Cumaceans

Cumacea is an order within the superorder Peracarida, and it comprises of small crustaceans that live in the marine environment. These crustaceans are also called comma shrimp or hooded shrimps for their distinct body shape and plan. They usually live on soft substrates on the bottom of the sea.

Anatomy

The body of cumaceans is well protected by hard shells, with an enlarged carapace protecting the head and the pereon protecting the first part of the abdomen. These animals also possess a slim abdomen and a tail that is forked at the end. The shape of their body with the curved tail is what brought them the name comma shrimp. Most species are small in size, with most of them ranging from 1 millimeter to no more than 10 millimeters.

The head piece of Cumacea species is usually composed of dorsal head parts that are fused together along with the thorax and the first three somites into a single carapace. Within this carapace can be found the appendages used for respiration and for feeding. Most cumaceans have two eyes situated on the dorsal side, with some species having them merged into a singular eye lobe. The pereon is formed from the last 5 somites of the thorax while the pleon, or elongated abdomen is composed of six somites of cylindrical shape.

Ecology

Most Cumacea species live in the marine environment. While many species require higher salinity levels in order to survive, there are some that can live in brackish water with lower salinity. There are some cumaceans in the Caspian Sea that even go upsteam rivers that flow into it, with other species able to live in intertidal zones.

The average life span of cumaceans is one year or less, and they manage to reproduce twice over the course of their lifetimes. The species that live at deeper sea levels have a slower metabolism and thus have an increased longevity. Cumaceans live on the sea floor in muddy or sandy substrates and feed on organic material or microorganisms within them. Some species filter water along with food, others go for singular grains of sand, while some cumaceans have specialized mandibles that form piercing organs with which they prey on small crustaceans and foraminiferans.

Most species that live in shallow waters appear to have a diurnal cycle, with males getting out of the soft sediment and emerging towards the surface. Cumacea species are more abundant at lower depths than at the surface of the water.

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