Euarche mexicana Pettibone 1989

Euarche mexicana

MATERIAL EXAMINED.-GULF OF MEXICO. SE and NW Gulf, R/V Alaminos cruises, from L.H. Pequegnat: sta A9-15, 11 Jun 1965, 23°N, 86°48′W, 604 m, holotype (USNM 98793); sta A13-4, 12 Nov 1968, 25°38.4′N, 96°18.3′W, 512 m, paratype (USNM 98794); sta A13-15, 18 Nov 1968, 27°34.5′N, 95°10.5′W, 658–860 m, paratype (USNM 98795); sta A13-24, 20 Nov 1968, 27°29.5′N, 95°31′W, 878 m, paratype (USNM 98796).

DESCRIPTION.—Length 32–84+ mm, width with setae 8–12 mm, with 41–90+ segments. Elytra delicate, transparent, transversely elongate-oval, attached eccentrically on lateral side, leaving middorsum uncovered (Figure 8D–H).

Prostomium oval, bilobed, without eyes but with pair of large oval whitish areas; ceratophore of median antenna, with few lateral papillae, attached on posterior part of prostomium, with style extending slightly beyond prostomium; lateral antennae attached on anterior part of prostomium, similar to median antenna; palps stout, long, tapered, with longitudinal rows of papillae extending most of their length (Figure 8A,B).

Tentacular segment distinct dorsally, with raised nuchal ridge to which ceratophore of median antenna is attached; tentaculophores lateral to prostomium, with 2 acicula, small nuchal lobe, and 2 groups of few long capillary setae; tentacular cirri longer and stouter than antennae, ventral tentacular cirri slightly longer than dorsal ones (Figure 8A–C).

Second segment with first pair of elytrophores and biramous parapodia; notopodia small, conical, with bundle of finely spinous capillary notosetae on lower part, extending slightly beyond tip of neuropodium; neuropodia rounded with hairy tapered neurosetae; ventral buccal cirri longer than following ventral cirri (Figures 8A,B, 9A,B).

Pharynx (not extended, cut open on paratype, USNM 98795) with 13 pairs of border papillae, middorsal one longer than others, on wide base; midventral one short (damaged?), on wide base; 2 pairs of stout hooked jaws with 6–8 lateral teeth.

Notopodia of segments 3 to 8 similar to those of segment 2 (Figure 9C,G,H), with bundle of short capillary setae; dorsal cirri on segments 3, 6, and 8 with short cirrophores and tapered styles extending beyond neuropodia (Figure 9C,H); neuropodia with slightly bilobed presetal acicular lobes and truncate postsetal lobes, with short upper anterior bracts enclosing upper group of slender, spinous, tapering neurosetae (Figure 9D,G–I) and ventroanterior bracts enclosing lower group of curved neurosetae, with large spines basally and close-set spines distally (Figure 9F–H); middle neurosetae stouter, acicular, with subdistal hairs and long hairy aristae (Figure 9E,H,J).

From segment 9 on, notopodia larger, flattened, on anterodorsal side of neuropodia, with development of internal spinning glands, with few short capillary notosetae (Figures 9K, 10B,C,G); lower group of neurosetae enclosed in anteroventral bracts, similar to more anterior ones (Figure 10J); middle acicular neurosetae with subdistal spines and long hairy aristae (Figures 9L, 10E,I); upper group of neurosetae enclosed in upper anterior bract, of 2 types: (a) long, slender, hairy, tapering to slender tips; (b) shorter, more slender, with whorls of widely spaced spines (Figure 10D,H). Dorsal cirri short, subulate, about same size as ventral cirri (Figure 10A,F). No distinct branchial vesicles, although parts of body and parapodia delicate, transparent.

DISTRIBUTION.—Gulf of Mexico. In 512 to 878 meters.