Leitoscoloplos acutus

Leitoscoloplos acutus (Verrill, 1873)

Figures 1–3

Anthosoma acutum Verrill, 1873: 305–306.

Scoloplos acutus: Verrill 1881: 301, 305, 309; Procter 1933: 141, Fig. 32. Not Curtis 1969; Not Zhadan 1998.

Scoloplos armiger: Hartman 1944, pl. 18, fig. 5. Not O.F. Müller 1776.

Scoloplos (Scoloplos) acutus: Pettibone 1963: 293–294, fig. 74g.

Leitoscoloplos acutus: Maciolek-Blake et al. 1985: B-5; Blake et al. 1998: C-1, C-2; Blake 2017: 18.

Scoloplos (Leitoscoloplos) acutus: Trott: 2004: 280.

Schroederella berkeleyi Laubier, 1971: 1483–1486, fig. 1. New synonymy.

Material examined. (2,726 specimens). Northeastern USA. Gulf of Maine, Damariscotta River Estuary, Lowes Cove, coll. J.A. Blake, 26 Jul 1967, 43°59.658′W, 69°33.255′W, intertidal (7, MCZ 161514); West Side Seal Cove, coll. G. Noyes, 03 Aug 1966, 43°53.087′W, 69°34.147′W, 1–2 m (1, MCZ 161515); Cove north of Wiley Point, coll. D. Dorsey and V. Walker, 15 Aug 1966, 43°59.063′W, 69°33.047′W, 1 m (5, MCZ 161516); Oyster Creek, coll. D. Dorsey, 05 Aug 1966, 43°53.363′N, 69°30.615′W, 1–2 m (1, MCZ 161517).— Connecticut, Long Island Sound, USACE Dredged Material Disposal Site Survey, Sta. NL 1KE, Rep. 2, 17 Feb 2000, 41°16.323′N, 72°03.877′W, 16 m (8, MCZ 161521); Rep. 3, 17 Feb 2000, 41°16.313′N, 72°03.894′W, 16 m (3, MCZ 161522). Sta. NL 2KE, Rep. 1, 17 Feb 2000, 41°16.303′N, 72°03.143′W, 12 m (7, MCZ 161523); Rep. 2, 17 Feb 2000, 41°16.297′N, 72°03.155′W, 12 m (5, MCZ 161524); Rep. 3, 17 Feb 2000, 41°16.312′N, 72°03.154′W, 12 m (5, MCZ 161525). Sta. NLLRF, Rep. 1, 17 Feb 2000, 41°16.688′N, 72°01.949′W, 16 m (8, MCZ 161526); Rep. 2, 17 Feb 2000, 41°16.710′N, 72°02.000′W, 16 (5, MCZ 161527); Rep. 3, 17 Feb 2000, 41°16.657′N, 72°01.908′W, 16 m (12, MCZ 161528). Sta. NLRLC, Rep. 1, 17 Feb 2000, 41°16.504′N, 72°04.492′W, 14 m (1, MCZ 161529); Rep. 3, 17 Feb 2000, 41°16.425′N, 72°04.464′W, 14 m (2, MCZ 161530). Sta. NLSEA, Rep. 2, 17 Feb 2000, 41°16.483’N, 72°04.887′W, 15 m (1, MCZ 161531). Sta. WLW5H, Rep. 2, 19 Feb 2000, 40°59.265′N, 73°29.669′W, 34 m (1, MCZ 161532).— Atlantic Ocean, off New Jersey, 14 Aug 2008; Excalibur Sta. 27B, 40°21.5148, 73°54.3525′W, 21 m (2, MCZ 161534).— Massachusetts, New Bedford Harbor, Long Term Monitoring Program, 1999 September–October Survey for USACE: Sta. 123, 29 Sep 1999, Rep. 1, 41°40.016′N, 70°55.034′W, 2.5 m (2, MCZ 161535). Sta. 128, Rep. 1, 29 Sep 1999, 41°39.926′N, 70°55.041′W, 3 m (8, MCZ 161536). Sta. 212, 24 Sep 1999, 41°38.826′W, 70°54.906′W, 3.3 m (132, MCZ 161537). Sta. 318, 10 Oct 1999, 41°35.664′N, 70°52.283′W, 6.6 m (2, MCZ 161538). Sta. 331, 15 Sep 1999, 41°34.198′N, 70°55.707′W, 7.3 m (2, MCZ 161539).— Massachusetts, Duxbury Bay, coll. J.A. Blake, 02 Aug 1981, 42°2.15′N, 70°40.06′W, low intertidal (10, MCZ 161533).— Massachusetts Bay, MWRA Harbor and Outfall Monitoring Program. 1992 May Survey: Sta. FF-4, 42°17.30′N, 70°25.49′W, 92 m (65, MCZ 161400). Sta. FF-5, 42°08.00′N, 70°25.35′W, 64 m (5, MCZ 161401). Sta. FF-9, 42°18.75′N, 70°39.40′W, 51 m (25, MCZ 161402). Sta. WH3, 42°23,39′N, 70°49.84′W, 36 m (292, MCZ 161403). 