphons. The right valve is free. The shell is somewhat inequilateral in form, the adductors large and slightly heteromyarian. The pallial retractor muscles are also large so that the ventral mantle is very thick. Because mantle fusion involves inner, middle and inner surfaces of the outer folds (type C), the periostracum is continuous so that shell and mantle are almost completely, except for the siphonal orifices and the pedal gape, enclosed in periostracum. The simple sunken primary ligament comprising inner ligament layer only and located between chondrophores is flanked anteriorly and posteriorly by fused periostracum, assisting, in the absence of teeth, in hinge alignment. Boring is probably a chemical process, a secretion from the inner surface of the anterior mantle being discharged onto the burrow wall from the pedal gape. The calcium carbonate eroded in this way is possibly used to partially line the burrow. The distal siphonal tube, however, is secreted from siphonal glands discharging from the tip of the siphons. In most other anatomical respects Clavagella is typical of the Anomalodesmata, the ctenidia and labial palps for example being of characteristic form. The statocysts, however, are unusual in that the statolith comprises a large number of small, diamond-shaped crystals that stimulate statocyst cilia. C. australis appears to be dioecious, whereas most other anomalodesmatans are simultaneous hermaphrodites. Clavagella may be linked to a pholadomyacean ancestor and most closely resembles members of the infaunal Latemulidae. It represents an evolutionary line that has adopted first a nestling then a boring mode of life. It seems probable that the more specialized infaunally buried clavagellids with both valves incorporated into the adventitious tube are derived from a nestling/boring ancestor.

Cretaceous clavagellid pelecypods are a poorly known group, and have previously received little study.Ascaulocardium armatumis conchologically the most complex burrowing pelecypod known. From the study of living clavagellids, it is possible to interpret the various tubes extending outward from the adventitious crypt ofA. armatumas devices for hydraulic burrowing and deposit feeding. The conchologically complexA. armatumoccurs near the beginning of the history of the Clavagellidae, and does not seem to have given rise to any younger species.Ascaulocardium armatumis known only from the Upper Cretaceous rocks (Santonian–Maastrichtian) of the east Gulf and Atlantic Coastal Plains of the United States of America, as is probably the genusAscaulocardium. All known Cretaceous clavagellids are burrowing species having a free right valve, and this is the ancestral mode of life of the Clavagellidae. Clavagellids that have a boring habit are a more recent evolutionary development, as are burrowing species having both juvenile valves cemented to the crypt. Clavagellids probably evolved from Jurassic–Early Cretaceous pholadomyids. Almost all Cretaceous clavagellids occur outside the Tethyan Zoogeographic Realm; this distribution is in marked contrast to the modern distribution of the family. Living species mostly inhabit clear, shallow seas in subtropical to tropical shelf areas.

Summary The recent species of the family Clavagellidae are revised and 17 species and sub-species are recognised in three genera. A new subgenus Humphreyia (Nipponoclava) subgen. nov. is introduced and the inter-relationships and zoogeography of the various species discussed.

The infaunal Clavagellacea (Anomalodesmata) are among the weirdest bivalves, and include the “watering pot” shells, with a minute true shell embedded in an adventitious tube. This paper describes the formation and function of the tube of Brechites vaginiferus and is correlated with an investigation of shell structure and anatomy. Because of extensive mantle fusion, the body is entirely covered by periostracum. The only apertures to the exterior are the pedal gape and the siphonal orifices (a small fourth pallial aperture progressively closes up). Glands lining the pedal gape secrete the basal plate of the tube. Perforations in it (the plate tubules and lateral tubules) are caused by papillae locally inhibiting the laying down of secretion. The siphonal part of the tube is secreted by glands discharging from the siphonal orifices (middle folds). The secretion presumably pours down the maximally expanded siphons, which compact the burrow wall and against which the tube is laid down, sand grains adhering to it. Fusion with the concave basal plate is at the margin of the pedal disc forming a fringe of fused tubules around it. Radial mantle glands in the siphonal orifices (again middle fold) produce a secretion that glues sand grains to the periostracum around the siphonal tips, for camouflage. The tube is secreted when an otherwise naked, infaunal juvenile reaches a mature size. The tube is produced only once so that further enlargement is impossible, except by addition of “plaited ruffles” at the siphonal end, as the siphons elongate and as the tube sink's into the sand. New tube material is laid down inside and beyond the existing tube opening. Similarly, the basal plate is internally strengthened by further secretion from the pedal gape. Progressively, lateral tubules and the orifice in the plate corresponding to the pedal gape are occluded; other disc tubules remain open. A juvenile clavagellid, possibly that of Humphreyia strangei but more likely a species of Brechites, has been examined. In most respects it is a typical bivalve. The true shell has an external ligament with a lithodesma and both adductor muscles are present. Visceral mass dimensions are typical, with a digging foot. The ctenidia are greatly enlarged within the expanded mantle cavity, mostly accounted for by long siphons, with a fourth pallial aperture mid-ventrally. The adult Brechites vaginiferus is functionally “amyarian” with only minute anterior pedal retractor muscles. The foot is reduced and strap-like. The body is minute in relation to the tube, with only the enormously elongated ctenidia extending to the base of the siphonal orifices. Most modifications concern the mantle (as noted above). In nearly all other respects the animal is simplified in recognition of its aberrant mode of life. The function of the tube of Brechites is discussed. A protective role is self-evident but burrowing can be achieved by water being expelled from the basal plate. The same action may be used to take in nutrients from the subsurface deposits. The relationships of Brechites and the Clavagellacea are discussed. Affinity is with the passive burrowing Laternulidae and origins lie in the Pholadomyacea.

By the end of the Cretaceous, the Clavagellidae (Mollusca: Pelecypoda) maintained a distribution that was marginal to the core-Tethys, occurring in both North America and the Old World. Traditional paleozoogeographic interpretation contends that the clavagellids then went extinct in the New World because no Cenozoic fossil or living clavagellids have been documented from the Western Hemisphere. This report describes the occurrence of Eocene clavagellids from the Ocala Group of peninsular Florida. The presence of these pelecypods in Upper Eocene strata is consistent with the large Tethyan faunal component already known from this unit and requires a reassessment of Tertiary zoogeographic patterns for the clavagellids.

There are nine species of the family Clavagellidae recognised from Australian waters, including two new species, Clavagella (Clavagella) majorina sp. nov. an Upper Oligocene fossil from Victoria and Tasmania and Brechites (Foegia) veitchi sp. nov. a living and fossil species from South Australia and Western Australia. A key to the genera and species is given and the three genera and five subgenera are redefined. New information is given on the fossil record and distribution of the species, and the zoogeography of the group is discussed.