Chaetozone truebloodi new species

Figures 17–18

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Material examined. North Equatorial Pacific Ocean, abyssal plain, Clarion-Clipperton Fracture Zone. NOAA BIE Project site, coll. D.D. Trueblood, Sandia box corer, Sta. DDT-8-94, 29 Jul 1994, 12°55.020′N, 128°35.400′W, 4880 m, holotype (USNM 1557556) .

Description. Holotype complete, 3 mm long, 0.23 mm wide across anterior setigers, 0.145 mm wide across posterior setigers, with 47–48 setigerous segments. Body elongate, narrow throughout; anterior segments not expanded (Figs. 17A, 18A), posterior segments gradually tapering toward posterior end (Fig. 18A). Several mid-body segments enlarged, due to intestinal folds filled with ingested sediment particles causing slight twist to preserved body (Fig. 18A). Dorsal and ventral grooves and ridges not present. Color in alcohol opaque white with no pigmentation.

Pre-setiger region relatively smooth, weakly triangular, about 1.5 times as long as wide (Figs. 17A, 18 A–C). Prostomium short, triangular, tapering to broadly rounded apex (Figs. 17A, 18C); eyespots absent, nuchal organs low mounds on posterior lateral margin. Peristomium smooth, with no distinct grooves or annular rings; no dorsal crest present (Figs. 17A, 18C). Paired dorsal tentacles arising from posterior quarter of peristomium, with first pair of branchiae also on peristomium immediately posterior and slightly lateral to dorsal tentacles (Fig. 17A). Second pair of branchiae on setiger 1 arising dorsal to notosetae; subsequent branchiae in similar location (Fig. 17A); branchiae or scars not observed in posterior fourth of body.

Parapodia reduced with distinct podial lobes not apparent, parapodial shoulders not developed. Dorsal surface between notopodia low, smooth, rounded. Posterior parapodia with cinctures of spines and capillaries partially elevated, but not on high membranes (Figs. 17B, 18D). All segments with long, natatory-like notosetae, 3–4 in anterior segments and 1–2 posteriorly (Figs. 17 A–B, 18C–D). Anterior setae all capillaries with about 4–5 each in noto- and neuropodia. Neuroacicular spines from setiger 9, with one spine at first increasing to 3–4 by setiger 13 and 4–5 in posterior cinctures; notoacicular spines from setiger 22, with one spine at first increasing to four per notopodium in posterior cinctures. Cinctures of 8–9 spines on a side with capillaries irregularly arranged, sometimes alternating with spines, or in multiples between spines. Individual spines curved, tapering to pointed tip (Figs. 17 C–D, 18E–F); internal core with long striations (Fig. 18F). Notoacicular spines longer (Fig. 17C) than neuropodial spines.

Posterior segments terminating in pygidium with rounded pygidial lobe ventral to anal opening (Figs. 17B, 18D).

Methyl Green stain. Stain concentrated on prostomium, a few dark speckles on dorsum of peristomium; some stain concentrated in intersegmental grooves of anterior setigers; rest of body not retaining stain.

Etymology. This species is named for Dr. Dwight David Trueblood, Project Manager and Chief Scientist for the Benthic Impact Experiment conducted for NOAA at the Clarion-Clipperton Fracture Zone in 1993–1994.

Remarks. The long, slender body of Chaetozone truebloodi n. sp. is similar to that of C. grasslei n. sp. The two species differ in the nature of the pre-setiger region where C.truebloodi n. sp. has a smooth peristomium without annular rings and C. grasslei n. sp. has two distinct rings with the first ring being large, rounded, and conspicuous. Both species have long, natatory-like capillaries, but in C. truebloodi n. sp. they are numerous and conspicuous along the entire body; whereas in C. grasslei n. sp. they are variable and mostly concentrated in a few anterior and middle segments. In addition, C. grasslei n. sp. has up to 11–14 spines on a side in posterior cinctures, whereas C. truebloodi n. sp. has no more than 8–9.

Distribution. Abyssal Pacific Ocean, 4880 m.