Exogone (Exogone) longicornis Westheide, 1974

Exogone (Exogone) longicornis Westheide, 1974 View in CoL

Fig. 77A–L

Exogone longicornis Westheide, 1974: 117 , figs. 54, 55.

Material examined. AUSTRALIA: WESTERN AUSTRALIA. 1 specimen, AM W26666, jetty adjacent to Fisheries Hut, Beacon Island, 28°25.5'S 113°47.0'E, dead coral with plate-like species ( Acropora and Montipora ), 12 m, P.A. Hutchings, 23 May 1994. 5 specimens, AM W26667, east side of West Wallabi Island, 28°27.9'S 113°40.9'E, in Posidonia australis root mat, plus epifauna, 2 m, P.A. Hutchings, 26 May 1994.

Additional material. Santa Cruz Island, Galápagos Islands, 2 specimens, W. Westheide. Coiba National Park, Panamá, Granito de Oro Island, intertidal coarse sand, 13 specimens.

Description. Both Australian specimens anterior fragments, about 22 chaetigers, one specimen is a mature male with natatory chaetae; complete specimens from Panamá 2.9 mm long, 0.2 mm wide, 33 chaetigers. Body long and slender, filiform. Prostomium square to oval, wider than long; 4 large eyes nearly in rectangular arrangement. Antennae inserted between anterior pair of eyes, close to each other; median antenna long, slightly thick, cylindrical, similar in length to prostomium and palps together or slightly longer; lateral antennae small, ovoid (Fig. 77A). Palps slightly longer than prostomium, fused all their length, with a distinct dorsal furrow, with a distal notch. Peristomium shorter than following segments, covering posterior margin of prostomium; tentacular cirri small, papilliform. Dorsal cirri ovoid, small, shorter than parapodial lobes, present on all segments (Fig. 77A). Parapodia of chaetiger 1 with 1, sometimes 2, shafts of compound chaetae enlarged, forming a large, stout, triangular process near tips; process covered by small, short spines on distal side of that process (Figs. 77B,C,D), blades relatively short, with moderate long marginal spines, distally bifid, about 14 µm long; in addition about 5–6 compound chaetae with shafts distally slightly enlarged, hemigomph articulations, and a few thin spines, and blades short, about 4–5 µm long, distal tooth slightly shorter than sub-distal tooth, and few thin, moderately long marginal spines (Fig. 77E). Remaining anteriormost parapodia with similar falcigers, and unmodified spinigerlike chaetae. Anterior and midbody parapodia each with solitary spiniger-like chaetae; shafts provided with short spines, and blades relatively short, indistinctly bidentate, with short marginal spines (Fig. 77G), 26 µm long, and 3– 4 falcigers, shafts distally slightly enlarged and provided with short spines, and small blades, smooth or provided with short marginal spines (Fig. 77H) similar in length to those of most anterior parapodia. Posterior parapodia of the fragments each with a similar spiniger-like chaetae, with slender blade, apparently unidentate, with minute marginal spines (Fig. 77J), 20 µm long, in addition 3 compound falcigers with short, small, smooth blades, distal tooth small (Fig. 77K), about 4 µm long. Dorsal simple chaetae from chaetiger 2, with rounded tips and finely spinulose subterminally (Fig. 77F,I). Ventral simple chaetae not seen. Acicula solitary, distally rounded (Fig. 77L). Pharynx long, through 5 segments; pharyngeal tooth on anterior margin (Fig. 77A). Proventricle similar in length to pharynx, through 4–5 segments, with 33–38 muscle cell rows.

Remarks. The original description omits the presence of compound spiniger-like chaetae with modified shafts on chaetiger 1; the examined specimens from Galápagos Islands, however, have them as do the Australian specimens and those from Panamá. The figured specimen of the original description (Westheide, 1974, fig. 54A) shows a shorter proventricle and a longer median antenna than those of the Australian specimens; the examined specimen from Galápagos and those from Panamá have a long proventricle, and some specimens have shorter median antenna than others, suggesting that they all represent a single species. Exogone (E.) rostrata Naville, 1933 , from the Mediterranean Sea, and the Canary and Madeira Islands, is apparently morphologically identical (see Alós et al., 1983; San Martín, 1984a, 2003; Pascual & Núñez, 1999). It could be a circumtropical species or a complex of similar species; until this problem has been resolved I am retaining the name longicornis for the Pacific specimens.

Distribution. Galápagos Islands. Pacific coast of Panamá. Australia (Western Australia).

Habitat. Interstitial in coarse sand; in dead corals. Shallow bottoms.