Cumaceans are an order of benthic crustaceans with worldwide distribution. There are about 1400 described species classified into eight families (some scientists recognize a ninth, the Ophthalmdiastylidae), although research on unsorted museum collections indicates described species probably make up only a quarter of the total diversity and that the order includes an estimated 3000-4000 species total. The number of new species of Cumaceans reported in the Mediterranean Sea has steadily increased since 1850 without showing any signs of tailing off, indicating that there are still many species yet undescribed (Anderson 2010; Gerken, 2005).
An excellent online source on the Cumacea is Gary Anderson's Peracarida Taxa and Literature website.
Most cumaceans are smaller than 8 mm long. The largest grow up to 25mm long; these large species tend to inhabit cold or deep water. They have a prominent carapace (cephalothorax) which covers their head and usually 3 thoracic segments, for this reason they are also called hooded shrimp. Cumaceans have two pairs of antennae, the first pair used as sensors, the second, which is reduced in the female but large and complex in the male, is thought to play a role in finding mates. Thoracic segments under the carapace (usually 3) each have a pair of short legs modified for manipulating food. The other five thoracic segments each have a pair of biramous (forked) appendages that they use for walking and swimming. They have a long, flexible abdomen, made up of 6 segments, which can bend under the rest of the body to clean the cephalothorax. The last abdominal segment has two cleaning appendages (uropods), and some species have a thin tail (telson). The first five of the six abdominal segments may also have appendages for swimming (called pleopods), but only in males. Females do not have pleopods.
This body plan is strongly conserved making cumaceans readily recognizable. However, cumaceans also show considerable diversity among species. Carapace can vary in color and texture, some are ornamented with setae, ridges and spines. Body shape also varies; some species have abdomens the width of the carapace, others are very slender, some are flattened and resemble flatworms. Leg length and number and size of eyes are also variable.
(Brusca and Brusca 2003; Kozloff 1990)
Cumaceans appear to show little dispersal. Their range is often limited by sand grain size, and other biotic variables. Adults do little to no swimming as they have reduced swimming appendages, and there is no planktonic larval stage. Human activity is responsible for one well-documented example of long distance dispersal: the species Nippoleucon himumensis traveled in ballast water from Japan to the Oregon coast, where it is now a very abundant invasive species (Gerkin 2005).
Cumaceans live in a diverse range of marine habitats from abyssal to tidal, usually in mud or sand. Some species inhabit brackish waters in estuaries. Their distribution is patchy, in some places they are in the top ten most abundant invertebrates, and can be a major food source for birds and fish.
(Brusca and Brusca 2003; Kozloff 1990)
Mating in cumaceans takes place swimming in open water. Male pleopods are used not only for swimming but also for clasping females. Like other members of the superorder Paricarida, female cumaceans have a ventral breeding chamber (marsupium) formed by plate-like structures on the most proximal section of the first thoracic legs, and eggs are laid into the pouch and brooded there through several moults. The juveniles leave the marsupium as mancae, a stage resembling miniature adults except that they lack their last pair of thoracic walking legs (pereopods). Mancae molt twice more to achieve adult size and develop this last pair of legs. Females also molt several times in between broods (they usually produce three broods in their lifespan).
(Brusca and Brusca 2003; Kozloff 1990)
Cumaceans are primarily described as deposit feeders in shallow burrows, feeding on organic materials and microorganisms. They are known to graze on algae growing on sand grains. However, the ecology of these organisms has been only superficially explored and future research will certainly reveal a broader range of lifestyles, as exemplified by members the family Nannastacidae, which have piercing mandibles and may prey on polychaetes and foraminifora, and species in the families Gynodiastylidae and Vaunthomsoniinae which have modified legs or feeding tubules for filter-feeding.
(Brusca and Brusca 2003; Kozloff 1990)
Cumacea is an order of small marine crustaceans of the superorder Peracarida, occasionally called hooded shrimp or comma shrimp. Their unique appearance and uniform body 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 enlarged cephalothorax with a carapace, a slim abdomen, 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 three somites of the thorax. This carapace encloses the appendages that serve for respiration 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. The pleon (abdomen) consists of six cylindrical somites.
The first antenna (antennule) has two flagella, the outer flagellum usually being longer than the inner one. The second antenna is strongly reduced in females, and consists of numerous segments in males.
Cumaceans have six pairs of mouthparts: one pair of mandibles, one pair of maxillules, one pair of maxillae and three pairs of maxillipeds.[2][3]
Cumaceans are mainly marine crustaceans. However, some species can survive in water with a lower salinity, like brackish water (e.g. estuaries). In the Caspian Sea they even reach some rivers that flow into it. A few species live in the intertidal zone.
Most species live only one year or less, and reproduce twice in their lifetime. Deep-sea species have a slower metabolism and presumably live much longer.
Cumaceans feed mainly on microorganisms and organic material from the sediment. Species that live in the mud filter their food, while species that live in sand browse individual grains of sand. In the genus Campylaspis and a few related genera, the mandibles are transformed into piercing organs, which can be used for predation on foraminiferans and small crustaceans.[4]
Many shallow-water species show a diurnal cycle, with males emerging from the sediment at night and swarming to the surface.[5]
Like Amphipoda, cumaceans are an important food source for many fishes. Therefore, they are an important part of the marine food chain. They can be found on all continents.
Cumaceans are a clear example of sexual 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 of pleopods in males, and the development of a marsupium (brood pouch) in females. There are generally more females than males, and females are also larger than their male counterparts.
Cumaceans are epimorphic, which means that the number of body segments does not change during development. This is a form of incomplete metamorphosis. Females carry the embryos in their marsupium for some time. The larvae leave the marsupium in the manca 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, when Ivan Ivanovich Lepechin described the species "Oniscus scorpioides" (now Diastylis scorpioides). At the time, many scientists thought that the cumaceans were larval stages of decapods. In 1846, they were recognised as a separate order by Henrik 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 zoologist Carl Wilhelm Erich Zimmer studied the order Cumacea very intensively.
The fossil record of cumaceans is very sparse, but extends back into the Mississippian age.[6] Fossil Cumaceans from the early Jurassic scarcely differ from living forms (Bacescu & Petrescu 1999).[7]
Eobodotria muisca was found in 2019 in strata from the Middle Cretaceous 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 of crown Cumacea.[8]
Cumaceans belong to the superorder Peracarida, within the class Malacostraca. The order Cumacea is subdivided into 8 families, 141 genera, and 1,523 species:[9]
One species is also placed incertae sedis in the order.
Cumacea is an order of small marine crustaceans of the superorder Peracarida, occasionally called hooded shrimp or comma shrimp. Their unique appearance and uniform body 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.
.jpg)
