Leitoscoloplos obovatus Mackie 1987

Leitoscoloplos obovatus Mackie, 1987

Figures 6–7

Haploscoloplos fragilis intermedius Hartman, 1965: 128 (in part). Fide Mackie 1987.

Leitoscoloplos cf. fragilis: Maciolek-Blake et al. 1985: Appendix B-5. Not Verrill 1873.

Leitoscoloplos sp. A: Maciolek-Blake et al. 1985: B-5, D-19.

Leitoscoloplos obovatus Mackie, 1987: 18–19, Fig. 19.

Material examined. (97 specimens) Northeastern USA, off New England, Gay-Head Bermuda Transect, R/V Atlantis Sta. S 1-3, 24 May 1961, 39°58.4′N, 70°40.317′W, 300 m, holotype (AHF-Poly 1450).— Georges Bank, Benthic Infauna Monitoring Program, coll. G.W. Hampson, Chief Scientist. Sta. 13A: Cruise M 4, R/ V Cape Henlopen, Rep. 6, 18 May 1982, 40°30.00′N, 70°00.5′W, 83 m (3, USNM 1620855); Cruise M5, R/V Oceanus, Rep. 1, 28 Jul 1982, 40°30.00′N, 71°00.5′W, 74 m (7, USNM 1620856); Rep. 4 (4, USNM 1620857); Rep. 6 (3, USNM 1620858); Cruise M6, R/V Oceanus, Rep. 2, 28 Nov. 1982, 40°30.00′N, 71°00.5′W, 78 m (3, USNM 1620859); Rep. 3 (6, USNM 1620860); Cruise M 8, R/ V Gyre, Rep. 1, 21 May 1983, 40°30.00′N, 71°00.5′W, 80 m (2, USNM 1620861); Rep. 2 (3, USNM 1620862); Rep. 3 (4, USNM 1620863); Rep. 5 (1, USNM 1620864); Rep. 6 (4, USNM 1620865); Cruise M 9, R/ V Gyre, Rep. 1, 20 Jul 1983, 40°30.0′N, 71°00.5′W, 80 m (1, USNM 1620866); Rep. 4 (4, USNM 1620867); Rep. 5 (1, USNM 1620868); Cruise M10, R/V Oceanus, Rep. 1, 13 Nov. 1983, 40°30.0′N, 71°00.5′W, 80 m (2, USNM 1620869); Rep. 2 (3, USNM 1620870); Rep. 4 (1, USNM 1620871); Rep. 5 (1, USNM 1620872); Rep. 6 (1, USNM 1620873); Cruise M11, R/V Oceanus, Rep. 1, 01 Feb 1984, 40°30.00′N, 71°00.5′W, 80 m (3, USNM 1620874); Rep. 2 (1, USNM 1620875); Rep. 3 (1, USNM 1620876); Rep. 4 (3, USNM 1620877); Rep. 5 (2, USNM 1620878); Cruise M 12, R/ V Gyre, Rep. 1, coll. 02 Jun 1984, 40°30.0′N, 71°00.5′W, 80 m (1, USNM 1620879); Rep. 2 (1, USNM 1620880); Rep. 3 (5, USNM 1620881); Rep. 4 (1, USNM 1620882); Rep. 5 (2, USNM 1620883); Rep. 6 (2, USNM 1620884).— Southeastern USA, US South Atlantic ACSAR program, coll. J.A. Blake, Chief Scientist. off Cape Hatteras, North Carolina. Sta. 9: Cruise SA-4, R/ V Cape Hatteras, Rep. 1, 24 May 1985, 35°28.41′N, 74°47.44′W, 640 m (1, USNM 1620885). Off Cape Fear, North Carolina, Sta. 11: Cruise SA 4, R/ V Cape Hatteras, Rep. 1, 22 May 1985, 33°04.86′N, 76°25.13′W, 800 m (2, USNM 1620886); Cruise SA-5, R/ V Gyre, Rep. 1, 23 Sep 1985, 33°94,83′N, 76°25.1′W, 796 m (6, USNM 1620887); Cruise SA-6, R/ V Cape Hatteras, Rep. 1, 22 Nov 1985, 33°04.95′N, 76°25.15′W, 804 m (1, USNM 1620888); Rep. 2, 22 Nov. 1985, 33°04.94′N, 76°25.06′W, 807 m (1, USNM 1620889); Rep. 3, 22 Nov 1985, 33°04.84′N, 76°25.06′W, 807 m (2, USNM 1620890). Off Charleston, South Carolina, Sta. 14: Cruise SA-4, R/ V Cape Hatteras, Rep. 2, 20 May 1983, 32°23.64′N, 77°01.1′W, 802 m (1, USNM 1620891); Cruise SA-5, R/ V Gyre, Rep. 2, 19 Sep 1985, 32°23.72′N, 77°01.24′W, 799 m (1, USNM 1620892); Cruise SA-6, R/ V Cape Hatteras, Rep. 1, 18 Nov 1985, 32°23.73′N, 77°01.10′W, 799 m (2, USNM 1620893).— Off New England, US North Atlantic ACSAR program,