1992 August Survey: Sta. NF-1, 42°20.35′N, 70°50.51′W, 42 m (5, MCZ 161404); Sta. NF-2, 42°20.31′N, 70°49.69′W, 26 m, (4, MCZ 161405). Sta. NF-5, 40°25.62′N, 70°50.03′W, 28 m (4, MCZ 161406). Sta. NF-7, 42°24.60′N, 70°48.89′W, 32 m (33, MCZ 161407); Sta. NF-8, 42°24.00′N, 70°51.81′W, 28 m (5, MCZ 161408). Sta. NF-11, 42°23.39′N, 70°50.25′W, 31 m (23, MCZ 161409). Sta. NF-12, 42°23.40′N, 70°49.83′W, 33 m (33, MCZ 161410). Sta. NF-13, 42°23.40′N, 70°49.35′W, 33 (1, MCZ 161411). Sta. NF-14, 42°23.20′N, 70°49.36′W, 32 m (13, MCZ 161412); Sta. NF-1 5, 42°22.93′N, 70°49.67′W, 32 m (17, MCZ 161413). Sta. NF-16, 42°22.70′N, 70°50.26′W, 29 m (31, MCZ 161414). Sta. NF-19, 42° 22.30’N 70° 48.30’7W, 32 m (23, MCZ 161415). Sta. NF-20, 42°22.69′N, 70°50.69′W, 27 m (10, MCZ 161416). Sta. FF-1, Rep. 2, 42°27.94′N, 70°37.31′W, 68 m (5, MCZ 161417). Sta. FF-4, Rep. 1, 42°17.30′N, 70°25.50′W, 86 m (7, MCZ 161418); Rep. 2, (5, MCZ 161419). Sta. FF-5, Rep. 1, 42°08.00′N, 70°25.35′W, 61 m (10, MCZ 161420); Rep. 3, (5, MCZ 161421). Sta. FF-6, Rep. 1, 41°53.90′N, 70°24.20′W, 33 m (2, MCZ 161422); Rep. 2 (2, MCZ 161423); Rep. 3 (4, MCZ 161424). Sta. FF-7, Rep. 3, 41°57.50′N, 70°16.00′W, 37 m (1, MCZ 161425). Sta. FF-9, Rep. 1, 42°18.75′N, 70°39.40′W, 48 m (14, MCZ 161426). Sta. FF-10, Rep. 1, 42°24.84′N, 70°52.72′W, 27 m (45, MCZ 161427); Rep. 2 (30+, MCZ 161428); Rep. 3 (53, MCZ 161429). Sta. FF-11, Rep. 1, 42°39.50′N, 70°30.00′W, 86 m (4, MCZ 161430); Rep. 2 (2, MCZ 161431). Sta. FF-12, Rep. 1, 42°23.40′N, 70°53.98′W, 22 m (67, MCZ 161432); Rep. 2 (65, MCZ 161433), Sta. FF-13, Rep. 1, 42°19.19′N, 70°49.38′W, 19 m (2, MCZ 161434); Rep. 2 (2, MCZ 161435); Rep. 3 (23, MCZ 161436). Sta. FF-14, Rep. 1, 42°25.00′N, 70°39.29′W, 69 m (4, MCZ 161437); Rep. 2 (2, MCZ 161438); Rep. 3 (15, MCZ 161439). 1995 August Survey: Sta. FF-1A, 42°33.84′N, 70°40.55′W, 32 m (10, MCZ 161440). Sta. FF-4, 42°17.30′N, 70°25.50′W, 87 m (~20, MCZ 161441). Sta. FF-9, 42°18.75′N, 70°39.40′W, 49 m (31, MCZ 161442). Sta. FF-10, 42°24.84′N, 70°52.72′W, 27 m (50+, MCZ 161443). Sta. FF-11, 42°39.50′N, 70°30.00′W, 87 m (37, MCZ 161444). Sta. FF-12, 42°23.40′N, 70°53.98′W, 22 m (25+, MCZ 161445); Sta. FF-13, Rep. 1, 42°19.19′N, 70°49.38′W, 19 m (50+, MCZ 161446). Sta. FF-14, 42°25.00′N, 70°39.29′W, 77 m (40, MCZ 161447). 1996 August Survey: Sta. NF-14, 42°23.20′N, 70°49.36′W, 33 m (7, MCZ 161448). Sta. NF-15, 42°22.93′N, 70°49.67′W, 32 m (10, MCZ 161449); Sta. NF-18, 42°23.80′N, 70°49.31′W, 35 m (7, MCZ 161450). Sta. NF-19, 42°22.30′N, 70°48.30′W, 32 m (5, MCZ 161451). Sta. NF-24, Rep. 1, 42°22.83′N, 70°48.10′W, 37 m, (27, MCZ 161452); Rep. 2 (22, MCZ 161453); Rep. 3 (35, MCZ 161454). Sta. MF-2, 42°20.31′N, 70°49.69′W, 30 m (27, MCZ 161455). Sta. MF-5, 42°25.62′N, 70°50.03′W, 36 m (6, MCZ 161456). Sta. MF-7, 42°24.60′N, 70°48.89′W, 33 m (17, MCZ 161457). Sta. MF-8, 42°24.00′N, 70°51.81′W, 30 m (53, MCZ 161458). Sta. MF-9, 42°23.99′N, 70°50.69′W, 29 m (42, MCZ 161459).

