Anatomy

Caridean shrimps can be distinguished from other shrimp-like creatures by the way in which the plate of the second abdominal segment overlaps both in front and behind. Shrimps have long muscular tails attac hed to the carapace and two pairs of nippers, the first usually stronger than the second. The size of the nippers varies considerably between species. Some shrimps have a claw almost as large as the carapace whilst others have slender a nd delicate ones. The carapace usually bears a rostrum, the length and shape of which can help to determine the species. The eyes are on mobile stalks each side of the rostrum and above the long antennae. The body ends with a tail fan composed of the flat telson and pair of uropods.

Reproduction

Caridean shrimps mate prior to the female spawning. The male mates with the female after she has moulted and her body is soft. Turning the female onto her back the male applies spermatophores or sperm sacs close to the opening of the female's genital duct. The sperm sacs are shed from a pair of holes at the base of the last legs and the eggs from holes on the third legs. Within 24 hours the female spawns, releasing eggs which become f ertilised as they pass by the spermatophores. The female holds the fertilised eggs in a brood chamber under the abdomen glued onto hairs on the pleopods. The eggs remain attached to the female during incubation. Once developed the eggs hatch into zoeae which are released from the abdomen by the female. The zoea spends its life in the plankton, moulting as it grows through the various stages of larval development. Eventually the zoea settles on the bottom as a shrimp after its final larval moult.

Shrimp or Prawn?
There is often confusion regarding the difference between a shrimp and a prawn. Physically they look very similar but there is one sure way to tell them apart. In shrimps or carideans the side plate of the second segment of the abdomen overlaps the segments in front and behind. Prawns, most of which belong to the family Penaeidae of the group Dendrobranchiata, have all the abdominal side plates overlapping tile-like from the front. A more fundamental difference but one impossible to appreciate in a single specimen is that female prawns do not brood eggs but shed them into the currents where they develop independently. It would therefore make sense to call all member s of the Penaeidae "prawns" and members of the Caridean "shrimps" and this is what most Australians do. King prawns and banana prawns are names understood in this continent for penaeids sold frozen at the markets. The tiny shrimps bought in cans or froz en are imported carideans. Confusion arises when we hear Americans refer to prawns as "shrimp".