Leitoscoloplos robustus

Leitoscoloplos robustus (Verrill, 1873)

Figures 10–11

Anthosoma robustum Verrill, 1873: 49, 54, 71, 134, 303, pl. 14, fig. 76.

Scoloplos robustus: Verrill 1881: 301, 317; Andrews 1891: 292; Sumner, et al. 1913: 624.

Scoloplos robusta: Webster & Benedict 1884: 724.

Scoloplos bustoris Eisig, 1914:422–423; Hartman 1942: 58–60, figs. 111–112; Horn & Bookhout 1950: 1, pls. 1–4. Fide Hartman 1957.

Haploscoloplos tortugaensis Monro, 1933a: 261–263, fig. 10a–d. Fide Mackie 1987.

Scoloplos rufa Treadwell, 1941: 1, figs. 1–6. Fide Hartman 1956.

Haploscoloplos bustoris: Hartman 1945: 30. Fide Hartman 1957.

Haploscoloplos robustus Hartman 1951: 78, pl. 21, figs. 4–6; 1956: 258, 268, 290; 1957: 272, pl. 25, figs 4–6; Day 1973: 91; Trott 2004: 280.

Scoloplos (Scoloplos) robustus: Pettibone 1963: 288–290, fig. 76g.

Leitoscoloplos robustus: Taylor 1984 1.17–1.19, fig. 1.16a–f; Mackie 1987: 16–18, fig. 17; Fauchald, Granados-Barba & Solís- Weiss 2009: 763; Blake 2017: 18.

