Arubolana aruboides (Bowman & Iliffe, 1983)

Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Isopoda
Family Cirolanidae

Arubolana aruboides (Bowman & Iliffe, 1983)

Taxonomic Characterization: A. aruboides is a blind, unpigmented cirolanid isopod. The body is moderately slender, slightly more than 3 times as long as it is wide. The anterior margin of the head is slightly concave on either side of a minute rostrum. Pereonites 1 and 5-7 are subequal in length and longer than pereonites 2-4 which are also subequal in length. The pleonites are all free and all reach the lateral margin of the pleon. The pleon is approximately half the length of the pereon. Maxilla 2 is strongly reduced and the maxilliped has sparse setation. The telson is linguiform and marginal spines are absent. Incisors of the mandibles have 3 cusps. The penes are well developed, narrowly cylindrical, and separated at the base. The distal position of the appendix masculina (on the second male pleopod) is also characterisitic.

Disposition of Specimens: Type specimens were deposited in the US National Museum; male holotype from Church Cave (USNM 195020), Church Cave paratypes (USMN 195021), Wonderland Cave paratypes (USNM 195022).

Ecological Classification: Stygobitic

Size: Total body length in males is 3.1 to 3.9 mm, in females, 3.3 to 4.1mm.

Number of Species in Genus: Three, all stygobitic.

Genus Range:

Species Range: Reported from Church and Wonderland Caves, Hamilton Parish, Bermuda (Bowman & Iliffe, 1983). Also reported from Bitumen and Wilkinson Quarry Caves in Bermuda (Botsaneanu & Iliffe, in preparation).

Closest Related Species: A. aruboides and A. imula have in common reduced segmentation of antennae 1 and 2, a greatly reduced maxilla 2, a maxilliped with a 4-segmented palp, an appendix masculina inserted subterminally, and interrupted marginal setae on the exopod of pleopod 5.

Habitat: Anchialine limestone caves

Ecology: A. aruboides inhabits anchialine lakes in the interior of limestone caves on Bermuda. All specimens were taken from open lake waters of marine salinity and were observed swimming several meters above the bottom, most likely as a food locating action as opposed to an escape mechanism. Specimens were captured at depths of 7-10 m and 10-15 m with the aid of SCUBA and suction bottles. A. aruboides is believed to be a predator, capturing its food from open waters.

Life History: Collected specimens included six males and five females.

Evolutionary Origins: Derived from a marine cirolanid and believed to share a common ancestor with A. imula. Since Bermuda and Aruba are separated by about 1400 miles (2250 km) and water of abyssal depth, dispersal of a small stygobitic isopod from one location to another is considered remote. Origin from a common marine ancestor is more likely, but faces two obstacles: 1) cirolanids are rarely found at abyssal depths and 2) prehensile pereopods (as an adaptation to predation) is known only in hypogean species (Bowman & Iliffe, 1983). The Gulf Stream played an important role in dispersal and speciation in this genus.

Conservation Status: Restricted to Church, Wonderland, Bitumen and Wilkinson Quarry Caves of Bermuda. This species is listed as critically endangered on the IUCN Red List. Wilkinson Quarry Cave is located in an active limestone quarry and is threatened with destruction.

References:

Botosaneanu, L. and J.H. Stock. 1979. Amsterdam expeditions to the West Indian Islands, report 6. Arubolana imula n. gen., n. sp., the first hypogean cirolanid isopod crustacean found in the Lesser Antilles. Bijdragen tot de Dierkunde, 49(2): 227-233.
Bowman, T.E., and T.M. Iliffe. 1983. Bermudalana aruboides, a new genus and species of troglobitic Isopoda (Cirolanidae) from marine caves on Bermuda. Proceedings of the Biological Society of Washington, 96(2): 291-300, 4 figures.
Notenboom, J. 1984. Amsterdam Expeditions to the West Indian Islands, Report 39: Arubolana parvioculata n. sp. (Isopoda, Cirolanidae) from the interstitial of an intermittent river in Jamaica, with notes on A. imula Botosaneanu and Stock and A. aruboides (Bowman and Iliffe). Bijdragen tot de Dierkunde, 54(1): 51-65.