Remipedes are 1–4 centimetres (0.4–1.6 in) long and comprise a head and an elongate trunk of up to thirty-two similarbody segments.[2] Pigmentation and eyes are absent.[3] Biramous swimmingappendages 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 ofdigestive enzymes andvenom into their prey,[5] but they also feed throughfilter feeding. Beinghermaphrodites, 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 extantpancrustaceans to lack significant postcephalictagmosis.[4] External respiratory structures like gills are absent.[7] 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).[8]
The larvae are free-living and appear to be lecithotrophic (non-feeding). Mouths, guts, and anuses appear in the juvenile stage. Because of the energy and nutrients required for swimming, molting, 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.[9][10]
With the exception ofSpeleonectes kakuki, which inhabits a fully marine, sub-seafloor cave in the Bahamas, all known species of remipedians have been found exclusively inanchialine cave systems.[11]
Historical phylogeny based on morphology and physiology has placed Remipedia underMandibulata, in the subphylumCrustacea, and distinct fromHexapoda.
New research inevolution and development reveals similarities between larvae and postembryonic development of remipedes andMalacostraca, 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.[15]
Recent molecular studies have grouped Remipedia withCephalocarida,Branchiopoda, andHexapoda in a clade namedAllotriocarida.[16][17] Remipedia was found as the sister group to Hexapoda both in phylogenomic[18][17] and combined morphological and transcriptome studies.[16] In other studies Remipedia andCephalocarida are grouped together form the cladeXenocarida, which in turn was sister to Hexapoda in a clade named Anartiopoda[19] 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 withOligostraca andMulticrustacea, as the three main divisions of subphylumPancrustacea, embracing the traditional crustaceans and the hexapods (including insects).[17]
Thirty extant species are recognized as of early 2022, divided among eight families and twelve genera.[20][21] All are placed in the orderNectiopoda. The second order, Enantiopoda, comprises the fossil speciesTesnusocaris goldichi andCryptocaris hootchi.[1]
^Yager J (2013). "Speleonectes cokei, new species of Remipedia (Crustacea: Speleonectidae) from a submerged ocean cave near Caye Chapel, Belize".Zootaxa.3710 (4):354–362.doi:10.11646/zootaxa.3710.4.4.PMID26106696.S2CID10850210.
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
Belize -Caye Chapel
Dominican Republic –Distrito Nacional Cueva Taína, Santo Domingo Este.[26]
Data related toRemipedia at Wikispecies