Corbicula fluminea - The Asian Clam

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The larval stages of the Asian clam differ significantly from the larval stages of other types of bivalves in several ways. First, most of the larval development occurs inside the gill compartments of the female clam. Secondly, the development of internal body structures, including the foot and siphon, occurs at a slightly different time schedule than seen in the free-living veliger larvae.

Developing Embryos or Pre-Shell Larvae

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Whereas larvae of Dreissenidae are completely pelagic (i.e., free-floating in the water column), other freshwater bivalves (e.g., Corbiculidea, Unionidae, Sphaeriidea) brood their larvae through early development stages in marsupial sacs on the gill. Shelled juveniles (arrows) of a fingernail clam, Musculium sp. (Sphaeriidae) can be seen in this scanning electron micrograph.

Developmental patterns identical to those seen in zebra and quagga mussels (dreissenids).

Can be differentiated from dreissenids by their location - found internally in female in gill chamber rather than in the water column.

Straight-Hinged Larvae

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First larval stage with shell; has straight-hinge appearance; larger than dreissenids (>195 痠).

Foot present; does not swim.

Velum present for only a short time - after shedding the velum, the foot provides locomotion; dreissenids do not shed their velum; they reabsorb it.

Umbonal Veligers

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Foot present.

Siphon present.

Larger than umbonal dreissenids (>280 痠).

Shell shape essentially similar to dreissenids, being rather round.

Pediveligers

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> 500 痠 in shell length.

Shell opaque and 倴lam-shaped.'

Foot present.

Siphon present.

No further development occurs except for continued growth and sexual maturity; the plantigrade stage does not occur in Asian clams.

Species Descriptions

Zebra Mussel Identification