Aphelochaeta spargosis, Blake, 2019

Blake, James A., 2019, New species of Cirratulidae (Annelida, Polychaeta) from abyssal depths of the Clarion-Clipperton Fracture Zone, North Equatorial Pacific Ocean, Zootaxa 4629 (2), pp. 151-187 : 159-161

Aphelochaeta spargosis new species

Figures 5–6

urn:lsid:zoobank.org:pub:6CA6FD2C-ABAF-4FCC-A328-4EB1854FD7C3

Tharyx sp. B: Wilson & Hessler 1987: Appendix E (in part).

Tharyx sp. C: Wilson & Hessler 1987: Appendix E (in part).

Material examined. North Equatorial Pacific Ocean, abyssal plain, Clarion-Clipperton Fracture Zone, ECHO I, DOMES Site C, R/ V Melville cruise, coll. R. Hessler, 0.25 m 2 Sandia box core, H351, 1– 5 cm fraction, 14 Jun 1983, 14°37.6334′N, 125°26.3840′W, 4516 m, holotype ( LACM-AHF Poly 11260) and fragments ( LACM-AHF Poly 11261) ; Sta. H 362C, 0–1 cm fraction, 18 Jun 1983, 14.7013°N, 125.4309°W, 4480 m, 1 paratype ( LACM- AHF Poly 11262) .

Description. A small species, but more robust, not threadlike as most other cirratulids from the CCFZ. Holotype complete, pygidium with minor damage, 6.2 mm long, 0.94 mm wide across swollen anterior segments, 0.65 mm wide across middle and posterior segments, with 58 setigerous segments. Holotype with body thick, robust, anterior segments swollen producing large dorsal hump and prominent ventral swelling ( Fig. 5A ); paratype with anterior segments not as swollen, dorsum appearing flaccid. Individual segments narrow, crowded along entire body; larger rounded segments entirely absent. Dorsum generally rounded throughout, venter flattened, with shallow groove ( Fig. 5B ). Body gradually narrowing in posterior segments; no enlargement or separate narrowing of far posterior segments; pygidial segment with terminal anus surrounded by several lobes ( Fig. 5B ). Color in alcohol light tan.

Pre-setiger region thick, about as long as first nine crowded setigers ( Fig. 5A ). Prostomium short, bluntly rounded on anterior margin; eyespots absent; nuchal organs narrow slits on posterior lateral margin. Peristomium with three annular rings, best developed laterally; dorsum with narrow crest, not crossed by annular rings ( Fig. 5A ). Dorsal tentacles on posterior margin of peristomium; first pair of branchiae lateral to tentacles ( Fig. 5A ). Second pair of branchiae on setiger 1 dorsal to notosetae; subsequent branchiae in similar locations. Most branchiae broken or stubs, short intact branchiae present in middle segments.

Parapodia well developed throughout with swollen podial lobes forming distinct lateral shoulders ( Fig. 5A ). Noto- and neurosetae all capillaries arising close together but on distinctly separate noto- and neuropodia. All capillaries of first 12–15 segments long, projecting dorso-laterally, providing a bristled appearance to anterior swollen segments. Anterior notosetae numbering 15 or more per fascicle; anterior neurosetae numbering about 10–12 per fascicle; capillaries of middle and posterior segments shorter, reduced to 7–8 in notopodia and 4–6 in neuropodia. Individual capillaries thin, with no fibrils evident in light microscopy. Long, natatory setae not evident.

Methyl Green stain. Prominent MG staining pattern evident ( Fig. 6 ). Holotype with distinct lateral bands crossing prostomium and peristomium, with heavy banding defining three peristomial rings. Prostomium crossed by single band. Parapodia with stain concentrated on posterior borders of noto- and neuropodia along entire body, continuing as a broad band across venter and also across dorsum on first 4–5 setigers, rest of dorsum generally unstained. Paratype also with bands encircling anterior segments, but less prominent.

Etymology. The epithet is from the Latin, spargosis , for distension or swelling, referring to the very enlarged and swollen anterior segments of this species.

Remarks. Aphelochaeta spargosis n. sp. is a unique species in the nature of the swollen anterior segments. All segments are crowded and narrow throughout with prominent parapodial shoulders along the entire body. There is no evidence of any enlargement or narrowing of the posterior segments. In addition, the species has a prominent and distinctive MG staining pattern. Aphelochaeta hormosa Blake, 2018 from Antarctica has a similar appearance to the anterior end and a distinctive MG staining pattern but a long section of the body has moniliform segments and the capillaries on anterior segments are short, not conspicuously long.

Distribution. Abyssal Pacific Ocean, 4480–4516 m.

Figures

FIGURE 5. Aphelochaeta spargosis n. sp. Holotype (LACM-AHF Poly 12260):A, anterior end, right lateral view; B, posterior end, right lateral view.

FIGURE 6. Aphelochaeta spargosis n. sp. Holotype (LACM-AHF Poly 12260): Anterior end, right lateral view methyl green staining pattern (arrows).