Martesia fragilis Verril & Bush, 1898Pholadoidea : Pholadidae
To size: To 50 mm. Shell Structure: Main body robust but brittle; posterior extension fragile. Equivalve: Equivalve. Equilateral: Inequilateral beaks close to the anterior. Tumidity: Tumid, especially across the umbos. Outline: Main body subovate, posterior extension narrower and may be irregular; anterior broadly rounded with initial pedal gape filled by the callum. Umbonal reflection covered by a large subcircular mesoplax; dorsal area behind mesoplax covered by a long lanceolate metaplax; posterior ventral region covered by a long lanceolate hypoplax. Contour: Main body of shell divided by a radial groove; posterior extension distinctly demarcated.
Sculpture: Area anterior of radial groove decussate; posterior area with weak concentric ridges; posterior extension with strong growth stops. Ligament: Small. Pallial Musculature: Apophysis long, thin; pallial sinus very deep; anterior adductor scar on umbonal reflection, posterior adductor scar large close to dorsal margin, siphonal muscle scar large in a vertical orientation; accessory ventral adductor scars on either side of condyle. Periostracum: Straw coloured, thin. Colour: Dirty white. Additional Characters: Shells of same species can vary and the most consistent species identifying character is the shape and design of the mesoplax, even in juvenile specimens. In M. fragilis the mesoplax is oval with a dorsal depression and concentric sculpture.
Distribution & Ecology
A wood borer, primarily a warm temperate to tropical species recorded rarely from British waters. Known only from Rossbrig, Galway and Lusty Glaze Cove, Cornwall in our waters.
Juveniles & Similar Species
The juvenile shell lacks the posterior extension, is more globular in form with a pedal gape. Only mesoplax present.
Key Features & Similar Species
Listed are literature citing Martesia fragilis Verril & Bush, 1898. Reference containing the species Type Description is highlighted.
Holmes, A., Fenwick, D., Ganey, P. & Williams, T. 2015. Martesia fragilis Verrill & Bush, 1898 in the North-east Atlantic. OVerlooked and a recent new discovery. Journal of Conchology. 42 (2):
Verrill A E & Bush K J 1898. Revision of the deep water Mollusca of the Atlantic Coast of North America with descriptions of new genera and species Part 1 Bivalvia. Proceedings of the United States National Museum. 20: 775-901.
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