Semiodera treadwelli, Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 39-41

Semiodera treadwelli n. sp.

Figure 15

Siphonostomum cariboum: Treadwell 1901:208 (non Grube & Ørsted in Grube 1859).

Type material. Grand Caribbean Region. Holotype (USNM-16163) and paratype ( USNM 1191185 ), U.S. Fish Commission Porto Rico Expedition, 1898–99, RV Fish Hawk, Stat. 134-5 (6062-3), 25–30, 137– 139 m, 20 Jan. 1899 (paratype damaged, dried-out, incurved, 5 mm long, 0.7 mm wide, cephalic cage 4 mm long, 36 chaetigers; falcate neurohooks from chaetiger 9, only one hook left).

Additional material: Grand Caribbean Region. Quintana Roo, México. Two specimens ( ECOSUR 1754 ), one complete, Punta Nizuc (21°01'23" N, 86°46'52" W), 3 m, 31 Aug. 1997, L. Carrera, coll. (complete 9.5 mm long, 2 mm wide, cephalic cage 4 mm long, 40 chaetigers; falcate neurohooks from chaetiger 9, two per bundle in median chaetigers). One specimen ( ECOSUR 1756 ), Punta Herradura (18°32'26" N, 87°44'30" W), 3 m, 28 Oct. 1997, L. Carrera & SISV, coll. (9 mm long, 1.5 mm wide, cephalic cage 4 mm long, 39 chaetigers). Two specimens ( ECOSUR), one complete, Punta Nizuc, 2 m, 31 Aug. 1997, L. Carrera, coll. (9.5 mm long, 2 mm wide, cephalic cage 4 mm long, 39 chaetigers). One specimen ( ECOSUR 1757 ), without posterior end, Punta Nizuc (21°01'23" N, 86°46'52" W), coralline rock, 4 m depth, 1 Sep. 1997, L. Carrera & SISV, coll. One specimen ( ECOSUR 1758 ), broken in two, Xahuayxol (18°30'15" N, 87°20'32" W), coralline rock, 3 m depth, 28 Sep. 1997, L. Carrera, coll. (6.5 mm long, 1 mm wide, cephalic cage 3.5 mm long, 33 chaetigers). Three specimens ( ECOSUR 1759 ), without posterior end, Rio Indio, coralline rock, 2 m depth, 17 Mar. 2001, L. Carrera & SISV, coll. One specimen ( ECOSUR 1760 ), Majagual (18°43'01" N, 87°42'23" W), 2 m depth, 18 Mar. 2001, L. Carrera & SISV (13 mm long, 2 mm wide, cephalic cage 3 mm long, 42 chaetigers). One specimen ( ECOSUR 1761 ), without posterior end, Majagual (18°43'01" N, 87°42'23" W), coralline rock, 2 m depth, 21 Mar. 2001, L. Carrera & SISV, coll. One specimen ( ECOSUR 1762 ), Cozumel, off SEDENA store, coralline rock, 3 m depth, 24 Mar. 2001, L. Carrera & SISV, coll. (8 mm long, 1 mm wide, cephalic cage 3.5 mm long, 36 chaetigers; falcate simple neurohooks from chaetiger 10). One specimen ( ECOSUR 1763 ), Punta Nizuc (21°01'23" N, 86°46'52" W), 2 m, 8 Feb. 2002, R. Bastida & SISV, coll. (10.5 mm long, 1.8 mm wide, cephalic cage 4 mm long, 37 chaetigers). Seven specimens (USNM-1177558s), Smithsonian Bredin Expedition, Stat. 72–60, Bahia Ascension (19º47'57" N, 87º28'31" W), central part of Nicchehabin Reef, 1.2–1.8 m, 14 Apr. 1960 (complete ones 5–11 mm long, 1.0– 1.5 mm wide, cephalic cage 2.5–3.0 mm long, 31–34 chaetigers; the modified cephalic shield is described below). Lesser Antilles. One specimen ( UMML), juvenile, off SW tip of Grenada, RV Pillsbury, Stat. 852 (11º53'N, 61º53' W), 13 m, 3 Jul. 1969 (6 mm long, 1 mm wide, cephalic cage 3.5 mm long, 40 chaetigers). Southeastern Brazil. One specimen, EP 264 (complete, 5.5 mm long, 1.3 mm wide, cephalic cage 3 mm long, about 34 chaetigers; falcate neurohooks from chaetiger 9, two hooks per bundle).

