Diplocirrus octobranchus (Hartman, 1965) Hartman, 1965

Salazar-Vallejo, Sergio I. & Buzhinskaja, Galina, 2011, Revision of Diplocirrus Haase, 1915, including Bradiella Rullier, 1965, and Diversibranchius Buzhinskaja, 1993 (Polychaeta, Flabelligeridae), ZooKeys 106, pp. 1-45 : 32-34

Diplocirrus octobranchus (Hartman, 1965) comb. n. Fig. 11

Ilyphagus octobranchus Hartman 1965:178-179, Pl. 39; Hartman and Fauchald 1971:120-121.

Diplocirrus octobranchus : Day 1973:107 (informal comb. n.); Darbyshire and Mackie 2009:97, Table 1.

Type material.

Eastern Atlantic Ocean. Holotype (LACM-AHF 540) and 19 paratypes (LACM-AHF 541), off New England, United States, RV Atlantis Stat. Slope 3 (39°58'24"N, 70°41'18"W), 300 m, 28 Aug. 1962, H. Sanders, coll. (two complete paratypes 7-16 mm long, 0.8-1.0 mm wide, cephalic cage 0.8-2.0 mm long, 24-42 chaetigers; gonopodial papillae not visible; smaller paratypes with relatively more sand particles over their bodies; broken mature female with oocytes about 120 µm).

Additional material.

North Carolina. One specimen (USNM-54938), Eastward Stat. 6269 (34°16.5'N, 75°44'W), 500-520 m, 11 Nov. 1966, G. Rowe, coll. One specimen (USNM-54932), Eastward Stat. 6241 (33°13.6' N, 76°13.4' W), small biological trawl, 1000-1020 m, 9 Nov. 1966, G. Rowe coll.

Description.

Holotype an anterior fragment, brownish. Body anteriorly swollen, posteriorly tapered (Fig. 11A); 8.5 mm long, 1 mm wide (widest by chaetigers 5-6, 2 mm), cephalic cage 2 mm long, 17 chaetigers. Tunic papillated, sediment particles mostly fine, adherent on papillae bases, and few larger sand grains, especially dorsally (Fig. 11B); smaller specimens with more sand particles on the body. Papillae of varying lengths, longer dorsally and on chaetal lobes, may be as long as chaetae, shorter in the rest of the body, 4-5 rows per chaetiger.

Cephalic hood tube long, made of two rings, basal one shorter, both smooth; cephalic hood margin smooth. Prostomium low, eyes not seen (Fig. 11C). Caruncle low, wide. Palps lost (pale, laterally corrugated, 1.5 times longer than branchiae in one paratype); palp keels rounded, elevated. Lateral lips thick, projected outwards, rounded. Ventral lip reduced. Dorsal lip projected as a triangular lobe. Branchiae cirriform of two different widths; posterior row with thicker filaments, rectangular, with a middorsal black band, branchial bases continuous, anterior row with branchiae thinner, cirriform, separated in two lateral pairs. Branchiae of about the same length; size relationships with palps unknown. Nephridial lobes in branchial plate low, whitish.

Cephalic cage chaetae as long as widest body section. Only chaetiger 1 involved in the cephalic cage; chaetae arranged in a short, dorsolateral line with 4(-5) noto- and 2(-8 in paratypes) neurochaetae. Anterior dorsal margin of first chaetiger papillated. Chaetigers 1-3 progressively larger. Post-cephalic cage chaetigers not elongated. Chaetal transition from cephalic cage to body chaetae abrupt, thicker neurospines present from chaetiger 2. Gonopodial lobes not seen.

Parapodia poorly-developed, chaetae emerge from the body wall (Fig. 11D). Parapodia lateral; median neuropodia ventrolateral. Noto- and neuropodia without pr ojected chaetal lobes. Papillae abundant, 2-4 larger ones in chaetal lobes. Noto- and neuropodia close to each other.

Median notochaetae arranged in a short transverse line, chaetae directed dorsally. All notochaetae multiarticulated capillaries. Median notochaetae 1.5-2.0 times as long as body width, 7 per bundle, articles short basally, feebly defined, become medium-sized medially, long distally (Fig. 11E). Neurochaetae multiarticulated capillaries in chaetiger 1; thicker multiarticulated neurospines from chaetiger 2, two (-5 in paratypes) per ramus, become thinner in the tapered median and posterior region, being 5 per ramus, arranged in a transverse line. Neurochaetae with feebly-defined short, basal articles, become very long medially, and decrease progressively to the straight tip (Fig. 11F).

Posterior end observed in one complete paratype, tapering to a swollen pygidium, with anus dorsoterminal, without anal cirri. One paratype is a damaged female, oocytes 100-150 µm.

Remarks.

Diplocirrus octobranchus (Hartman, 1965), comb. n., is closely allied to an undescribed species from Antarctica, and both differ from other species with long papillae because they have sand particles over the body. These two species differ in the extent of sediment particles along the papillae and on the relative length of the neurochaetal anchylosed region. Thus, in Diplocirrus octobranchus sediment particles are restricted to the base of papillae, and their neurochaetae have an anchylosed region of about one-fifth of the chaetal length, whereas in the Antarctic undescribed species, the sediment particles spread along the papillae, and the anchylosed region might be about half or one-third of the chaetal length.

Diplocirrus octobranchus is a typical member of the genus because its branchiae are of two different widths. It does not belong in Ilyphagus because it has multiarticulated neurospines, with long articles in the medial and distal regions, and short articles only basally, whereas in Ilyphagus neurochaetae are aristate spines with very short articles basal- and medially, and distally hyaline. Further, the cephalic cage chaetae in Ilyphagus are clearly dorsal whereas in Diplocirrus they are lateral, or dorsolateral at most. After Hartman amended Ilyphagus ( Hartman 1965:177), the correct placement for her new species as a member of Diplocirrus was indirectly stated by comparing it to Diplocirrus glaucus , the type species for the genus ( Hartman 1965:179). This made Day (1973:106) suggest the informal, new combination, which is herein confirmed after the examination of the type material and of the redefinition of Diplocirrus .

Distribution.

Apparently discontinuous; off New England in 300-1000 m, and off northeastern South America in 770-805 m.