SMITH, W.L.; WEBB, J.F.*: Phylogenetic Variation in the Morphology of the Laterophysic Connection in Butterflyfishes of the Genus Chaetodon

The laterophysic connection is a unique linkage between paired anterior diverticula (horns) of the swimbladder and mesial openings in the cranial lateral-line canals in the supracleithra, which may allow the lateral-line system of butterflyfishes in the genus Chaetodon to detect pressure stimuli. A histological examination of 19 species in 10 of the 12 Chaetodon subgenera has revealed two laterophysic connection types (direct and indirect) and six laterophysic connection variants on these two types. A direct laterophysic connection (where swimbladder horns lie deep to the lateral-line canal in the supracleithrum with only or without intervening mucoid connective tissue) was found in 9 species in 6 subgenera. Two variants on the direct laterophysic connection differed in the presence or absence of the mucoid connective tissue and in swimbladder morphology. An indirect laterophysic connection (where epaxial muscle lies between the lateral-line canal in the supracleithrum and the swimbladder horns) was found in 10 species in 5 subgenera. Four variants on the indirect laterophysic connection also differed in the presence or absence of mucoid connective tissue and in swimbladder morphology. We hypothesize that the variation in soft tissue morphology that defines the laterophysic connection types and variants is functionally significant. In addition, we used four characters derived from this study to hypothesize new subgeneric relationships for Chaetodon and to examine the phylogenetic distribution of these laterophysic connection characters among species in the genus. Supported by NSF IBN-9603896 to J.F.W.