Allogramma formosa (Jeffreys, 1882)Pandoroidea : Lyonsiidae
To size: To 15mm. Shell Structure: Thin, fragile. Equivalve: Equivalve. Equilateral: Inequilateral, beaks slightly in front of midline. Tumidity: Moderate. Outline: Subrectangular; anterior rounded, posterior truncate, ventral margin gently curved, dorsal margins long sloping gently. Contour: Umbos prominent; posterior area set off by a radial carina running from the beaks to the posterior ventral junction.
Sculpture: Anterior area with few oblique weak ridges, anterior and median areas with dense, radial rows of minute spines, these larger on dorsal anterior area; posterior area with radial riblets bearing spines, these becoming larger on dorsal area and projecting above the margin. Margin: Inner margin smooth. Ligament: Small, set on a shallow internal lithodesma below the beaks. Hinge: Lacking teeth. Pallial Musculature: Obscure. Periostracum: Obscure. Colour: White.
Distribution & Ecology
Mostly from lower slope and abyssal depths, widely distributed in the North Atlantic including Rockall Trough and Porcupine Bight.
Bathyal (500 - 2000m)
Abyssal Rise (2000 - 4000m)
Juveniles & Similar Species
Small shells are more trapezoidal in outline, the anterior distinctly narrower than posterior.
Key Features & Similar Species
Listed are literature citing Allogramma formosa (Jeffreys, 1882). Reference containing the species Type Description is highlighted.
Jeffreys J.G. 1882. On the Mollusca procured during the ‘Lightning’ and ‘Porcupine’ Expeditions, 1868-70. (Part IV). Proceedings of the Zoological Society of London. 1881: 921-952.
Olabarria C. 2005. Patterns of bathymetric zonation of bivalves in the Porcupine Sea Bight and adjacent abyssal plain, NE Atlantic. Deep-Sea Research I. 52: 15-31.
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