Amethyst Gemclam
Gemma gemma
Comprehensive description 2
The Amethyst Gem Clam (Gemma gemma) is a tiny, somewhat triangular clam (usually less than 3mm) with a smooth, glossy shell. The inner shell has a finely scalloped margin (visible with a hand lens). Shell color is whitish or gray, often tinted with purple. (Morris 1973; Gosner 1978; Kozloff 1993) This clam is an Atlantic species introduced into Pacific waters. It lives in soft mud and is therefore found on muddy beaches. The short siphons never extend more than a few millimeters beyond the end of the shell. (Narchi 1971)
Distribution 3
Nova Scotia to Florida, Texas and the Bahamas; Puget Sound, Washington (introduced)
Morphology 4
The shell of Gemma gemma is small, subtrigonal, moderately inflated and rather thin. The exterior is polished and has numerous fine concentric riblets. There are three teeth in the left valve and two teeth in the right (this seems to have been reversed in error in Sellmer 1967). Color is whitish to tan, with purplish over the beak and posterior areas. The animals may be so abundant along the coast of New England that the beaches appear purple, due to the many shells. The shell may reach 5.0 mm long, 4.5 mm high, and 3.0 mm wide, but is usually half this size. Several authors have noted the alga Enteromorpha [now in Ulva: Hayden et al. 2003] attached to the posterior region of the shell. Algal growth is confined to the siphonal region because the animal is buried so that the posterior part of the shell and siphons are exposed. Near the tips of the siphons, irregular patches and streaks of reddish brown pigment occur on the outer surface. Elsewhere the siphons are smooth creamy white, due to opaque white patches on the inner surfaces, which shine through the tissues. The siphons are fused along as much as half their lengths and their tentacles are well developed. There is a ring of simple tentacles surrounding the inhalant aperture. The tentacles are of two alternating sizes. The inhalant siphon bears 8 to 12 tentacles which are loosely interdigitated over the opening when the animal is pumping water. The exhalent siphon in both species has a thin semitransparent sleeve, the valvular membrane, which is an extension of the siphon. The foot and siphons may be withdrawn quickly when the animals are disturbed. When this occurs, the valvular membrane is drawn into the inside of the base of the exhalent siphon. When the animal is undisturbed, the siphons protrude slowly without showing the valvular membrane; then suddenly with explosive force the valvular membrane is extruded. The foot is well developed, wedge-shaped, and adapted to burrowing. It can be extended to a distance approximately equal to the length of the shell. The tip has considerable mobility, moving readily and quickly. When placed flat on the surface of the sand, the animal disappears into the substratum in a minute or less. (Narchi 1971 and references therein).
Reproduction 5
Amethyst Gemclam sexes are separate. The fertilized eggs develop within the female's mantle (the fleshy outer structure covering a mollusk's vital organs and usually containing glands that secrete the shell). The young hatch and leave the mother's shell to burrow into mud or sand. (Green and Hudson 1970; Rehder 1981). In California, Narchi (1971) found animals brooding juveniles in the gills in February, March, and April.
Link to Access Genomic Data 1
http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=345461&lvl=0
Sources and Credits
- (c) matbio, all rights reserved
- (c) Shapiro, Leo, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/17763395
- Adapted by matbio from a work by (c) WoRMS for SMEBD, some rights reserved (CC BY), http://eol.org/data_objects/28469976
- Adapted by matbio from a work by (c) Shapiro, Leo, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11289724
- Adapted by matbio from a work by (c) Shapiro, Leo, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/11289728
