in the Congo Basin

The caridean shrimp Alvinocaris muricola has been observed forming high density populations over mussel beds on the giant pockmark cold seep site Regab in the Gulf of Guinea at 3150m depth. Samples were collected using the ROV Victor 6000, a beam trawl and a TV grab from two sites. The specimens were sexed and measured for population structure analysis. In one sample the sex ratio was 1:1, but the other sample had a sex ratio signi¢cantly biased towards females. The maximum size of females is larger than males. A sub-sample was used for gametogenesis and fecundity analysis. The oogenesis and spermatogen-esis of A. muricola is characteristic of caridean shrimps. The oogonia proliferate from the germinal epithelium and develop into previtellogenic oocytes that migrate to the growth zone. Vitellogenesis starts at 80^100 mm oocyte size and the developing oocytes are surrounded by a monolayer of accessory cells.The maximum oocyte size was 515 mm. There was no evidence of synchrony in oocyte development, with all oocyte stages present in all ovaries analysed. However, seasonal sampling would be necessary to con¢rm the lack of seasonality in reproduction. In males, the sperm develops in sperm sacs in the testis. As in all caridean shrimp, the broods of A. muricola are held on the pleopods P11 to P14. Total fecundity was related to female size and ranged between 1432 and 5798 embryos. Within a brood all embryos are at the same stage of development, but three di¡erent stages were identi¢ed in di¡erent females, with no clear seasonal trend.The embryos were small, with mean dimensions of 0.660.55mm, suggesting planktotrophic larvae and a potential extended larval development