Leitoscoloplos gordaensis, 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 : 10

Leitoscoloplos gordaensis new species

Figures 3–4

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Material examined. Gorda Ridge, off northern California, Escanaba Trough, HOV Alvin Dive 2042, coll. J.F. Grassle, 12 May 1988, 41°00.4′N, 127°29.3′W, 3271 m, holotype ( MCZ 153564 ) and 30 paratypes ( MCZ 153565 ) ; same station, clam washings, 2 specimens ( MCZ 153566 ) .

Description. A moderate-sized species, holotype incomplete, 23 mm long and 1 mm wide for 63 setigers; some paratypes complete, up to 20 mm long and 1.7 mm wide for approximately 90 setigers. Body elongate, with narrow crowded segments throughout ( Figs. 3 A–B, 4A–C); thoracic and 1–2 transitional segments about six times wider than long; middle and posterior segments narrower, more crowded. Transition from thoracic to abdominal segments marked by development of three annular rings ventral to neuropodia, consisting initially of a broad medial ring joined on subsequent segments by two thin lateral intersegmental rings ( Fig. 4 B–C), thus providing ventral surface of each abdominal segment with three rings and an intersegmental groove between each segment. These rings most prominent in middle body segments ( Fig. 4C ), becoming shallower and less evident in posterior segments. Both dorsal and ventral surfaces smooth, lacking longitudinal grooves or ridges. Some paratypes mature females with large irregularly shaped eggs, ranging from 290–350 µm in diameter. Color in alcohol: opaque white.

Prostomium triangular, short ( Figs 3A , 4A ), with nuchal organs elongate slits on posterior lateral margin ( Fig. 4A ), eyespots absent. Peristomium with one or two annular rings, first longer and narrower than second when two present ( Figs. 3A , 4A ); presence of one or two peristomial rings not size related. Thorax with ten setigers followed by 1–2 transitional setigers ( Fig. 4B ); boundary between last thoracic setiger and first abdominal demarcated by loss of most neurosetae and increase in size of neuropodial lobe on setigers 11–12 ( Fig. 4B ).

Thoracic notopodial and neuropodial lobes elongate with triangular base, both similar in form ( Fig. 3C ); abdominal notopodia becoming narrower, more elongate, shifting dorsally in position ( Figs. 3 D–E, 4D); abdominal neuropodia thickened, with two terminal lobes ( Figs. 3 D–E, 4D); subpodial flanges and papillae absent. Branchiae first present from setiger 14–16 as rudiments; gradually increasing in size over middle abdominal segments, becoming broad and flattened, about one-third longer than notopodial lobe ( Figs. 3 D–E, 4D).

All notosetae camerated capillaries; thoracic notosetae arranged in a tight fascicle with capillaries appearing to arise from a spiral, numbering about 30–40 per fascicle; abdominal capillaries numbering 15–20 per notopodium in anterior and middle setigers, reduced to 10–18 in posterior setigers. Thoracic neurosetae all capillaries, with one prominent anterior row and 2–3 poorly organized secondary rows, numbering about 25–30 fascicle; abdominal neurosetae include 2–5 capillaries and 1–3 narrow aciculae with tips emergent, each short, smooth with rounded tip; furcate and flail setae absent.

Pygidium bluntly rounded, bearing two thin elongate cirri ( Fig. 3B ).

Variability. The separation of the two peristomial rings is sometimes apparent only laterally, with the groove not crossing the dorsum. The anal cirri are usually lost, best observed on smaller specimens.

Methyl Green stain. No pattern, body stains uniformly.

Remarks. Leitoscoloplos gordaensis n. sp. belongs to the L. kerguelensis group in having branchiae first present from anterior abdominal setigers ( Blake 2017). The five species in this group from the eastern North Pacific are separated from the others in the key above and by additional characteristics in Table 1 . Of the four species that lack furcate setae, L. gordaensis n. sp. and L. lunulus n. sp. each have a relatively short pre-setal region where the prostomium and peristomium are separated from one another by a distinct groove. The two species differ significantly from one another in that L. lunulus n. sp. has a ventral cirrus and subpodial flange on the abdominal neuropodia that are lacking in L. gordaensis n. sp.

Etymology. The species is named for its occurrence on the Gorda Ridge.

Distribution. Eastern Pacific, off northern California in the vicinity of hydrothermal vents on the Gorda Ridge, Escanaba Trough, 3271 m.

Figures

FIGURE 3. Leitoscoloplos gordaensis n. sp. Holotype (MCZ 153564): A, anterior end, dorsal view. Paratype (MCZ 153565): B, posterior end, dorsal view; C, thoracic setiger, anterior view; D, anterior abdominal setiger, posterior view; E, posterior abdominal setiger, posterior view.

FIGURE 4. Leitoscoloplos gordaensis n. sp. Holotype (MCZ 153564):A, anterior end, left lateral view; B, posterior thoracic and anterior abdominal setigers, left lateral view, setigers numbered; C, middle abdominal setigers, left lateral view, arrows denote tri-annular rings on venter. Paratype (MCZ 153565): D, posterior abdominal setiger, anterior view. Stained with Shirlastain A.