Aphelochaeta brandtae Blake 2018, new species

Aphelochaeta brandtae new species

Figures 6–7

Material examined. Weddell Sea, E of Antarctic Peninsula, R / V Polarstern, ANDEEP II (ANT-XIX/4), Sta. PS 61/133-5, 07 Mar 2002, 65°20.27ʹS, 54°12.54ʹW, MUC, 1166 m, holotype (SMF 24954); Sta. PS 61/132-6, 07 Mar 2002, 65°17.77ʹS, 54°0.00ʹW, box corer, 2086 m, 1 paratype (MCZ 1439888).— Weddell Sea, off Coats Land, USCG Glacier, Sta. 69-20, 12 Mar 1969, 73.823°S, 31.682°W, 2288 m (1, USNM 1490706).— Drake Passage, North of South Shetland Islands, R / V Polarstern, ANDEEP I (ANT-XIX/3), Sta. PS61/43-2, 29 Jan 2002, 60°26.95ʹS, 56°4.96ʹW, box corer, 3957 m, 3 paratypes (SMF 249556).— Scotia Sea, R / V Polarstern, ANDEEP I (ANT-XIX/3), Sta. PS61/46-3, 01 Jan 2002, 60°37.92ʹS, 53°57.17ʹW, box corer, 2888 m, 8 paratypes (SMF 24956); Sta. PS61/46-5, 01 Jan 2002, 60°38.13ʹS, 53°57.68ʹW, box corer, 2894 m, 2 paratypes (SMF 24957).

Description. A small species, all specimens incomplete; holotype an ovigerous female, mostly complete, 6.4 mm long, 0.4 mm wide across anterior segments, with 39 setigers; paratype from Sta. 46-3, 5.9 mm long, 0.44 mm wide across expanded anterior setigers, with 31 segments. Anterior 7–10 segments narrow, about eight times wider than long (Fig. 6 A–B), then narrowing to 12–20 middle rounded segments about as wide as long, not moniliform (Fig. 7B); last 7–10 segments narrow, elongate. Anterior expanded segments with prominent parapodial shoulders and low rounded dorsum slightly elevated over parapodia (Fig. 6 A–B), without longitudinal groove. Venter weakly rounded, typically without ventral groove, specimen from Glacier Sta. 69-20 (USNM 46797) with narrow ventral groove from middle segments to end of fragment; each anterior segment with broad band of glandular tissue across venter, that stains with MG (Fig. 7 A–B). Holotype with large oblong eggs protruding from body in pairs (Fig. 7 D–E), four per segment; individual eggs approximately 280 x 150 µm. Color in alcohol light tan; no accessory pigment.

Prostomium triangular, narrowing to pointed tip on anterior margin (Fig. 6 A–B); eyespots absent; nuchal organs narrow slits located laterally just anterior to peristomium (Fig. 6B). Peristomium with two annular rings, second twice as long as first, best seen laterally (Fig. 6 A–B); second ring sometimes subdivided into a third ring; annular grooves lateral, not extending over dorsum; dorsal surface with prominent dorsal crest extending from end of first annular ring to anterior margin of setiger 1 (Fig. 6 A–B). Dorsal tentacles arising at posterior margin of peristomium lateral to dorsal ridge (Fig. 6 A–B). First pair of branchiae posterior and lateral to dorsal tentacles on posterior margin of peristomium; second pair of branchiae arising from posterior margin of setiger 1, posterior to notosetae (Fig. 6B).

Anterior parapodial shoulders elevated over dorsum, prominent on setigers 7–10, depending on size of specimen (Fig. 6 A–B); holotype with eight anterior setigers (Fig. 6B); paratype with 10 (Fig. 6A); anterior setae arising from low podial lobes; noto- and neurosetae arising close together along entire body. Setae all capillaries, some long but not natatory, with about 11–13 per notopodia and 8–10 in neuropodia in expanded anterior setigers, reduced to 4–5 in middle and posterior segments. Capillaries all thin, appearing smooth in light microscopy.

Methyl Green stain. Prominent and distinctive MG pattern present; some specimens staining strongly, others lightly. Prostomium and peristomium with distinct pattern dorsally, separated by unstained area (Fig. 7A, C); dorsally stained area terminating abruptly at posterior margin of peristomium (Fig. 7C); peristomial stain continuing around to ventral side, but not as prominent and limited to posterior half of peristomium. Holotype with strong prostomial stains dorsally and ventrally, but with peristomial stain lighter, reduced to a speckled pattern. Stain concentrated in dorsal segmental grooves on a few anterior segments. Ventrally, broad glandular bands of anterior segments staining intensely producing broad dark blue stripes across venter of anterior segments (Fig. 7 A–B), some specimens with ventral stripes on most anterior segments, others limited to 2–4 segments, but these very intense and distinctive; ventral stripes extending laterally up and onto neuropodia, but not crossing dorsum.

Etymology. This species is named for Prof. Dr. Angelika Brandt, prominent pericarid specialist, deep-sea ecologist, and friend. Dr. Brandt was the expedition leader for the ANDEEP surveys of deep-sea habitats in Antarctica. She is currently Head of the Department of Marine Zoology at the Senckenberg Research Institute and Natural History Museum Frankfurt, Germany.

Remarks. Aphelochaeta brandtae n. sp. is a relatively small deep-sea cirratulid that is readily distinguished from its congeners in having a smooth pre-setiger region, short expanded anterior thoracic region, and a distinctive MG staining pattern. Anterior setigers transition abruptly to more or less rounded or oval abdominal segments with reduced parapodia; these segments are not moniliform.

The large, paired oblong eggs that protrude from the body wall of this species (Fig. 7 D–E) are unusual and suggest a modified type of reproduction with direct development and possible brood protection.

The MG stain is distinctive with a defined pre-setiger staining pattern on prostomium and peristomium and with a clear ocular area between them, similar to that of A. spectabilis n. sp. However, the very intensely stained broad transverse MG stripes on the venter are unique among Antarctic bitentaculate cirratulids. In addition, A. spectabilis n. sp. does not have rounded abdominal segments.

Habitat. Sediments from the Drake Passage and Scotia Sea samples were typical deep-sea silt-clay with some cobble; samples from the Weddell Sea were greenish grey, silt-clay with some sand and pebbles (Diaz 2004; Howe et al. 2004).

Distribution. Antarctica: Drake Passage, Scotia Sea, Weddell Sea; slope and abyssal depths, 1166–3957 m.