by Piter Kehoma Boll
It’s time to bring the first brachiopod as a Friday Fellow. Unfortunately, it is a hard task because, as with other fossil-famous groups such as Foraminifers and Diatoms, there is very little available knowledge of living brachiopods.
The species I chose, Terebratalia transversa, is usually called lampshell, although this name can also be used for other closely related species. Thus, I decided to call it the common lampshell.
The common lampshell can be found in intertidal and subtidal waters of the Pacific coast of North America, from Alaska to Baja California. The larval stage, as in all brachiopods, swims in the water, but the adult individuals are attached to a substrate, usually the undersides or vertical parts of rocks, and remain attached for the rest of their lives. If for some reason they are detached, they are unable to reattach and die soon after.
The adult common lampshell has a bivalve shell measuring about 5 cm in length, although some specimens can reach up to 9 cm. The upper or dorsal valve of the shell, called the pedicle valve, bears the pedicle by which the animals attaches itself to the substrate. The pedicle is basically composed by connective tissue surrounded by epithelium and cannot contract, although it can be twisted or moved otherwise with the use of muscles connected to its proximal end in the valve. In the common lampshell, the pedicle is very short, which restricts its movements and ability to reorient the body according to the water current. The lower or ventral valve, called the brachial valve, contains the lophophore, a U-shaped crown of tentacles used for filtering particles from the water. The two sides of the lophophore are called the arms or “brachia”, from which the phylum Brachiopoda gets its name.
The overall shape of the common lampshell is quite variable. The shell may be longer or more circular, with more or less marked grooves, so that shell morphology is not very useful to identify it.
Adult common lampshells reproduce during winter, usually from December to February, releasing gametes in the water, where they meet and originate a zygote. The larval stage that develops after fertilization swims in water, but after about 6 days it settles on the substratum and directs its small pedicle toward it, eventually attaching to it and starting to grow until reaching the adult stage, which takes some years, with a growth of about 6 mm per year.
Despite being one of the most “popular” brachiopod species, little is yet known about the ecology or the behavior of the common lampshell. We need more people studying them!
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Dyer, A. (2002) Terebratalia transversa (Sowerby, 1846): Common Lampshell. Invertebrates of the Salish Sea. Available at < https://inverts.wallawalla.edu/Brachiopoda/Class%20Articulata/Order%20Telotremata/Terebratalia_transversa_Page.html >. Access on December 29, 2018.
Eshleman, W. P., & Wilkens, J. L. (1979). Brachiopod orientation to current direction and substrate position (Terebratalia transversa). Canadian Journal of Zoology, 57(10), 2079–2082. doi:10.1139/z79-274
Stricker, S. A.; Reed, C. G. (1985) Development of the pedicle in the articulate brachiopod Terebratalia transversa (Brachiopoda, Terebratulida). Zoomorphology 105: 253–264.
Thayer, C. W. (1977) Growth and mortality of a living articulate brachiopod, with implications for the interpretation of survivorship curves. Paleobiology 3(1): 98–109.
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