AN ULTRASTRUCTURAL STUDY OF EUSPERMATOZOA, PARASPERMATOZOA AND NURSE CELLS OF THE COWRIE CYPRAEA ERRONES (GASTROPODA, PROSOBRANCHIA, CYPRAEIDAE)

The sperm duct of the cowrie Cypraea errones Linné containseuspermatozoa, paraspermatozoa and nurse celts, the latter bearingclumps of attached euspermatozoa. Nurse cell/euspermatozoa associationshave been described in certain littorinacean gastropods, butare previously unrecorded in the Cypraeacea. Euspermatozoa ofC. errones resemble those of many other mesogastropods and someneogastropods (for example members of the Strombidae, Epitoniidae,Naticidae, Volutidae; shared features include structure of theacrosome, nucleus, glycogen piece, and helically coiled midpieceelements). However in C. errones, radially arranged paracrystallinefibres partly occupy the space between adjacent midpiece elements.Paracrystalline material is only rarely observed in spermatozoaof prosobranch gastropods and in all cases (including C. errones),is readily discernible form the complex paracrystalline layerspresent in the mitochondria) derivative of opisthobranch andpulmonate spermatozoa. Paraspermatozoa of C. errones are elongate,vermiform cells containing: multiple axonemes (bunched anteriorly,peripherally distributed posteriorly); granulated deposits (anteriorly);numerous dense vesicles (posteriorly) and scattered mitochondria(elongate, with parallel cristae). The axonemal attachment complexesfuse apically to form a sharp, conical structure. Comparisonwith available electron microscopic and light microscopic accountsof prosobranch euspermatozoa and paraspermatozoa suggests closeties between the higher Mesogastropoda (with which the Cypraeidaeshould be included) and the Neogastropoda. Further researchwill be required to determine whether the paracrystalline fibresobserved in euspermatozoa of C. errones are characteristic ofthe Cypraeidae or perhaps shared with the Ovulidae or Triviidae. (Received 26 November 1985;