Description. Holotype (USNM-16163) complete, pale brown, incurved ventrally ( Fig. 15A). Body cylindrical, tapering posteriorly into a short thick cauda; 7 mm long, 1.3 mm wide, cephalic cage 5 mm long, 30 chaetigers. Tunic thin, free from sediment cover; body papillae large, capitate, arranged in two irregular rows per segment, papillae few, eroded (non-type specimens with 4–6 rows per segment, Fig. 15E), with two small interramal papillae; posterior region with longer, club-shaped papillae.

Anterior end not exposed; not dissected to avoid further damage. Observed in non-type specimens (ECOSUR Rio Indio, 17 Mar. 2001). Cephalic hood exposed, short, margin smooth. Prostomium low cone with four eyes, medium-sized, dark-brown, not coalescent. Caruncle not projected dorsally. Palps twice as long and four times thicker than branchiae; palp keels rounded, elevated. Lateral lips rounded, well developed.

Branchiae cirriform, sessile on branchial plate, decreasing in size laterally; 6 larger, distal filaments, 3–4 proximal smaller filaments. Nephridial lobes arise internally, below distal larger branchiae, and before smaller lateral branchiae.

Cephalic cage chaetae about as long as body length, or about four times longer than body width. Chaetigers 1–2 involved in the cephalic cage; chaetae arranged in short rows, about the body corners; chaetiger 1 with 7–8 chaetae per ramus, chaetiger 2 displaced dorsally, with 4–5 chaetae per ramus.

Anterior dorsal margin of chaetiger 1 projected ventrally, papillated ( Fig. 15B, E, F), two longer distal median papillae and 2–3 additional smaller ones per side. Anterior chaetigers without especially long papillae, probably eroded; chaetal lobes with digitate papillae, slightly longer than body ones. Chaetigers 1–2 shorter than chaetiger 3. Sand cemented anterior shield probably eroded or removed ( Fig. 15B, C); in non-type specimens (USNM- 1177558), cemented sand grains extending posteriorly through chaetigers 2–8 ( Fig. 15D–F), and ventrally along chaetigers 1–2 (in some specimens), not reaching the midventral line. Chaetal transition from cephalic cage to body chaetae gradual; pseudocompound hooks in chaetigers 3–8 ( Fig. 15G). Falcate simple neurohooks from chaetiger 9. Gonopodial slits short, transverse slits in chaetiger 5 ( Fig. 15F, arrow).

Parapodia poorly-developed, chaetae emerge from the body wall. Parapodia lateral, median neuropodia ventrolateral. Noto- and neuropodia without projections, lobes, or longer papillae. Noto- and neuropodia distant to each other. Median notochaetae eroded, posterior ones arranged in a tuft; all notochaetae multiarticulate capillaries, probably as long as ¼ body width, 1–2 per bundle, articles irregularly sized. Neurochaetae thick multiarticulate capillaries in chaetigers 1–2; neuropodia 3–8 with long pseudocompound hooks, 2 per ramus, decreasing in size posteriorly; falcate yellow neurohooks from chaetiger 9, arranged in transverse rows, 2 per ramus in most chaetigers ( Fig. 15H); posterior chaetigers with a single neurohook.

Posterior end tapering in to a hemispheric lobe; pygidium with terminal anus; no anal cirri.

Etymology. This species is named after the late Aaron L. Treadwell in recognition of his many publications on Caribbean polychaetes.

Type locality. Puerto Rico, in 137–139 m.

Remarks. Semiodera treadwelli n. sp. belongs in the group with a poorly-developed dorsal shield and having two neurohooks in median chaetigers, and includes S. nishi and S. salazarae n. sp. However, unlike the other species, S. nishi has neurohooks from chaetiger 8 (as opposed to chaetiger 9), rendering S. treadwelli more similar to S. salazarae . These two species differ because in S. treadwelli the dorsal shield includes small particles and they are sparse, whereas in S. salazarae sand grains are large and densely packed. An additional difference lies in the ventral extension of the dorsal shield because in S. treadwelli these lateral projections do not reach the midventral line but in S. salazarae the shield is ventrally connected.

The shallow-water specimens are in better condition and the abundant papillae are more easily seen than in the type material from deeper water, where the papillae have been severely eroded. It would be interesting to compare with fresh materials from the type locality to confirm that the specimens from shallow water are in fact the same species as the deeper water specimens, or whether the specimens from shallow water represent as yet an undescribed species.

Distribution. Northwestern Caribbean, Puerto Rico to Brazil, in shallow to about 140 m depth.