Sta. MF-10, 42°23.57′N, 70°50.29′W, 35 m (38, MCZ 161460). Sta. MF-12, Rep. 1, 42°23.40′N, 70°49.83′W, 34 m (37, MCZ 161461); Rep. 2 (31, MCZ 161462); Rep. 3 (39, MCZ 161463). Sta. MF-16, 42°22.70′N, 70°50.26′W, 29 m (14, MCZ 161464). Sta. MF-20, 42°22.69′N, 70°50.69′W, 28 m (35, MCZ 161465). Sta. MF-21, 42°24.16′N, 70°50.19′W, 33 m (22, MCZ 161466). Sta. MF-22, 42°20.87′N, 70°48.90′W, 36 m (22, MCZ 161467). Sta. FF-1A, Rep. 1, 42°33.84′N, 70°40.55′W, 32 m (2, MCZ 161468); Rep. 2 (3, MCZ 161469); Rep. 3 (15, MCZ 161470). Sta. FF-4, Rep. 1, 42°17.30′N, 70°25.50′W, 87 m (7, MCZ 161471); Rep. 2 (6, MCZ 161472); Rep. 3 (3, MCZ 161473). Sta. FF-5, Rep. 1, 42°08.00′N, 70°25.35′W, 61 m (13, MCZ 161474); Rep. 2 (3, MCZ 161475); Rep. 3 (7, MCZ 161476). Sta. FF-9, Rep. 1, 42°18.75′N, 70°39.40′W, 49 m (5, MCZ 161477); Rep. 2 (3, MCZ 161478); Rep. 3 (8, MCZ 161479). Sta. FF-10, Rep. 1, 42°24.84′N, 70°52.72′W, 27 m (41, MCZ 161480); Rep. 2 (28, MCZ 161481); Rep. 3 (35, MCZ 161482). Sta. FF-11, Rep. 1, 42°39.50′N, 70°30.00′W, 87 m, (3, MCZ 161483); Rep. 2, (10, MCZ 161484); Rep. 3, (10, MCZ 161485). Sta. FF-12, Rep. 1, 42°23.40′N, 70°53.98′W, 22 m, (56, MCZ 161486); Rep. 2, (44, MCZ 161487); Rep. 3 (40, MCZ 161488). Sta. FF-13, Rep. 1, 42°19.19′N, 70°49.38′W, 19 m (83, MCZ 161489); Rep. 2 (38, MCZ 161490); Rep. 3 (116, MCZ 161491). Sta. FF-14, Rep. 1, 42°25.00′N, 70°39.29′W, 77 m (6, MCZ 161492); Rep. 2 (15, MCZ 161493); Rep. 3 (13, MCZ 161494). 1997 August Survey: Sta. MF- 2, 42°20.31′N, 70°49.69′W, 30 m (2, MCZ 161495). Sta. MF-5, 42° 25.62′N, 70° 50.03′W, 36 m (4, MCZ 161496). Sta. MF-9, 42°23.99′N, 70°50.69′W, 29 m (22, MCZ 161497). Sta. MF-10, 42°23.97′N, 70°50.29′W, 35 m (34, MCZ 161498). Sta. MF-12, Rep. 1, 42°23.40′N, 70°49.83′W, 34 m (20, MCZ 