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Speleonectes tanumekes from the Exuma Cays, Bahamas

Speleonectes tanumekes from the Exuma Cays, Bahamas

Over trunk : Molting animals (Ecdysozoa)
Trunk : Arthropod (arthropoda)
Sub-stem : Crustaceans (Crustacea)
Class : Remipedia
Scientific name
Yager , 1981

The Remipedia represent a class within the crustaceans . So far, twenty-four species are known from this group of animals, which was only discovered in the 1980s, and more are expected in caves with sea contact. All species found so far are restricted to the tropics.

Way of life of the Remipedia

The Remipedia were discovered during dives in limestone cave systems flooded by seawater in the Bahamas and the Yucatán Peninsula ( called " Cenotes " here ) as well as in lava tunnels on Lanzarote , recently also in similar habitats in Western Australia (Bundera Sinkhole, Cape Range Peninsula). The common feature of these caves is the connection to the sea and access from the land. For this reason, the deep sea water in the caves is covered by fresh and brackish water ( anchialine caves). The Remipedia always live in the oxygen-poor seawater zone below the stratification boundary. The habitat is quite hostile to life and therefore poor in food.

The animals are predatory and use their mouthparts to catch smaller crabs. This behavior was observed with a shrimp that was grasped by the maxillae and maxillipede and brought to the mouth. They move through the water with their swimming legs, with their legs being continuously beaten in a wave motion. This swimming behavior can be converted into a synchronous stroke when escaping.

Construction of the Remipedia

The Remipedia are colorless and eyeless cave animals that reach a body length of 9 to 45 millimeters. Their body is divided into a head and a trunk, the trunk consisting of a large number of segments (in the known species 16 to 38). These trunk segments are all equipped with double-branched swimming legs of the same type, the two branches ( endopodite and exopodite , see also split leg ) being about the same length, the extremities decrease in length towards the rear end. Limb buds on the rearmost segments, even on sexually mature animals, indicate that the animals gain segments with each moult even after sexual maturity. The last segment of the body, the telson , has an appendix on each side, which are collectively referred to as furca (also furka, lat. "Fork"). The anatomy with only two body sections (Tagmata) and the high number of trunk limbs of the same type are considered to be signs of a particularly ancient, little modified body structure.

The head (cephalon) into which the first trunk segment is fused (recognizable by a maxillipede as a mouth tool ) is covered by a head shield. The first antenna has two branches and is relatively long. It has an enlarged base on which several rows of sensory receptors (aesthetasques) sit. The second antenna also consists of two branches, whereby the exopodite constantly conducts water over the sensory cells in the form of a leaf. The mandibles have a movable part (Lacinia mobilis) and the two maxillae and the maxilliped are designed as single-branch gripping tools. The 1st maxilla carries the opening of a large gland that is believed to produce digestive enzymes.

Reproduction and development

The Remipedia are (simultaneous) hermaphrodites . They have an ovary above the intestine with outlets on the protopodites of the pair of legs on the 7th trunk segment and testicles with outlets in the 14th trunk segment. The sperm are Spermatophoren grouped into six sperm. So far nothing is known about the pairing of the Remipedia.

The development has so far been described in a kind of Pleomothra apletocheles , researching it is difficult because the animals cannot be kept alive in the laboratory for long and cannot be bred at all. The first larval stage is an (ortho-) nauplius . Further development takes place over at least four metanauplius stages. So far, only one older young animal has been found that already resembles the adult animal in terms of its morphology. Up to this stage the larvae do not consume any food, they live on the yolk supply from the egg. The existence of other larval stages is possible, but they have not yet been found.

Systematics of Remipedia

All living Remipedia belong to the order Nectiopoda. The order Enantiopoda was established for two extinct fossil species from the Carboniferous . The living species are divided into three families: Speleonectidae , Godzilliidae and Micropacteridae , with a total of eight genera.

The position of Remipedia within the system of crustaceans is discussed very controversially. Various taxonomists have drawn the conclusion from the simple physique that it is a particularly primitive group that should be arranged basally within the crustaceans, possibly as a sister group of all other crustaceans. The likewise simply structured Cephalocarida were also often regarded as a sister group. Numerous other groupings, e.g. B. with the Cirripedia or the Malacostraca as sister group are currently being discussed. In some analyzes they are even considered a sister group of the Hexapoda (also the Diplura or Collembola ), so they would be a basal taxon of the Tetraconata as a whole and would not even count among the crustaceans (in the narrower sense). If any of these hypotheses were correct, the simple outline should be viewed as a secondary simplification.


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