Speleonectes epilimnius Yager & Carpenter, 1999
Taxonomic Characterization: The most distinctive morphological trait of S. epilimnius, that separates it from all other remipede species, is the lack of appendages on the last two pre-anal segments (Yager & Carpenter, 1999). A distinctive trait of S. epilimnius is the relatively small number of trunk segments to body length, the smallest range of all remipede species.
Ecological Classification: Stygobitic
Size: Adult lengths range from 8.7 - 18.3 mm
Number of Species in Genus: Nine, all stygobitic
Species Range: Know only from Major's Cave, San Salvador Island, Bahamas.
Closest Related Species: Shares most characteristics with S. gironensis Yager, 1994.
Habitat: Anchialine limestone caves
Ecology: Found free-swimming within surface waters (salinity of 24-25 mg/l). This is the only remipede collected above the density interface. It appears the cave fauna usually associated with remipedes is lacking. Remipedes are typically found with other crustaceans: thermosbaenaceans, hadziid amphipods, cirolanid isopods and ostracods. Ostracods and cirolanid isopods are present in Major's Cave but thermosbaenaceans and hadziid amphipods have never been found in caves on this island. It is possible that the "normal" habitat for S. epilimnius is much deeper, and that the typically associated fauna may also be found there. The lack of the freshwater layer allows for remipedes to come to the surface without an osmotic shock (Carpenter, 1999).
As is typical of remipedes, S. epilimnius specimens nearly always swam ventral side up, with rapid metachronal beating of trunk appendages (160-190 beats/min.). When trunk appendages slowed down to 80-150 beats/min., swimming stopped, but the appendages continued to beat slowly, apparently for respiration. Undisturbed specimens often rested on the side or bottom of the container, head or ventral side up, occasionally with the head curled toward the tail; when physically disturbed, they soon straightened out and swam (Carpenter, 1999).
Remipedes produce a mucus which tends to catch debris on appendages. In addition to locomotion, trunk appendages function in grooming. The long dorsal ramus and short ventral ramus of antenna 1 were cleaned by brushing them against the anterior 5-10 swimming appendages, which simultaneously stroked the antenna with a more forceful power stroke by extending further anteriorly and laterally than normal. Maxillae 1-2 and maxillipeds were all used to clean the mouth area and each other and in one case, the posterior third of the body (Carpenter, 1999)
S. epilimnius uses maxillae 1-2 to manipulate and pierce prey. Maxillae 1-2 are quite nimble in the manipulation of food and grooming of mouthparts. This makes it highly unlikely that there is any automatic injection of secretion with flexion. While remipedes were feeding on worms, the walls of the atrium oris were spread apart to render that part of the "mandibular mill" ineffective as a sieve. The mandibles were clearly exposed and they chewed food in a typical crustacean fashion (Carpenter, 1999).
Life History: According to Yager (1994): "Remipedes are simultaneous hermaphrodites. The ovary originates in the posterior portion of the head and lies dorsal to the midgut. The oviducts extend ventrally to the 7th swimming or trunk appendages where the female gonopores are located. The female gonopore is a semicircular structure on the posterior base of the protopod.
The testes are paired organs which originate in the 7th trunk segment and extend posteriorly until about the 10th trunk segment. At this position there is a transition from testes to vas deferens. The vas deferens extends to the male gonopores located at the base of the 14th swimming or trunk appendages. Spermatids are flagellate with a 9 + 2 microtubular arrangement. As they mature and move posteriorly they are packages into spermatophores.
To date, nothing is known about remipede development. Small juveniles have been collected which resemble adults. They are about one-third or less the length of adults."
Evolutionary Origins: The large number of trunk segments, each with similar, laterally directed, biramous, swimming appendages, plus a combination of the other characteristics necessitated the erection of a new crustacean class, the Remipedia (Yager, 1981). Remipedes are believed to be the most primitive of living crustaceans. The fossil species Tesnusocaris goldichi Brooks from Late Mississippian deposits in Texas has been placed in this class. The recent discovery of remipedes from anchialine caves in Western Australia is further evidence for a Tethyan distribution (Yager & Humphreys, 1996).
Conservation Status: Known only from one anchialine cave on San Salvador.
Contributor: Jill Yager, Antioch College, Yellow Springs, OH
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