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Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Isopoda
Family Atlantasellidae

Atlantasellus cavernicolus Sket, 1979



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Atlantasellus cavernicolus: habitus, after Sket, 1979

Taxonomic Characterization: A. cavernicolus is unpigmented and translucent with an elongated, semi-cylindrical, transversely bendable body. The 2nd antenna is twice as long as the 1st. The female differs from the male in the presence of 2 aesthetascs on the 1st antenna instead of 4. Atlantasellus differs from the known families of Aselloidea in the following ways. The inner lobe of the 1st maxilla has only a single long seta distally. The epipodit of the maxilliped is developed. The female 2nd pleopods are missing and the endopodite of the 2nd pleopod of the male has one article. The 3rd pleopod is not articulated and the endopodit is absent. The 1st and 2nd pleonites are normal and the habitus is basically sphaeromatoide. The 3rd pleopods are strongly sclerotized and have a superficial sculpture with very prominent keels and edges. The uropods are reduced (Sket, 1979).

Ecological Classification: Stygobitic

Size: Male holotype 1.1 mm; females same length or slightly longer than the male.

Number of Species in Genus: Two, both inhabiting anchialine caves

Genus Range:

  • Bermuda: Atlantasellus cavernicolus Sket, 1979
  • Dominican Republic: A. dominicanus Jaume, 2001

Species Range: Known only from Walsingham Sink Cave, Hamilton Parish, Bermuda.

Closest Related Species: A. cavernicolus is most closely related to the only other species in the family, A.
dominicanus from the Dominican Republic. 

Habitat: Anchialine limestone caves

Ecology: Specimens were collected from the steep bottom of an anchialine pool in Walsingham Sink Cave. It is doubtful whether the benthic environment is typical for the species; it could be an immigrant from abyssal or interstitial waters (Sket, 1979).

Life History: Collected specimens included one male and 5 females (1 postmanca).

Evolutionary Origins: Atlantasellus represents an independent phyletic line of the Aselloidea, developed towards the sphaeromatoide Lebens-form. The discovery of a marine aselloid in caves follows the assumption that the group requires refuge from their modern newly evolving relatives with whom they are unable to compete. The ability of the body shape to volve is of phylogenetic importance and has not been found in the Aselloidea until now (Sket, 1979). 
Analysis of palaeogeographic and ecological evidence supports the interpretation of the Atlantasellidae as a thalassoid lineage, contrary to previous phylogenetically supported assumptions considering them to be an ancient, freshwater lineage (Jaume, 2001).

Conservation Status: A. cavernicolus is considered to be critically endangered (IUCN, 2000). It is restricted to a single anchialine cave in Bermuda.

References:

  • IUCN, 2000. The 2000 IUCN Red List of Threatened Species. Gland, IUCN, 61 pages.
  • Jaume, D. 2001. A new atlantasellid isopod (Asellota : Aselloidea) from the flooded coastal karst of the Dominican Republic (Hispaniola): evidence for an exopod on a thoracic limb and biogeographical implications. Journal of Zoology, 255: 221-233.
  • Sket, B. 1979. Atlantasellus cavernicolus n. gen., n. sp. (Isopoda Asellota, Atlantasellidae n. fam.) from Bermuda. Biol. vestn. (Ljubljana), 27(2): 175-183, 21 figures, 1 table.

Contributor: Boris Sket, University of Ljubljana, Slovenia


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