Prionospio kaplani Paterson, Neal, Altamira, Soto, Smith, Menot, Billett, Cunha, Marchais-Laguionie & Glover, 2016, sp. nov

Prionospio kaplani sp. nov. Altamira, Glover, & Paterson (Figure 1, 2.5, 7, 8b, Table 2) Material examined: 12 specimens examined. Holotype: CVAP: RSS Discovery October 1993, 12600 # 45 October 1993, 21�� 3.4 ���N 31 �� 9.8 ��� W, 4524 m, 1 individual (NHMUK 2015: 1190) Paratypes: Equatorial Pacific: 2 ��N 140 ��W, 4300 m, 4 individuals (EP 410, EP 425, EP 427, EP 444); 5 ��N 140 ��W 4300 m, 3 individuals (EP 431, 432, 473); 9 ��N 140 ��W, 4900 m, 1 individual (EP 414). MAP: RSS Discovery August 1990,12174#53, 31 5.2 ��� N 21 1.2 ��� W, 4942 m, 1 individual. Other material examined: CVAP: RSS Discovery October 1993,12600#28, 21�� 4.8 ��� N 31 �� 11.1 ��� W, 4613 m, 1 individual. Equatorial Pacific: EqPac 0��N 140 ��W, 4300 m, 1 individual (EP 488). Diagnostic features. Two pairs of branchiae on chaetigers 2 and 3, sabre chaetae lacking, dorsal crests from chaetiger 7, neuropodial hooded hooks from chaetiger 11. Description. Body cylindrical, narrow throughout; holotype 1.86 mm long for 20 chaetigers, (0.62 mm up to chaetiger 10); 0.08 mm wide at chaetiger 1. Prostomium rectangular with flat, entire anterior margin; one pair prostomial peaks present; caruncle short with rounded apex, extending to anterior margin of chaetiger 2. Eyes absent. Peristomium incomplete dorsally, not forming lateral wings, separate from chaetiger 1 (Fig 7 a). Branchiae from chaetiger 2, two pairs, very small. Branchiae on chaetiger 2 digitiform, blunt-tipped, inserted lateral and slightly posterior to dorsal lamellae; branchiae approximately one-half chaetiger long, subequal to notopodial lamellae; branchiae on chaetiger 3 conical, inserted posterior to dorsal lamellae and obscured by them, one quarter the length of lamellae (Fig. 2.5). Notopodial lamellae start on chaetiger 2, sub-quadranular, slightly angled toward dorsal midline (Fig 2.5 a); largest on chaetiger 3, sub-quadrangular with slightly produced tips overlapping dorsal midline, three times as long as lamellae of chaetiger 2 (Fig 2.5 b); thereafter, notopodial lamellae decrease in size, becoming low and subtriangular by chaetiger 7. Dorsal crests present from chaetigers 7 to chaetiger 17 (Fig. 2.5 f chaetiger 14). Neuropodial lamellae start on chaetiger 1, papilliform, length equal to one-fifth chaetiger length; neuropodial lamellae on chaetigers 2���5 leaf-like, narrow with short tips; neuropodial lamellae largest on chaetiger 3, length equal to chaetiger length and nearly twice that of chaetiger 2, neuropodial lamellae thereafter decreasing in length and increasing in width, becoming broadly ovoid by chaetiger 9. Interparapodial pouches absent. Notochaetae limbate capillaries, long, inserted in two densely packed rows from chaetigers 2���8 with up to 12 chaetae per row; thereafter, notochaetae reduced in number and density; all notochaetae angle forward on chaetigers 1���8 and anterior row always with shorter. Neurochaetae smooth and limbate capillaries, inserted in two distinct rows to chaetiger 8, up to eight chaetae per row, anterior row always shorter; thereafter, number of chaetae decrease, rows become indistinct. Neuropodial sabre chaetae not observed through 20 chaetigers (all specimens incomplete). Neuropodial hooded hooks present from chaetiger 11; shaft narrow with slender main fang, surmounted by two to three fine small teeth in one row, up to six chaetae per fascicle, inner hood absent; notopodial hooded hooks not observed. Pygidium not observed. Methyl green pattern. Not observed. Remarks. The key feature of this species is the presence of only two pairs of branchiae, the apparent absence of sabre chaetae, dorsal crests occurring from chaetigers 7 to 17, and the hooded hooks starting on chaetiger 11. Two other species of Prionospio have only two pairs of branchiae: P. sexoculata Augener, 1923 and P. h er m es i a sp. nov. Prionospio kaplani sp. nov. differs from P. sexoculata because in the latter species all the branchiae are pinnate while in P. kaplani sp. nov. all are apinnate. P. h e r m e s i a sp. nov. is similar to P. kaplani sp. nov., but differs in the shape of the prostomium in particular, having a flat anterior margin as opposed to a rounded one as in P. hermesia sp. nov. (Fig. 7); the caruncle extends to anterior boundary of chaetiger 1 in P. h er m es i a, while in P.kaplani sp nov it extends to anterior boundary of chaetiger 2; the neuropodial lamellae in P. kaplani sp. nov. are rounded with extended tips while in P. h e r m e s i a sp. nov. they are merely rounded. Prionospio kaplani sp. nov. also resembles P. branchilucida sp. nov. in having similarly shaped branchiae, a similarly shaped prostomium, and the peristomium being separated from chaetiger 1. They differ in the number of pairs of branchiae, two in P. kaplani sp. nov. but three in P. branchilucida sp. nov.; the dorsal crests start on chaetiger 7 rather than 10; and the neuropodial hooded hooks start on chaetiger 11 rather than chaetigers 14���17 as in P. branchilucida sp. nov. Etymology. This species in named in honour of the Kaplan Foundation in grateful acknowledgement of their support. Distribution. Prionospio kaplani sp. nov. has been recorded from the central Pacific and NE Atlantic Oceans from depths of 4300���4942 m (Fig. 1).
Published as part of Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cunha, Marina R., Marchais-Laguionie, Claire & Glover, Adrian G., 2016, New Prionospio and Aurospio Species from the Deep Sea (Annelida: Polychaeta) in Zootaxa 4092 (1) on pages 15-18, DOI: 10.11646/zootaxa.4092.1.1, http://zenodo.org/record/259914