Phylum Arthropoda
Subphylum Crustacea
Subclass Copepoda
Order Cyclopoida
Family Cyclopidae
Subfamily Halicyclopinae

Halicyclops ytororoma Lotufo & Rocha, 1993

	Halicyclops ytororoma: habitus, after Rocha & Iliffe, 1993

Taxonomic Characterization: Female: Posterior borders of all body somites denticulate. Genital double somite as long as wide and with small expansions in proximal half. Anal pseudoperculum always deeply notched medially, although with outlines differing in detail. Caudal rami about twice longer than broad. Middle apical setae heterogeneously ornamented. Legs 1-4 spine formula 3, 4, 4, 3. Endopod segment 2 of all legs with only 1 seta. Both inner setae on leg 4 endopod segment 3 spiniform and ornamented similarly to spines. Leg 5 exopod with 3 spines shorter than segment. Male: Expect for sexually dimorphic features in geniculate antennules, 6-segmented urosome and leg 6 represented by inner spine and 2 setae, otherwise as in female (Lotufo & Rocha, 1993).

Disposition of Specimens: Bermuda specimens were deposited in the National Museum of Natural History, Smithsonian Institution, Washington, D.C. (USNM 257020, 257022), and in the Museu de Zoologia da Universidade de São Paulo (11381, 11382).

Ecological Classification: Stygophilic

Size: Female 420-430 microns, prosome:urosome ratio = 1.42-1.54 : 1. Male: 350-385 microns, prosome:urosome ratio = 1.43-1.69 : 1.

Number of Species in Genus: Numerous

Species Range: Known from Walsingham and Bee Pit Caves in Hamilton Parish, Bermuda.

Closest Related Species: Halicyclops ytororoma closely resembles H. gauldi which was recorded from the interstitial water in a beach in Ghana. They are distinguished only by the number of inner setae on the terminal segment of leg 1 exopod (4 setae in H. ytororoma and 3 in H. gauldi) (Lotufo & Rocha, 1993).

Habitat: Anchialine limestone caves

Ecology: Marine, found at 0-4 m depths in cave entrance pools open to daylight and on submerged dimly lit soil slopes.

Life History: Bermuda specimens included 83 females, 101 males and 98 copepodids.

Evolutionary Origins: Halicyclops is a cosmopolitan genus found mainly in coastal brackish waters such as estuaries, lagoons, ponds. marshes, wells, interstitial water in sandy beaches, and cave. Other non-stygobitic species of Halicyclops show a similar wide geographic distribution (Rocha & Iliffe, 1993).

Conservation Status: Restricted to Walsingham and Bee Pit Caves in Hamilton Parish, Bermuda and from sandy beaches in the state of São Paulo, Brazil.

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Contributor: Carlos Eduardo F. da Rocha, Universidade de São Paulo, Brazil