Abstract: Interpretation of the well-studied temporal record of predation by drilling gastropods requires understanding spatial patterns in drilling, in order to dissect any environmental trends from evolutionary patterns. However, current knowledge of spatial patterns in drilling at one time is incomplete; some studies have observed an increase, and others a decrease, in drilling with latitude. Because drilling is a slow process that puts the predator at risk, it has been hypothesized that frequency of successful drilling should increase, and that of failed drilling should decrease, at higher latitudes, where enemies pose fewer risks. To test this hypothesis, we collected bulk samples of modern molluscs from beach assemblages from Maine (43° N latitude) to the Florida Keys (25° N). The frequency of complete (successful) and incomplete and multiple (failed) drillholes was tabulated for higher and lower taxa from 24 samples (> 11,000 specimens). We explored latitudinal variation in drilling by comparing patterns among the Nova Scotian, Virginian, Carolinian, and Gulf molluscan provinces. Results were more complex than predicted. Drilling frequencies were greatest in the Carolinian Province and declined to the north and south for arcid bivalves, infaunal bivalves, and the total fauna (bivalves + gastropods; provincial frequencies for the total fauna were as follows: Nova Scotian, 8%; Virginian, 13%; Carolinian, 28%; and Gulf Province, 15%), and for the genus Spisula. In contrast, failed drilling, though infrequent, was typically more common in the Gulf Province than in the Carolinian Province (4% vs. 1% for most groups). Possible explanations for the patterns include: (1) taxa from more tropical localities may be better defended against predators, producing lower drilling frequencies and higher incidence of failed drilling; (2) presence of multiple predators in warmer waters may decrease drilling on bivalve prey if predators interfere with or prey upon one another; (3) at cooler latitudes, slower metabolisms may produce lower drilling frequencies; (4) alternative predation modes such as smothering may be more common at higher latitudes, resulting in lower drilling frequencies. Despite the apparent patterns, spatial variability reinforces the need to examine multiple samples in order to characterize the drilling frequency at a single location (or time interval).

Abstract A survey of marine bivalve biodiversity in the Florida Keys, an island archipelago off southern Florida, was compiled from original collecting, museum specimens and the literature. Assembly of over 6000 records resulted in 325 species, 47% of which can be considered common to abundant in the Keys. This represents a 100% increase over the previously known fauna, largely attributable to critical review of museum specimens. Capture of species occurrences from the literature, especially when non-traditional sources (newsletters, agency reports) are excluded, is shown to be least effective, producing only 44% of the total. Bivalve distributions within the Keys show that the fauna is tropical. One-third of the species are wide ranging along the island chain; however, a latitudinal cline in faunal similarity exists from the Upper Keys southwestwards to Dry Tortugas. The fauna of Florida Bay is the most divergent within the study region and also compared to other, ecologically complex, western Atlantic tropical–subtropical regions. Limited historical records indicate little species turnover in the Keys, although population reductions along the main highway and habitat shifts (from natural to artificial substrata) are evident. These results have implications for biodiversity survey methods and, more locally, for management of the Florida Keys National Marine Sanctuary.

Abstract All Lucinidae species studied so far possess sulphide-oxidizing, chemosymbiotic bacteria housed in bacteriocytes of gill filaments. The ecology, functional anatomy and evolution of the Lucinidae must be considered in relation to this symbiosis. The ctenidia have been extensively studied but other anatomical structures peculiar to lucinids have received much less attention. Reviewed are the morphological diversity of living lucinids, highlighting features of their anatomy including ctenidia, pallial apertures, anterior adductor muscle, pallial blood vessel and mantle gills. The latter are much more complex than previously understood and are here redescribed. They comprise folded structures located near the anterior adductor muscle in Codakia, Phacoides and Lucina , and on the septum of Anodontia. These are interpreted as secondary respiratory surfaces, their location enabling the separation of the anterior inflow of oxygenated water from sulphide-containing water. The latter is released from the sediment by the probing activities of the highly extensible foot and is pumped over the gill through the pedal gape and perhaps also via the exhalant tube. The shell features of Ilionia from the Silurian Period suggests that the lucinid chemosymbiosis is an ancient association.