Reproduction

Abstract

The evolution of gonads and genitalia of major shrimp taxa has resulted in major differences between the pleocyemates (carideans, stenopodideans, procaridideans) and dendrobranchiates (penaeoids, sergestoids). The relatively simple male gonads of pleocyemates are composed of the testes, vasa deferentia, and ejaculatory bulb. Dendrobranchiate gonads have the same components, but the vasa deferentia are often quite complex, with different areas contributing materials to make elaborate spermatophores. Male genitalia in all shrimps are modifications of the endopods of pleopods 1–2, relatively simple in pleocyemates but intricately structured petasmata in dendrobranchiates. Pleocyemate eggs (oocytes) include significant amounts of yolk to sustain an often lengthy incubation on females. Embryos hatch at an advanced larval stage, the zoea. In contrast, the penaeoid egg contains little yolk and is spawned directly into the water, with embryos hatching as primitive nauplius larvae. During copulation and insemination, males are positioned below the female so that male and female genitalia are opposed. However, the actual role of male genitalia in sperm transfer is still controversial. All pleocyemate females molt shortly before mating and spawning. In many dendrobranchiate species, females mate after molting but use stored sperm to fertilize multiple spawns between molts; in other species, females mate and spawn without molting. Female pleocyemates aerate and clean incubated embryos until hatching, while dendrobranchiate females provide no incubation or other embryo care.