Trochochaeta kirkegaardi Pettibone 1976

Trochochaeta kirkegaardi

Disoma orissae.—Kirkegaard, 1959:26 [not Fauvel, 1932].

MATERIAL EXAMINED.—West Africa, Atlantide Expedition (as Disoma orissae by Kirkegaard, 1959): off Liberia, 06°03′N, 10°25′W, 44 m, sta. 55, 8 January 1946, paratype (UZMC); off Gold Coast, 05°37′N, 0°35′E, 150–175 m, sta. 84, 30 January 1946, holotype (UZMC); off Nigeria, 04°01′N, 07°56′E, 66 m, sta. 116, 23 February 1946, paratype (UZMC).

DESCRIPTION.—Body long, slender, divided into short, flattened, wider thoracic region and long, cylindrical, more slender abdominal region (Figures 8a–d). Length of incomplete holotype of 60 segments (anterior and two middle fragments) 24 mm, greatest width in thoracic region 2 mm, including setae. Length of incomplete paratype (sta. 55, off Liberia) of 43 segments 15 mm, width 1 mm. Length of incomplete paratype (sta. 116, off Nigeria) of 25 segments 12 mm, width 3 mm.

Prostomium (Figure 8a) small, fusiform, narrowing and truncate anteriorly, with nuchal crest beginning anteriorly as small subtriangular median antenna and continuing posteriorly on segment 3; without eyes. Pair of tentacular palps wedged between prostomium and parapodia of first segment; palps ribbon-like, long (about 16 mm in length on holotype, free in vial; missing on paratypes).

Anterior four segments of thoracic region with modified biramous parapodia, differing from one another (Figures 8a,b, 9a–m).

First or peristomial segment (Figures 8a, 9a,b) with parapodia shifted dorsally, directed anteriorly and enclosing prostomium; notopodial and neuropodial lobes indistinct, with short and longer, slender, smooth capillary setae (Figure 9b); notosetae relatively few (about 10); neurosetae numerous, forming fan-shaped spreading bundles; notopodial and neuropodial postsetal lobes elongate, subulate, wider basally.

Second segment (Figures 8a, 9c–e) with parapodia shifted ventrally, lateral to mouth; notosetae lacking but with subconical notopodial lobe; neuropodial setal lobe low, wide, with fan-shaped group of acicular neurosetae (about 8), alternating with equal number of more slender capillary neurosetae, both types curving dorsally (Figure 9e); postsetal neuropodial lobe oval, much smaller than notopodial.

Third segment (Figures 8a, 9f–j) with parapodia lateral; notopodial lobe low, with fan-shaped bundle of smooth capillary notosetae (Figure 9h), shorter anterior row and longer posterior row, and with suboval postsetal lobe; neuropodial lobe wide, low, with fan-shaped bundle of stout, reddish amber-colored acicular neurosetae (about 5), alternating with equal number of slender, curved capillary neurosetae, both types curving dorsally (Figure 9i); postsetal neuropodial lobe suboval, similar to notopodial. Right third parapodium of holotype (Figure 9j) differing from that on left side (Figure 9f,g), with more numerous neurosetae (9 acicular, light amber-colored, and 9 capillary, resembling those of segment 2) and smaller bundle of notosetae. Parapodia of third segment on two paratypes symmetrical and not asymmetrical, as on holotype.

Fourth segment (Figure 8a, 9k–m) with parapodia lateral, with similar notopodial and neuropodial lobes; setal lobes low, wide, with capillary setae, anterior row of shorter ones and posterior row of longer ones; setae limbate and somewhat frayed (Figure 9l,m); postsetal lobes wide, subrectangular.

Following 11 thoracic segments (segments 5 to 15) with prominent lateral parapodia, with reddish-brown glandular areas ventral to neuropodia (Figures 8a,b, 10a–i). Parapodia of segments 5 to 10 similar, with lateral biramous parapodia (Figures 8a, 10a–f). Notopodial setal lobes low, wide, with limbate, frayed capillary notosetae—anterior row of shorter ones and posterior row of longer ones. Notopodial postsetal lobes wide, subrectangular. Neuropodial setal lobes short, wide, subcylindrical, with compact bundles of neurosetae of two slightly different types—shorter, slightly stouter, reddish amber-colored, frayed or spinous, tapered rather abruptly to short slender tips and longer, frayed, tapered gradually to capillary tips (Figure 10b,d). Neuropodial postsetal lobes wide, subrectangular, subequal to notopodial (segment 5, Figure 10a) or larger than notopodial (segments 6–10, Figure 10c,e,f). Parapodia of segments 11 to 15 with notopodia represented only by small subconical lobes, lacking notosetae (Figure 10g,i); neurosetae similar to those of preceding thoracic segments but becoming fewer in number, especially stouter, shorter type (Figure 10h); neuropodial postsetal lobes smaller than those of preceding segments (Figures 8b, 10g,i).

Abdominal region beginning on segment 16 (Figure 8b), long, narrower than thoracic region, thin-walled, with paired round to oval structures visible dorsally (Figure 8c) and paired delicate papillae ventrally (Figure 8d). Parapodia inconspicuous, lacking notopodial lobes and notosetae (Figure 10j). Neuropodial lobes small, rounded, with few (2–3), slender, non-limbate capillary neurosetae and few (3–4), stouter, acicular neurosetae with subterminally attached aristae (Figure 10k). Postsetal neuropodial lobes digitiform, continuing posteriorly as delicate, flat, longitudinal flanges (Figure 10j). Posterior abdominal region and pygidium unknown.

DISTRIBUTION.—West Africa, in 44 to 175 m.