Protandric hermaphroditism in the bivalve Arca noae (Mollusca: Arcidae)

Following the histological analysis of Arca noae samples from the south-western Adriatic Sea, five hermaphroditic specimens were found out of 168 sexed individuals (3.0%). The hermaphrodite gonads showed the co-occurrence of male and female germ cells within the same acini, i.e. both spermatozoa in the lumen and oogonia lining its wall. Oogonia increased in size through winter, thus suggesting that the direction of sex change is from male to female. Both the biometrical analyses and theoretical considerations strongly suggest that A. noae is an obligate protandric species.

Development of external sexual characters of deep sea Bythocaris shrimps (Crustacea: Decapoda: Hippolytidae)

The development of sex-specific characters is described for the deep sea North Atlantic/Arctic shrimp genus Bythocaris. A number of species were examined in the collections of Russian institutions including B. biruli, B. curvirostris, B. irene, B. leucopis and B. payeri. The pattern of size-specific variation in the masculine characters, i.e. the development of the modified appendix interna on the endopodite of the first pleopod and the appendix masculina do not indicate the presence of sex change (protandric hermaphroditism) in the life history.

Postembryonic development of Apseudes heroae and Allotanais hirsutus (Tanaidacea, Crustacea) in Magellanic and sub-Antarctic waters

Apseudes heroae Sieg, 1986 (Family Apseudidae) and Allotanais hirsutus (Beddard, 1886) (Family Tanaidae) are common Tanaidacea of the southern Magellanic region. The aim of the investigation is to elucidate the postmarsupial development of these tanaid species that differ in their biogeography. Population structures are analysed from size frequency data and from different postembryonic stages of specimens collected in the Atlantic entrance of the Beagle Channel and from the Atlantic continental slope to the south-east. The population of Apseudes heroae shows three age groups, the one of Allotanais hirsutus probably at least three. Some large specimens indicate that the latter sub-Antarctic species might reach an age of several years. Both species are probably gonochoristic, and protandric hermaphroditism was not observed. The fecundity of Apseudes heroae and Allotanais hirsutus was analysed. No significant correlation could be found between cephalothorax width and egg number or number of larvae. For both species hypothetical life cycles are reconstructed. As sub-Antarctic temperatures are low and seasonality is strong in the Magellanic region, it is possible that these species are reasonably adapted in reproduction as shown in some polar species of Isopoda and Cumacea.

Ultrastructural characteristics of spermatogenesis in three species of deep-sea hydrothermal vent mytilids

To enhance our understanding of the reproductive biology of deep-sea hydrothermal vent mytilids, the histology of the male gonad and the ultrastructure of its gametes were studied in Bathymodiolus thermophilus, B. puteoserpentis, and B. elongatus. Specimens of B. thermophilus were collected at the 13°N site on the East Pacific ridge, while B. puteoserpentis were sampled from the Snake Pit site of the mid-Atlantic ridge and B. elongatus were obtained from the North Fiji Basin. Gonad histology conformed to the typical bivalve profile; the differences in the proportions of acinal and interacinal tissue, as well as differences in acinal fullness in B. puteoserpentis, indicate that gametogenesis is discontinuous in these deep-sea mytilids. Evidence of protandric hermaphroditism was observed in B. elongatus, which exhibited acini containing both maturing and residual male gametes and immature oocytes. The ultrastructural characteristics of the male gametes conform to those described for littoral bivalve species, and the spermatozoon is of the primitive type. No species-specific differences in spermatozoon ultrastructure were discerned. No evidence of bacterial inclusions was found in either the gametes or the associated gonad cells in any of the species examined. The male gametes are thus probably not vectors for the endosymbiotic bacteria that characterize the nutritional biology of the adults in this genus.