Veneridae projects:
Venerid Classification has been the subject of continual debate and rearrangement since the 1930s. One commonly used classification (Keen, 1969) recognizes twelve nominal subfamilies (of untested monophyly), listed here with some of the more common genus-level taxa:
Chioninae: Chione, Mercenaria, Protothaca
Circinae: Circe, Gouldia
Clementinae: Clementia, Compsomyax
Cyclinae: Cyclina
Dosiniinae: Dosinia
Gemminae: Gemma, Parastarte
Meretricinae: Meretrix, Tivela, Transennella
Pitarinae: Pitar, Macrocallista, Saxidomus
Samaranginae: Samarangia
Sunettinae: Sunetta
Tapetinae: Tapes, Irus, Venerupis, Paphia
Venerinae: Venus, Periglypta, Globivenus
A review of traditional characters in Veneridae revealed that most are based on the shell alone, that many are variable or ambiguously defined, and when subjected to a phylogenetic analysis (see figure, right), perform poorly in resolving traditional subfamilies. There are no recognized synapomorphies for Veneridae or any of its subfamilies. Examples:
| Heart-shaped shell | Probably plesiomorphic (e.g., Cardiidae) | ||||
| Equivalve shell | Plesiomorphic (most Bivalvia) | ||||
| Umbones incurved anteriorly | Variable (pointed centrally in Liocyma, Gemma, Compsomyax) | ||||
| Ligament external | Variable (that of Transennella deeply immersed) | ||||
| Hinge strong | Variable (that of Compsomyax is weak) | ||||
| Lunule well-developed | Variable (absent in Compsomyax, Saxidomus, Liocyma; weak in Pitar) | ||||
| Escutcheon well-developed | Variable (absent in many genera) | ||||
| Three cardinal hinge teeth in each valve | Variable (four cardinals in Saxidomus; two in Gemma and Transenella) | ||||
| Lateral hinge teeth | Variable (week or absent) | ||||
| Pallial sinus | Variable in shape and depth | ||||
| Inner shell margin | Variable (smooth or finely crenulated) | ||||
Despite their relative abundance and commercial presence, there are fewer than a dozen published anatomical descriptions of venerids, and even fewer applications of these characters to infer relationships. Ansell's (1961) paper on the functional morphology of the British Veneroidea was perhaps most comprehensive yet included only 12 venerids. Only one molecular study (Canapa et al., 1996) has addressed Veneridae as a whole, but this was poorly sampled, using partial sequences for 9 species in 5 subfamilies. GenBank includes sequences for 21 venerid species, representing 12 genera and 7 subfamilies, but these are not directly applicable to a single analysis.
SUBFAMILY VENERINAE s.l. currently comprises 31 extant genera and over 150 species. The overall research objective of this project is to clarify evolutionary relationships both within the marine clam subfamily Venerinae and also to its morphologically very similar sister taxon Chioninae. Detailed phylogenetic analyses are based on soft body anatomy (dissections and SEM) and shell structure of museum specimens and newly collected material, as well as by molecular sequencing of mitochondrial and nuclear genes. Phylogenetic patterns obtained from each dataset will be compared and contrasted with one another. The molecular data will yield a framework for the re-evaluation of classical morphological data. Morphometric tools will be used to study the evolution of morphological diversity in this group. This study is the first to examine phylogenetic relationships within this subfamily using multiple data sets.
SUPERFAMILY PTERIOIDEA is an ancient branch of pteriomorph bivalves extending from the Middle Ordovician to the present. The four living pterioidean families - Pteriidae, Isognomonidae, Malleidae, and Pulvinitidae - were traditionally exclusively defined by shell shape and ligament structure. Preliminary phylogenetic analyses of morphological and molecular data sets representing all genera of living Pterioidea strongly support monophyly for the superfamily but render all families (with the exception of the monotypic Pulvinitidae) polyphyletic. There is strongly supported evidence for multiple origins of a multivincular ligament and the absence of an anal funnel in the Pulvinitidae, the latter rejecting this character as the only anatomical apomorphy of the superfamily. Given the considerable morphological disparity and ecological diversity of the constituent taxa, the new phylogeny will provide insight into the nature and possible causes of morphological trends and adaptive aspects of shell shape, and will establish the foundation for evaluating taxon-specific associations of pterioidean species with their coral, sponge, or mangrove substrata.
John Wilk
GENUS ISOGNOMON, long the focus of much taxonomic disagreement, is being re-examined at the population and species levels to test the current classification scheme for this group. This investigation uses a combination of molecular systematics and population genetics to illustrate both the hierarchical and reticulate relationships among and within the approximately 24 species currently comprising this genus. Population and species level structure, which should be revealed by these analyses, will then be compared to the existing taxonomic framework and allow for the re-assessment of the classification within this group. Upon identifying separately evolving lineages, morphometric analysis is used to find characters that can consistently distinguish these confirmed, redefined, or newly described species.