Daylithos nudus ( Caullery, 1944 ) Salazar-Vallejo, 2012

Salazar-Vallejo, Sergio I., 2012, 3562, Zootaxa 3562, pp. 1-62 : 56-58

Daylithos nudus ( Caullery, 1944) n. comb.

Figure 23

Stylarioides nudus Caullery 1944:32–34 , Fig. 24; Bleeker & van der Spoel 1992:160.

Type material. Western Pacific Ocean. Lectotype (ZMA-1526) and paralectotypes (ZMA-1526a), off Makian, Maluku, RV Siboga, Stat. 139 (00°11' S, 127°25' E), 397 m. One paralectotype (ZMA-1527), off Madura, Java Sea, RV Siboga, Stat. 12 (07°15' S, 115°15' E), 289 m ( Caullery 1944:32 indicated many specimens; there is a single anterior fragment).

Additional material: Western Pacific Ocean. Indonesia. One specimen ( MNHN 889 d), Karubar cruise, Stat. 31 (05°40' N, 132°51' E), 288–289 m, 26 Oct. 1991 (damaged, without posterior end, 17.5 mm long, 2.5 mm wide, cephalic cage 11 mm long, 41 chaetigers) . China. One specimen ( SMF-15387 ), Chinese-German Expedition to Hainan Island , Sanya Bay , Stat. B 92-B11-12, ottertrawl, 44 m, 23 Mar. 1992, R. Sun, coll. (8 mm long, 1.3 mm wide, cephalic cage 4 mm long, 46 chaetigers; first neurohooks in chaetiger 7). Three specimens ( SMF-15352 ), fixed inside their tubes, chaetigers difficult to count, Chinese-German Expedition to Hainan Island, Stat. B 92-26B/ Stat. 7, dredge, 11–14 m, 7 Apr. 1992, D. Fiege & R. Sun, coll. (11–13 mm long, 1.0– 1.5 mm wide, cephalic cage 3–4 mm long) .

Description. Lectotype (ZMA-1526) complete, stiff, pale greenish, slightly damaged ( Fig. 23A). Body cylindrical, tapering posteriorly into a cauda; 22 mm long, 2.8 mm wide, cephalic cage 8 mm long (damaged), 56 chaetigers. Tunic thin, free from sediment; body papillae short, rounded, arranged in two transverse bands with more papillae in the anterior band, posterior band with larger papillae; ventrally papillae sparse, arranged in longitudinal rows.

Cephalic hood and anterior end slightly exposed in one paralectotype (dissection avoided); short, margin finely papillated. Palps large, slightly darker than branchiae; palp keels and lips not seen.

Branchiae cirriform (probably sessile on branchial plate, arranged in rows); 12 filaments of different length exposed; largest ones as long as palps. Nephridial lobes in branchial plate not seen.

Cephalic cage chaetae as long as 1/3 body length, or about three times longer than body width. Chaetigers 1–2 involved in the cephalic cage; chaetae arranged in short dorsoventral lines; chaetiger 1 with 10 chaetae per bundle, chaetiger 2 with 8–9 chaetae per bundle.

Anterior dorsal margin of first chaetiger covered by an anterior extension of the dorsal shield. Anterior chaetigers without especially long papillae. Chaetigers 1–3 of about the same length. Sand cemented anterior shield dorsal, extending over chaetigers 1–4, with large sediment particles including forams, posterior margin rounded ( Fig. 23B). Chaetal transition from cephalic cage to body chaetae abrupt; chaetiger 6 with falcate neurohooks. Gonopodial lobes in chaetiger 5 low, slightly pigmented areas close to neuropodia ( Fig. 23C).

Parapodia poorly developed, chaetae emerge from the body wall. Parapodia lateral; median neuropodia ventrolateral. Noto- and neuropodia as low lobes, without especially long papillae. Noto- and neuropodia well separated.

Median notochaetae arranged in short longitudinal rows; all notochaetae multiarticulate capillaries, about as long as 1/3–1/4 body width, 2–3 per bundle, articles short basally, medial- and distally longer ( Fig. 23E). Neurochaetae in chaetigers 1–5 broken distally (two multiarticulate neurospines in chaetigers 4–5 in paralectotypes, Fig. 23F), falcate hooks from chaetiger 6, arranged in transverse rows, 2 per bundle anteriorly, up to 3 in median chaetigers ( Fig. 23G), 1–2 in posterior chaetigers ( Fig. 23H).

Posterior end subdistally swollen ( Fig. 23D); pygidium with terminal anus (or ventral in a paralectotype), without anal cirri.

Variation: Medium-sized paralectotype (ZMA-1527) is an anterior fragment, partly dehydrated; 6 mm long, 1.5 mm wide, cephalic cage 8 mm long, 17 chaetigers; dorsal shield reaches chaetiger 4, posterior margin rounded. Larger paralectotypes (ZMA-1526a) are one complete and an anterior fragment; they are 18–22 mm long, 2.8–3.0 mm wide, cephalic cage 10–11 mm long, 55 chaetigers (28 in the anterior fragment); dorsal shield reaches chaetiger 4–5, posterior margin rounded.

Remarks. Daylithos nudus ( Caullery, 1944) n. comb. groups with D. amorae n. sp. and D. dieteri n. sp. as they all have few neurohooks in far posterior chaetigers. As stated above, D. dieteri can be distinguished from the other two species by the posterior projection on its dorsal shield (against having a smooth margin). Thus, D. nudus more closely resembles D. amorae ; however, they differ in the relative number of anterior multiarticulate neurospines and in the number of transverse series of body papillae. In D. nudus there are 2 multiarticulate neurospines in chaetigers 4–5, and the body papillae are arranged in in two rows per segment, whereas in D. amorae there are 4–5 multiarticulate neurospines in chaetigers 5–6, and the body papillae are in single rows.

Caullery (1944) did not select any holotype; thus, the best specimen is being designated as the lectotype. Five syntypes (ZMA-1515, off Jolo, Sulu Archipelago, RV Siboga, Stat. 105 (06°08' N, 121°19' E), 275 m) do not belong in this species because they have small sediment particles in the dorsal shield, and pseudocompound hooks in chaetigers 3–5. Consequently they belong in Semiodera but better specimens are needed to fully describe the species. Their features for the four complete specimens (the fifth was previously cut in sections) are: 7–11 mm long (mean 9.1), 0.7–1.5 mm wide (mean 1.1), cephalic cage 3.5–6.0 mm long (mean 4.4), 28–36 chaetigers (mean 32). The dorsal shield reached chaetigers 4–5, posterior margin rounded; neurohooks of chaetigers 4–5 were pseudocompound hooks .

The South China Sea specimens (SMF-15352, SMF-15387) have been included here with some hesitation because they were collected in shallow water, and because they have falcate neurohooks from chaetiger 7; they might belong to an undescribed species, but additional material is neded before they can be described.

Distribution. Several localities in the Western Tropical Pacific Ocean, in 275–397 m deep. This species occurs at the deepest locations known for this genus.