Prionospio austella sp. nov.

Figure 1 A – X

Material examined. GULF OF MEXICO. Yucatan: Off Alacranes Island, E15, 22°26'N, 90°27'W, 91.2 m, 30 October 1990, DINAMO II, holotype (CNAP-ICML, UNAM: POH-09-00).

Description. A large species. Holotype incomplete, 17.0 mm long with 51 chaetigers, 1.0 mm wide. Color in alcohol, opaque, white. Prostomium bottle-shaped, truncate on anterior margin, with a small medial peak (Fig. 1 A), posteriorly tapered, with a long, narrow caruncle extending to the anterior edge of chaetiger 3 without (not observed) nuchal organs on either side (Fig. 1 A). Two pairs of orange subdermal eyes, arranged in a trapezoid: first pair crescent-shaped, posterior pair with large eyespots (Fig. 1 A). Palps lost. Peristomium moderate, collar-like, surrounding the prostomium, partially fused dorsally with large rounded notopodial lamellae of chaetiger 1 (Fig. 1 B). Neuropodial postchaetal lamellae on chaetiger 1 large, rounded (Fig. 1 C), slightly shorter than the notopodial lamellae.

Four pairs of long, thin branchiae present on chaetigers 2–5; first pair longest and thickest, extending up to chaetiger 6. Pairs 1 and 4 with long, dense digitiform pinnules on the posterior face, branchiae with smooth, long, naked distal tips (Fig. 1 D). Distribution of pinnules on these two pairs similar, pinnules numerous, distributed in the middle region, but pair 4 with longer, naked distal tips; the central stem of branchial pairs 1 and 4 pinnate, elongate. Pairs 2 and 3 apinnate, densely ciliated laterally, triangular, wider, with short sharp tips (Fig. 1 E); branchiae subequal in size and length to the notopodial lamellae and smaller than those on pair 4.

Notopodial postchaetal lamellae triangular on chaetigers 2–5 (Fig. 1 F, G); largest on chaetigers 3–5 with prolonged tips directed upwards; lamellae wider and squarer with triangular tips on chaetiger 6 (Fig. 1 H), becoming elongated, square on chaetiger 8 (Fig. 1 I). Lamellae of chaetiger 13 gradually becoming smaller, rounder (Fig. 1 J, K). Notopodial lamellae of middle and posterior chaetigers small, wider, dorsally directed with subtriangular dorsal edge (Fig. 1 L). Notopodial lamellae united across dorsum, forming low dorsal folds on chaetigers 6–11 (Fig. 1 M). Chaetiger 3 with the ventral and dorsal edges of the notopodial and neuropodial lamellae touching. Notopodial prechaetal lamellae very large on chaetigers 2–7, basally fused with the notopodial postchaetal lamellae (Fig. 1 F – H), smaller on chaetigers 8–26 (Fig. 1 I – K) and rudimentary from chaetiger 27.

Neuropodial postchaetal lamellae on chaetiger 2–3 large and subtriangular, ventrally pointed (Fig. 1 N, O), largest on chaetiger 2; becoming oval on chaetigers 4–8 (Fig. 1 P), and subsequently rounded and small on far posterior chaetigers (Fig. 1 Q). Neuropodial prechaetal lamellae large on chaetigers 3–11 (Fig. 1 O, P), not basally fused to postchaetal lamellae, progressively decreasing in size on subsequent chaetigers. Interparapodial pouches lacking.

All capillaries thicker on anterior notopodial chaetigers, alimbate, heavily granulated, with very long capillary tips (Fig. 1 R), arranged in two rows, the anterior row shorter than posterior row; notopodial and neuropodial capillaries of chaetiger 1 with short, thin chaetae, notopodial chaetae longer. Chaetae of middle notopodia arranged in two rows, with the dorsal chaetae long and ventral chaetae short, without granulations (Fig. 1 T); posterior notopodia with thinner, shorter chaetae than middle notopodia. Anterior neuropodial capillaries slender, heavily granulated, alimbate, with very long capillary tips (Fig. 1 S). Chaetae of middle neuropodial capillaries slender, not granulated, with long capillary tips (Fig. 1 U); posterior neuropodial capillaries with thinner, shorter chaetae than those on the middle neuropodia. Sabre chaetae in neuropodia from chaetiger 10, up to two per fascicle, stout, long, with slightly curved tips, distinctly granulated, without sheaths (Fig. 1 V). Neuropodial hooded hooks (Fig. 1 W) from chaetiger 16, up to 10 per fascicle, accompanied by up to three capillaries. Notopodial hooded hooks (Fig. 1 X) from chaetiger 46, up to four per fascicle, accompanied by up to three capillaries; all hooks with four pairs of small teeth above long main tooth, without secondary hood (Fig. 1 W, X); hooks with a slightly curved main tooth, neuropodial hooks with a thicker tooth and a very large principal hood (Fig. 1 W); notopodial hooks with very large stems (Fig. 1 X).

Pygidium not known.

Remarks. From the descriptions of the 35 previously known species in the P. s t e en s t r up i group (Sigvaldadóttir & Mackie, 1993: Table 2; Blake, 1996; Sigvaldadóttir 1997; Zhou & Li 2009), Prionospio austella is very similar to P. steenstrupi in having a bottle-shaped prostomium that is truncate on the anterior margin; large, subtriangular neuropodial lamellae on chaetiger 2 and ventrally pointed, low dorsal folds on the postbranchial chaetigers. However, P. austella can be distinguished from the redescription of P. steenstrupi by Sigvaldadóttir & Mackie (1993) in that the former has a prostomium with a small medial peak on the anterior margin; wider and more rounded notopodial lamellae with triangular tips on chaetiger 6, becoming square on chaetiger 8; dorsally directed notopodial lamellae with subtriangular dorsal edges on the middle and posterior chaetigers; low dorsal folds limited to chaetigers 6–11; large, rounded neuropodial postchaetal lamellae on chaetiger 1; large, subtriangular neuropodial lamellae on chaetiger 3; ventrally pointed, not ventrally open, pockets on the anterior chaetigers; all hooks with 4 pairs of small teeth above the long, main tooth and no secondary hood. P. austella is also very similar to P. oligopinnulata sp. nov. in having large, subtriangular ventrally pointed lamellae on chaetigers 2 and 3 and dorsal folds on the postbranchial chaetiger. However, P. austella differs from P. oligopinnulata in having a bottleshaped prostomium that is truncate on the anterior margin with a small medial peak; a long, narrow caruncle extending to the anterior edge of chaetiger 3; branchial pairs 1 and 4 with long, dense digitiform pinnules on the posterior face; low dorsal folds limited to chaetigers 6–11; the ventral and dorsal edges of the notopodial and neuropodial lamellae touching on chaetiger 3; very large notopodial prechaetal lamellae on chaetigers 2–7, basally fused with the notopodial postchaetal lamellae; large neuropodial prechaetal lamellae on chaetigers 5–11; neuropodial hooded hooks from chaetiger 16; notopodial hooded hooks from chaetiger 46 and all hooks without a secondary hood. Further differences between this new species from the other species examined are provided in the key and Table 1.

Type locality. Southern from Mexico Gulf: Campeche.

Etymology. The specific name is from the Latin austellus meaning south and refers to the southern region of the Gulf of Mexico.