Material examined. (145 specimens) Northeastern USA, Gulf of Maine, Damariscotta River Estuary, Lowes Cove, coll. G. Noyes, 7 Aug 1966, 43°56.012′N, 69°34.688′W, intertidal (5, MCZ 161587); upper end Pleasant Cove, coll. V. Walker, 19 Aug 1966, 43°54.956′N, 69°35.844′W, intertidal (21, MCZ 161588); Cove inside of Little Point, coll. D. Dorsey and V. Walker, 12 Aug 1966, 44°01.196′N, 69°32.823′W, 1–2 m (3, MCZ 161589); Seal Cove, coll. D. Dorsey and G. Noyes, 03 Aug 1966, 43°53.161′N, 69°34.119′W, 1–2 m (4, MCZ 161590); Peter’s Island, coll. V. Walker, 01 Sep 1966, 43°54.504′N, 69°33.764′W, 1–2 m (16, MCZ 161591); Middle Pleasant Cove, coll. D. Dorsey and V. Walker, Sep 1966, 43°55.259′N, 69°35.167′W, 1–2 m (66, MCZ 161592); Long Cove, coll. D. Dorsey and V. Walker, 04 Aug 1966, 43°54.299′N, 69°33.859′W, 1 m (5, MCZ 161594).— Connecticut, Long Island Sound, US EPA Dredged Material Disposal Site Survey, Sta. NLLRF, Rep. 2, 17 Feb 2000, 41°16.710′N, 72°02.000′W, 16 m (1, MCZ 161596).— New York, Long Island Sound, off Northport, pipeline survey, Sta. IG- 01, coll. P.L. Neubert, 27 Oct 1999, 40°55.75′N, 73°20.73′W, 3 m (1, MCZ 161682). Eastchester Bay, off Locust Point, pipeline survey, Sta. LP 2, Rep. 1, coll. P.L. Neubert, 14 Jul 2000, 40º49.201′N, 73º48.016′W, 4.5 m (14, MCZ 161593).— Off New Jersey, Atlantic Ocean, August 2008; Excalibur pipeline survey, Sta. 39B, coll. P.L. Neubert, 40°16.4468′N, 73°42.6671′W, 28 m (1, MCZ 161595).— Massachusetts, New Bedford Harbor, Long-term Monitoring Program, 1999 September-October Survey. Sta. 208-2, 23 Sep 1999, 41°38.981′N, 70°55.022′W, 1.3 m (1, MCZ 161575); Sta. 306-3, 14 Sep 1999, 41°37.15′N, 70°52.237′W, 2.8 m (1, MCZ 161576).— Off Massachusetts, Georges Bank, Benthic Infauna Monitoring Program, coll. G.W. Hampson, Chief Scientist. Sta. 4: Cruise M 6, R/V Oceanus, Rep. 2, 25 Nov 1982, 40°50.7′N, 68°00.2′W, 65 m (2, USNM 1620911); Cruise M10, R/V Oceanus, Rep. 2, 14 Nov 1983, 40°50.7′N, 68°00.2′W, 67 m (1, USNM 1620912). Sta. 10: Cruise M 1, R/ V Eastward, Jul 1981, Rep. 5, 40°,42.0′N, 68°36.0′W, 62 m (1, USNM 1620913); Cruise M 3, R/ V Endeavor, Rep. 5, 12 Feb 1982, 40°42.0′N, 68°35.1′W, 62 m (1, USNM 1620914); Cruise M 4, R/ V Cape Henlopen, Rep. 2, 16 May 1982, 40°42.0′N, 68°35.2′W, 62 m (1, USNM 1620915); Cruise M5, R/V Oceanus, Rep. 6, 28 Jul 1982, 40°42.0′N, 68°35.3′W, 56 m (1, USNM 1620916); Cruise M 8, R/ V Gyre, Rep. 4, 20 May 1983, 40°42.0′N, 68°35.2′W, 62 m (1, USNM 1620917); Rep. 5, (4, USNM 1620918). Sta. 11: Cruise M 2, R/V Oceanus, Rep. 2, 12 Nov 1981, 40°30.8′N, 68°33.5′W, 80 m (1, USNM 1620919); Rep. 5 (1, USNM 1620920); Cruise M 3, R/ V Endeavor, Rep. 1, 12 Feb 1982, 40°30.8′N, 68°33.6′W, 86 m (1, USNM 1620921); Rep. 2 (1, USNM 1620922); Cruise M 4, R/ V Cape Henlopen, Rep. 3, 16 May 1982, 40°30.8′N, 68°33.7′W, 83 m (2, USNM 1620923); Cruise M 6, Rep. 3, R/V Oceanus, 26 Nov 1982, 40°30.8′N, 68°33.7′W, 83 m (1, USNM 1620924); Cruise M 8, R/ V Gyre, Rep. 4, 20 May 1983, 40°30.8′N, 68°33.7′W, 84 m (1, USNM 1620925); Cruise M11, R/V Oceanus, Rep. 1, 14 Nov 1983, 40°30.8′N, 68°33.7′W, 86 m (1, USNM 1620926); Cruise M 12, R/ V Gyre, Rep. 6, 3 Jun 1984, 40°30.8′N, 68°33.7′W, 86 m (2, USNM 1620927).

Description. A large species, specimens from Georges Bank (USNM 1620918) up to 9.5 cm long, 3.5 mm wide across thoracic setigers, with 280 setigers (one complete); smaller specimens from Maine up to 17.5 mm long, 1 mm wide across thoracic setigers, with 125 setigers (complete specimen). Body elongate, with thoracic segments and anteriormost abdominal segments dorsoventrally flattened, with individual segments short, about 4–5 times wider than long; individual segments separated by narrow transverse groove (Figs. 10A, 11A). Individual thoracic and anterior abdominal segments with thin, transverse ridge extending between parapodia and entirely across dorsal and ventral surfaces producing a biannulate appearance (Fig. 11 A–C). Abdominal segments becoming longer with a narrow intersegmental ring anterior to larger segmental ring continuing ventrally between neuropodia. Middle and posterior segments about twice as wide as long. Shallow mid-ventral groove present from middle abdominal segments to near posterior end. Color in alcohol light tan.

Pre-setiger region triangular, elongate, as long as first 2½ setigers (Fig. 10 A–C). Prostomium conical, tapering to pointed tip; nuchal organs curved slits on posterior lateral margin (Fig. 10A); eyespots absent. Peristomium a single smooth achaetous ring dorsally (Fig. 10 A–B), ventrally encompassing mouth with upper lip formed of two large lobes and lower lip with curved row of ten or more narrow elongate lobes (Fig. 10C). Proboscis with one or more lobes when everted.

