Patterns and Processes in the Evolution of Vetigastropoda

The Vetigastropoda includes abalone, top-snails, and keyhole limpets, along with some lesser-known families. I take a comprehensive approach, integrating data taken from both fossil and Recent material as well as molecules (Histone 3, COI, 18S) and morphology to resolve evolutionary questions. I investigate species to family-level relationships, and use phylogenies to gain insight into the macroevolutionary processes of heterochrony, the on-shore/off-shore pattern, and the colonization of the hydrothermal vent environment.

Heterochrony has historically been invoked in evolutionary scenarios concerning the vetigastropod family Scissurellidae. This family consists exclusively of small species (size 1 - 5 mm). Adult scissurellid radulae very closely resemble those of juveniles of other vetigastropods, and from this observation it has been inferred that scissurellids are neotenic forms. However, the striking differences between adult radulae in the large bodied forms such as Haliotidae, Pleurotomariidae, and Trochoidea are also consistent with a peramorphic interpretation of these families from a small ancestral form. Preliminary data indicates that a small sized ancestor can be reconstructed for all Vetigastropoda. Continuous character state reconstruction is applied to address these questions.

The on-shore/off-shore pattern suggests that lineages originate in shallow water and are competitively pushed into deeper water over geological time. It is based on the fossil record of such groups as sea lilies and the molluscan class Monoplacophora. Conflicting results have emerged from collaborative work I have carried out on the phylogeny of some key hole limpets (McLean & Geiger, 1998). On the phylogenetic tree, some of the predominantly shallow subtidal forms (Diodora) are found nested within a clade of deep water representatives (Managnasepta and Cornisepta). Accordingly, the generality of the on-shore/ off-shore pattern is called into question. Preliminary data suggest that the hydrothermal vent environment was colonized repeatedly by vetigastropods.

Monograph of World-Wide Scissurellids

Following a number of publications on Scissurellidae s.l., including description of thus far 25 new species and three new genera (Geiger, 2003, Geiger & Jansen, 2004a, 2004b, Geiger 2006a 2006b 2006c, Nützel & Geiger 2006, Zelaya & Geiger 2007, Geiger & Sasaski in review), I continue with a larger project the will result eventually in a monograph of the family world-wide. I am collaborating with a number of co-workers on some selected projects (Angel Luque, Emilo Rolan, Bruce Marshall, Pierre Lozouet), while advancing the comprehensive review.

I am always looking for additional material in any state of preservation: shells for distribution records and SEM of shell, formalin fixed specimens for anatomy and histology, ethanol fixed specimens for molecular work. Please let me know if you have any material even if it is of common species.

Some first three dimensional reconstructions using Amira software package have been undertaken. Additional work is in progress.

Pea-crabs in Abalone

The frequency of the commensal pea-crab Orthotheres haliotidis Geiger & Martin, 1999, was first thought to be rare, but turns out to be not uncommon. I am collaborating with Dan Jackson and Nerida Wilson of the University of Queensland on a more detailed analysis of the biology of this species.

Evolution of Fissurellidae

The keyhole limpets are a highly diverse group with many interesting modification having occurred during their evolutionary history. Generic concepts and generic assignments of many species are uncertain, because the character complexes on which these genera are based are poorly understood. I am currently in the initial phase of reviewing the approximately 600 species level taxa, and to obtain a handle on fissurellid diversity.