Streptosyllis varians Webster & Benedict, 1887

Figures 18–20

Streptosyllis varians Webster and Benedict, 1887:718–719, pl. 2, figs 24–31, pl. 3, figs 32–34.

Streptosyllis varians — Pettibone 1963:127, figs. 31k. Not Saint Joseph 1895 fide Southern 1914; Not Fauvel 1923.

Material examined. (24 specimens from 4 stations) Northwest Atlantic Ocean. —off Massachusetts, Georges Bank. GBMP Sta. 1: coll. G. Hampson, Chief Scientist, Cruise M 4, R / V Cape Henlopen, 12 May 1982, 41°12.4′N, 67°14.5′W, 58 m, rep. 1 (1, USNM 1750470); Cruise M 10, R / V Oceanus, 15 Nov 1983, 41°13.0′N, 67°15.3′W, 55 m, rep. 4 (1, USNM 1750471). Sta. 10: coll. M. Rawson, Chief Scientist, Cruise M 1, R / V Eastward, Jul 1981, 40°39.4′N, 67°46.4′W, no depth recorded, rep. 4 (10, USNM 1750472); coll. G. Hampson, Chief Scientist, Cruise M 3, R / V Endeavor, 12 Feb 1982, 40°42.0′N, 68°35.1′W, 62 m, rep. 3 (1, USNM 1750473); Cruise M 4, R / V Cape Henlopen, 16 May 1982, 40°42.0′N, 68°35.2′W, 62 m, rep. 6 (2, USNM 1750474); Cruise M 6, R / V Oceanus, 25 Nov 1982, 40°42.0′N, 68°35.1′W, 58 m, rep. 1 (7, tiny, USNM 1750475).— New York / New Jersey Bight: coll. NOAA, Ocean Pulse Sta. 8, 40°21.8’ N, 73°51.6’W, 24 m (1, MCZ IZ 172052). Port Liberty pipeline survey, coll. P. Neubert for AECOM, 19 Jan 2012, Sta. 17, 40°24.328′N, 73°31.497′W, 26 m (1, incomplete, MCZ IZ 172053).

Description (based on new material). Largest specimens with up to 63 setigers, 5 mm long, first few setigers narrow, 0.4 mm wide, middle region twice as wide up to 0.8 mm including parapodia, tapered again toward posterior end; juvenile specimens 1–1.5 mm long. Color in ETOH creamy white or yellowish, eyes red. Palps with broadly rounded, wide bases fused on proximal half, smaller conical section with tapered distal tip (Fig. 18A); distal sections may be turned ventrally leaving only basal portion visible dorsally (Fig. 18B); large accessory papilla on basal portion near beginning of conical section (Fig. 18B). Prostomium rectangular, nearly twice as wide as long, with small anterior medial peak and corresponding posterior indentation; four dark red eyes arranged in open square, anterior pair close to base of palps, usually smaller than posterior pair (Fig. 18A). Median prostomial antenna smooth or slightly wrinkled, reaching to setigers 8–10, up to 3–5 times length of club-shaped, lateral antennae (Figs 18A; 20B). Peristomium clearly demarcated, shorter than setiger 1, with two pairs smooth tentacular cirri similar to lateral prostomial antennae, ventral pair slightly wider, shorter, than dorsal pair (Fig. 18B). Pharynx unarmed, sometimes dark (Fig. 18A, B), without papillae but sometimes with thickened nodes of tissue near rim of proboscis (Fig. 18B). Proventricle cylindrical, with indistinct junction with pharynx (Figs 18A; 20A, B) but slightly tapered at posterior end, extending through 8–11 setigers (depending on size of specimen), with about 60–80 indistinct muscle cell rows, no medial raphe (Fig. 18A, B). Parapodia short, square, blunt in first few setigers (Figs 18A, C; 20B), becoming longer, rectangular, through middle setigers, slightly narrowed distally in posterior setigers; with small clear lobe or papilla on distal dorsal edge, largest in middle setigers (Figs 18D; 20D). Dorsal cirri short, club-shaped, smooth, for at least half or more of body (Fig. 18A, D) but some posterior cirri with 4–5 articles, each with one or two dark golden inclusions (Fig. 18G; 20A). Ventral cirri inserted in middle of parapodium, with wide base and tapered, digitiform tip, shortest on setiger 1, rapidly increasing in length over next setigers, extending beyond parapodia throughout (Fig. 18C, D, F). Pygidium rounded or somewhat triangular, with short median cirrus robust at base, tapering to tip (Fig. 18F, G); lateral anal cirri exceedingly long, curled, twisted, often lost (Fig. 18G). Internal glands in middle and posterior setigers near base of parapodia (Fig. 20E).