161499); Rep. 2 (32, MCZ 161500); Rep. 3 (40, MCZ 161501). Sta. MF-16, 42°22.70′N, 70°50.26′W, 29 m (32, MCZ 161502). Sta. MF-20, 42°22.69′N, 70°50.69′W, 28 m (19, MCZ 161503). Sta. MF-21, 42°24.16′N, 70°50.19′W, 33 m (13, MCZ 161504). Sta. MF-22, 42°20.87′N, 70°48.90′W, 36 m (38, MCZ 161505). Sta. FF-9, Rep. 1, 42°18.75′N, 70°39.40′W, 49 m (3, MCZ 161506); Rep. 2 (5, MCZ 161507); Rep. 3 (4, MCZ 161508). Sta. FF-10, Rep. 1, 42°24.84′N, 70° 52.72′W, 27 m (9, MCZ 161509); Rep. 2 (46, MCZ 161510). Sta. FF-12, Rep. 1, 42°23.40′N, 70°53.98′W, 22 m (50, MCZ 161511); Rep. 2 (32, MCZ 161512); Rep. 3 (34, MCZ 161513).— Off Massachusetts, Georges Bank, MMS Benthic Infauna Monitoring Program, coll. G.W. Hampson, Chief Scientist. Sta. 11: Cruise M 4, Rep 1, 16 May 1982, 40°30.8′N, 68°33.7′W, 83 m (2, USNM 1620840); Cruise M 5, Rep. 2, 28 Jul 1982, 40°30.8′N, 68°33.7′W, 77 m (2, USNM 1620841); Cruise M 6, Rep. 5, 26 Nov 1982, 40°30.8′N, 68°33.7′W, 83 m (1, USNM 1620842); Cruise M 11, Rep. 1, 02 Feb 1984, 40°30.8′N, 68°33.7′W, 86 m (1, USNM 1620843); Rep. 3 (3, USNM 1620844). Sta. 13: Cruise M 1, Rep. 4, Jul 1981, 40°29.5′N, 70°12.6′W, 65 m (1, USNM 1620845); Cruise M 2, Rep. 3, 9 Nov 1981, 40°29.2′N, 70°12.4′W, 60 m (2, USNM 1620846); Cruise M 3, Rep. 1, 11 Feb 1982, 40°29.2′N, 70°12.4′W, 69 m (1, USNM 1620847); Rep. 5 (1, USNM 1620848); Cruise M 5, Rep. 5, 28 Jul 1982, 40°29.5′N, 70°12.6′W, 62 m (1, USNM 1620849); Cruise M 6, Rep. 5, 27 Nov 1982, 40°29.3′N, 70°12.4′W, 67 m (1, USNM 1620850); Rep. 6 (1, USNM 1620851); Cruise M 8, Rep. 1, 21 May 1983, 40°29.3′N, 70°12.5′W, 70 m (1, USNM 1620852); Cruise M 12, Rep. 1, 03 Jun 1984, 40°29.5′N, 70°12.6′W, 70 m (1, USNM1620853). Sta. 18: Cruise M 3, Rep. 6, 18 Feb 1982, 40°33.5′N, 67°13.7′W, 145 m (8, USNM 1620854).

