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Remipedes

Remipedia

Brief Summary

    Remipedia: Brief Summary
    provided by wikipedia

    Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The first described remipede was the fossil Tesnusocaris goldichi (Lower Pennsylvanian), but, since 1979, at least seventeen living species have been identified in subtropical regions around the world.

    Genetic studies have implied that remipedes are the arthropods most closely related to insects, so much so that they and insects may be considered a sister group to all other crustacea.

    Brief Summary
    provided by EOL authors

    Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater. Populations have been found in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, the Atlantic Ocean. The first described remipede was the fossil Tesnusocaris goldichi from the Lower Pennsylvanian period, but, since 1979, twenty-four living species have been identified from throughout the neo-tropics.[1,2]

    Remipedes are 10–40 millimetres (0.4–1.6 in) long and comprise a head and an elongate trunk of up to forty-two similar body segments.[3] The swimming appendages are attached on the side of each segment, and the animals swim on their backs. They are generally slow-moving. They have fangs connected to secretory glands; it is still unknown whether these glands secrete digestive juices or poisonous venom, or whether remipedes feed primarily on living organisms or on detritus (dead organisms).

    They have a generally primitive body plan in crustacean terms, and have been thought to be a basal crustacean group- more distantly related to other crustacean groups than those groups are to each other.However, this is disputed: Fanenbruck et al. showed that at least one species, Godzilliognomus frondosus, has a highly organised and well-differentiated brain, with a particularly large olfactory area which is a common feature for species that live in dark environments.[4] The size and complexity of the brain suggested to Fanenbruck et al. that Remipedia might be the sister taxon to Malacostraca, regarded as among the most derived (havingevolved many phenotypic changes,compared with related taxa)of the crustaceans. They have also been grouped together with the Cephalocarida, and recently with the Hexapoda[5].

Comprehensive Description

Distribution

    Distribution
    provided by EOL authors

    The three species described together in this paper, Speleonectes tanumekes, Speleonectes parabenjamini and Speleonectes minnsi, herein present another remarkable example of sympatry for remipedes, especially since these crustaceans are exclusively known from marine subterranean habitats. Groundwater environments are typically characterized by a limitation of nutrients and, in part as a consequence, low abundances of stygobiont organisms. The fact that remipedes are hermaphrodites may also point towards an adaptation to small population sizes. Interestingly, the sympatry of the three new species described herein is not exceptional for Remipedia. There are several other instances of two or three sympatric species (see Table 1, below).However, sympatric remipedes are known only from the Bahamas and nearby West Indian islands (Fig. 14) . The high abundance of remipedes and their taxonomic diversity at and below the family level in this region forms a sharp contrast to the disjunct occurrences of a few remote taxa. The Remipedia in the northwestern region of the West Indies and the Bahamas comprise 12 species (6 genera and 2 families). Of the remaining three taxa, S. tulumensis Yager, 1987b, from the Yucatan Peninsula could be regarded as a peripheral isolate of the main cluster. By contrast, S. ondinae (Garcia-Valdecasas, 1984) from the Canary Islands and L. exleyi Yager & Humphreys, 1996, from western Australia are extreme disjunct occurrences (Fig. 15). [ed. note: since this paper was published other species have been described.See Neiber et al. 2011]

    Table 1: Recorded localities of Remipedia, with several occurrences of sympatric species of (see also Fig. 14). TL = type locality, AL = additional locality.

    Species

    Localities with sympatric species

    Localities with single species

    Cryptocorynetes haptodiscus Yager, 1987a

    Bahamas: Dan’s Cave (TL), Abaco Island

    Bahamas: Old Freetown Cave System (AL), Grand Bahama Island

    Pleomothra apletocheles Yager, 1989

    Bahamas: Dan’s Cave (TL), Abaco Island; Sagittarius Cave (AL), Grand Bahama Island

    none

    Speleonectes benjamini Yager, 1987a

    Bahamas: Dan’s Cave (AL), Abaco Island; Sagittarius Cave (AL), Grand Bahama Island

    Bahamas: Asgard Cave (TL), Grand Bahama Island

    Godzilliognomus frondosus Yager, 1989

    Bahamas: Sagittarius Cave (TL), Grand Bahama Island

    none

    Lasionectes entrichoma Yager & Schram, 1986

    West Indies: Cottage Pond (AL), Turks and Caicos Islands

    West Indies: Old Blue Hill Cave (TL), Airport Cave (AL); Turks and Caicos Islands

    Godzillius robustus Schram et al., 1986

    West Indies: Cottage Pond (AL), Turks and Caicos Islands

    none

    Speleonectes tanumekes n. sp.

    Bahamas: Basil Minns Blue Hole (TL), Great Exuma Island

    none

    Speleonectes parabenjamini n. sp.

    Bahamas: Basil Minns Blue Hole (TL), Great Exuma Island

    none

    Speleonectes minnsi n. sp.

    Bahamas: Basil Minns Blue Hole (TL), Great Exuma Island

    none

    Lasionectes exleyi Yager & Humphreys, 1996

    none

    Western Australia: Cave C-28 (TL), Cape Range Peninsula

    Speleonectes epilimnius Yager & Carpenter, 1999

    none

    Bahamas: Major’s Cave (TL), San Salvador Island

    Speleonectes lucayensis Yager, 1981

    none

    Bahamas: Lucayan Cavern (TL), Grand Bahama Island

    Speleonectes gironensis Yager, 1994

    none

    Cuba: Cueva de los Carboneros (TL), Matanzas Province

    Speleonectes ondinae (Garcia-Valdecasas, 1984)

    none

    Canary Islands: Tunel de la Atlantida (TL), Lanzarote

    Speleonectes tulumensis Yager, 1987b

    none

    Mexico: Carwash Cenote (TL), Najaron Cenote (AL); Quintana Roo

    The high availability of suitable habitats (anchihaline caves) within a relatively small region (Bahamas, West Indies) may have had, and still have, an important impact on the unique geographic distribution of Remipedia. In this light, the frequent occurrences of sympatry could be result of dispersal and, subsequently, multiple invasions of available anchihaline caves.

