Leitoscoloplos drakei Hartman 1967, new combination

Leitoscoloplos drakei (Hartman, 1967) new combination

Figures 19–21

Orbiniella drakei Hartman, 1967: 106, pl. 34; Rozbaczylo 1985: 130. Haploscoloplos sp. Hartman 1978: 156 (in part).

Haploscoloplos kerguelensis: Hartman 1978: 156 (In part). Not McIntosh 1885.

Material examined. Drake Passage, Eltanin Sta. 4-145, 11 Aug 1962, 60.00°S, 64.82°W, 3312–3532 m, holotype and paratype (USNM 55534–5).—Drake Passage, ANDEEP I ANT XIX-3, R/V Polarstern, Sta. PS-61/043- 2, 3958 m (1, ZMH P-27789); PS-61/114- 6, 2905 m, (1, ZMH P-27790).— Weddell Sea, Glacier Sta. 68 - 18, 1664 m (20, USNM 46602); Sta. 68- 55, 2936 m (3, USNM 46603); Sta. 69- 19, 1622 m (3, USNM 46608); Sta. 69- 21, 2288 m (3, USNM 46609); Sta. 69- 27, 4575 m (1, USNM 46610).—Weddell Sea, ANDEEP II ANT XIX/4, R/V Polarstern, Sta. PS-61/131- 8, 3068 m, (1, ZMH P-27791); PS-61/132- 4, 2085 m (2, ZMH P-27792); (1, SEM, JAB); Sta. PS-61/132- 6, 2086 m (1, ZMH P-27793); Sta. PS-61/136-5, 4 741 m (1, ZMH P-27794); Sta. PS-61/138- 7, 4539 m, 4541 m (1, ZMH P-27795); Sta. PS-61/138- 8, 4539 m (1, SEM, JAB), Sta. PS-138-9, 4 538 m (2, JAB, photographic records); Sta. PS-61/138- 10, 4537 m (1, SEM, JAB); ANDEEP III ANT XXII-3, R/V Polarstern, Sta. PS-67/078- 8, 2167 m (1 juvenile, JAB); PS-67/102- 8, 4803 m (1, ZMH P-27798); Sta. PS-67/142- 7, 3406 m (1, ZMH P-27797).— South African Basin, ANDEEP III Sta. PS-67/021- 3, 4551 m (1, ZMH P-27796).

Description. Body thin, threadlike, fragile, largest complete Weddell Sea specimens 15 mm long, 0.35–0.5 mm wide for 36 setigerous segments; type specimens from Drake Passage shorter, due to absence of most of abdominal region. Color in life (ANDEEP I–II specimens) iridescent blue cuticle on transparent body (Fig 21 A); in alcohol opaque white to light tan.

Thoracic region with 8–9 short, annulated setigers, with last segment sometimes longer, transitional (Figs. 19 A, 20B); thoracic region followed by long abdominal region composed of distinctly elongated segments with parapodia located on elevated ridge on posterior border of each segment (Figs. 19 B–C, 20 C); anterior and middle abdominal segments up to 2.5x longer than wide; far posterior segments over 7x longer than wide (Figs. 19 D, 21B); fragile nature of far posterior segments probably accounting for lack of complete specimens in preserved samples. Demarcation between thorax and abdomen also identified by a reduced number of neurosetae and elongation of neuropodial lobes.

Prostomium narrowing anteriorly, conical in shape (Figs. 20 A–B, 21A–C) sometimes appearing pointed (Fig. 19 A); appearing dorsoventrally flattened with SEM in lateral view (Fig. 20 B); eyespots and nuchal organs not observed in light microscopy; nuchal organs observed in SEM (Fig. 20 B, inset); peristomium swollen, sometimes elongate and fused with setiger 1 (Fig. 20 A), weakly divided into two separate annulations (Figs. 19 A, 20B), or not.

Thoracic parapodial lobes short, stubby, indistinct (Figs. 19 A, 20B); notopodia becoming elongated and cirriform in anterior abdominal setigers (Fig. 19 B), then becoming narrower and more fingerlike in posterior setigers (Fig. 19 C–D). Abdominal neuropodia thickened, apically expanded (Figs. 19 B–D, 20C).

Thoracic noto- and neurosetae thin crenulated capillaries. Abdominal notosetae including 6–8 capillaries, furcate setae absent; abdominal neurosetae including 1–2 long capillaries; acicula imbedded, rarely with tip emergent.

Branchiae from setiger 18–20 (Fig. 19 C); branchial region missing from type specimens. Pygidium with two thin anal cirri (Figs. 19 E–F, 21B).

Description of juvenile. A complete juvenile believed to belong to this species was found in a sample from the Weddell Sea (Sta. PS-67/078-8) as part of the ANDEEP III Program on the RV Polarstern. Specimen complete, consisting of 18 setigerous segments 1.24 mm long and 0.15 mm wide (Fig. 19 F). Thorax with seven setigerous segments; separation between thoracic segments and abdomen abrupt. All thoracic segments narrow, wider than long; first two abdominal segments longer, with setiger 8 about as long as wide; following abdominal segments narrow, wider than long. Thoracic noto- and neuropodia with simple fingerlike postsetal lamellae; abdominal notopodia also with simple postsetal lamellae; abdominal neuropodia expanded into inflated glandular lobe bearing weakly notched tip. Thoracic noto- and neurosetae all camerated capillaries; abdominal notosetae also camerated capillaries; abdominal neurosetae simple, smooth capillaries, some minute, hairlike. Branchiae not developed on this juvenile. Pygidium with two lobes surrounding anus; with two long, thin anal cirri.

Remarks. Leitoscoloplos drakei is a small, fragile deep-sea species that was depicted by Hartman (1967: pl. 34) as having two distinct asetigerous segments preceding the first setiger and with branchiae absent, resulting in her referring the species to the genus Orbiniella. The illustrated specimen was the paratype. The peristomial region of that specimen, upon subsequent examination, was found to have only a single asetigerous segment. The entire peristomial area is swollen and stretched on all specimens and distinct segmental boundaries are not clear, although extra grooves may be apparent providing an appearance of an extra asetigerous segment, but this is variable. Since this species has branchiae and the abdominal parapodia are elevated and modified, it belongs to the subfamily Orbiniinae instead of Microrbiniinae and is here reassigned to the genus Leitoscoloplos. Branchiae are lacking on the type specimens. The Weddell Sea specimens, however, are more complete, with most retaining all or part of their abdominal region.

In life, complete specimens are very fragile, with posterior abdominal segments at least 7x as long as wide. It is unlikely that such specimens would often remain intact in preservation with the typical benthic sieving procedures. However, on the ANDEEP I–II cruises, an elutriation device was used where the organisms were floated out of the sediment on to a 63µm sieve. These specimens were subsequently set up in Petri dishes in a refrigerator for later examination in life. On those specimens the body in life by reflected light was observed to be of an iridescent blue color (Fig. 21 A). Branchiae were clearly present by at least setiger 20. Further, it was possible to observe the pygidium and two thin anal cirri (Fig. 21 B). Leitoscoloplos drakei differs from other species in the nature of the elongated segments, the overall threadlike appearance of the body, and lack of furcate setae.

Distribution. Drake Passage, 3312–3532 m; Weddell Sea, 1622–4575 m; South African Basin, 4551 m.