Gouldia cerina (C. B. Adams, 1845) Waxy Gouldclam

Gouldia cerina (C. B. Adams, 1850)

Gouldia cerina (C. B. Adams, 1850)
    Interior view R valve 9 mm; exterior view L valve 9 mm. Trawled by scallop boat ~32 mi. E. St. Augustine, St. Johns Co., Florida. C. M.  Thorpe! Feb., 1979. H. G. Lee Collection.  

Gouldia bermudensis (E. A. Smith, 1885)

Gouldia bermudensis (E. A. Smith, 1885)

    Interior view R valve 7 mm; exterior view L valve 6 mm. Drift, Trunk Is., Coney Is. Bay, Bermuda. A. T. Guest! 1960-1970. H. G. Lee Collection.

 

Thetis cerina C. B. Adams, 1845

Circe insularis (Dall and Simpson, 1901: pl. 55, fig. 2; USNM 160061).

    Marlo Krisberg of Merritt Is., FL recently posted a  webfeature treating the venerid Gouldia cerina (C. B. Adams, 1845). A discussion ensued both on his website and on Conch-L, the Conchologists of America affiliate listserve. Members of that group expressed an interest in seeing an authentic figure of the other western Atlantic species, Gouldia bermudensis (E. A. Smith, 1885) [+ G. insularis (Dall and Simpson, 1901) fide Moolenbeek 19 Nov., 2002 in litt.].

    Left above is the lectotype (MCZ 155584) of Thetis cerina C. B. Adams, 1845 (Clench and Turner, 1950: pl. 44, fig. 7), but we have produced a mirror image of that right valve, making it appear to be a left valve, for ease of comparison with right above: the figured type of Circe insularis (Dall and Simpson, 1901: pl. 55, fig. 2; USNM 160061).

    Examination of several specimens (25 lots of G. cerina from Bermuda to the southern Caribbean, and eight of G. bermudensis from Bermuda to Estado São Paulo, Brazil) indicates the following differential diagnosis: G. cerina has a rounded subtrigonal shape, and G. bermudensis is subcircular/oval and is less compressed. The beaks of G. b. are more blunt, tumid, prosocline and anteriorly-placed than those of G. c. The radial sculpture is less effaced on the middle third of the valves of G. b. G. b. appears to grow not much larger than 6 mm while G. c. often exceeds 10 mm. Colors are more subdued in G. b. The pallial sinuses of  these species are relatively small and spindle-shaped. That of G. bermudensis arises higher than, and extends ventrally proportionately twice as far as, that of G. cerina. Finally, the inner valve margins of mature G. b. have distinct fine commarginal sulci (usually two) whereas, the inner margins of mature G. c. have less distinct commarginal sculpture and are weakly crenulate. In a mixed Bermuda lot, shape alone allowed prompt and consistent separation.

Clench, W. J. and R. D. Turner, 1950. The western Atlantic marine mollusks described by C. B. Adams. Occ. Pap. Moll. 1(15): 233-403 incl. pls. 29-49. June 26.
Dall, W. H. and C. T. Simpson, 1901. The Mollusca of Porto Rico. U. S. Fisheries Commission Bulletin 20: 351-524 + pls. 53-58.