Brachidontes pharaonis Fisher, 1870

Oliver, P. Graham, Holmes, Anna, Killeen, Ian, Light, Janice & Wood, Harriet, 2004, Annotated checklist of the marine Bivalvia of Rodrigues, Journal of Natural History 38 (23), pp. 3229-3272 : 3236

MYTILINAE Brachidontes pharaonis Fisher, 1870

Habitat. This species is found in a number of distinct habitats from mid to low levels in the intertidal. Low in the intertidal it may form dense rafts totally covering the surface of the rock, especially the limestone platforms at sites such as Coton Baie, Petite Butte and Ile Gombrani. At mid-tide it can be found in the pitted surface or undersides of basaltic rocks wherever these occur. On large boulders B. pharaonis may form a dense band on the lower surfaces and fill cracks at a higher level, as can be seen adjacent to the road from Port Mathurin to Anse aux Anglais.

Distribution. This is believed to be the most abundant bivalve species and can be found all around the island and lagoon islets wherever intertidal hard substrates are available.

Remarks. More commonly known by its preoccupied name, B. variabilis, Krauss , the shell morphology of B. pharaonis is, as the former name suggests, variable and correlates to the habitat type. The typical form is roughly triangular with prominent bifurcating ribbed sculpture and this form is found at mid-tide levels on or under rocks and stones. When it inhabits exposed platforms and forms dense rafts the outline is more rectangular, the shell is thinner, almost shiny and the sculpture is almost absent. When forming dense bands around boulders or on sheltered rocks the size is greater and the outline more elongate. These shells are often badly eroded and surface features are not apparent. Similar observations were made for Red Sea populations and it was concluded that despite the variation only a single species is present (Arcidiacono and di Geronimo, 1976).

Range. Indo-Pacific [R/M/S].

Figured specimen. 22.09 mm, NMW.Z.2000.086.00036.