Aphelochaeta aubreyi Blake 2018, new species

Aphelochaeta aubreyi new species

Figures 2–3

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

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

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

Material Examined: East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer Cr. 2000- 03, coll. J.A. Blake, SM grab, Sta. 01, 14 May 2000, 64°17.625ʹS, 058°34.678ʹW, 768 m, 12 paratypes (LACM- AHF Poly 10202); Sta. 03, 15 May 2000, 64°53.533ʹS, 059°30.694ʹW, 385 m, 18 paratypes, some juveniles (MCZ 149879); Sta. 35A, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m, holotype (LACM-AHF Poly 10200) and 9 paratypes (LACM-AHF Poly 10201); Sta. 27, 23 May 2000, 64°22.934ʹS, 058°36.976ʹW, 684 m (10, MCZ 149833); Sta. 28, 23 May 2000, 64°22.018ʹS, 058°30.942ʹW, 794 m (5, MCZ 149884); Sta. 29, 24 May 2000, 64°21.361ʹS, 058°26.637ʹW, 690 m (2, MCZ 149885); Sta. 30, 24 May 2000, 64°16.875ʹS, 058°26.985ʹW, 843 m (2, JAB); Sta. 33, 24 May 2000, 64°11.959ʹS, 058°41.857ʹW, 587 m (14, MCZ 1498819); Sta. 34, 24 May 2000, 64°10.995ʹS, 058°34.140ʹW, 865 m (4, MCZ 149882); Sta. 35, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m (2, JAB); off Cape Longing, Sta. 02, 15 May-2000, 64°18.387ʹS, 058°37.911ʹW, 504 m, (6, MCZ 149880); Former Larsen A Ice Shelf area, Sta. 04, 16 May 2000, 64°49.209ʹS, 060°32.033ʹW, 668 m (1, JAB); Sta. 21, 20 May 2000, 64°45.827ʹS, 060°19.450ʹW, 912 m (2, JAB); Sta. 26, 23 May 2000, 64°39.564ʹS, 059°13.226ʹW, 564 m (3, MCZ 149886).— Weddell Sea, South of Cape Norvegia, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-091, 4 Feb 1998, MG, 1510 m, 73°28.4ʹS, 22°48.8ʹW, 1510 m (1, SMF 24879); Sta. 48-136, 09 Feb 1998, 74°33.0ʹS, 27°12.7ʹW, MG, 2012 m (1, SMF 24881).— Drake Passage, R / V Polarstern, EASIZ II (ANT- XV/3), coll. B. Hilbig, Sta. 48-345, 20 Mar 1998, 61°53.3ʹS, 59°06.9ʹN, MG, 218 m (5, SMF 24880).— South Shetland Islands, King George Island , R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-299, 14 Mar 1998, 62°15.8ʹS, 58°42.7ʹW, MG, 207 m, (1, SMF 24875); Sta. 48-300, 14 Mar 1998, 62°16.8ʹS, 58°42.1ʹW, MG, 423 m (3, SMF 24876); Sta. 48-326, 17 Mar 1998, 62°20.1ʹS, 58°38.8ʹW, MG, 606 m (3, SMF 24877); Sta. 48-330, 18 Mar 1998, 61°20.6ʹS, 58°15.1ʹW, MG, 2009 m, (2, SMF 24878).— West Antarctic Peninsula, Anvers Island, off Palmer Station, R / V Hero Sta. 731-1912, 06 Mar 1973, 64°46ʹ52ʺS, 064°03ʹ35ʺW, 25–55 m, (1, USNM 1490701); off Melchior Islands, R / V Hero Sta. 824-16-2, 22 Mar 1982, 64°19.50ʹS, 62°59.58ʹW, 85 m, 18 paratypes (USNM 1490702). Biscoe Islands, Grandidier Channel, Larrouy Island , R / V Hero Sta. 824-5-1, 65.94°S, 65.297°W, 16 Mar 1982, 246– 270 m (5, USNM 1490703).

Description. A small to moderate-sized species, holotype complete, body coiled, approximately 10 mm long, 0.5 mm wide across anterior and posterior segments (Fig. 3 A–B), 0.3 mm across middle segments, with 85 setigerous segments; large paratypes from Sta. 35A (LACM-AHF Poly 10201) up to 10 mm long, 0.5 mm wide with about 110 segments. Body elongate, more or less cylindrical in cross section; anterior segments expanded laterally and ventrally with anterior 15–20 segments narrow (Figs. 2B, 3A), each segment six times wider than long. Segments becoming longer and rounded in middle and posterior body regions (Figs. 2C, 3 A–B), each about as wide as long, some oval or weakly to strongly moniliform (Fig. 2C), but variable; posterior 12–15 segments again becoming weakly to moderately inflated, with venter flat or weakly grooved, tapering to pygidium consisting of terminal anus and ventral lobe (Figs. 2C, 3B). Dorsal groove narrow, inconspicuous and weakly developed, limited to posterior thoracic segments and first few abdominal segments. Color in alcohol tan; small black pigments spots normally visible on posterior lateral margins of peristomium (Fig. 2 A–B). Anterior thoracic segments with mid-ventral glands visible across a few middle segments.

