Species Account

Syssitomya pourtalesiana Oliver, 2012

Galeommatoidea : Montacutidae

Tebble name: n/a
Smith & Heppell name: Axinodon symmetros Jeffreys, 1876

To size: To 4.5mm. Shell Structure: Thin, fragile. Equivalve: Equivalve. Equilateral: Inequilateral, beaks distinctly behind midline. Tumidity: Somewhat inflated. Outline: Subovate, longer than high, length to height ratio 1.3:1, distinctly expanded anteriorly becoming a little oblique; anterior dorsal margin short as a depressed but ill-defined lunule; anterior broadly rounded; posterior dorsal margin sloping merging smoothly with rounded posterior margin; anterior distinctly more rounded than posterior; ventral margin gently curved.

Sculpture: Of dense, fine commarginal ridges. Margin: Inner margin smooth. Ligament: Internal, short, attached to a shallow resilifer situated beneath and posterior of the beaks. Hinge: Right valve with a single, projecting, cardinal peg, immediately anterior to this tooth a prominent depression; left valve with a short, marginal flange in a posterior lateral position. Pallial Musculature: Scars weakly impressed, indistinct but adductor muscles subequal, pallial line entire. Periostracum: Insignificant. Colour: Shell off-white, translucent.

Distribution & Ecology

Known from the Norwegian Sea and the NE Atlantic as far south as the Bay of Biscay. It is commensal, living attached to the spines of the echinoid Pourtalesia. The gills host symbiotic bacteria and this species is presumed to be chemosymbiotic.

The depth range is large from the upper bathyal and abyssal zones, 800-3617m.

Depth Range
Bathyal (500 - 2000m)
Abyssal Rise (2000 - 4000m)

Additional Information & Related Species

Key Features & Similar Species

Such small species of the Montacutidae are difficult to identify if not associated with their host. At bathyal depths the only other echinoid associate is Kelliola symmetros but it is not so expanded anteriorly and is hosted by the echinoid Aeropsis.

Related Species


Listed are literature citing Syssitomya pourtalesiana Oliver, 2012. Reference containing the species Type Description is highlighted.

Oliver P.G. 2012. Taxonomy of some Galeommatoidea (Mollusca, Bivalvia) associated with deep-sea echinoids: A reassessment of the bivalve genera Axinodon Verrill & Bush, 1898 and Kelliola Dall, 1899 with descriptions of new genera Syssitomya gen. nov. and Ptilomyax gen. nov. . European Journal of Taxonomy. 12: 1-24.


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Record last modified: 11/04/2016