Based upon a DNA barcoding study of Brachidontes from two ecologically distinct intertidal habitats on Long Key, Florida Keys (Bennett, et al., 2011), the name Brachidontes exustus (Linnaeus, 1758) was confirmed as representing a cryptic species complex of five species.  This study confirmed an earlier DNA study that found B. exustus to be a cryptic species of four species (Lee and Foighil, 2004).  While both studies identified multiple species within the B. exustus complex and reported that there were “some obvious qualitative differences in gross morphology,” neither attempted to name and assign specific morphological descriptions to each species.   Bennett, et al. separated the five species by their regionally dominant ranges in the western Atlantic, and adopted and expanded the names assigned by Lee, et.al.; namely, Antilles, Atlantic, Bahamas, Gulf, and Western Caribbean.  All five fall under the rubric B. exustus and, although Bennett et al. stated that the five cryptic species have not yet been formally described and remain under the rubric of B. exustus, he did recognize that Abbott (1974) and others had distinguished 

B. domingensis as a distinct species separate from B. exustus.  Rehder (1981) also distinguished 

B. domingensis as a distinct species “Very similar” and “related” to B. exustus.”  Redfern (2001) treated them as separate but pointed out they were synonymized by others.  Mikkelsen & Bieler (2008) reported that 

B. domingensis “is now regarded as a form of B. exustus.”   As of Dec 2024, WoRMS accepts

B. domingensis as a valid species.  In effect, the recognition of B. exustus as a cryptic species delegitimatizes the names B. exustus and B. domingensis (and their morphological descriptions and distinctions) as applicable to specific and separate morphological species.  Until the works of Bennett, et al. and Lee & Foighil are taken into consideration, and the five cryptic species are specifically linked to morphological and other information that convincingly distinguishes between them,  descriptions of

B. exustus and B. domingensis cannot be accepted as applying to any specific shell.  In my view B. exustus must be treated as a five-component cryptic species until all five components are named and distinguished.  

 

References: 

Abbott, R. Tucker. 1974 American Seashells, Second Edition, Van Nostrand Reinhold Company.

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Bennett, Reed, & Lutz. Jun 2011. DNA barcoding reveals Brachidontes (Bivalvia: Mytilidae) from two ecologically distinct intertidal habitats on Long Key, Florida Keys, are cryptic species, not ecotypes. The Nautilus 125(2), pg. 63.

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Lee & Foighil. 2004. Hidden Floridian biodiversity: mitochondrial and nuclear gene trees reveal four cryptic species within the scorched mussel, Brachidontes exustus, species complex.  Molecular Ecology 13: 3527-3542.

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Lee & Foighil. 2005. Placing the Floridian marine genetic disjunction into a regional evolutionary context using the scorched mussel, Brachidontes exustus, species complex. Evolution 59(10): 2139-58.

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Mikkelsen, Paula M. and Bieler, R. 2008. Seashells of Southern Florida - Bivalves.

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Redfern, Colin.  2001.  Bahamian Seashells: A Thousand Species from Abaco, Bahamas.  Bahamianseashells.com, Inc: Boca Raton, Florida.

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Rehder, Harald A.  1981.  The Audubon Society Field Guide to North American Seashells.  Alfred A. Knopf, New York.