SPERMATOPHORE STRUCTURE AND ANATOMY OF THE EJACULATORY DUCT IN PENAEUS-SETIFERUS, P-DUORARUM, AND P-AZTECUS (CRUSTACEA, DECAPODA) - HOMOLOGIES AND FUNCTIONAL-SIGNIFICANCE

Spermatophore structure inside the male ejaculatory duct, immediately following ejaculation, and after exposure to seawater is described and compared for three species of Penaeus, P. setiferus (external attachment of the spermatophore to an "open" thelycum of the female) and P. duorarum and P. aztecus (spermatophore storage behind a "closed" thelycum). Detailed investigation of the origin and disposition of spermatophore materials in the ejaculatory duct permits hypotheses of homologies among the species of Penaeus investigated. The sperm sac of the spermatophore of P. setiferus is homologous to the main body of the spermatophore of P. duorarum and P. aztecus. The adhesive glands and material have been lost entirely in the latter two species, and the appendages of their spermatophores are homologous to the glutinous material of P. setiferus. Structures for mechanical attachment found in the externally attached spermatophore of P. setiferus are lost or reduced in the phylogenetically advanced P. duorarum and P. aztecus. Reduction in complexity of the spermatophore in the species with closed thelycum is postulated to have evolved concomitantly with spermatophore enclosure and storage. In the species with closed thelycum, exposure of the spermatophore to seawater causes a striking reaction, consisting of an unfolding of its "appendage." Spreading of the appendage material throughout the aperture of the seminal receptacle to insure its complete seal after insemination is suggested as the function of the spermatophore reaction. In P. setiferus, the spermatophore reaction consists of changes in the adhesive and glutinous materials, as well as in extrusion of the sperm mass.