There are 85 species of krill ranging in size from the smallest millimeters long to the largest deep sea species which can reach 15cm in length. Amphipod also similar to that of a shrimp have a size smaller than krill they can range from 1 to 140 mm in body length and 4 to 10 mm long in mid-latitude region. Their genetic diversity is higher in cool water than in warm water. Isopods come in many different shapes and sizes and half of them live in the ocean. The larger isopods live in the deep sea and the smaller ones live like parasite on a fish. Crustacean come from the Latin root crustaceus which means having a crust or shell. They are important members of benthic communities which are animals that live at the bottom of the ocean. There are two divided groups, filter feeders and the deposit …show more content…
Most individual barnacles have simultaneous hermaphroditism, both male and female reproductive organs, and in some groups the males, are much smaller than the hermaphrodites. Characteristic differences in structure or behavior between sexes are widespread in the Crustacea and can be extreme, males of some groups may be so small that they are difficult to find on the much larger female some of the parasitic copepods especially. Males are found in a small pouch in the female genital tract this is known as Gonophysema gullmarensis. Normal sexual reproduction requires merging of a sperm with an egg, but some crustaceans are parthenogenetic and produce eggs that develop without being fertilized by a sperm. Females of some crustacean species release their eggs freely into the water and some carry their eggs between the thoracic limbs. Most decapods carry their eggs attached to the abdominal appendages special egg-containing setae secrete a cement that flows over the eggs and binds them to the setae. There are a few with a brood pouch behind the limbs that is made by carapace superorder peracarida, some isopods, sphaeroma, branchiopods, the notostaca and the order