COMPARATIVE MORPHOLOGY OF COTYLEPHORES IN PLATYSTACUS AND SOLENOSTOMUS - MODIFICATIONS OF THE INTEGUMENT FOR EGG ATTACHMENT IN SKIN-BROODING FISHES

External skin brooding evolved independently in several groups of fish es. Cotylephores, sites for the attachment of developing embryos, occu r within the fused pelvic fins of the ghost pipefishes, Solenostomus, on the ventral surface of the South American catfish, Platystacus, and on other aspredinid cattfishes of the tribe Aspredini. Cotylephores a re transient outgrowths of tissue that occur only on brooding fish. Th ey consist of a pedicle that extends from the abdomen or fin and termi nates in an apical calyx. The calyx supports and adheres to the egg en velope that encloses the developing embryo. The pedicle of the catfish cotylephore is a single, large structure (1615 +/- 23.25 mu m), while those of ghost pipefishes are small and branched (687 +/- 3.89 mu m; number of branches: 26 +/- 0.63). In both instances, a simple cuboidal epithelium, whose cells bear microplicae, encloses an extensive conne ctive tissue core that contains large blood vessels that ramify into a capillary plexus in the calyx. Cotylephores of Platystacus are more h eavily vascularized than those of Solenostomus and contain 34.77% more blood vessel surface area at the calyx, to which the egg envelope adh eres. In addition to their role in attachment, cotylephores may functi on in embryonic maintenance through the exchange of gas across the egg envelope, mediated by female circulatory vessels within the cotylepho re calyx. Comparisons of morphology and development suggest that cotyl ephores are the result of convergent evolution of a reproductive adapt ation.