Acicula one per parapodium, distinctively enlarged in anterior third of body, setigers 2 through 20–23 with dome-shaped cap surrounded by narrow lip or rim (Figs. 18C; 20C, D); in 55-setiger specimen (USNM 1750470) largest cap dimension 8 µm in setiger 1, 13–14 µm in setigers 2–3, 20 µm in setigers 4–11, 23–24 µm in setigers 12–18, 20 µm in setiger 19–20; thereafter becoming smaller, thinner, with flat oval cap measuring 10 µm across through remaining setigers (Fig. 19). Dorsal simple setae present in all setigers from setiger 1, positioned in close association with acicula (Figs 18C–E; 19); one (rarely two) per setiger, thick, with blunt tip, clearly serrated on distal half; measuring 30 µm in first several setigers, gradually becoming longer, thinner, up to 75–80 µm in middle and posterior setigers, 20–30 µm in pre-pygidial setigers; with minute bifid tip in posterior setigers. Ventral simple seta in last setiger of some specimens, similar to dorsal simple seta, with minute bifid tip (Fig. 18H). Compound setae numbering 12–16 per fascicle in setigers with enlarged acicula (Fig. 18C), reduced to 4–6 per fascicle in setigers with smaller acicula (Fig. 18D, E). Shafts of compound setae shorter, homogomph or nearly so in anterior setigers, up to 50 µm long, one prong with small subdistal tooth, opposite prong oval, smoothly rounded (Fig. 18I–M); posterior setigers with longer, thinner, hetero- or hemigomph shafts up to 80 µm long, with small subdistal tooth or flange, flange more pronounced in posterior setigers (Fig. 18N); opposite shorter prong with two very small side-by-side points or teeth, not visible in lateral view (Fig. 18N, inset). All compound setae with short falcigerous blades; anterior blades up to 10 µm long, middle third of body with blades mostly 20 µm long (some 12–16 µm), posterior blades up to 25–26 µm long; blades in first setigers may appear smooth or with minute serrations, with one smaller distal tooth on convex side slightly below tip (Fig. 18I–M); posterior blades with deep basal and short distal serrations, subequal distal teeth side-by-side (Fig. 18N, inset). All setae lack hoods.

Reproduction. Reproductive individuals with larger eyes, sometimes doubled in size. No natatory setae were observed, although such setae were noted for both males and females by Webster & Benedict (1887:719).

Methyl Green staining pattern. MG stain generally not retained, small glandular areas at base of parapodia retain stain the longest. No stain associated with pharynx or proventricle.

Remarks. Streptosyllis varians is unique among Streptosyllis species, having acicula with greatly enlarged tips in 20 or more setigers, roughly the anterior third of the body, rather than those being restricted to four or five anterior setigers. The acicula, which have an elevated dome-like central area surrounded by an obvious rim, are golden in color and are so large in relation to the parapodia that they are obvious even at low power on a dissecting microscope, especially if the animal is viewed laterally. Also, the middle prostomial antenna is exceedingly long, as are the lateral anal cirri. In the original description, Webster & Benedict (1887:719) described the pharynx as “terminat(ing) in front in a circle of triangular papillae”; however, in the present study, papillae were not observed on the several specimens in which the pharynx was everted, although some areas of puckering or thickened tissue were noted. Apart from this detail of the proboscis and the lack of natatory setae, the new material agrees well with the description and illustrations by Webster & Benedict (1887).

The record of this species from France (Saint-Joseph 1895) was rejected by Southern (1914) because, among other distinguishing characteristics, it has “very thick” acicula in the first setiger and those thick acicula are limited to only a few anterior setigers, unlike Str. varians where they start from setiger 2 and continue for several setigers. Fauvel (1923), however, repeated Saint Joseph’s record. Based on a single report (Marinov 1966), Str. varians was implicated as an invasive species in the Black Sea (Skolka & Preda 2010) or cryptogenic (Băncilă et al. 2022); as with Str. arenae (see Faulwetter et al. 2008 re S. nunezi), single distant reports are probably a misidentification.

Habitat. The type locality of Streptosyllis varians was reported as coarse sand and gravel (Webster & Benedict 1877) and the new material is from similarly sandy sediments.

Distribution and depth records. Type locality: West Quoddy, Maine, low water. Reported from Gulf of St. Lawrence, Gulf of Maine, Georges Bank off Massachusetts, Long Island Sound (New York), low water to 66 m.