WOURMS, J.P.: Rudimentary trophotaeniae of Ataeniobius embryos: an evolutionary intermediate of teleost trophotaenial placentae.

Embryonic trophotaeniae, external hindgut derivatives, and the maternal ovarian epithelium comprise the trophotaenial placenta of goodeid and other fishes. For 60 years, Ataeniobius toweri was considered the only goodeid fish whose embryos lack trophotaeniae. Scanning EM, however, reveals three, external, rudimentary trophotaeniae. Together, they form an hemispherical peduncle continuous with the hindgut, bearing three lobes, one median dorsal and two lateral ventral. Trophotaenial cells have microvilli whereas adjacent skin cells have microplicae. Rudimentary trophotaeniae are the terminal developmental phase in Ataeniobius and are equivalent to those of Phase 2 embryos of Ameca, a species in which continued growth produces trophotaeniae 15 mm long. Ataeniobius represents an intermediate stage in the evolutionary model: 1: Hindgut externalization; 2. Establishment of rudimentary trophotaeniae; 3. Trophotaenial growth and morphogenesis; 4. Trophotaenial ecodysis and anal remodelling. (Supported by NSF).