Fiddler crabs

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Fiddler crabs
Fiddler crab, "left-scissor" male

Fiddler crab, "left-scissor" male

Systematics
Class : Higher crabs (Malacostraca)
Order : Decapods (decapoda)
Subordination : Crab (Brachyura)
Superfamily : Ocypodoidea
Family : Ocypodidae
Genre : Fiddler crabs
Scientific name
Uca
Leach , 1814

The fiddler crabs ( Uca ) are a genus of crabs (Brachyura). Together with the rider crabs, they belong to the family of the Ocypodidae . There are currently 92 known species of fiddler crabs.

features

The fiddler crabs have a typical crab habit with a wide carapace on the front body, which is known as the carapace . The abdomen is very much reduced and is beaten under the front body. The head is also under the carapace and the eyes sit on stalks at its front edge. The antennas are very short. In addition to the mandibles and the two pairs of maxillae, there are three other pairs of extremities in the mouth area , which have been transformed into oral tools ( maxillipedas ).

Like all decapods , they have five pairs of extremities that attach to the sides of the body. The first pair of legs is fitted with scissors ( cheles ), while the back four pairs serve as walking legs . What is striking about the male fiddler crabs is the different size of the claws with a very large claw that can be placed on the right or left and a small claw. The females carry small scissors on both scissor legs.

distribution and habitat

Fiddler crabs live as beach dwellers in tropical areas around the world, especially on the Atlantic and Pacific coasts of the American double continent, Australia and the islands of the Indo-Pacific . One species also lives on the coast of West Africa ( Uca tangeri ). They mainly occur on sandy stretches of beach or in the area of mangrove forests .

Way of life

Fiddler crab colony in a mangrove

The nocturnal and dawn active fiddler crabs live mostly aggregated in large accumulations in Tidenbereich the sea. The individual caves are surrounded by a small-scale area that is defended by a male crab. The females also form breeding caves within the colony. During the high tide , the animals are in their caves and leave them to forage at low tide.

Territorial behavior could be observed in Australian fiddler crabs, in which neighboring territory owners support each other during the defense of the territories, whereby the support mostly applies to the weaker rivals. This tactic, which at first glance seems illogical, was explained by the fact that it is more advantageous for the males to have weaker crabs in their environment than to have to assert themselves against more dominant conspecifics. The territorial fights as well as the rival fights during the breeding season (see below) can be so violent that the large scissors used are lost. In this case, with the next moults, the small scissors enlarge to the new large scissors, while a new small scissors is formed.

nutrition

Fiddler crabs are omnivores and eat vegetable, animal and other food that they can find in the detritus when they forage in the dry beach area . They guide the food to the mouth with their small scissors, which earned them the common name fiddler crabs due to the resulting movement .

Reproduction and development

Waving male of the species Uca perplexa

When it comes to finding a partner, the fiddler crabs have the eponymous behavior of the males. They stand at their caves and lift their large scissors at regular intervals, creating a waving gesture. This leads to a synchronization of the males of an entire colony, all of which wave in unison. This behavior attracts the females, who look for the right sexual partner among the males. There is also rivalry between the males.

New observations show that the mating behavior of the females can depend on how a male crab supports the female in defending the territory.

After copulation, the female lays the eggs in the form of egg balls and attaches them to the underside of the body, where it holds it with the extremities of the abdomen that has been beaten. With this ball it remains in its burrow for the development time of about two weeks and then leaves it to release the eggs that are ready to hatch into the tidal water. The larva hatches in the water and develops into a new crab over several stages. After a planktonic phase of about two weeks, the young crabs come back on land.

The lifespan of the crabs depends on the species and can be a maximum of two years.

Systematics

The fiddler crabs, together with the genus ghost crabs or riding crabs ( Ocypode ), whose sister group they represent, belong to the family of the Ocypodidae.

According to the width of the carapace between the two eye stalks, a distinction is made between two subgenus groups within the fiddler crabs. The Uca group represents the narrow-fronted crab and the Minuca group represents the broad-front group. The Minuca group is also characterized by a specific support structure of the abdomen, which the Uca group lacks, which is why it is regarded as a derived monophyletic group .

A distinction is made between eleven sub-genera: Afruca , Australuca , Austruca , Cranuca , Gelasimus , Leptuca , Minuca , Paraleptuca , Tubuca , Uca and Xeruca .

Individual evidence

  1. Sammy De Grave, N. Dean Pentcheff, Shane T. Ahyong et al .: A classification of living and fossil genera of decapod crustaceans . In: Raffles Bulletin of Zoology . Supplement No. 21. 2009, p. 1–109 ( pdf 7.73Mb [accessed March 11, 2012]).
  2. Article on Spiegel.de - http://www.spiegel.de/wissenschaft/natur/0,1518,659040,00.html
  3. Peter KL Ng, Danièle Guinot, Peter JF Davie: SYSTEMA BRACHYURORUM: PART I. AN ANNOTATED CHECKLIST OF EXTANT BRACHYURAN CRABS OF THE WORLD. The Raffles Bulletin of Zoology 17: 1–286, 2008 ( PDF; 7.74 MB ( Memento of the original of September 28, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. ). @1@ 2Template: Webachiv / IABot / lkcnhm.nus.edu.sg
  4. Hsi-Te Shih: Uca (Xeruca), a new subgenus for the Taiwanese fiddler crab Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae), based on morphological and molecular evidence. Zootaxa 3974 (2): 151–169, 2015 ( doi : 10.11646 / zootaxa.3974.2.1 - PDF; 6.44 MB ).

Web links

Commons : Fiddler Crabs ( Uca )  - Collection of images, videos and audio files