Prionospio hermesia, Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cu, 2016

Paterson, Gordon L. J., Neal, Lenka, Altamira, Iris, Soto, Eulogio H., Smith, Craig R., Menot, Lenaick, Billett, David S. M., Cu, 2016, New Prionospio and Aurospio Species from the Deep Sea (Annelida: Polychaeta), Zootaxa 4092 (1): 13-15

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Prionospio hermesia

sp. nov.

Prionospio hermesia  sp. nov. Neal & Paterson

( Figures 1View FIGURE 1, 2.4, 6, 8f, Table 2)

Material examined: 9 specimens examined in total.

Holotype: Setúbal canyon, RSS Charles Darwin 179, April –May 2006, St. 56804 #6, 38º 09.26 N, 9 º. 36.94 W, 3275 m (NHMUK 2015: 1041).

Paratypes. Nazaré canyon, RSS Discovery 297, August 2005, St. 15760 #1, 39º 30.02 N, 09º 56.17 W, 3465 m, 2 individuals; St. 15762 #1, 39º 30.02 N, 09º 56.22 W, 3464 m, 1 individual; St. 15758 #2, 39º 34.94 N, 10 º 19.00 W, 4332 m, 1 individual.

Nazaré canyon, RSS Charles Darwin 179, April/ May 2006, St. 56851 #1, 39º 29.99 ’ N, 9 º 55.97 ’ W, 3517m, 2 individuals.

Setúbal canyon, RSS Charles Darwin 179, April/ May 2006, St. 56816 #1, 38º09.27’ N, 9.36.94’W, 3275m, 1 individual.

Cascais canyon, RSS Charles Darwin 179, April/ May 2006, St. 56821 #2, 38º 17.97 ’ N, 9 º 46.89 ’ W, 3214m, 1 individual.

Diagnostic features. Two pairs of branchiae; lack of sabre chaetae; hooded hooks bi- or tridentate.

Description. Very small and slender species, holotype incomplete with 53 chaetigers, measuring 5.65 mm long and 0.08 mm wide at chaetiger 1. Colour in alcohol pale yellow. Body narrow and cylindrical, of uniform width throughout. Prostomium oval, anteriorly slightly rounded, prostomial margin entire, prostomial peaks absent, posteriorly elongated into short blunt caruncle, extending to anterior of chaetiger 1 ( Fig. 6View FIGURE 6 a –b); eyes not observed. Peristomium well developed, ventrally and laterally distinct, dorsally partially fused to chaetiger 1, forming a collar around prostomium, without forming distinct lateral wings.

Branchiae 2 pairs, on chaetigers 2 and 3, both pairs apinnate with surface smooth to slightly wrinkled ( Fig. 6View FIGURE 6 a,b); first pair longest, very slender, cylindrical, at least twice the length of corresponding notopodial lamellae, inserted laterally to the base of notopodial lamellae, but not connected to it ( Fig 6View FIGURE 6 a); second pair short, about half the length of corresponding notopodial lamellae and one-third the length of first branchial pair, attached near the base of notopodial lamellae (Fig. 2.4 b).

Notopodial lamellae on chaetiger 1 not developed; lamellae small, subquadrangular on chaetiger 2; lamellae greatly enlarged on chaetiger 3, subtriangular, the distal tip bent and pointed to the midline of the dorsum (Fig. 2.4 b), in subsequent chaetigers notopodial lamellae reducing in size, becoming rounded. Dorsal chests from chaetiger 8 ( Fig. 6View FIGURE 6 c) to approximately chaetiger 25.

Neuropodial lamellae on chaetiger 1 not developed, thereafter well developed if small and rounded on all segments, with the exception of chaetiger 3, on which they are shifted dorsally (Fig. 2.4), enlarged (at least twice the size of neuropodial lamellae on other segments), oar-shaped, sometimes extending from body horizontally.

Capillary chaetae particularly dense in anterior region, arranged in two rows in both noto- and neuropodia, capillaries in anterior row very long capillaries in posterior row shorter, all lightly granulated, limbate. Sabre chaetae absent. Neuropodial hooded hooks present from chaetiger 13 in holotype, from chaetiger 14 in other specimens, often only single hooks present at first but up to seven hooks per fascicle in subsequent chaetigers; primary hood rounded, tightly follows the head of the hooks, secondary hood present and well developed; some hooks bidentate with large main fang and smaller secondary tooth, others appear to be multidentate (at least tridentate) with main fang and at least two smaller teeth above, arranged in a single row. Notopodial hooks present singly from chaetiger 48. Pygidium unknown.

Methyl green pattern: The anterior half of prostomium and peristomium stain strongly, the margins of the notopodial and neuropodial lamellae on chaetigers 4–14 stain less intensely.

Remarks. The distinguishing feature of this species is that it has only two pairs of branchiae. This species has affinities with Prionospio branchilucida  sp. nov. and P. kaplani  sp. nov. from abyssal plains. Lack of sabre chaetae is unusual, but was encountered in all three species ( P. hermesia  sp. nov., P. branchilucida  sp. nov., and P. kaplani  sp. nov.). Further similarity with Prionospio kaplani  sp. nov. is that it also possesses a combination of bidentate and multidentate hooks (1 + 3 combination), and these hooks also appear to be flattened in SEM images (unlike the chunky, more inflated style of hooks in other Prionospio  species). In both species dorsal crests begin on segment 8, but only a single pair of very short branchiae on the second chaetiger was found in P kaplani  sp. nov. compared with in P. hermesia  sp. nov. Prionospio branchilucida  sp. nov. has a prostomium similar to that of P. hermesia  sp. nov. and has similar branchiae on the second chaetiger, but at least three pairs of branchiae were confirmed to be present in P. branchilucida  sp. nov., hooks appear to be more like the usual shape found in Prionospio  in SEM images, and the dorsal crests begin after chaetiger 8.

Etymology. P. hermesia  sp. nov. named after the research programme HERMES.

Distribution. P. hermesia  sp. nov. has been recorded from the Nazaré, Setúbal and Cascais canyons of the Portuguese margin at depths of 3214–4364 m.