Aphelochaeta dearborni Blake 2018, new species

Aphelochaeta dearborni new species

Figures 9–10

Tharyx sp. Hartman 1967: 118 (in part).

Chaetozone sp.: Hartman 1978: 166 (in part).

Aphelochaeta cf. epitoca: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 717 (in part). Not Monro 1930.

Aphelochaeta sp. 2: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717, 719 (in part).

Aphelochaeta cincinnata: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717, 719 (in part). Not Ehlers 1908.

Material Examined. South Shetland Islands: West of Elephant Island, USNS Eltanin Cr. 6, Sta. 428, 1 Jan 1963, 61.30°S, 56.142°W, 662–1120 m, holotype (USNM 1013879); USNS Eltanin Cr. 6, Sta. 410, 1 Jan 1963, 61.30°S, 56.142°W, 220–240 m (1, USNM 56080); King George Island, King George Bay , R / V Hero Sta. 721- 705, 22 Dec 1971, 62.1067°S, 57.9733°W, 39 m (1, USNM 1013920); King George Island, Martel Inlet, R / V Hero Sta. 721-813, 15 Jan 1972, 62.152°S, 58.422°W, 452 m, 1 paratype (USNM 1013883); R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-325, 17 Mar 1998, 62°21.9ʹS, 58°42.6ʹW, MG, 805 m (33, SMF 24882); Sta. 48-326, 17 Mar 1998, 62°20.1ʹS, 58°38.8ʹW, MG, 606 m (11, SMF 24883); Deception Island, Foster Bay, R / V Hero Sta. 721-1048, 17 Dec 1971, 62.975°S, 60.720°W, 24 m (20, USNM 1013919).— Antarctic Peninsula: Anvers Island, Arthur Harbor, R / V Hero Sta. 721-1077, 23 Feb 1972, 64.792°S, 64.113°W, 73–128m, 1 paratype (USNM 1013880); Sta. 721-5444, 29 Mar 1972, 64.7742°S, 64.0817°W, grab, 40 m, 1 paratype (USNM 1013881); Melchior Islands , R / V Hero Sta. 824-16-4, 22 Mar 1982, 64.326°S, 62.993°W, 87 m (2, USNM 1490707); Wilhelm Archipelago, Grandidier Channel, R / V Hero Sta. 731-1887, 3 Mar 1973, 65.048°S, 64.917°W, 340–370 m, 1 paratype (USNM 1013882); Adelaide Island, R / V Hero Sta. 824-7-1, 17 Mar 1982, 66.678°S, 67.523°W, 510–730 m (1, USNM 1490708).— East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer, coll. J.A. Blake, 24 May 2000, 64°21.361´S, 058°26.637´W, SM grab, 690 m (1, JAB).— Weddell Sea, east of Antarctic Peninsula , USCG Glacier, Sta. 69-8, 02 Mar 1969, 77.603°S, 42.50°W, 585 m (5, USNM 46815); Sta. 69-11, 05 Mar 1969, 77.15°S, 38.97°W, 851 m (1, USNM 1490709); R / V Polarstern, ANDEEP II (ANT XIX/3), Sta. 61-133-6, coll. J.A. Blake, 07 Mar 2002, 65°20.18ʹS, 54°143.6ʹW, MUC, 1120 m, 1 paratype (SMF 24884); South of Cape Norvegia, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-091, 4 Feb 1998, 73°28.4ʹS, 22°48.8ʹW, MG, 1510 m (1, SMF 24885); off Halley Bay, R / V Polarstern, EASIZ II, (ANT-XV/3), coll. B. Hilbig, Sta. 48-136, 9 Feb 1998, 74°33.0ʹS, 27°13.1ʹW, MG, 2012 m (4, SMF 24886); Sta. 48-146, 10 Feb 1998, 74° 39.4ʹS, 27° 08.0ʹW, MG, 1021 m (2, SMF 24887).— East Antarctica, Leopold and Astrid Coast, Davis Station, coll. Australian Antarctic Division, Sta. STP7-P2 R4, 01 Mar 2010, 68.5767°S, 77.9450°E, diver cores, 16–19 m (1, AM).

