Thyonella gemmata Pourtales 1851

Thyonella gemmata (Pourtalès, 1851)

Figure 12

Colochirus gemmatus Pourtalès, 1851: 11.

Thyonella gemmata. — Verrill, 1872: 437; Hendler et al, 1995: 263, figs. 143, 179A,B,C,D. Thyone gemmata. — Deichmann, 1930: 177, pl.17 figs.1–3.

Material examined. USNM 14252, N.C., Beaufort, no date given (gift), 2. USNM E2655, N.C., Vinyah Bay, R/V Fish Hawk Sta 1645, no date given. USNM E22466, N.C., Beaufort, March 28, 1941, town marsh, 2. USNM E34103, Florida, 28°50’06”N, 80°44’12”W, R/V Delaware II, Sta 0 70, May 21, 1984,14.6m. USNM E46901, N.C., Surf City, Topsail Island, NE Wilmington, July 17, 1996, washed ashore, 2. SERTC S# 2065, Dewee Inlet, SC, 32º49'N, 79º43'W, coll. GML Staff, June 30 1967. DML 3722, Bird Shoal, Beaufort, NC, May 1, 1973, intertidal.

Diagnosis. Burrowing form up to 150 mm long. Color mottled gray, brown, olive green, sometimes tan to black. Body usually U-shaped, sometimes straight to slightly curved, swollen medially, slender near ends. Feet cylindrical medially, papillate distally, arranged in distinctive double rows along radii, also scattered in interradii. Body wall rigid with ossicles consisting mostly of knobbed buttons (80–120 μm), shallow cups (45–55 μm in diameter), and perforated plates (up to 400 μm).

Distribution. MA to FL, Gulf of Mexico, Cuba, Yucatàn Peninsula.

Habitat. Muddy or sandy areas, often associated with seagrasses. Low tide to 6m.

Remarks. In some areas (for example off Folly Beach, SC), this species can be very common, and may wash ashore during storms. Manwell & Baker (1963) and Manwell (1966), based on their analyses of hemoglobin, concluded that two cryptic or sibling species of Thyonella were present in Alligator Harbor, NW Florida. These they named “stout” and “thin” but no formal scientific names were applied. Deichmann (personal communication to Manwell & Baker), using conventional taxonomic characters, could find no consistent morphological differences between the stout and thin forms.