Phylum Arthropoda
Subphylum Crustacea
Class Copepoda
Order Calanoida
Family Epacteriscidae

Balinella yucatanensis Suárez-Morales, Ferrari & Iliffe, 2006

	Balinella yucatanensis: A, female, dorsal view; B, female, lateral; C, male, lateral; after Suárez-Morales et al., 2006

Taxonomic Characterization: Body with a typical calanoid shape, relatively slender, prosome slightly wider anteriorly and widest at first prosome somite. Prosome 5-segmented, while urosome 4-segmented in females, 5-segmented in males. Rostrum wide, rostral points long, curved and visible in lateral view. Caudal rami asymmetrial in females with left ramus 1.3 times longer than right.  Antennules 27-segmented in females; in males, left antennule 25-segmented, right 22-segmented. Males slightly smaller than females; body relatively slender compared to female. B. yucatanensis is distinguished from its only known congener B. ornata from the Bahamas, by the strong asymmetry of the caudal rami in females, a modified left fifth leg of the male in which the proximal and middle exopodal segments are attenuate at the point of origination of the outer spine, and by differences of the armature of mouthparts (Suárez-Morales, Ferrari & Iliffe, 2006).

Disposition of Specimens: Holotype adult female from Cenote Ponderosa deposited in the collection of Zooplankton of El Colegio de la Frontera Sur (ECOSUR) in Chetumal, Mexico under catalogue number ECO-CHZ-02358. Allotype adult male from Cenote Mayan Blue (USNM 1082690) and paratype adult female from Cenote 27 Steps (USNM 1082691) deposited in the National History Museum of Natural History, Smithsonian Institution.

Ecological Classification: Stygobitic

Size: Body length of female 1.45 mm; male 1.39 mm.

Number of Species in Genus: Two

Genus Range: The genus Balinella was originally reported from the Exuma Cays on the Great Bahama Bank (Fosshagen et al., 2001) and Sweetings Cay, near Grand Bahama Island, on the Little Bahama Bank (Fosshagen & Iliffe, 2004).  These two shallow water banks are separated from one another by a deep water channel.  Balinella yucatanensis is the first member of the calanoid family Epacteriscidae to be reported from Mexico.

Species Range: This species has been collected from three anchialine cave systems - Cenote Ponderosa, Cenote Mayan Blue and Cenote 27 Steps - spread over a distance of 40 km along the Caribbean coast of the Yucatan Peninsula.

Closest Related Species: B. yucatanenis is most closely related to its only congener B. ornata inhabiting anchialine caves in the Bahamas.  The genus Balinella resembles Erebonectes and Erebonectoides in retaining many plesiomorphic characters and few reductions and modifications of the mouthparts (Fosshagen et al., 2001).

Habitat: Anchialine limestone caves

Ecology: All specimens were collected by cave divers from below the halocline in saline waters isolated from the sea.  The halocline, separating surface freshwater from underlying salt water, occurs at 12-15 m depth in the three caves where this species was collected.

Life History: 3 adult females and 1 adult male have been collected.

Evolution: Epacteriscid copepods frequently co-occur with remipeds, considered among the oldest crustaceans, suggests an ancient origin for the Epacteriscidae (Fosshagen et al., 2001).  In Yucatan, the presence of the remipede Speleonectes tulumensis and the thermosbaenacean Tulumella unidens in the same area as B. yucatanensis supports an ancient origin and isolation of anchialine fauna in the Yucatan Peninsula.

Conservation Status: Restricted to three caves on the Caribbean coast of the Yucatan Peninsula.

References:

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Contributors: Eduardo Suárez-Morales, El Colegio de la Frontera Sur (ECOSUR), Chetumal, Mexico and Frank D. Ferrari, National Museum of Natural History, Smithsonian Institution