Spermatozoa and spermiogenesis in XyIopIax (Class Concentricycloidea): a new type of spermatozoon in the Echinodermata

In Xylopax turnerae Rowe et al., 1988 (Class Concentricycloidea, Subphylum Asterozoa) from the Caribbean spermiogenesis culminates in the formation of a complex spermatozoon unlike that of any other echinoderm. Mature testicular spermatozoa are composed of: (1) an elongate, tapered acrosome, segmented internally; (2) a nucleus, finely tapered anteriorly, extremely elongate and rod‐shaped posteriorly; (3) a single flagellum attached via a centriolar rootlet to the anterior portion of the nucleus; (4) a single elongate mitochondrion located posterior to the nucleus. Spermatozoa deposited in the ovary have acrosomes which are distinctly granular internally: otherwise these cells resemble testicular spermatozoa. Spermiogenesis differs substantially from the pattern observed in other echinoderms, especially in relation to acrosome development. Examination of alcohol‐fixed testes from the New Zealand species Xyloplax medusiforrnis confirmed the presence of filiform spermatozoa, but no details could be established. In contrast to Xyloplax, spermatozoa of Caymanostella sp. (Asteroidea) from a similar habitat to Xyloplax are not modified from those of externally fertilizing Asteroidea, Ophiuroidea, Crinoidea and Holothuroidea. Results lend further support to the existence of a separate class of extant echinoderms (Concentricycloidea) for Xyloplax spp.

[1]  H. Clark,et al.  The morphology, development and taxonomic status of Xyloplax Baker, Rowe and Clark (1986) (Echinodermata: Concentricycloidea), with the description of a new species , 1988, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[2]  Alan N. Baker,et al.  A new class of Echinodermata from New Zealand , 1986, Nature.

[3]  B. Jamieson.  The Spermatozoa of the Holothuroidea (Echinodermata): an Ultrastructural Review with Data on two Australian Species and Phylogenetic Discussion , 1985 .

[4]  C. Walker,et al.  Ultrastructure of the male reproductive system and of spermatogenesis in the viviparous brittle‐star, Amphipholis squamata , 1984, Journal of morphology.

[5]  B. Jamieson.  Spermatozoal Ultrastructure: Evolution and Congruence with a Holomorphological Phylogeny of the Oligochaeta (Annelida) , 1983 .

[6]  B. Afzelius.  Spermatozoa and spermatids of the crinoid Antedon petasus, with a note on primitive spermatozoa from deuterostome animals. , 1977, Journal of ultrastructure research.

[7]  N. Holland.  Morphologically Specialized Sperm from the Ovary of Isometra vivipara (Echinodermata — Crinoidea) , 1976 .

[8]  B. Afzelius,et al.  The biology of the sperm cell. , 1975, Monographs in developmental biology.

[9]  R. Summers,et al.  The Functional Anatomy of the Echinoderm Spermatozoon and its Interaction with the Egg at Fertilization , 1975 .

[10]  D. Atwood,et al.  Comparative Morphology of Echinoderm Sperm and Possible Phylogenetic Implications , 1975 .

[11]  D. Atwood.  Fine structure of an elongated dorso‐ventrally compressed echinoderm (holothuroidea) spermatozoon , 1975, Journal of morphology.

[12]  D. Atwood.  Fine structure of spermatogonia, spermatocytes, and spermatids of the sea cucumbers Cucumaria lubrica and Leptosynapta clarki (Echinodermata: Holothuroidea). , 1974, Canadian journal of zoology.

[13]  D. Atwood,et al.  Fine structure of an unusual spermatozoon of a brooding sea cucumber, Cucumaria lubrica. , 1974, Canadian journal of zoology.

[14]  G. Yasuzumi,et al.  Electron microscope observations on the chemical component of the sheath of the middle piece of atypical spermatozoa of the pond snail, Cipangopaludina malleata Reeve. , 1970, Archivum histologicum Japonicum = Nihon soshikigaku kiroku.

[15]  P. Siekevitz,et al.  The Ultrastructure of the Animal Cell , 1967 .

[16]  J. Young.  Echinodermata , 1871, Transactions of the Glasgow Geological Society.