The

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 ...

Rhynchocinetidae are a group of small, reclusive red-and-white

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 ...

. This family typically has an upward-hinged foldable rostrum, hence its taxon name ''Rhynchocinetidae'', which means ''movable beak''; this gives these shrimps their common name of hinge-beak shrimps. The family contains only two genera, '' Cinetorhynchus'' and '' Rhynchocinetes''.

Taxonomy

Rhynchocinetidae has historically been considered to include the single genus ''Rhynchocinetes'', which was subdivided into two sub-genera. However, in 1995, Holthuis elevated the subgenus ''Cinetorhynchus'' to full generic status based on morphology. Members of ''Rhynchocinetes'' have two acute teeth on the central carina of the carapace, a supraorbital spine and no spine on the margins of the fourth and fifth abdominal somites. ''Cinetorhynchus'' differs in having three teeth on the carapace, no supraorbital spine and a single spine each on the margins of the fourth and fifth abdominal somites.

Description

Members of the family Rhynchocinetidae are colourful crustaceans, mostly banded or patterned in red and white. The rostrum is partially or completely articulated with 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 ...

and can be moved in a variety of ways. The advantages of this adaptation are unclear, but in combination with the spiny rostrum, it may enable the shrimp to wedge itself into a crevice and avoid being dislodged by a

predator 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 ...

. The first pair of chelipeds are more robust than the second pair, and the carpus of the second pair is undivided. In males, particularly in larger, older individuals, the third pair of

maxillipeds An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

and the first pair of chelipeds are exceptionally large in proportion to those of females and younger males. Both pairs of chelipeds bear a bundle of spines at the tip which when retracted form a basket-like cage.

Distribution and habitat

Members of the family Rhynchocinetidae are found in both tropical and some temperate waters, from the

littoral zone The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...

down to the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

, inhabiting both coral and rocky reefs.

Ecology

The biology of the family has been little studied. '' Cinetorhynchus rigens'' in Bermuda was not attracted to baited traps but on examination, its faecal pellets contained mollusc shell fragments, algae and sponge spicules. It was nocturnal, hiding by day in crevices and emerging at night to feed.

References

{{Taxonbar, from=Q2393338 Caridea Decapod families