Posted: Jun 20 2014 by Harry Lee:

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Great job on an off-the-beaten-track topical gastropod!

(1) I give up on italics, so bear with me.
(2) I'd give "Blainvile" a third "l" as in in "Blainville."
(3) Although I seem to have misplaced this paper:

van der Spoel S., J. Bleeker, and H. Kobayasi, 1993. From Cavolinia longirostris to twenty-four Diacavolinia taxa, with a phylogenetic discussion. Bijdrage tot de Dierkunde 62(3): 127-166.

I seem to remember a geographic parsing of several species in the D. longirostris species-complex. Have you seen this work?

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Colin Redfern:

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Abaco has D. deblainvillei and D. deshayesi.

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Harry:

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Through the kindness of Drs. Arie Janssen and of Jim Carlton of my alma mater (Williams College), I have gotten two relevant papers and can carry my earlier comment to completion.

Spoel et al. (1993) conducted an exhaustive morphological scrutiny of the genus Diacavolinia and found many morphospecies within what had been previously regarded as a single species, your Diacavolinia longirostris. In arriving at this conclusion they created a glossary of no less than 53 morphological characters and metrics. Twenty-four taxa (22 species, 2 formae) eventuated. Of these, 16 were new species. They placed eight species in the western Atlantic, including the Caribbean Province, but only three were placed close to the Florida coast - D. deblainvillei, D. deshayesi, and D. elegans, all new spp.

Your shell matches D. elegans van der Spoel, Bleeker, and Kobayasi, 1993.

However, Maas et al. (2013) did DNA barcoding of several related "species" including D. elegans and D. longirostris, and found no significant genetic divergence between these (and three other Spoel et al.-recognized taxa found in the W. Atlantic). The former (later) authors concluded that only one biospecies was involved.

Short version: you got it right. You might indicate that this is a recognized morph (form, variety) called elegans by the previous authors.

Maas, A.E., L. Blanco-Bercial, and G.L. Lawson, 2013. Reexamination of the species assignment of Diacavolinia pteropods using DNA barcoding. Plos One 8(1): 1-12. Jan.

Spoel S. van der, J. Bleeker, and H. Kobayasi, 1993. From Cavolinia longirostris to twenty-four Diacavolinia taxa, with a phylogenetic discussion. Bijdrage tot de Dierkunde 62(3): 127-166.