Thorax on larger specimens with 22–25 setigers with abrupt transition to abdominal segments. Boundary between thorax and abdomen indicated by elongation of neuropodia and decrease in number of neurosetae. Thoracic notopodial postsetal lobes short, weakly triangular in shape, narrowing apically, arising directly from body wall (Fig. 10 D–E). Abdominal notopodia becoming longer, digitiform in middle and posterior segments (Fig. 10 F– G).Thoracic neuropodial postsetal lobes short, stubby, arising from broadly rounded base (Fig. 10D); last 1–3 thoracic neuropodia with extra postsetal lobe and usually a short subpodial papilla resulting in one or two final thoracic setigers with three short lobes on largest specimens (Fig. 10E). Abdominal neuropodia thickened, becoming relatively short in middle and posterior segments, each narrowing to pointed apical lobe bearing subterminal ventral cirrus on lateral margin (Fig. 10F); extra postsetal lobes or subpodial papillae appearing to merge into subpodial flange over first 3–4 abdominal setigers (Fig. 10F); subsequent middle and posterior abdominal setigers with large, thickened, subterminal flange ventral to neuropodium (Fig. 10G); subpodial papillae absent on abdominal segments. Prominent interramal cirrus present on anterior abdominal setigers (Fig. 10F); narrow, conical or fingerlike at first, continuing for about 75 setigers, then reduced to short ciliated patch and/or protuberance in middle setigers (Fig. 10G); entirely absent in posterior setigers.

Branchiae typically from setiger 20–23, usually 22; initial thoracic branchiae short, papilliform (Fig. 10E), becoming full size by about setigers 25–27 or anterior abdominal segments (Fig. 10F). Anterior branchiae triangular, tapering to rounded apex; branchiae of middle and posterior segments becoming narrower and longer (Fig. 10G); each branchia with transverse folds and cilia on inner and outer margins.

Notosetae all camerated capillaries; furcate and flail setae not observed; capillaries of thoracic notopodia numbering about 50 in 4–5 irregular rows, reduced to about 25 in abdominal segments. Thoracic neurosetae all camerated capillaries with about 75–100 in 5–6 rows; abdominal neurosetae 8–9 long stiff capillaries with barbs along one edge and 1–3 imbedded aciculae, none observed protruding.

Pygidium consisting of numerous lobes surrounding anal opening; with two thin anal cirri attached laterally (Fig. 10H).

Variability. Smaller specimens with 14–19 thoracic setigers and branchiae from setigers 13–17 have been recorded (Mackie 1987; specimens from Maine in the present study). However, the nature of the extra postsetal lobes in the last thoracic neuropodia and relatively smooth form of the abdominal subpodial flanges of the neuropodia are similar to those of the larger specimens.

Remarks. Leitoscoloplos robustus is the largest known species of the genus (Pettibone 1963; Mackie 1987). Pettibone (1963) reported specimens having 300 setigers, a length of 37.5 cm and a thoracic width of 10 mm. The largest specimen measured in this study had 280 setigers and was 9.5 cm long and 3.5 mm wide across thoracic setigers. It is likely that larger specimens are in the Georges Bank samples, but most specimens were coiled upon preservation, including one that was complete and could not be accurately measured.

Leitoscoloplos robustus differs from the closely related L. fragilis in that the latter species has extra subpodial papillae in abdominal segments that continue posteriorly along most of the body and that typically divide the subpodial flange into separate lobes. In contrast, L. robustus has no abdominal subpodial papillae or lobes after the first 2–3 abdominal setigers and the borders of the subpodial flanges are therefore smooth and entire along most of the body. In addition, L. robustus has prominent neuropodial ventral cirri in abdominal setigers that is reduced or inconspicuous in L. fragilis.

Although similar morphologically, the distinction between L. fragilis and L robustus among specimens from the eastern U.S. was supported in a molecular analysis by Bleidorn (2009). In the same analysis, L. robustus specimens from Maine and Florida were shown to exhibit only minor genetic differences.

Distribution. Eastern Canada to Florida, intertidal to 86 m; northern Gulf of Mexico, Florida, intertidal to 10 m.