Description. A small to moderate-sized species, holotype complete, 7.65 mm long, 0.5 mm wide across anterior setigers, 0.6 mm wide across middle segments, 0.2 mm wide across posterior segments for 60 setigers; paratype from King George Island (USNM 1013883) 21.2 mm long for ca. 100 setigers; ovigerous specimen from EASIZ II, Sta. 48-326 (SMF 24883), 8 mm long, 0.38 mm across anterior segments, 0.63 across expanded ovigerous segments, 55 setigerous segments. Anterior or thoracic region consisting of 9–10 setigers in small specimens, up to 15–20 in larger ones; anterior segments expanded, then narrowing in middle segments (Fig. 9B); posterior region narrow, cylindrical in cross-section (Figs. 9C, 10 A–C), weakly expanded on some specimens (Fig. 10G) with rounded pygidium bearing simple ventral lobe (Figs. 9C, 10 A–B, G). Ovigerous specimens with

enlarged segments in anterior and middle abdominal segments (Fig. 10A, G). Thoracic segments short, crowded (Fig. 9 A–B), becoming longer in middle abdominal segments; segments of far posterior region about as long as wide. Ventral groove absent; shallow dorsal groove present or absent on anterior segments. Ventral glands visible on mid-ventral surface of thoracic segments (Fig. 9B). Color in alcohol: tan to brown; most specimens with distinct transverse lines of black pigment spots on ventral surface of last peristomial annulus (Fig. 10 E–F).

Prostomium triangular, about as long as width of base, rounded on anterior margin (Fig. 9 A–B); eyespots absent; nuchal organs simple slits on posterior lateral margins, difficult to see in light microscopy; proboscis (ventral pharynx) everted with three lobes in one specimen (Fig. 9B, D). Peristomium compressed, elongate, with three annuli visible to variable degrees, surmounted with low dorsal crest, with narrow extension onto setiger 1. Dorsal tentacles arising medially on posterior margin of peristomium at interface with setiger 1. First pair of branchiae lateral to dorsal tentacles, positioned either at interface of peristomium and setiger 1 or on anterior margin of setiger 1 (Fig. 9 A–B); second pair of branchiae at posterior margin of setiger 1, dorsal to notosetae (Fig. 9A); subsequent segments also with branchiae arising from posterior margin, continuing on each segment for about 30 setigers, thereafter becoming fewer and irregularly distributed.

Parapodia well developed in thoracic setigers, with low shoulders set off from dorsal surfaces by longitudinal grooves (Fig. 9A); middle and posterior parapodia less distinct. Each parapodium with simple setal tori bearing fascicles of smooth-bladed capillaries; notosetae of first 9–10 setigers numbering 6–8 long capillaries; neurosetae similar but shorter. Noto- and neurosetae of mid-body numbering 5–7 per fascicle, reduced to 3–5 in posterior segments. Ovigerous specimens with long notopodial natatory-like capillaries in mid-body.

Methyl Green stain. Pattern consisting of distinct speckles from the prostomium to setiger 1, stain concentrated in small subdermal cells or glands on pre-setigerous region, providing a light green cast; ventral surface of prostomium often deeply stained (Fig. 10E); on anterior segments, narrow bands of stained speckles concentrated on posterior edge of individual segments including intersegmental groove, these narrow bands extending completely around body from dorsum to venter (Fig. 10E). In some specimens, segmental staining reaction strong, with distinct narrow transverse stripes prominent on both surfaces along body (Fig. 10E); in other specimens staining reaction weak, perhaps due to prolonged preservation in alcohol.

Etymology. This species is named for the late Professor John H. Dearborn of the University of Maine, former teacher, member of my doctoral committee, and prominent Antarctic marine biologist. Professor Dearborn introduced me to the unique biology of the Antarctic fauna. We were both part of a University of Maine team on the shakedown cruise of the R/V Hero to the eastern Canadian Arctic in August 1968.

Remarks. Aphelochaeta dearborni n. sp. is closely related to A. palmeri n. sp. (see below) in having a pearshaped prostomium, elongated peristomium formed of three weak annular rings, expanded thoracic region, and the presence of ventral glandular bands on the anterior segments. The main difference between the two species is that the posterior region of the body of A. dearborni n. sp. is narrow and not expanded as in A. palmeri and that A. dearborni n. sp. typically has lines of black pigment spots on the lower lip of the mouth. Aphelochaeta dearborni n. sp. also lacks the distinct ventral groove that is present in A. palmeri n. sp.

Habitat & Biology. Little information is available for the samples. The R/V Hero Sta. 824-7-1 sample (USNM 1490708) from Adelaide Island was collected from a bottom of rock and mud.

Holotype ovigerous, with eggs 140–190 µm across widest diameter (Fig. 10A). Gravid specimens from EASIZ II Sta. 48-326 (SMF 24883) with large mature eggs, up to 305 µm in largest diameter. Eggs of this size suggest direct development, likely in burrows of adults.

Distribution. Widespread in Antarctica, mainly shelf depths, 24–1510 m.