Axiidea is an

infraorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

of decapod

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 ...

s. They are colloquially known as mud shrimp, ghost shrimp, or burrowing shrimp; however, these decapods are only distantly related to true

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

. Axiidea and

Gebiidea Gebiidea is an infraorder of Decapoda, decapod crustaceans. Gebiidea and Axiidea are divergent infraoders of the former infraorder Thalassinidea. These infraorders have converged Ecology, ecologically and Morphology (biology), morphologically as ...

are divergent infraoders of the former infraorder

Thalassinidea Thalassinidea is a former infraorder of decapod crustaceans that live in burrows in muddy bottoms of the world's oceans. In Australian English, the littoral thalassinidean ''Trypaea australiensis'' is referred to as the ''yabby'' (a term which al ...

. These infraorders have converged

ecologically Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...

and morphologically as burrowing forms.Dworschak, Peter C. (2012). ''Treatise on Zoology - Anatomy, Taxonomy, Biology. The Crustacea, Volume 9 Part B''. BRILL. pp. 109–100. . Based on molecular evidence as of 2009, it is now widely believed that these two infraorders represent two distinct lineages separate from one another. Since this is a recent change, much of the literature and research surrounding these infraorders still refers to the Axiidea and Gebiidea in combination as "thalassinidean" for the sake of clarity and reference. This division based on molecular evidence is consistent with the groupings proposed by Robert Gurney in 1938 based on larval developmental stages.Pohle, G. and Santana, W., Gebiidea and Axiidea (=Thalassinidea), in ''Atlas of Crustacean Larvae'', Baltimore: Johns Hopkins Univ. Press, 2014, pp. 263–271. Axiidea are noted for the burrows with complex architecture that they make in the ocean floor sediment. These burrows can be classified based on their external characteristics in the sediment as well as the trophic group that the species falls into.Kornienko, E.S. "Burrowing shrimp of the infraorders Gebiidea and Axiidea (Crustacea: Decapoda)" Russ J Mar Biol (2013) 39: 1. The population density of most species of Axiidea tends to be high, so these organisms play an important role in the

biogeochemical Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, t ...

processes of the ocean floor sediments, and in the creation of habitats that favor various marine

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

communities.

Classification

The

Axiidea belongs to the group

Reptantia Reptantia is a clade of decapod crustaceans named in 1880 which includes lobsters, crabs and many other well-known crustaceans. Classification In older classifications, Reptantia was one of the two sub-orders of Decapoda alongside Natantia, wi ...

, which consists of the walking/crawling decapods (

lobsters Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...

and

crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

). The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

below shows Axiidea as more basal than

within the larger

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

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

, from analysis by Wolfe ''et al.'', 2019. The infraorder Axiidea comprises the following

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

: *

Axiidae Axiidae is a family of thalassinidean 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, ...

Huxley, 1879Huxley, T. H. (1879). On the classification and the distribution of the crayfishes. ''Proceedings of the Scientific Meetings of the Zoological Society of London'', 1878(3), 752–788. *

Callianassidae Callianassidae is a family of ghost shrimp of the order Decapoda. Subfamilies and genera ''Callianassidae'' is divided into 41 genera: * '' Aqaballianassa'' Poore, Dworschak, Robles, Mantelatto & Felder, 2019 * '' Arenallianassa'' Poore, Dwors ...

Dana, 1852Dana, J. D. (1852). Conspectus Crustaceorum, &c. Conspectus of the Crustacea of the Exploring Expedition under Capt. C. Wilkes, U. S. N. ''Proceedings of the Academy of Natural Sciences of Philadelphia'', 6, 10–28. * Callianideidae Kossmann, 1880Kossmann, R. (1880). Malacostraca Anomura. In ''Reise in die Küstengebiete dea Rothen Meeres, Erste Hälfte''. Leipzig: Zweite Hälfte. * Ctenochelidae Manning and Felder, 1991Arthur Anker (2010). ''Ctenocheloides attenboroughi'' n. gen., n. sp. (Crustacea: Decapoda: Axiidea: Ctenochelidae), a new ghost shrimp with pectinate claw fingers from Madagascar, Journal of Natural History, 44:29-30, 1789-1805. *

Gourretiidae Gourretiidae is a family of crustaceans belonging to the infraorder Axiidea Axiidea is an infraorder of decapod crustaceans. They are colloquially known as mud shrimp, ghost shrimp, or burrowing shrimp; however, these decapods are only dist ...

Micheleidae Micheleidae is a family of crustaceans belonging to the infraorder Axiidea, within the order Decapoda. It contains the following genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil or ...

Sakai, 1992Sakaim K. (1992). The families Callianideidae and Thalassinidae, with the description of two new subfamilies, one new genus, and tew new species (Decapoda, Thalassinidea). ''Naturalists, Tokushima Biological Laboratory, Women's University'', 4, 1–33. *

Strahlaxiidae Strahlaxiidae is a family of crustaceans belonging to the infraorder Axiidea, within the order Decapoda. It contains the following genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil ...

