''Acrocnida'' is a genus of

brittle star Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

s in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Amphiuridae Amphiuridae (commonly called long-armed burrowing brittle stars or burrowing brittle stars) are a large family of brittle stars of the suborder Gnathophiurina The Gnathophiurina are a group of Ophiuroidea mostly treated as suborder (but at ...

. The genus contains three members: '' Acrocnida brachiata, Acrocnida semisquamata,'' and ''Acrocnida spatulispina.'' There has also been observed hybridization between both '' Acrocnida brachiata'' and ''Acrocnida spatulispina'.'' It is a fairly common genus, usually found along the coasts of Northwestern Europe, but with some species like semisquamata appearing around West Africa. Members of this genus primarily prefer intertidal and sub-tidal habitats, and they are they are less likely to be found in intertidal areas by comparison. This genus was not officially classified until 1926, by T. Gislén. One study found that due to the increased calcification that '' Acrocnida brachiata'' causes could be a potential source of Carbon Dioxide for not only the warm, shallow environments they live in, but also for the atmosphere.

Species

The

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

lists the following species. * '' Acrocnida brachiata'' (Montagu, 1804) * '' Acrocnida semisquamata'' (Koehler, 1914) * '' Acrocnida spatulispina'' (Stöhr & Muths, 2010) ''The species, Acrocnida brachiata,'' was recently found to be two species'', Acrocnida brachiata'' and '' Acrocnida semisquamata, by Stöhr & Muths in 2010.''

Distribution

This genus can be found spread around Northwestern Europe and off the Western coast of Africa. ''Acrocnida'' members generally prefer the sandy bottoms (specifically fine or muddy sand) of shallow coastal zones for their habitats. ''Acrocnida brachiata'' is a fairly widespread member of this genus in terms of distribution. While it was discovered in 1808 by George Montagu, their spread was still being recorded as far as the 1970s, with it being found in the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

. In recency, ''Acrocnida brachiata'' has been found in the

Aegean Sea The Aegean Sea is an elongated embayment of the Mediterranean Sea between Europe and Asia. It is located between the Balkans and Anatolia, and covers an area of some . In the north, the Aegean is connected to the Marmara Sea, which in turn con ...

for the first time in 2007, after only being noted on the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

facing coast of

Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...

in 1995. ''Acrocnida semisquamata'' is primarily located off of the coast of

Ghana Ghana, officially the Republic of Ghana, is a country in West Africa. It is situated along the Gulf of Guinea and the Atlantic Ocean to the south, and shares borders with Côte d’Ivoire to the west, Burkina Faso to the north, and Togo to t ...

, and ''Acrocnida spatulispina'' has only been observed in the

English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...

Morphology

''Acrocnida'' follows the body plan of other ''

,'' as they possess central disks surrounded by five long, thin arms. They only possess one outer mouth papilla, which is removed from the infradental papillae. Members of ''Acrocnida'' possess mucous glands described as "multecellular aggregations of pyriform cells with elongate necks" Like other members of ''

Ophiurida The Ophiurida are an order of echinoderms within the class Ophiuroidea. It includes the vast majority of living brittle stars. Characteristics Ophiurida have bursae for respiration and excretion, and dorsal and ventral arm shields are present an ...

, Acrocnida'' can part with limbs and regenerate a new limb.

Reproductive cycle

These sea stars mainly follow an annual schedule for their reproductive cycle. Looking at ''Acrocnida brachiata'', gonads begin forming in late Summer and Autumn, with the spawning taking place within a range of March to May. This places ''Acrocnida brachiata'' and other members of the genus in the category of "discreet annual breeder." Eggs created by ''Acrocnida brachiata'' lie in a range of 180 to 350 micrometers. This size places ''Acrocnida'' with an "intermediate level of fecundity" and a larval development similar to other genera of sea stars.

Common behavior

''Acrocnida'' and other ''

'' practice very similar behaviors. In order to avoid predation, these organisms dig a semi-permanent hole, which they reinforce using the mucus they naturally produce. They then dip their disk into the hole, and leave the arms just poking out enough so that they may still explore and interact with the area outside of their burrow. Members of the genus ''Acrocnida'' utilize their Water vascular system to ventilate their burrows. '' Acrocnida brachiata'' is usually seen with '' Echinocardium cordatum'', commonly known as the Sea Potato.

References

{{Taxonbar, from=Q3468058 Amphiuridae Ophiuroidea genera