Other material examined. Massachusetts, Craigsville Beach, Centerville, Barnstable County, coll. W.J. Wall, 26 Jun 1969, intertidal, holotype of Schroederella berkeleyi Laubier, 1971 (USNM 44946).

Description. A moderate-sized species, typically about 20–22 mm long with 75–80 setigers; specimen from Georges Bank (USNM 1620847) complete, long and narrow, with 125 setigers, 25 mm long and about 1.5 mm wide across middle of thorax; recorded up to 40 mm long by Pettibone (1963). Body elongate, with thoracic region dorsoventrally flattened, with individual segments short and narrow, 6–8 times wider than long (Figs. 1A, 2A); individual segments separated by narrow transverse groove. Abdominal segments also narrow, crowded without obvious annulations; posterior segments crowded (Fig. 2E). Body with no longitudinal grooves or ridges; abdominal segments with a light-colored thin line along venter. Color in alcohol light tan.

Pre-setiger region triangular, relatively short, about as long as first two or three setigers. Prostomium thickened basally, narrowing to pointed apex (Fig. 1 A–B); nuchal organs oval slits on posterior lateral margin; eyespots absent. Peristomium a single short smooth achaetous ring (Fig. 1A), weakly divided ventrally due to upper and lower lips of mouth. Upper lip of mouth with two rounded medial lobes and 2–3 smaller lateral lobes (Fig. 1B); lower lip of mouth bordered with about 7–8 smaller lobes (Fig. 1B). Proboscis when everted with 1–3 lobes.

Thorax with 14–16 setigers with abrupt transition to abdominal segments (Figs. 1A, 2A). Boundary between thorax and abdomen best observed by elongation of neuropodia and decrease in number of neurosetae. Thoracic notopodial lobes more or less triangular in shape, digitiform, narrowing apically arising from narrow base (Figs. 1D, 2B); neuropodial lobes also digitiform, shorter than notopodial lobe, arising from broadly rounded base (Figs. 1D, 2B). Abdominal notopodia elongate, narrow, digitiform (Figs. 1E, 2C). Abdominal neuropodia thickened, becoming relatively short in middle and posterior segments, each narrowing to pointed apical lobe and with subterminal ventral cirrus on lateral margin (Figs. 1E, 2C); with elongate, narrow subterminal flange ventral to neuropodium; subpodial papillae absent (Figs. 1E, 2C). Interramal cirrus or protuberance entirely absent.

Branchiae typically from setiger 10–13, initially thoracic branchiae small and short, becoming full size by about setigers 14–15 (Fig. 1A). Anterior branchiae triangular, tapering to rounded apex; branchiae of abdominal segments becoming weakly asymmetrical with bulge on inner margin (Figs. 1E, 2C); each branchia with transverse folds and cilia on inner margin (Fig. 2C, arrows).

Notosetae including camerated capillaries and furcate setae; up to 20–30 capillaries in 2–3 irregular rows in thoracic notopodia or largest specimens reduced to 10–15 long, thin capillaries in abdominal segments accompanied by 1–3 furcate setae (Fig. 2D). Thoracic neurosetae all capillaries with about 45–55 setae in 4–5 rows; abdominal neurosetae including 2–7 capillaries with barbs along one edge and 1–2 short protruding aciculae, these minute, with rounded apex (Fig. 1E inset). Furcate setae of abdominal notopodia with unequal tynes, each tyne with a flattened rounded apex within which an opening and narrow channel can be observed with light microscope; narrow elongate fibrils present between tynes (Fig. 1F); flail setae absent.

Pygidium with lateral, dorsal, and ventral lobes surrounding anal opening; with two long, thin anal cirri arising dorsolateral (Figs. 1C, 2F).

Variability. Apart from small juveniles, the morphology presented here is consistent over the range of sizes considered to represent adults. In the very largest specimens, however, a rounded, rudimentary subpodial flange may be present on the last thoracic setiger and/or the first abdominal setiger. This rudimentary flange transitions into the larger subpodial flange that develops on anterior abdominal segments and that continues on all abdominal neuropodia.

Juvenile morphology. Juveniles of this species that were present with the adults were initially thought to be similar to Schroederella berkeleyi Laubier, 1971, a species established for small meiofaunal orbiniids from an intertidal sand beach in Massachusetts (Laubier 1971). However, examination of the holotype of S. berkeleyi and numerous juveniles in the new collections suggests that the juveniles represent part of a growth sequence for Leitoscoloplos acutus. Juveniles from Massachusetts Bay (MCZ 161433, MCZ 161464, and MCZ 161511) were examined in detail.

