PALEOECOLOGY OF THE ENIGMATIC "SHIPWORM" KUPHUS INCRASSATUS (GABB, 1873)

Robust calcite tubes in mid-to-late Cenozoic marine deposits of the Gulf Coast and Caribbean are the remains of an extinct bivalve mollusk, Kuphus incrassatus. The calcareous tube, which in part lines the animal's burrow, is an accessory calcification or shell; it supplements the two valves, which at times it enclosed in the crypt. Most of what is known about the biology of K. incrassatus is the result of comparison with other "shipworms" (Teredinidae) that bore into wood substrates, including Kuphus polythalamius (Linnaeus), the sole extant species, which also burrows in marine sediments. The strength of these resemblances, however, is an open question, including the placement of Kuphus incrassatus within the genus. The tubes of both fossil and living Kuphus species are a palimpsest of marks with potential to elucidate life history and paleoecology: growth bands, growth lines, agglutinated particles, xenoglyphs, borings, and repair scars. Previous work has identified subtle features of the K. incrassatus tube that appear to distinguish it from K. polythalamius. Unfortunately, disagreement over whether tube features are appropriate taxobases, where the valves are unknown, has probably limited recognition of important morphological differences. While many tube features are likely to be records of environment, some are clearly independent of the surrounding substrate and mollusk assemblage. I provide evidence that a tube morphology--sieve-like, hummocky sheets--unambiguously separates K. incrassatus from K. polythalamius and other teredinid bivalves. Incorrectly identified as an encrustation in previous studies, the porous shell represents a distinct phase of tube accretion at its anterior (lower) end, providing increased communication between the crypt and surrounding sediment. While pores also occur in the tube of K. polythalamius, these are larger, fewer in number, and perforate typical shell. With consistently identifiable differences in tube morphology between K. incrassatus and K. polythalamius, I explore whether these differences correspond to (paleo-) environmental preferences as previous studies have hypothesized. These new observations and existing data suggest that the life history and paleoecology of Kuphus incrassatus represents a distinct condition among teredinid bivalves.