Cumacea is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

of small marine

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

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 morphology (biology), morphological phenotypic trait, features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually app ...

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 The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

with a

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

, a slim

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

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somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along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

s of the

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of 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 di ...

. 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 anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these ma ...

(abdomen) consists of six cylindrical somites. The first antenna ( antennule) has two

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

, 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

maxilliped An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

Ecology

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

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

, 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 estuary ...

(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 environm ...

). In the

Caspian Sea The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...

they even reach some rivers that flow into it. A few species live in the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

. Most species live only one year or less, and reproduce twice in their lifetime. Deep-sea species have a slower

metabolism Metabolism (, from ''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 cellular processes; the co ...

and presumably live much longer. Cumaceans feed mainly on

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

s and

organic material Organic matter, organic material or natural organic matter is 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 come fro ...

from the

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

. 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 in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

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

Amphipoda Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

, 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, often starting with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as ...

. They can be found on all continents.

Reproduction and development

Cumaceans are a clear example of

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

: 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

pleopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...

s 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 Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

. Females carry the embryos in their marsupium for some time. The

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

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 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, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order (biology), order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfis ...

. 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 Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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, parti ...

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 is the second largest of the six classes of pancrustaceans behind insects, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crab ...

. 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, 1912 (106 species in 12 genera) *

Lampropidae Lampropidae is a family of cold-water crustaceans belonging to the order Cumacea. Members of Lampropidae are relatively easily recognised because they all at have at least three terminal setae on the telson (rigid fibres on the end of the tail). ...

Sars Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the virus SARS-CoV-1, the first identified strain of the SARS-related coronavirus. The first known cases occurred in November 2002, and the ...

, 1878 (114 species in 15 genera) * Leuconidae 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 is a term used for a taxonomy (biology), 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, uncertainty ...

'' in the order.

References

External links

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