Prostomium triangular, rounded on anterior margin (Fig. 2 A–B); eyespots absent; nuchal organs narrow slits on posterior margin (Fig. 2B), difficult to observe; proboscis or ventral pharynx, consisting of 2–4 lobes everted on some specimens (Fig. 2B). Peristomium relatively smooth, elongate, with one short annular ring posterior to prostomium followed by longer second ring (Fig. 2 A–B), sometimes incised by 2–3 thin furrows producing 2–3 additional rings when contracted, these best observed laterally and when stained with Shirlastain A; weak dorsal crest or ridge present over peristomium extending to near posterior margin (Fig. 2A), not observed on all specimens unless stained with Shirlastain A. Dorsal tentacles arise from posterior margin of peristomium (Fig. 2 A–B); first pair of branchiae lateral to dorsal tentacles; second pair of branchiae on setiger 1, dorsal to notosetae (Fig. 2A); subsequent branchiae in same position.

Parapodia reduced to low mounds with setae emerging directly from body wall. All setae capillaries with notosetae of anterior segments long, up to 10–12 per fascicle, reduced to about six setae in middle body segments, and 3–4 setae in far posterior segments. Neurosetae always shorter than notosetae, with about 8–9 per fascicle in anterior segments and 3–4 posteriorly. Natatory setae not observed.

Methyl Green stain. Pre-setiger area not retaining stain; stain concentrated in intersegmental grooves of thoracic and anterior abdominal segments, mainly on venter; stain dissipates rapidly.

Etymology. This species is named for my late colleague, Mr. Stephen B. Aubrey, who left us too soon. Steve was one of the best at-sea field scientists I have ever known, with expertise ranging from the application of sophisticated electronic data gathering to the collection of water column and benthic biology samples. Steve was also an Antarctic veteran, having participated in research on the ecology of the Dry Valley lakes.

Remarks. Aphelochaeta aubreyi n. sp. has dorsal tentacles arising from the posterior margin of the peristomium and the first pair of branchiae located lateral to the dorsal tentacles; the second pair of branchiae are on setiger 1. This pattern is typical for most of the Antarctic species of Aphelochaeta. The characters that define A. aubreyi n. sp. are the relatively smooth nature of the elongate peristomium with only two weakly developed annular rings, the first of which is short, followed by a long second ring; the presence of black pigment spots on the dorsolateral margins of the peristomium; the enlarged, rounded, and weakly moniliform setigers in the middle and posterior segments; a weak to moderately expanded posterior end; and a nearly complete lack of any MG staining reaction. Among Antarctic species, A. aubreyi n. sp. is most closely related to A. hormosa n. sp. in having an expanded thoracic region, moniliform abdominal segments, and lateral black spots on the posterior lateral margins of the peristomium. The two species differ in that A. hormosa n. sp. has a strong and distinctive MG staining pattern and prominent lateral grooves on the peristomium that produce two distinct partial annular rings. In addition, the posterior segments of A. aubreyi n. sp. are enlarged dorsally and flattened ventrally; whereas, in A. hormosa n. sp. the posterior segments, while rounded dorsally and flattened ventrally, are not enlarged dorsally.

Aphelochaeta aubreyi n. sp. is similar to A. monilaris, the type-species from off California (Hartman 1960), in having expanded anterior and posterior body regions joined by a long section with narrow, rounded, or moniliform segments. The two species differ most importantly in that A. monilaris, when stained with MG, has prominent transverse bands across the venter of anterior segments (Blake 1996) that are lacking in A. aubreyi n. sp.

Habitat. Seafloor sediments in the vicinity the former Larsen-A ice shelf area were collected together with biological samples in May 2000 (Domack et al. 2001). Due to the glacial cover formerly overlying the area, the surficial sediments contained high concentrations of sand (20–40%) from particles dropped to the seafloor (Gilbert & Domack 2003). The sample from R/V Hero Sta. 824-5-1 (USNM 1490703) in the Grandidier Channel was collected on a rocky bottom.

Distribution. Drake Passage, South Shetland Islands, West Antarctic Peninsula, 25–606 m; East Antarctic Peninsula, 385–912 m; Weddell Sea, 1500 m.