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1 June 2012 B-type Protoconchs and All Three Modes of Larval Development in Eastern North American Boonea (Pyramidellidae)
Robert Robertson
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The genus Boonea Robertson (1978), ectoparasitic on mollusks, consistently has a B-type protoconch morphology thought by Thorson (1946) to indicate planktotrophy in other pyramidellid genera. Studies in the laboratory of the eggs and larval development of Boonea seminuda (C. B. Adams, 1839), the type species, B. bisuturalis (Say, 1822), and B. impressa (Say, 1822) on the eastern North American seaboard confirmed planktotrophy. The egg diameter range there was 68 to 80 µm. Boonea bisuturalis had been reared through metamorphosis using algal cultures (Robertson 1967; Leibowitz 1979 [unpublished]). The developmental stages are newly illustrated here. Boonea seminuda and B. bisuturalis have different teleoconch sculptures, similar but different spermatophores, and are closely related. Northern B. bisuturalis and southern B. impressa are allopatric and hybridize or intergrade conchologically in a cline between Long Island Sound and Chesapeake Bay. One population of B. “impressa” had been found to be lecithotrophic on the Texas coast, at Port Aransas (White et al. 1985). A second Texan population, at Galveston, is shown here consistently to undergo intracapsular metamorphosis. The eggs were reared to hatching crawlers in the laboratory. The Galveston protoconch sizes and morphologies are the same as at North Carolina, but eggs from Galveston were much larger (212 to 236 µm in diameter). Durations of intracapsular development through metamorphosis and the pelagic larval stage in laboratory B. bisuturalis were virtually the same (respectively 15 to 20 and 16 to 20 days). In the three species, egg sizes greatly affect oviposition to hatching times, hatching sizes, and whether or not there is planktotrophy. Egg sizes do not affect oviposition to metamorphosis times, or protoconch sizes. North Carolinian and Texan B. impressa teleoconch sculptures and spermatophore sizes differ slightly. There could be a wide and continuous intraspecific range of conchological and/or reproductive variation, or allopatric poecilogony, or a chemically-induced ecotype, or (as seems most likely) one or more as-yet unnamed sibling species in the Gulf of Mexico. Regardless, this appears to be the first known exception to the “shell apex theory” (Thorson 1950). Everywhere, B. “impressa” is a serious pest of Crassostrea virginica (Gmelin, 1791). Some new data on Boonea systematics, adult ecology, and life history are presented. “Booneascymnocelata Pimenta et al. (2009), from Brazil, is not a Boonea because it has a C-type protoconch; its teleoconch is convergent with that of B. seminuda.

Robert Robertson "B-type Protoconchs and All Three Modes of Larval Development in Eastern North American Boonea (Pyramidellidae)," American Malacological Bulletin 30(2), 229-246, (1 June 2012).
Received: 7 May 2011; Accepted: 1 September 2011; Published: 1 June 2012

allopatrically variable development
exception to “shell apex theory”
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