coll. G.W. Hampson, Chief Scientist. Sta. 12: Cruise NA-2, R/V Oceanus, Rep. 1, 04 May 1985, 39°54.31′N, 70°55.04′W, 551 m (2, USNM 1620894); Cruise NA-4, R/ V Gyre, Rep. 1, 30 Nov 1985, 39°54.28′N, 70°55.12′W, 560 m (2, USNM 1620895); Rep. 2, 30 Nov 1985, 39°54.28′N, 70°55.12′W, 559 m (2, USNM 1620896); Cruise NA-6, R/ V Gyre, Rep. 3, 30 Jul 1986, 39°54.24′N, 70°55.09′W, 563 m (2, USNM 1620897).

Description. Holotype small, incomplete, with 21 setigers, 4 mm long, 0.40 mm wide across thorax (Mackie 1987). Many specimens complete, but coiled, difficult to measure; one large complete specimen from Georges Bank (USNM 1620861) with 80 setigers, 12.5 mm long, 0.6 mm wide across thoracic region (Fig. 6B). Body elongate, about same width along most of body, narrowing in far posterior setigers. Body generally cylindrical in cross section with thoracic segments short, about five times wider than long. Abdominal segments shorter, but still wider than long with dorsal surface becoming flattened with parapodia and branchiae shifted dorsally; ventral surface rounded. A shallow, narrow ventral groove present along entire body from middle thoracic segments; groove appearing as a light line when body stained with Shirlastain A. Dorsal grooves and ridges absent. Color in alcohol opaque white.

Pre-setiger region triangular, about as long as first two-and-a-half setigers (Fig. 6 A–C). Prostomium triangular, narrowing to pointed apex; nuchal organs narrow curved slits on posterior lateral margin (Fig. 6A); eyespots absent. Peristomium a single ring, smooth dorsally (Fig. 6B), ventrally forming upper and lower lips of mouth (Fig. 6C); upper lip formed by two thickened lobes separated medially by short papilla; lateral and ventral lips of mouth formed by ten or more lobes; proboscis, when everted formed of three or more filaments or lobes.

Thorax of most specimens with 11 setigers abruptly transitioning to abdominal segments (Fig. 6 A–B); small specimens with 9 or 10 thoracic setigers. Transition to abdominal segments best observed by elongation and thickening of neuropodia and commensurate reduction in number of neurosetae. A prominent interramal cirrus first appearing on tenth thoracic setiger, continuing between noto- and neuropodia along entire body (Figs. 6B; 7 C–D); in addition, one or two extra subpodial papillae appear ventral to neuropodial lobe on thoracic setigers 10–11 (Fig. 7B); these continuing over anterior abdominal segments (Fig. 7C), one lobe typically located on a short subpodial neuropodial flange. In addition, 1–3 small stomach papillae also occurring on posterior thoracic and anterior abdominal setigers (Figs. 6A (arrows); 7B–C), with an occasional one occurring on middle abdominal segments.

Branchiae typically first present on setiger 11, or last thoracic setiger (Fig. 6B); narrow and short at first, becoming longer in middle and posterior abdominal segments (Fig. 7 B–D), but not noticeably longer than notopodial postsetal lobes; branchiae of middle and posterior abdominal segments becoming asymmetrical with enlargement typically directed laterally (Fig. 7D). Each branchia with a central blood vessel and transverse folds and cilia on inner and lateral margins.

