Molecular phylogeny and evolution of the cone snails (Gastropoda, Conoidea).

We present a large-scale molecular phylogeny that includes 320 of the 761 recognized valid species of the cone snails (Conus), one of the most diverse groups of marine molluscs, based on three mitochondrial genes (COI, 16S rDNA and 12S rDNA). This is the first phylogeny of the taxon to employ concatenated sequences of several genes, and it includes more than twice as many species as the last published molecular phylogeny of the entire group nearly a decade ago. Most of the numerous molecular phylogenies published during the last 15years are limited to rather small fractions of its species diversity. Bayesian and maximum likelihood analyses are mostly congruent and confirm the presence of three previously reported highly divergent lineages among cone snails, and one identified here using molecular data. About 85% of the species cluster in the single Large Major Clade; the others are divided between the Small Major Clade (∼12%), the Conus californicus lineage (one species), and a newly defined clade (∼3%). We also define several subclades within the Large and Small major clades, but most of their relationships remain poorly supported. To illustrate the usefulness of molecular phylogenies in addressing specific evolutionary questions, we analyse the evolution of the diet, the biogeography and the toxins of cone snails. All cone snails whose feeding biology is known inject venom into large prey animals and swallow them whole. Predation on polychaete worms is inferred as the ancestral state, and diet shifts to molluscs and fishes occurred rarely. The ancestor of cone snails probably originated from the Indo-Pacific; rather few colonisations of other biogeographic provinces have probably occurred. A new classification of the Conidae, based on the molecular phylogeny, is published in an accompanying paper.

Radula Tooth Structure of the Gastropod Conus imperialis Elucidated by Scanning Electron Microscopy.

Scanning electron microscopy of the hollow, harpoon-like radula tooth of the toxoglossan gastropod Conus has elucidated the structure and relationships of its component parts: apex, cutting edge, barbs, serration, adapical and basal openings of the lumen, external and internal folds of the shaft, and base. The functional roles of these components in prey capture are proposed.

Size-Related Obligate and Facultative Parasitism in the Marine Gastropod Trichotropis cancellata.

The marine gastropod Trichotropis cancellata, previously considered to be exclusively a suspension feeder, is also a kleptoparasite, stealing food from several species of suspension-feeding polychaetes. When feeding independently, T. cancellata uses its pseudoproboscis, an elongate, ciliated extension of the lower lip, to transport particles captured on its ctenidium to its mouth. When parasitizing, the snail positions its pseudoproboscis in the mouth of a host polychaete and diverts a large proportion of the particles captured by the polychaete to its own mouth. In subtidal habitats around San Juan Island, Washington, most individuals of T. cancellata are found in association with the tube openings of suspension-feeding polychaetes. In laboratory experiments, parasitism significantly enhanced fitness in T. cancellata. Juvenile snails that parasitized polychaetes grew faster and survived in greater numbers than those deprived of access to hosts, and parasitic adult snails reproduced more than those without hosts. Parasitism in T. cancellata and related capulid gastropods may have originated in early post-metamorphic stages as a response to constraints on the efficiency of suspension feeding at small sizes; however, because parasitism is more effective than suspension feeding for snails of all sizes, it now persists throughout life.

Interior remodeling of the shell by a gastropod mollusc.

As the Conus shell grows by spiraling of the outer lip around the axis, profound internal shell dissolution thins the walls of the protected penultimate whorl from several millimeters to <50mum. Shell material is added to the inside of the spire and the anterior part of the columella. The resulting shell has a uniformly thick last whorl and thickened spire that enhance defense against crushing predators and a greatly expanded interior living space for the animal.