Sperm storage in male elasmobranchs: a description and survey.

Two basic types of spermatozoan aggregates, spermatophores and spermatozeugmata, found in 14 different species of sharks, one species of skate, and one species of chimaera (holocephalan), were investigated using light and scanning electron microscopy. Spermatophores, aggregates (usually 1,000-6,000 microns in diameter and larger) of randomly clumped sperm embedded in and surrounded by an eosinophilic matrix, were found in Alopias superciliosus, Odontaspis taurus, Carcharodon carcharias, Isurus oxyrinchus, and Lamna nasus. Three types of spermatozeugmata, sperm structures without a surrounding capsule or matrix, are described. The first, clumps of 60-200 sperm unbound in a supporting matrix, are found in Squalus acanthias and Hydrolagus colliei. In the second type, single-layered spheres are formed of sperm clumps with the sperm heads bound in a common supporting matrix. These are found in Carcharhinus limbatus and Carcharhinus plumbeus. The third type of spermatozeugmata are large multilayered, compound structures formed by the accretion of several single-layered aggregates. These multilayered structures characteristically are found in Carcharhinus falciformis, C. limbatus, Carcharhinus obscurus, C. plumbeus, Carcharhinus porosus, Prionace glauca, Rhizoprionodon terraenovae, and Sphyrna lewini. Sperm aggregates of all types are stored between the septa and in the lumen of the terminal ampulla of the epididymis. In their various forms they are the final product of the mature male elasmobranch reproductive tract. In a male with mature claspers, the presence of sperm aggregates is a more reliable indicator of maturity and sexual activity than is clasper condition alone.