Scoloplos bathytatus Blake, 2017, new species

Scoloplos bathytatus new species

Figure 22, 23 A–F

Scoloplos (Leodamas) marginatus: Hartman 1967: 108 (in part, Sta. 480). Not Ehlers 1897. Scoloplos (Leodamas) ohlini: Hartman 1978: 156. Not Ehlers, 1901.

Haploscoloplos kerguelensis: Hartman 1978: 156 (in part, some found in Sta. 68-1). Not McIntosh 1885.

Material examined. Drake Passage, Eltanin Sta. 6-384, 25 Dec 1962, 57.03°S, 56.47°W, 3138–3426 m, 1 paratype (USNM 60685); R/V Polarstern, ANDEEP I, Sta. PS-61/042- 6, 3692 m. 28 Jan 2002, box core, (1, ZMH P-27783); Sta. PS-61/046- 3, 2888 m, (1, ZMH P-27784); Sta. PS-61/046-5, 30 Jan 2002, 2893.6 m, box core (1, ZMH P-27785); Sta. PS-61/114- 6, 2905 m (1, ZMH P-27786); Sta. PS-61/114- 8, 2905 m (1, ZMH P-27787; 1, SEM, JAB).—near South Orkney Islands, Eltanin Sta. 7-480, 15 Feb 1963, 58.13°S, 44.85°W, 2800 m, 2 paratypes (USNM 56464).—near South Georgia, Eltanin Sta. 9-720, 7 Sep 1963, 56.10°S, 34.02°W, 2828–2873 m, holotype (USNM 60684).— Weddell Sea, Glacier Sta. 69- 22, 3111 m (3, USNM 46611); Glacier Sta. 68-1, 13 Mar 1969, 73°28.4′S, 30°26.9′W, 650 m (8 paratypes, USNM 1013915); R/V Polarstern, ANDEEP III ANT XXII-3, R/V Polarstern, Sta. PS-67/078- 4, 2164 m (1, ZMH P-27788); Sta. PS-67/121- 12, 2657 m (1, SEM, JAB); Sta. PS-67/153- 4, 2079 m (1, SEM, JAB).

Description. A small species, mostly represented by posteriorly incomplete specimens; holotype 4 mm long, 0.5 mm wide for 20 setigers; paratype (USNM 60685) 7.5 mm long, 0.5 mm wide for 29 setigers; specimen from (ZMH P-27788) larger, complete in two parts, 13 mm long for about 57 setigers. Color in alcohol: light tan.

Body cylindrical throughout; thoracic region with 11–12 setigerous segments; peristomium and first 3–4 setigers swollen, partially inflated, with segmental boundaries somewhat obscured (Figs. 22 A, 23A–B); subsequent segments smooth, distinct from one another, with prominent dorsal intersegmental annulations apparent from between setigers 4 and 5; each annulation with medial swollen area, sometimes bearing black reticulated pigment (Figs. 22 A, 23A–B); ventral annulations apparent from setigers 13–14.

Prostomium elongated, pointed on anterior margin (Figs. 22 A, 23A–B); no eyespots; nuchal slits observed with SEM (Fig. 23 B–C); peristomium with one simple achaetous ring.

Setigers 1–2 lacking parapodial appendages, but with well-developed setal fascicles. Notopodia with minute postsetal lamellae from setiger 3 (Fig. 22 A), becoming longer, cirriform over subsequent segments (Fig. 22 B); thoracic neuropodia dorsoventrally elongated, with postsetal lamellae present from setiger 3–4 (Fig. 22 B); initially lamellae fingerlike, becoming triangular near end of thoracic region (Fig. 22 B); abdominal notopodia, elongate, fingerlike as in thoracic segments (Fig. 23 E); abdominal neuropodia elongated, flattened, expanded apically, with short ventral cirrus (Fig. 23 E); interramal cirri absent. Branchiae from setiger 9–10, continuing to end of fragments; each branchia broad basally, somewhat flattened (Figs. 22 A, 23E).

Thoracic notopodia with fascicles of crenulated capillaries (Fig. 22 E); with those of setigers 2–5 unusually long (Fig. 22 A); abdominal notopodia with 2–3 non-crenulated, smooth capillaries and 3–4 furcate setae (Fig. 22 C). In light microscopy, furcate setae appearing to have a web between two unequal tynes (Fig. 22 C); in SEM furcate setae observed with a curved array of 8–9 teeth, fused basally, and partly free at tips connecting and fused to tynes; both tynes with a distinct apical opening (Fig. 23 F). Thoracic neurosetae with 1–2 rows of uncini (Fig. 22 D) and 2–3 rows of long crenulated capillaries (Fig. 22 E); uncini blunt tipped, curved, bearing distinct ribs (Figs. 22 D, 23D); abdominal neuropodia with 2–3 embedded or partially protruding aciculae. Posterior end with two dorsolateral anal cirri (ZMH P-27788).

A juvenile from ANDEEP I Sta. PS-61, 046-5 (ZMH P-2785), 1.5 mm long, and with same expanded thorax and long capillary notosetae found in adults. Thorax with nine setigers, branchiae from setiger 8. Noto- and neuropodia first evident from setiger 3. Fascicles of thoracic noto- and neurosetae fewer than in adults, arranged in no more than two rows; 2–3 neuropodial uncini per fascicle, only found on setigers 3–5, these with distinct ribs along shaft forming shelves along one side, with tip of uncini surrounded by partial hyaline hood on shortest emerging setae; crenulated capillaries with individual facets rib-like, each with finely barbed or serrated border. Abdominal notopodia with narrow, fingerlike lamella, slightly enlarged and rounded apically; abdominal neuropodia expanded, with short ventral cirrus. Abdominal notosetae including 1–2 furcate setae and 3–4 long, minutely serrated capillaries; abdominal neurosetae smooth capillaries or with minute, barely discernible barbs.

Etymology. Bathytatus, Greek for deepest.

Remarks. Scoloplos bathytatus n. sp. is a small deep-sea species that differs from related forms in having a cylindrical body throughout, and unusually long capillary notosetae in anterior setigers. The intersegmental annulations are especially prominent in this species, as is the swollen and elongated anterior end. The closest relative to S. bathytatus n. sp. appears to be S. ehlersi Blake, 1985, described from sediments near deep-sea hydrothermal vents at the Galápagos Rift off Ecuador. S. ehlersi superficially resembles S. bathytatus n. sp. in size and form, but differs significantly in having branchiae from setiger 21, an anterior abdominal segment, instead of setigers 9–10 (Blake 1985).

Distribution. Off South America, in subantarctic areas from the Drake Passage to South Georgia, 2800–3463 m; Weddell Sea, 650–3111 m.