Julia thecaphora (Carpenter, 1857)

¡¿A bivalved gastropod from Mexico?!

    San Agustinillo, Oaxaca, Mexico. Both specimens depicted above are views of the interior and exterior of a single valve and measure about 3 mm. Digital images by David Kirsh.

San Agustinillo, Oaxaca, Mexico. Digital image by David Kirsh.

A note about the nomenclatorial and taxonomic history of Julia thecophora

    This species was regarded as a pelecypod for most of the century following its description. However, the solitary specimen Rev. Philip Carpenter had before him, a right valve, was assigned to the genus Smaragdinella A. Adams and Reeve, 1848 [TS Bulla viridis Quoy and Gaimard, 1832 (= Bulla calyculata Broderip and G.B. Sowerby I, 1829)] as evidenced in the original description (Carpenter, 1857: 533) [Fig. 1] and its drawing by the author [Fig. 2 ].¹ The hinge process of this specimen, which Carpenter likened to as a "theca" [Greek theikos, meaning sheath], is apparently homologous to the "calycula" [diminutive of Greek kalyx, little cup] of the univalve shells of that genus as exemplified by the type species [Fig. 3], and recapitulated in its specific epithet.

    Interestingly, as noted in his original description (q.v.), Carpenter borrowed the word "Thecophora," from a manuscript name penned by naturalist Thomas Nuttall, who was almost certainly referring to the hinge process of a right valve of what was to become the congeneric Julia exquisita Gould, 1862 (see figure and references below) found on an Hawaiian shore. Thus, while Carpenter regarded the "theca" as evidence of a gastropod affinity, Gould, being provided with a left valve as well as a right, considered it a familiar part of of a pelecypod hinge apparatus.

 ¹All sixty plates of these drawings languished in the archives of the U.S. National Museum for over a century until being organized and published (Brann, 1966), from which Fig. 2 is taken.

Acknowledgment: Figure 3 is borrowed from www.femorale.com.

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