Yellow lampmussel (Lampsilis cariosa) COSEWIC assessment and status report: chapter 3

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Species Information

Name and classification

The Yellow Lampmussel, Lampsilis cariosa (Say 1817) was originally described in 1817 by Thomas Say in a contribution to the American Edition of the British Encyclopedia or Dictionary of Arts and Sciences (Volume II) as Unio cariosus. It was later placed in the genus Lampsilis. The description was based on a limited number of specimens and did not adequately differentiate the species from others with similar morphology. This has led in the past to some confusion with Lampsilis (Leptodea) ochracea (Say 1817), Lampsilis ventricosa (Barnes 1823) and Lampsilis ovata (Say 1817).

The species name cariosa is Latin for 'corroded' and was applied by Say as the specimens that he examined were all heavily corroded around the area of the beaks.

Description

The Yellow Lampmussel is one of twelve species or subspecies of freshwater mussels found in Atlantic Canada. L. cariosa has been well described and figured in recent publications particularly Burch (1975), Clarke (1981), Smith (1986), Strayer and Jirka (1997) and Nedeau et al. (2000). These authors with the exception of Clarke (1981) and Nedeau et al. (2000) also provide keys for identification. The descriptions are based on both external and internal characters of the shell and mantle edge and are adequate for the identification of living animals as well as shells. It is not necessary to sacrifice animals in order to identify them properly.

The following description is based upon information provided in the publications mentioned above and personal observations of specimens from Sydney River, Nova Scotia. Figure 1 a, b and c show typical examples from Sydney River. Bivalve shells up to about 110 mm in length, but typically smaller, up to about 75 mm in length. When seen laterally almost oval in outline, but sexually dimorphic so that adult males appear more elongated than adult females, which are higher posterior to the beaks than they are anterior to the beaks. The beaks are moderately inflated and project beyond the hinge line. The shell is moderately thick, up to 4.0 mm in the largest specimens. The exterior surface is smooth except for concentric growth rest lines. The periostracum is normally bright yellow-orange, or reddish brown in some cases, and glossy. Specimens are usually without rays but when present these are well defined and restricted to the posterior slope of the shell. Specimens collected from Sydney River often have a mineral deposit on the posterior end, which may obscure the rays. Inside the shell the nacre is white with some pink colour in the area of the beaks. The hinge teeth are complete and well developed but may vary in form between individuals from different localities. Pseudocardinal teeth are often strong and conical. The lateral teeth are elevated, of medium length and straight or slightly curved, there being two in the left valve and one in the right valve. In juvenile shells the beak sculpture is composed of 5 or 6 moderately coarse, curved, singly or slightly double-looped concentric bars. These characteristics have been illustrated by Marshall (1890) and reproduced by Strayer and Jirka (1997). Most adult specimens are heavily corroded at the beaks and so these beak characters are not visible.

Soft parts of the living animals are visible along the shell margins. The mantle margin is smooth with grey streaks or dots and with a well developed and brightly pigmented flap-like extension and a dark eyespot. These characters are best developed in the female and are well illustrated by Smith (1986).

The larval stage, or glochidium is described in Hoggarth (1999). It is 0.22 mm long and 0.28 mm high, roughly elliptical in shape with a straight hinge line and no hooks.