Cumacea is an order of small marine

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s of the superorder Peracarida, occasionally called hooded shrimp or comma shrimp. Their unique appearance and uniform

body plan A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually applied to animals, envisages a "blueprin ...

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.

Anatomy

Cumaceans have a strongly enlarged cephalothorax with a carapace, a slim

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...

, and a forked tail. The length of most species varies from . The carapace of a typical cumacean is composed of several fused dorsal head parts and the first three

somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryonic stage of somitogenesis, along the head-to-tail axis in segmented animals. In vertebrates, somites subdivide ...

s of the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

. This carapace encloses the appendages that serve for

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

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 The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

(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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, one pair of maxillules, one pair of maxillae and three pairs of maxillipeds.

Ecology

Cumaceans are mainly marine crustaceans. However, some species can survive in water with a lower salinity, like

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

(e.g.

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...

). In the

Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central Asia ...

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 Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

and presumably live much longer. Cumaceans feed mainly on

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s and

organic material Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...

from the

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

. 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 Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

ns and small crustaceans. Many shallow-water species show a diurnal cycle, with males emerging from the sediment at night and swarming to the surface.

Importance

Like Amphipoda, cumaceans are an important food source for many fishes. Therefore, they are an important part of the marine

food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...

. They can be found on all continents.

Reproduction and development

Cumaceans are a clear example of

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

: 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.

History of research

The order Cumacea has been known since 1780, when

Ivan Ivanovich Lepechin Ivan Ivanovich Lepyokhin (Иван Иванович Лепёхин; , in Saint Petersburg – , in Saint Petersburg) was a Russian naturalist, zoologist, botanist and explorer. He began his studies in the Academy of Sciences of Saint-Petersbu ...

described the species "''Oniscus scorpioides''" (now '' Diastylis scorpioides''). At the time, many scientists thought that the cumaceans were larval stages of

decapods The Decapoda or decapods (literally "ten-footed") are an order (biology), order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, Caridea, shrimp and Dendrobranchiata, prawns. Most ...

. 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.

Fossil record

The

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

of cumaceans is very sparse, but extends back into the Mississippian age. Fossil Cumaceans from the early

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

scarcely differ from living forms (Bacescu & Petrescu 1999). ''Eobodotria muisca'' was found in 2019 in strata from the Middle

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

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 A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...

Cumacea.Luque, J., & Gerken, S. (2019). Exceptional preservation of comma shrimp from a mid-Cretaceous Lagerstätte of Colombia, and the origins of crown Cumacea. ''Proceedings of the Royal Society B'', 286:20191863.

Taxonomy

Cumaceans belong to the superorder Peracarida, within the class

Malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, l ...

. The order Cumacea is subdivided into 8 families, 141 genera, and 1,523 species: * Bodotriidae Scott, 1901 (379 species in 36 genera) * Ceratocumatidae Calman, 1905 (10 species in 2 genera) * Diastylidae Bate, 1856 (318 species in 22 genera) * Gynodiastylidae

Stebbing Stebbing is a small village in the Uttlesford district of northern Essex, England. The village is situated north of the ancient Roman road Stane Street. It is from the nearest railway station (), and from nearest airport (London Stansted). Th ...

, 1912 (106 species in 12 genera) * Lampropidae

Sars Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''seve ...

, 1878 (114 species in 15 genera) *

Leuconidae Leuconidae is a family (biology), family of marine hooded shrimp (order (biology), order Cumacea). The family was established by Georg Ossian Sars in his 1878 study of Mediterranean cumaceans. Description Leuconidae retain the original number ...

Sars, 1878 (139 species in 16 genera) * Nannastacidae Bate, 1866 (426 species in 25 genera) * Pseudocumatidae Sars, 1878 (30 species in 12 genera) One species is also placed ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' in the order.

References

External links

Cumacea pageCumaceans of the WorldCumacea World Database
{{Authority control Malacostraca Mississippian first appearances Extant Carboniferous first appearances Taxa named by Henrik Nikolai Krøyer Crustacean orders