| Cumacea | |
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| Iphinoe trispinosa | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Superorder: | Peracarida |
| Order: | Cumacea Krøyer, 1846 [1] |
| Families | |
8, Seetaxonomy | |
Cumacea is anorder of small marinecrustaceans of the superorderPeracarida, occasionally calledhooded shrimp orcomma shrimp. Their unique appearance and uniformbody plan makes them easy to distinguish from other crustaceans. They live in soft-bottoms such as mud and sand, mostly in the marine environment. There are more than 1,500 species of cumaceans formally described. The species diversity of Cumacea increases with depth.
Cumaceans have a strongly enlargedcephalothorax with acarapace, a slimabdomen, and a forked tail. The length of most species varies from 1 to 10 millimetres (0.04 to 0.39 in).
The carapace of a typical cumacean is composed of several fused dorsal head parts and the first threesomites of thethorax. This carapace encloses the appendages that serve forrespiration and feeding. In most species, there are two eyes at the front side of the head shield, often merged into a single dorsal eye lobe. The five posterior somites of the thorax form the pereon. Thepleon (abdomen) consists of six cylindrical somites.
The first antenna (antennule) has twoflagella, the outer flagellum usually being longer than the inner one. Thesecond antenna is strongly reduced in females, and consists of numerous segments in males.
Cumaceans have six pairs ofmouthparts: one pair ofmandibles, one pair ofmaxillules, one pair ofmaxillae and three pairs ofmaxillipeds.[2][3]
Cumaceans are mainly marine crustaceans. However, some species can survive in water with a lowersalinity, likebrackish water (e.g.estuaries). In theCaspian Sea they even reach some rivers that flow into it. A few species live in theintertidal zone.
Most species live only one year or less, and reproduce twice in their lifetime. Deep-sea species have a slowermetabolism and presumably live much longer.
Cumaceans feed mainly onmicroorganisms andorganic material from thesediment. Species that live in the mud filter their food, while species that live in sand browse individual grains of sand. In the genusCampylaspis and a few related genera, the mandibles are transformed into piercing organs, which can be used forpredation onforaminiferans and small crustaceans.[4]
Many shallow-water species show adiurnal cycle, with males emerging from the sediment at night and swarming to the surface.[5]
LikeAmphipoda, cumaceans are an important food source for many fishes. Therefore, they are an important part of the marinefood chain. They can be found on all continents.
Cumaceans are a clear example ofsexual dimorphism: males and females differ significantly in their appearance. Both sexes have different ornaments (setation, knobs, and ridges) on their carapace. Other differences are the length of the second antenna, the existence ofpleopods in males, and the development of amarsupium (brood pouch) in females. There are generally more females than males, and females are also larger than their male counterparts.
Cumaceans areepimorphic, which means that the number of body segments does not change during development. This is a form of incompletemetamorphosis. Females carry the embryos in their marsupium for some time. Thelarvae leave the marsupium in themanca stage, in which they are almost fully grown and are only missing their last pair of pereiopods.
The order Cumacea has been known since 1780, whenIvan Ivanovich Lepechin described the species "Oniscus scorpioides" (nowDiastylis scorpioides). At the time, many scientists thought that the cumaceans were larval stages ofdecapods. In 1846, they were recognised as a separate order byHenrik Nikolaj Krøyer. Twenty-five years later, about fifty different species had been described, and currently there are more than 1,500 described species. The German zoologistCarl Wilhelm Erich Zimmer studied the order Cumacea very intensively.
Thefossil record of cumaceans is very sparse, but extends back into theMississippian age.[6] Fossil Cumaceans from the earlyJurassic scarcely differ from living forms (Bacescu & Petrescu 1999).[7]
Eobodotria muisca was found in 2019 in strata from the MiddleCretaceous of Colombia. Exceptional details such as the gut, mouth parts, pereopods, setae bearing uropods, antenna with developed flagella, and even small eyes with ommatidia were preserved.Eobodotria straddles a gap of almost 165 million years in the fossil record of sea commas, providing a reliable calibration point for phylogenetic studies. This species is considered the first certain representative ofcrown Cumacea.[8]
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Cumaceans belong to the superorderPeracarida, within the classMalacostraca. The order Cumacea is subdivided into 8 families, 141 genera, and 1,523 species:[9]
One species is also placedincertae sedis in the order.
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