Poore, 1994Poore, G. C. B. (1994). A phylogeny of the families of Thalassinidea (Crustacea: Decapoda) with keys to families and genera. ''Memoirs of the Museum of Victoria'', 54, 79–120. A few

subfamilies In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

of Axiidea have been proposed to become families, but have not for a variety of reasons. Examples of these subfamilies include the subfamily

, discovered by Sakai in 1999. Gourretiidae is a subfamily of the Ctenochelidae, and has been proposed to become a family instead, but

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses do not yet support that proposal. Similarly, molecular studies do not support the subfamily Eiconaxiidae being separate from family

. There is also no molecular evidence to separate the subfamily Calocardidae from Axiidae. The cladogram below shows Axiidea's internal

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

relationships from analysis by Wolfe ''et al.'', 2019.

Description

The length of an adult Axiidea can range from about in some species, to over in other species.Dworschak, P.C. “Methods Collecting Axiidea and Gebiidea (Decapoda): a Review.” ''Annalen Des Naturhistorischen Museums in Wien. Serie B Für Botanik Und Zoologie'', vol. 117, 2015, pp. 5–21. ''JSTOR'', JSTOR, www.jstor.org/stable/43922304 The color of the Axiidea can range a variety of colors, including white, pink, red, orange, and dark brown. The

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

can range from being nearly invisible, to fairly rigid and extending past the eyes. The

carapace A carapace is a Dorsum (biology), 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 tor ...

also ranges from fairly rigid to transparent, showing the organs underneath. Axiidea can range from having a well-calcified

exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton (endoskeleton) in for example, a human. In usage, some of the ...

, to barely calcified elongated exoskeletons, which show an adaptation to burrowing in certain species. The sex of the Axiidea can be determined by the

pleopod 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 ...

structure on the underbelly of the organism. This structure is underdeveloped or absent in the males. The sex ratio in most species of Axiidea tends to be 1:1, although in certain habitats one sex can slightly outnumber the other. Duration of egg incubation periods, and therefore also larval development, is dependent on the environmental factors surrounding the habitat of each individual species. Environmental factors tend to include developmental constraints, salinity of the marine environment, and temperature of the water. Furthermore, the duration of the zoeal, or larval, phase ranges quite a bit, and has been estimated to last as little as 2 to 3 days in some species of Axiidea, to 5 to 6 months in other species. The pre-zoeal hatching stage is marked by poor swimming ability and lack of

seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

e, and the zoeal stages are planktonic. The

megalopa Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The ...

stage represents the transition from plankton to their benthic habitats, and morphological development is marked by the growth of functional mouthparts resembling those of juveniles or adults.

Burrows

Burrows can be divided into two groups in terms of external characteristics, depending on the existence of a mound of sediment around the entrance of the burrow. These two groups can be further divided based on whether they contain plant material within the burrow. Burrows tend to be narrow, and can range from Y or U shaped in certain species, to intricate branching tunnels and deep wells in other species. Burrows can also differ within the classifications of external characteristics, based on the feeding mode for each organism. There are three general

trophic Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to: * Trophic cascade * Trophic coherence * Trophic egg * Trophic function * Trophic hormone * Trophic level index * Trophic level * Trop ...

groups that the families within the infraorder Axiidea can fall into. The first trophic group are the detritophages, or deposit feeders. The other two trophic groups are the drift catchers, which collect plant matter that drifts based on ocean currents, and the suspension feeders, which feed on plant matter that is suspended in the water. Drift catcher burrows tend to lack the external characteristic of the mound around the entrance of the burrow, and their burrows tend to be very deep and contain chambers that are filled with seagrasses and other sea debris. Suspension feeder burrows tend to be in the Y or U shapes, and also lack seagrasses and debris within them in contrast to the drift catchers; furthermore, 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, sand an ...

within the lower parts of these burrows can also serve as food for the suspension feeders. The feeding mode affects the burrow, because Axiidea consume amounts of sediment, and the sediment that is rejected makes up parts of the burrow. The seagrasses consumed by the Axiidea are therefore present in the burrows and provide a way to classify the species. The burrows created by detritophage species of Axiidea are more likely to change over the life of the organism than the burrows of filter feeders because detritophage species of Axiidea can build new passages and chambers over the course of their feeding. Each burrow is typically inhabited by one organism, however, certain species of Axiidea live in pairs.

Distribution and ecology

Axiidea typically live in marine environments with soft-bottom sediments. Axiidea are found in most oceans and seas, except for high

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

polar seas. Distribution shows a clear gradient based on latitude, with low species numbers at higher latitudes and higher species numbers in low latitudes. Therefore, Axiidea are most diverse in

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

regions. Within the

intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of Marine habitat, habitats with var ...

regions, Axiidea can be used as fishing bait or even for human consumption. Axiidea rarely range into the deep sea with depths more than , instead with 95% of species preferring the shallow water of intertidal or subtidal (less than ) areas.

References

{{Taxonbar, from=Q21446174 Thalassinidea Arthropod infraorders