Species Account

Policordia gemma (Verrill, 1880)

Verticordioidea : Verticordiidae

Tebble name: n/a
Smith & Heppell name: Policordia gemma (Verrill, 1880)

To size: To 10 mm. Shell Structure: Very thin, fragile, hyaline. Equivalve: Equivalve. Equilateral: Inequilateral, beaks close to the anterior margin. Tumidity: Moderate. Outline: Rounded subquadrate; posterior dorsal margin long, straight, posterior margin, straight, as long or longer than post-dorsal margin; posterior ventral junction distinct, rounded; ventral margin curving to small rounded anterior margin. Contour: Deep indentation in front and below umbos.

Sculpture: With increasing number of narrow radial raised lines, c. 35 at 5 mm to 50 at 10 mm; fine, dense, concentric striations between ribs. Margin: Inner margin smooth. Ligament: Internal with a lithodesma. Hinge: Teeth lacking. Pallial Musculature: Obscure. Periostracum: Thin, pale straw in colour. Colour: White.

Distribution & Ecology

Allen & Turner give a bathymetric range of 138-3917m. We believe that in British waters this species is limited to bathyal and abyssal depths. It is likely to occur along the entire Atlantic margin

Depth Range
Continental Shelf (to 200m)
Continental Margin Zone (200 - 500m)
Bathyal (500 - 2000m)
Abyssal Rise (2000 - 4000m)

Additional Information & Related Species

Key Features & Similar Species

The Atlantic species of Policordia are difficult to identify on shell characters alone (see Allen & Turner, 1974). So far we have not seen enough material to add to Allen & Turner's comments. From the material that we have examined we are unable to be certain of the distinction between P. gemma and P. densicostata. Here we have included shells identified by others as P. gemma but we would probably have considered these to be the same as P. densicostata. P. densicostata was described from the Biscay region where most of our material has come from and therefore we would refer this material to this taxon. P. gemma has been identified from material collected further north and the shells have generally been much smaller rarely exceeding 5mm.

Related Species

Verticordioidea : Verticordiidae

References

Listed are literature citing Policordia gemma (Verrill, 1880). Reference containing the species Type Description is highlighted.

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.
Verrill A E 1880. Notice of recent additions to the marine Invertebrata, of the northeastern coast of America, with descriptions of new genera and species and critical remarks on others. Proceedings of the United States National Museum. 3: 356-409.

Resources

  • Conchological Society of Great Britain & Ireland
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  • CLEMAM
    Check List of European Marine Mollusca
  • MarLIN
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  • NBN Gateway
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  • BivAToL
  • MarBEF
  • Malacological Society
  • Unitas Malacologica
  • Census of Marine Life
  • MarBEF
    MarBEF, a network of excellence funded by the European Union and consisting of 94 European marine institutes, is a platform to integrate and disseminate knowledge and expertise on marine biodiversity, with links to researchers, industry, stakeholders and the general public.

Image Gallery

Policordia gemma (Verrill, 1880)
Policordia gemma (Verrill, 1880)
Policordia gemma (Verrill, 1880)
Policordia gemma (Verrill, 1880)
Record last modified: 17/05/2016