Specimens elongate, usually coiled in preservation and somewhat contracted (Fig. 3 A–E). Complete specimens ranged from 2.1 mm long with 21 setigers (Fig. 3A) to 3.7 mm long with 48 setigers (Fig. 3F); posterior pre-pygidial segments crowded due to active growth zone. Thoracic setigers through middle abdominal setigers all about same width, narrowing in far posterior segments. Color white to light tan.

Prostomium long, triangular, acutely pointed; eyespots absent; nuchal organs not observed. Peristomium with a single achaetous ring vaguely separated laterally and ventrally by weakly developed lines, but not into two separate rings. Anterior lip of mouth with two large lobes; posterior lip with five or six small lobes forming a posterior border.

Thorax with 7–9 setigers in smallest juveniles (21–28 setigers and 2.1–2.5 mm long); thorax with 11–13 setigers in larger juveniles (40–48 setigers and 3.0– 3.7 mm long); thoracic setigers each shorter than abdominal segments. Branchiae from setigers 10–11, short, minute at first, becoming longer in anterior abdominal segments. Thoracic notopodia initially short, papillate, increasing in length, becoming digitiform by about setiger 6–7; abdominal notopodia long and narrow. Thoracic neuropodia initially papillate, becoming longer and digitiform by about setigers 7–8; abdominal neuropodia with thickened base, apically separated into two lobes, initially equivalent in size and shape; larger juveniles with inner lobe becoming longer as in adults. Neuropodia with short, narrow subpodial flange with smooth border. Subpodial papillae and interramal cirri absent.

Thoracic notosetae of small juveniles with 4–6 camerated capillaries in a single row, increasing to about 15–16 capillaries in larger juveniles, most in one row, a few in a second posterior row; abdominal notosetae 3–4 camerated capillaries; furcate setae observed only on larger 45–48-setiger juveniles in far posterior segments. Thoracic neurosetae consisting of 12–15 capillaries arranged in two rows, increasing to 20–25 capillaries in two rows in larger juveniles. Abdominal neurosetae with 2–3 capillaries, these smooth, barbs not observed; a short, thin, sharply pointed acicula present.

Pygidium with two anal cirri; short and thick in small juveniles (Fig. 3 C–D), long and thin in 40-setiger juveniles (Fig. 3E).

Remarks. Leitoscoloplos acutus, although first described by Verrill (1873) from Vineyard Sound, has never been fully described and illustrated from New England waters. The present paper is the first to provide such detail for the species. The species is common and typically found in sediments with mixed sand and silt.

Leitoscoloplos acutus is most similar to L. pugettensis (Pettibone, 1957), a widely distributed species along the North American Pacific coast from British Columbia to Central America (Mackie 1987; Blake 1996; Dean & Blake 2015). Both species lack extra subpodial lobes or papillae and have a prominent subpodial flange ventral to the abdominal neuropodia. L. pugettensis, however, although similar, is a much larger species, up to 200 mm long and with more than 200 setigers. The largest specimens of L. acutus, in contrast, are about 40 mm long with ca. 150 setigers; the largest specimens in the present study (more than 2700 specimens) are about 25 mm long with 125 setigers. The number of thoracic setigers in L. pugettensis is 14–20 with branchiae from setigers 13–18 or the penultimate segment based number of thoracic setigers; whereas in L. acutus, the number of thoracic setigers ranges from 14–16 with the branchiae occurring more anteriorly from setigers 9–13.

Curtis (1969), working in the Canadian Arctic (Ellesmere Island, 81°N), evaluated a growth sequence of speci- mens of Scoloplos collected at depth of 10 m. He provided data suggesting that Leitoscoloplos acutus represented a developmental phase of S. armiger where neuropodial uncini and subpodial papillae were entirely absent in small specimens having a width of 0.5 mm and fully present in specimens with a width of 2 mm; intermediate sizes had differing stages in the acquisition of these characters. However, there was no descriptive data provided to confirm the identity of either species he studied and given the much greater diversity of orbiniids recently revealed, it is unlikely that Curtis (1969) was dealing with either L. acutus or S. armiger.