    FIG2

    Fig. 14. Geographic distribution of Remipedia on the Bahamas and in the northwestern West Indies, including 12 of a total of 15 species known to science. Rectangular labels indicate occurrences of two or three sympatric species; circles show records of non-sympatric occurrences. Abbreviated taxa: Ch = Cryptocorynetes haptodiscus; Gf = Godzilliognomus frondosus; Gr = Godzillius robustus; Le = Lasionectes entrichoma; Pa = Pleomothra apletocheles; Sb = Speleonectes benjamini; Se = S. epilimnius; Sg = S. gironensis; Sl = S. lucayensis; Sp = S. parabenjamini n. sp.; Sm = S. minnsi n. sp.; St = S. tanumekes n. sp.

    Sympatric remipedes are likely to be subjected to strong competition, which could lead either to niche differentiation or competitive exclusion. For example, the new species S. tanumekes (12 specimens collected) seems to be more abundant than S. parabenjamini (2 specimens) and S. minnsi (1 specimen). However, whether this is a sampling bias, a seasonal fluctuation or indeed related to population dynamics of the three remipedes in Basil Minns Blue Hole needs to be confirmed by additional collections.

    FIG2

    Fig. 15. Global distribution of Remipedia. Filled circle represent individual species. Horizontal lines indicate the equator, and latitudes 30º north and south of the equator.

Morphology

    Morphology
    provided by Animal Diversity Web

    Other Physical Features: ectothermic ; bilateral symmetry

Evolution

    Evolution
    provided by EOL authors

    Sympatric remipedes are likely to be subjected to strong competition, which could lead either to niche differentiation or competitive exclusion. For example, the new species S. tanumekes (12 specimens collected) seems to be more abundant than S. parabenjamini (2 specimens) and S. minnsi (1 specimen). However, whether this is a sampling bias, a seasonal fluctuation or indeed related to population dynamics of the three remipedes in Basil Minns Blue Hole needs to be confirmed by additional collections.

    Since their discovery, a plethora of opinions has been offered regarding the evolutionary history and phylogenetic status of Remipedia (see any Invertebrate Zoology textbook). Yet, we can be fairly certain that Remipedia are an ancient group of crustaceans. Remipedes share several well defined features with the Carboniferous fossil Tesnusocaris goldichi Brooks, 1955, from the Tesnus Formation (Upper Mississippian/Lower Pennsylvanian) in Texas (see Emerson & Schram, 1991, for a detailed redescription). The most distinctive shared characters comprise a homonomously segmented trunk equipped with paddle-shaped, biramous swimming appendages, and the modification of three post-oral cephalic appendages as subequal prehensile limbs. However, does the global, circum-tropical distribution of remipedes support an ancient origin for this group? Such disjunct occurrences of taxa are often interpreted as relicts of an ancient marine distribution, as postulated for various crustacean stygobionts, e.g., hadziid and bogidiellid amphipods (Stock, 1981; Holsinger, 1986; Koenemann & Holsinger, 1999). Alternative theories favor a deep-sea origin for some stygobiontic crustaceans (Wilson, 1999; Manning et al., 1986; Hart et al., 1985). These theories are particularly interesting since all remipedes occur in regions that are comparatively young in geological time. For example, the Canary Islands were probably formed during the Late Tertiary, and anchihaline cave systems resulting from volcanic activity, such as lava tubes, must have been colonized subsequently. Yet, we have to be careful not to jump to conclusions. Too little is still known about the biology of Remipedia, and at present, each additional discovery seems to add a piece to a more complete mosaic. The current distribution consists of a prominent cluster of taxa in the northern Caribbean region including the Bahamas. Whether this cluster is an ancient center of origin and the disjunct taxa are isolated relicts remains to be seen. At this point, it is equally conceivable that we are observing a distribution pattern subjected to biased sampling in less accessible diving regions. We cannot even exclude the possibility that the two most disjunct localities on the Canary Islands and in western Australia are the result of some kind of passive dispersal (see Koenemann et al. 1998).

    (From Koenemann, Iliffe and van der Ham 2003)

Taxonomy

    Taxonomy
    provided by EOL authors

    Remipedia Yager, 1981: 328. Schram, Yager & Emerson, 1986: 6.

    Diagnosis. – Hermaphroditic crustaceans with 6-segmented cephalon (including maxillipeds), head shield present. Trunk lacking tagmosis, composed of at least 15 segments; carapace absent; female gonopores on trunk segment 7, male gonopores on trunk segment 14. Antennules and antennae biramous. Labrum well developed. Post-oral cephalic appendages modified as subequal, uniramous, prehensile, raptorial mouthparts. Transverse sternal bars present. Trunk limbs as biramous, paddle-shaped swimming appendages.

    Remarks. – The class Remipedia includes two orders, the Nectiopoda Schram, 1986 and the Enantiopoda Birshtein, 1960. The latter order contains the fossils Tesnusocaris goldichi Brooks, 1955, and Cryptocaris hootchii Schram, 1974, as subordinate taxa.

    From Koenemann, Iliffe and van der Ham 2003