Notosetae including camerated capillaries and furcate setae; about 30 capillaries in two rows in thoracic notopodia, reduced to 10–15 long, thin camerated capillaries (Fig. 7F); in abdominal notopodia, capillaries accompanied by 0–2 furcate setae. Thoracic neurosetae all capillaries with about 60 setae in three rows; abdominal neurosetae include 3–5 capillaries and 1–2 short protruding aciculae, these minute, with pointed tip. Capillaries of abdominal neuropodia appearing weakly jointed along length with oblong lobes only observed at 1000x in light microscope (Fig. 7G). Furcate setae of abdominal notopodia with unequal tynes, each tyne with a rounded apex; narrow elongate fibrils present between tynes; shaft of furcate setae with cross bars or low ribs along length (Fig. 7E). Flail setae absent.

Pygidium with two or three thickened lobes surrounding anal opening and two long dorsolateral cirri (Fig. 6D).

Remarks. More than 70 newly collected specimens encountered at a single location, Sta. 13A on Georges Bank, the so-called “mud patch” (Maciolek-Blake et al. 1985); additional specimens from upper continental slope stations off New England and the Carolinas also identified. Collection includes a range of sizes from juveniles to mature adults.

The specimens of Leitoscoloplos obovatus reported here represent only the second account of the species. Mackie (1987) described L. obovatus from specimens previously reported as Haploscoloplos fragilis intermedius by Hartman (1965) from a 300 m site southeast of Georges Bank. Other specimens reported by Hartman as this subspecies from deeper slope depths (ca. 1400 m) were raised to full species status by Mackie (1987) and referred to the genus Scoloplos (S. intermedius is treated separately in this paper, see below). The majority of specimens reported here are from outer shelf depths on Georges Bank located near the original collection site reported by Hartman (1965) and Mackie (1987).

Leitoscoloplos obovatus is unusual within the genus in having an interramal cirrus in posterior thoracic and all abdominal setigers, 1–3 subpodial papillae in posterior thoracic and most abdominal setigers, and 2–6 small stomach papillae in posterior thoracic and anterior abdominal setigers. Mackie (1987) had only four small incomplete specimens, each with fewer than 40 setigers; the present collection includes more than 70 specimens, many complete, with up to 80–100 setigers. The new materials confirm Mackie’s (1987) observation that the small sessile papillae on the venter are in actuality stomach papillae; although sparse and inconspicuous, they do form partial rows on the venter.

In addition to L. obovatus, only five other species of Leitoscoloplos have interramal cirri: L. fragilis (Verrill, 1873), L. mackiei Eibye-Jacobsen, 2002, L. multipapillatus Hernández-Alcántara & Solís-Weiss, 2014, L. panamen- sis (Monro, 1933b), and L. robustus (Verrill, 1873). Leitoscoloplos pustulus n. sp. has a short interramal process, but not distinct cirri. Of these, only L. multipapillatus has stomach papillae. However, rather than being sparse as in L. obovatus, the stomach papillae of L. multipapillatus are formed into prominent rows that produce a conspicuous ventral fringe in posterior thoracic and anterior abdominal setigers.

Biology. Large, elongate eggs were observed in one Georges Bank specimen (USNM 1620882) with 3– 4 eggs per individual swollen segment in the anterior abdomen; individual eggs measured about 190 µm in average diameter. These results from a June 1984 sample indicate a summer spawning and the large eggs suggest either a direct or lecithotrophic mode of development. A specimen collected in May 1985 from off Cape Hatteras (USNM 1620885) contained large eggs that were partially extruded from the body, indicating they were being discharged. These eggs measured 192–236 µm in diameter, again implying a direct mode of development.

Sediment grain size at Station 13A, the only location on Georges Bank where L. obovatus occurred, has finegrained sediments consisting of 80–90% silt and clay (Maciolek-Blake et al. 1985). The site is locally termed the “Mud Patch.”

Distribution. Off northeastern USA, in shelf and upper slope depths, 80–550 m; off southeastern USA, upper slope depths, ca. 640– 800 m.