There were hundreds of juveniles present in the collections due to the use of 300-µm-mesh sieves in the offshore monitoring surveys. Examination of juvenile morphology of various sizes confirmed a consistent agreement with the adults. Although a full growth sequence has not been developed, the samples are archived and available if such an analysis is required in the future. As part of the examination of juveniles, a comparison with the holotype of Schroederella berkeleyi suggests that the specimen agrees with juveniles of Leitoscoloplos acutus and is here referred to synonymy. There is nothing in the original account of S. berkeleyi that sets it aside as either a separate genus or species within the Orbiniidae. It should be noted that the only other possible synonyms locally would be either L. fragilis or L. robustus. However, none of the juveniles of L. acutus exhibit interramal cirri/processes or subpodial papillae which have been observed on smaller specimens of those species (see account of juvenile morphology for L. fragilis, below).

Zhadan (1998) reported two Scoloplos species from the White Sea, North Sea, Barents Sea, and East Greenland as S. armiger, the type species of the genus, and S. acutus previously known only from North America. Zhadan based her identification of S. acutus on observations that smaller specimens (<1.75 mm wide) lacked hooks or uncini in thoracic neuropodia and subpodial papillae in posterior thoracic and abdominal neuropodia, whereas specimens larger than 1.75 mm wide had these characters. However, she did not have a full size range of specimens from the type locality in New England (USA). In the present study no specimens were found with either thoracic uncini or subpodial papillae in the neuropodia at any stage of development and are thus referred to the genus Leitoscoloplos. A comparison of these U.S. Atlantic specimens of L. acutus with Scoloplos verrilli n. sp., the only local New England species of Scoloplos having characteristics similar to the larger S. acutus specimens reported by Zhadan (1998), indicates that her specimens represent a different species. Leitoscoloplos actus reported here have a long, smooth subpodial neuropodial flange on abdominal segments; in contrast, S. verrilli n. sp. has a short glandular neuropodial flange. Further, specimens of S. verrilli n. sp. that are smaller than the largest specimens of L. acutus have both thoracic neuropodial uncini and neuropodial subpodial papillae. Recent investigations of S. armiger from the North Sea have shown that shallow and subtidal populations are both ecologically and reproductively isolated from one another (Kruse & Reise 2003; Kruse et al. 2003, 2004). Results from molecular sequence data support these observations that shallow and subtidal North Sea populations likely represent separate species (Bleidorn et al. 2006). Additionally, these authors determined that Norwegian specimens from near the type locality of S. armiger represented yet a third species. To date, these three taxa have not been described or compared with regard to their morphology.

Biology. Mature females of Leitoscoloplos acutus with internal eggs of various sizes arranged segmentally in middle abdominal setigers were collected in May 1992 in Massachusetts Bay, suggesting a late spring spawning. Adult females 25 mm long and 1.5 mm wide from Station FF-4 (MCZ 161400) had large eggs that ranged from 106 to 204 µm in diameter. The eggs have a smooth cytoplasm and clear germinal vesicle. These data suggest that mature eggs will likely exceed 210 µm in diameter, indicating direct development or a brief lecithotrophic larval development similar to that of the related species L. pugettensis (Pettibone, 1957) reported by Blake (1980) from California.

Sediment grain size at stations 11 and 13 on Georges Bank, where Leitoscoloplos acutus was most prevalent, consisted of 60–95% fine sands and reduced amounts of silt-sized particles, whereas at Station 13A, where the related species L. obovatus occurred, the sediments were fine grained, consisting of 80–90% silt and clay (Maciolek- Blake et al. 1985: Appendix J). These data suggest that closely related deposit-feeding polychaete species may be spatially partitioned by the nature of sediments in their habitat. Specimens of L. acutus were often observed with large sand grains in their guts, reflecting the nature of the sandy sediments where they were found, whereas this was not the case for L. obovatus, which inhabits fine-grained sediments. In Massachusetts Bay, L. acutus is abundant at several MWRA nearfield stations that have sediments consisting of fine-grained sands with lesser amounts of silt (Blake et al. 1998); 30 or more specimens in one 0.04 m 2 grab sample was a common occurrence at several stations.

Distribution. Maine to New Jersey, intertidal to offshore in mixed sand/silt sediments; Massachusetts Bay, 22–92 m; Georges Bank, 65– 145 m. Pettibone (1963) recorded the species from the Canadian Arctic to Chesapeake Bay, 6–180 m, but this wider distribution is not confirmed in the present study.