Sthenolepis spargens Fauchald 1972

Sthenolepis spargens Fauchald, 1972 Figs. 1–2, Table 1 Sthenolepis spargens Fauchald, 1972: 36–38, Pl. I, figs. f–i. Material examined. Holotype. North Pacific Ocean, Mexico, Mazatlán, 151 km from Mazatlán lighthouse, 22.733° N, 108.079° W, 2926 m, 13 Nov 1967, R/ V Velero IV, Campbell grab (LACM-AHF-Poly 1053). Description. Holotype incomplete with 73 segments, 17 mm long, 5 mm to segment 30, 1 mm wide. Body slender, tapered, fragile posteriorly due to poor condition; pale orange, slightly translucent (Fig. 1A). Mid-dorsal line smooth, no elytra remain, venter smooth. Elytrophores on segments 2, 4, 5, 7, then alternate segment to 25, then present in all segments. Elytrophores short, longer and thinner in posterior segments. Prostomium pale orange, darker on cerebral lobes; oval, wider than long. Eyes lacking. Lateral antennae short, inconspicuous, inserted on inner dorsal side of tentacular segment. Median antenna with ceratophore slightly shorter than prostomial length; style lost; inserted centrally on prostomium. Auricles semispherical, half as long as ceratophore; inserted basally and laterally on ceratophore. Tentacular segment uniramous, chaetae verticillate. Dorsal tentacular cirri 12× longer than tentacular neuropodia, ventral tentacular cirri short, 2× longer than tentacular neuropodia (Fig. 1B). Inner tentacular lobes ¼ larger than inner palpal sheaths (Fig. 1C). Palps reaching segment 20. Inner and outer palpal sheaths subequal. Buccal cirri, slightly larger than remaining ventral cirri. Buccal ctenidial pads, enlarged, inserted anterolaterally on buccal aperture (Fig. 1C). Ctenidial pads from segment 1; segment 1 with only one dorsal ctenidial pad, succeeding segments with 3–6 ctenidial pads: 2 large and bulbous pads placed on dorsolateral surface of segment; 1–2 smaller, half as large as dorsolateral ones, placed on dorsal side of notopodia; 0–1, small pads, placed on anterior inner side of parapodia; and 1 truncated pad, inserted ventrally. Branchiae from segment 2, small, becoming slightly larger from segment 7, filiform, cilia not seen. Nephridial papillae not observed. Elytra unknown. Segment 3 (Fig. 1E): Notopodia conical, ½ as long as neuropodia. Notacicula slender, protruding from the body wall. Notochaetae with up to 10 simple verticillate chaetae (Fig. 1E, inset), smallest 4× longer than notopodia, longest 7× as long. Neuropodia lanceolate. Prechaetal lobe entire, without stylodes. Postchaetal lobes well differentiated, without stylodes. Neuracicula thick, inserted in prechaetal lobe, protruding from the body wall. Neurochaetae only spinigers (Fig. 1D). Upper group (unit A) with 4 chaetae, handles thick with a subdistal row of small denticles, blades medium-sized, 18–20× as long as wide. Upper middle group (unit B) with 5 chaetae, blades medium-sized to long, 24–26× as long as wide. Middle group (unit C) with 4 chaetae, blades short, 12–13× as long as wide. Lower middle group (subunit 1) with 6 chaetae, blades medium-sized to long, 23–24× as long as wide. Lowest group (unit D) with 5 chaetae, blades short, 13× as long as wide. Ventral cirri 1/3 as long as neuropodia (Fig. 1E). Segment 20 (middle segment) (Fig. 2A–C): Notopodia conical, as long as neuropodia. Notacicula thick. Notochaetae with up to 20 simple verticillate chaetae (Fig. 2E, inset), smallest as long as notopodia, longest 2× longer than notopodia. Neuropodia conical. Prechaetal lobe entire with a few small dendritic stylodes on it. Postchaetal lobes well differentiated, without stylodes. Neuracicula thick, inserted in prechaetal lobe, protruding from body wall. Neurochaetae only spinigers (Fig. 2D). Upper group (unit A) with 4 chaetae, handles thick with an enlarged subdistal tooth (Fig. 2D, inset); blades short, 14–15× as long as wide. Upper middle group (unit B) with 7 chaetae, handle thick with an enlarged subdistal tooth, blades medium-sized, 23× as long as wide. Middle group (unit C) with 6 chaetae, blades medium-sized, 19–20× as long as wide. Lower middle group (subunit 1) with 3 chaetae, blades medium-sized, 20–21× as long as wide. Lowest group (unit D) with 4 chaetae, blades medium-sized, 16–17× as long as wide. Ventral cirri half as long as neuropodia (Fig. 2E). Posterior region lost. Pygidium unknown. Remarks. Fauchald (1972) described Sthenolepis spargens based on specimens from the southern Gulf of California collected at 3,108 m depth. In the original description, Fauchald (1972) stated that S. spargens possesses long lateral antennae, as well as a small dorsal cirrus on segment 3. However, examination of the holotype revealed that what Fauchald interpreted as lateral antennae are the dorsal tentacular cirri. The lateral antennae in Sthenolepis are small and located on the dorsal side of the tentacular segment but displaced to the inner side of the notopodium, very close to the anterior prostomial border covered by the auricles on the median antennal ceratophore. Therefore, they were likely overlooked by Fauchald. It was also noticed that the holotype lacks a dorsal cirrus on segment 3 and instead, has an enlarged tubercle. Fauchald (1972) discussed in the remarks section of Sthenolepis racemosa Fauchald, 1972 that S. spargens differs from all the eye-less Sthenolepis species in having four fimbriae (=stylodes) in the notopodium. The comparison between S. spargens and the eye-less Sthenolepis species was pertinent at the time. However, all those species are now contained either in Neoleanira or Leanira (e.g. Neoleanira racemosa), and both genera are known for having members eyes-less (Pettibone 1970b). The observation on the stylodes was confirmed, but their number was noticed to vary according to the segment observed, increasing in posterior segments. Currently, S. spargens differs from all Sthenolepis species, by lacking eyes and having long palps and dorsal tentacular cirri (Table 1). Distribution. Northeastern Temperate Pacific, Western Mexico, Gulf of California, 1,750 –3,400 m.