''Achaeus spinosus'' is a small

decapod The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and p ...

which belongs to the large

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 ...

of the

Inachidae Inachidae is a family of crabs, containing 39 genera: *'' Achaeopsis'' Stimpson, 1857 *''Achaeus'' Leach, 1815 *'' Anisonotus'' A. Milne-Edwards, 1879 *'' Anomalothir'' Miers, 1879 *'' Bothromaia'' Williams & Moffitt, 1991 *'' Calypsachaeus'' Ma ...

or the spider crabs.

Description

The ''Achaeus spinosus''

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 ...

has an oval shape and does not exceed in length. This crab possesses long fine clawless legs, except the front pair which is smaller and bears

chelae A chela ()also called a claw, nipper, or pinceris a pincer-shaped organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through Neo-Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds ...

(pincers). The pedunculate eyes are red. The whole whitish body is thickly covered with fine hairs which help to fix some pieces of

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

or fixed

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds, ...

for camouflage.

Distribution and ecology

''Achaeus spinosus'' can be observed in the tropical waters of the Indo-west Pacific area, including the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

. ''Achaeus spinosus'' usually lives in association with some species of

soft coral Alcyonacea is the old scientific order name for the informal group known as "soft corals". It is now an unaccepted name for class Octocorallia. It became deprecated . The following text should be considered a historical, outdated way of treatin ...

. ''Achaeus spinosus'' feeds on

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

and suspended particles which it catches by climbing on the host with whom it's in association to expose itself to the current. ''Achaeus spinosus'' is often observed on its living support. This crab is mainly active at night.

References

External links

* {{Taxonbar, from=Q12981313 Majoidea Crustaceans described in 1879