Other Physical Features: ectothermic ; bilateral symmetry
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
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.
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.
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.
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)
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].
Remipedia is a class of blind crustaceans, closely related to hexapods, 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). Since 1979, at least seventeen living species have been identified in subtropical regions around the world.[1]
Remipedes are 1–4 centimetres (0.4–1.6 in) long and comprise a head and an elongate trunk of up to thirty-two similar body segments.[2] Pigmentation and eyes are absent.[3] Biramous swimming appendages are laterally present on each segment. The animals swim on their backs and are generally slow-moving.[4] They are the only known venomous crustaceans, and have fangs connected to secretory glands, which inject a combination of digestive enzymes and venom into their prey,[5] but they also feed through filter feeding. Being hermaphrodites, the female pore is located on the seventh trunk segment and the male pore on the fourteenth.[6]
Remipedia have a generally primitive body plan compared to other extant crustaceans, and are the only extant pancrustaceans to lack significant postcephalic tagmosis.[4] Previously regarded as 'primitive', remipedia have since been shown to have enhanced olfactory nerve centers (a common feature for species that live in dark environments).[7]
Based on studies of the free-living larvae, they appear to be lecithotrophic (non-feeding). Mouths, guts, and anuses appear in the juvenile stage. Because of the energy and nutrients required for swimming, molt several times and to grow in size and length, it has been speculated that the larvae may have other sources of growth than its yolk, possibly symbiotic bacteria.[8][9]
The class Remipedia was erected in 1981 by Jill Yager, in describing Speleonectes lucayensis from the Bahamas.[10] The name "Remipedia" is from the Latin remipedes, meaning "oar-footed".[10]
Historical phylogeny based on morphology and physiology has placed Remipedia under Mandibulata, in the subphylum Crustacea, and distinct from Hexapoda.
New research in evolution and development reveals similarities between larvae and postembryonic development of remipedes and Malacostraca, singling Remipedia as a potential crustacean sister group of Hexapoda. Similarities in brain anatomy further support this affinity, and hexapod-type hemocyanins have been discovered in remipedes.[11]
Recent molecular studies have grouped Remipedia with Cephalocarida, Branchiopoda, and Hexapoda in a clade named Allotriocarida.[12][13] Remipedia was found as the sister group to Hexapoda both in phylogenomic[14] [13] and combined morphological and transcriptome studies.[12] In other studies Remipedia and Cephalocarida are grouped together form the clade Xenocarida, which in turn was sister to Hexapoda in a clade named Anartiopoda[15] or Miracrustacea ('surprising crustaceans').[4]
The relationship of Remipedia and other crustacean classes and insects is shown in the following phylogenetic tree, which shows Allotriocarida, along with Oligostraca and Multicrustacea, as the three main divisions of subphylum Pancrustacea, embracing the traditional crustaceans and the hexapods (including insects).[13]
Pancrustacea Multicrustacea AllotriocaridaRemipedia
HexapodaThirty extant species are recognized as of early 2022, divided among eight families and twelve genera.[16][17] All are placed in the order Nectiopoda. The second order, Enantiopoda, comprises the fossil species Tesnusocaris goldichi and Cryptocaris hootchi.[1]
Bahamas – Andros, Sweetings Cay, Grand Bahama, Great Exuma, Great Guana Cay (Exuma Cays), Cat Island, Abaco Islands, San Salvador Island
Turks and Caicos Islands – North Caicos, Providenciales
Australia – North West Cape (Western Australia)
Cuba – Matanzas Province
Spain – Lanzarote (Canary Islands)
Mexico – Quintana Roo
Dominican Republic – Distrito Nacional Cueva Taína, Santo Domingo Este.[22]
Remipedia is a class of blind crustaceans, closely related to hexapods, 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). Since 1979, at least seventeen living species have been identified in subtropical regions around the world.
