Leitoscoloplos simplex Blake, 2017, new species

Leitoscoloplos simplex new species

Figure 6 D–E

Material examined. North equatorial Pacific Ocean, abyssal plain, Clarion-Clipperton Fracture Zone, NOAA BIE Sta. DDT-08-93, 0 2 September 1993, 12°55.633′N, 128°36.011′W, 0.25 m 2 box core, 4843 m, coll. D.T. Trueblood, holotype (USNM 1407119).

Description. Holotype incomplete, 5.5 mm long, 0.6 mm wide across thorax for 22 setigers. Body cylindrical in cross section; parapodia lateral, abdominal parapodia only partially elevated dorsally. Thoracic and anterior abdominal segments about 4.5x as wide as long; more posterior abdominal segments about as long as wide. Thorax with eight setigers, transition to abdominal segments evident by enlargement of neuropodium and development of a ventral cirrus. Branchiae entirely absent from fragment. Pygidium unknown. Color in alcohol, light tan; no body pigment.

Prostomium conical, wide, basally tapering to rounded anterior margin; without eyespots, nuchal organs not observed (Fig. 6 D). Peristomium a single ring, wider than long, about 1.5x as long as anterior thoracic setigers.

Thoracic notopodia enlarged, somewhat swollen, with narrow, finger-like postsetal lobe which becomes wider basally and more triangular in shape along thoracic segments (Fig. 6 D); thoracic neuropodia not as large as notopodia (Fig. 6 D); postsetal lamellae absent on setiger 1, short, fingerlike postsetal lobe present from setiger 2 and continuing through thoracic setigers (Fig. 6 D); abdominal neuropodia enlarged, elongate, swollen apically with short, ventral cirrus., only partially elevated dorsally (Fig. 6 E).

Thoracic noto- and neurosetae long crenulated capillaries in dense fascicles of 75 or more setae. Notosetae of first 2–3 abdominal setigers similar to thoracic segments with dense fascicles of long capillaries; subsequent abdominal segments with fewer and shorter capillaries, reduced in number to 20–25 per notopodium (Fig. 6 D–E). Abdominal neurosetae few, reduced to 4–6 very fine capillaries; 1–2 embedded aciculae present (Fig. 6 E).

Etymology. The species name is from the Latin simplex and refers to the overall lack of typical orbiniid morphology.

Remarks. Leitoscoloplos simplex n. sp. is similar to L. abranchiatus in lacking branchiae, having long capillary setae in dense fascicles, and by having abdominal parapodia only weakly elevated instead shifted dorsally as in most orbiniids. These two deep-sea species differ in that L. simplex n. sp. has a peristomium with a large single ring instead of 2–3 weak lobes, has ventral cirri in abdominal neuropodia instead of lacking them, and most significantly, lacks furcate setae that are present in L. abranchiatus.

Distribution. Abyssal Pacific, 4843 m.