ADAPTATIONS FOR REPRODUCTION AND DEVELOPMENT IN THE SKIN-BROODING GHOST PIPEFISHES, SOLENOSTOMUS

Ghost pipefishes comprise a small family (Solenostomidae) of skin-broo ding fishes related to true pipefishes and seahorses (Syngnathidae). S olenostomus embryos develop within the fused pelvic fins of the female , unlike syngnathids in which males brood the eggs. Embryos, enclosed in egg envelopes, are attached to epidermal stalks, termed cotylephore s, that occur only in brooding females. Cotylephores are cellular outg rowths of the epithelium on the inside surface of the pelvic fins. The y attain a mean length of 687 +/- 3.89 mu m and diameter of 105 +/- 3. 38 mu m. Cotylephores originate on the epithelial surface that lies ov er the lepidotrichia and they develop into multi-headed cylindrical br anches approximately 125 +/- 3.65 mu m in length and 78 +/- 2.19 mu m in diameter. A mean of 26 +/- 0.63 lateral branches are found on fully developed cotylephores. Each branch terminates in a wide apical calyx , approximately 112 +/- 4.16 mu m in diameter, to which the egg envelo pe adheres. Adjacent calyces of the same cotylephore establish attachm ents with the envelope of a single egg. Cotylephores are composed of a surface epithelium that is continuous with the skin and a fibrous con nective tissue core that contains blood vessels that ramify into an ap ical capillary plexus. The plexus may function in maternal-embryonic m etabolic exchange. The cotylephores of Solenostomus closely resemble t he epidermal stalks (cotylephores) that are the sites of egg attachmen t in the skin-brooding South American catfish, Platystacus cotylephoru s. Based on similarity in structure and probable function, cotylephore s in the two groups of fishes are an example of evolutionary convergen ce.