The Morphology of the Laterophysic Connection

 

          The laterophysic connection (LC) is a unique association of anterior diverticula (“horns”) of the swim bladder and the lateral line canal in the supracliethrum of fishes in the specious genus Chaetodon (Perciformes: Chaetodontidae).   Blum described the presence of a medial fossa in the supracleithrum (Blum, 1988) and anterior horns of the swim bladder.  Webb and Blum (1990) examined this structure histologically and determined that the medial fossa is indeed the site of a linkage between the anterior horns of the swim bladder and the medial fossa that perforates the medial wall of the lateral line canal that runs through the dorsal end of the supracleithrum.  We named this feature the “laterophysic connection” to draw attention to its similarity to the “otophysic connection”, present in other taxa, which links anterior extensions of the swim bladder with the otic capsule and serves to increase pressure sensitivity of the ear.  It seems likely that the laterophysic connection uniquely imparts pressure sensitivity to the lateral line canal system (Webb, 1998).   The medial fossa in the supracleithrum is filled with multiple layers of soft tissue which forms a barrier between the fluid-filled lumen of the lateral line canal and the air-filled lumen of the swim bladder horns (Webb and Blum, 1990; Webb, 1990).  In Chaetodon octofasciatus, the tunica externa of the swim bladder horn comes into direct contact with a cushion of mucoid connective tissue (unlike the fibrous tissue of the stratum compactum, which composes the dermal tissue in this vicinity), which sits just deep to the fossa and the lining of the lateral line canal in the supracleithrum.  This configuration was named the “direct connection.”  In two other species, C. sedentarius and C. kleinii, the swim bladder horn sits deep to the fossa, but muscle is present between the fossa and the swimbladder horn.  This configuration was named the “indirect connection” (Webb, 1998).  Thus, variation in the type of laterophysic connection is present within the genus Chaetodon, but the source of this variation could not be determined.


 

Two types (including 6 variants)

of LC’s have been defined based on variation

in soft tissue morphology and could only be

revealed by histological analysis.

 

 LC diagram goes here
This work, started in collaboration with Stanley Blum, was initially presented at several conferences in 1990 and published subsequently in Copeia (1998)  and Proc. Roy Soc. (2000).

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