Leodamas bathyalis, Blake, 2020

Blake, James A., 2020, New species and records of deep-water Orbiniidae (Annelida, Polychaeta) from the Eastern Pacific continental slope, abyssal Pacific Ocean, and the South China Sea, Zootaxa 4730 (1), pp. 1-61 : 35-37

Leodamas bathyalis new species

Figure 17

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Material examined. South China Sea, off Brunei, Island of Borneo, Site CA1 , R / V Emma , coll. J.A. Blake, box corer, Sta. 45, 2 Jun 2011, 5°48.965′N, 114°17.317′E, 1260 m, holotype ( MCZ 153569 ) ; Sta. 38, 3 Jun 2011, 5°42.99′N, 114°09.269′E, 1353 m, paratype ( MCZ 153570 ) ; Sta. 28, 4 Jun 2011, 5°44.496′N, 114°07.708′E, 1557 m, 1 juvenile specimen ( MCZ 153571 )

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Description. A moderately sized species, all specimens incomplete. Holotype largest, 32 setigers, 6.7 mm long, 0.87 mm wide across thoracic segments; paratype 23 setigers, 2.3 mm long, 0.44 mm wide; juvenile, 13 setigers, 1.4 mm long, 0.3 mm wide. Body with narrow thoracic segments ( Fig. 17A ), flattened dorsally, rounded on venter, with lateral parapodia; thoracic segments about seven times wider than long, with prominent intersegmental furrow ( Fig. 17A ). abdominal segments narrower, with parapodia dorsally elevated. Number of thoracic segments size related: holotype with 13 thoracic setigers, smaller paratype with 10 thoracic setigers; juvenile with six thoracic setigers, all with branchiae from setiger 6. Color in alcohol: light tan.

Pre-setiger region triangular. Prostomium narrowing to rounded tip ( Fig. 17A ); nuchal organs distinct lateral grooves ( Fig. 17A ); eyespots absent. Peristomium longer, but narrower than first setiger, with a single annular ring ( Fig. 17A ) bearing dorsolateral grooves suggesting a simple dorsal crest. Proboscis everted on holotype, dendritic with numerous narrow lobes.

Thoracic notopodia low mounds, with long, narrow, digitiform postsetal lobe ( Fig. 17 A–B). Thoracic neuropodia broadly swollen, bearing up to three short postsetal lobes ( Fig. 17B ); initially a single lobe increasing to two, and then three by setiger 7 in holotype; paratype with up to two thoracic postsetal lobes; juvenile with a single thoracic postsetal lobe. Transition to abdominal segments abrupt, with fewer noto- and neurosetae. Notopodium of abdominal segments similar to those of thoracic setigers with long, digitiform postsetal lobe ( Fig. 17C ); neuropodium becoming narrow, elongate, shifted dorsally; with narrow rounded setal lobe and a short lateral ventral cirrus ( Fig. 17C ).

Branchiae from sixth thoracic setiger ( Fig. 17A ), continuing along body through posterior setigers. Branchiae of thoracic setigers narrow, triangular in shape ( Fig. 17B ); abdominal branchiae becoming larger, thickened basally, tapering to narrow tip ( Fig. 17C ).

Thoracic notosetae numerous camerated capillaries arranged in 3–4 rows. Thoracic neurosetae include heavy spines or uncini among numerous camerated capillaries ( Fig. 17B ). Uncini in two rows, with first row curving ventrally and joining second row in a U-shaped pattern. Capillaries of first four segments reduced to a fascicle dorsal to uncini; subsequent setigers with multiple rows of numerous capillaries accompanying uncini through thoracic setigers. Uncini of larger holotype thick, with blunt tip covered with a thin cloak of fibrils, shaft with transverse rows of ribs worn down to low ridge ( Fig. 17D ); smaller paratype with uncini narrower with transverse rows of ribs more prominent, resembling low barbs ( Fig. 17E ). Abdominal notosetae 2–3 long, relatively smooth capillaries with short barbs along with one edge and 1–2 furcate setae; flail setae absent. Furcate setae with unequal, blunt-tipped tynes, connected by thin web of stiff fibrils ( Fig. 17F ). Abdominal neurosetae with 2–3 long, smooth capillaries; internal acicula present but not emergent in available specimens.

Pygidium not observed.

Variability. The three specimens available represent a size range with the most obvious difference being the number of thoracic setigers: 6 in the small juvenile, 10 in the paratype and 13 in the larger holotype. All three specimens, however, have branchiae first present from setiger 6. These results suggest that the number of thoracic setigers is size-related, but the first occurrence of branchiae is invariant.

The thoracic uncini of the paratype and juvenile exhibit distinct low barbs along the shaft; these are worn down and barely visible in the larger holotype.

Methyl Green stain. Prostomium not staining; rest of body stains uniformly; de-stains rapidly.

Remarks. Leodamas bathyalis n. sp. is a distinctive species in the nature of the thoracic neuropodial uncini and the presence of up to three short postsetal lobes in thoracic neuropodia. The reduced number of capillaries in the first 3–4 thoracic neuropodia accentuates the visibility of the uncini, which are more visible than in the following setigers where they are obscured by the numerous capillaries. Superficially the more obvious neuropodial uncini in a few anterior setigers are reminiscent of species of Califia , in which heavy uncini of the first three setigers provide a prominent armature. Unlike species of Califia , however, these same uncini continue through all thoracic setigers.

Etymology. The epithet is from the Greek, bathys for deep.

Distribution. South China Sea, off Brunei, Island of Borneo, 1260–1557 m.

Figures

FIGURES 17. Leodamas bathyalis n. sp. A, anterior end dorsal view; B, thoracic setiger 9, right, posterior view; C, middle abdominal setiger, anterior view; D, neuropodial uncini (holotype); E, neuropodial uncini (paratype); F, furcate setae. A–D, F, holotype (MCZ 153569); E, paratype (MCZ 153700).