Stygiomysis cokei Kallmeyer and Carpenter, 1996

Pesce, Giuseppe L. & Iliffe, Thomas M., 2002, New records of cave-dwelling mysids from the Bahamas and Mexico with description of Palaumysis bahamensis n. sp. (Crustacea: Mysidacea), Journal of Natural History 36 (3), pp. 265-278 : 268-270

Stygiomysis cokei Kallmeyer and Carpenter, 1996

Material examined. Yucatan, Mexico: Cenote Pabakal , Eknakan; 25 June 1998; one female (8.5 mm) and one male (7.7 mm), collected with vials from the water column in 20±33 m depths. Cenote San Eduardo, Tecoh; 26 June 1998; two females (7.9, 8.1 mm) and one male (7.7 mm) collected with vials from the water column in 15±27 m depths. Cenote Kankirixche, MucuycheÂ; 1 July 1998; one female (9.1 mm) and one juvenile collected with vials from the water column in 30±50 m depths. Cenote Kankirixche, MucuycheÂ; 19 November 1998; one female (9.0 mm) collected with vials from the water column in 30±50 m depths. Cenote Pabakal, Eknakan; 26 June 1999; two females (8.3, 8.5 mm) collected with vials from the water column in 20±26 m depths. Cenote Dzonot-ila, AbalaÁ; 30 October 1999, two juv. collected with vials from water column in 30-40 m depths. Cenote Pabakal, Eknakan; 31 October 1999; three females (7.9±8.6 mm) and one male (7.9 mm), collected with vials from water column in 20±33 m depths . Quintana Roo, Mexico: Actun Ko , Akumal; 28 June 1999; one female (8.8 mm) and one juvenile collected with vials from the water column in 8±13 m depths .

Remarks. Caroli (1937) created the family Stygiomysidae and the genus Stygiomysis to accommodate material from anchialine cave waters of the Salentine Peninsula (south Italy). The genus Stygiomysis at present includes six described species:

Stygiomysis hydruntina Caroli, 1937 [anchialine and phreatic waters; south Italy] Stygiomysis holthuisi ( Gordon, 1958) [cave waters; Bahamas, Anguilla, St. Martin, Puerto Rico]

Stygiomysis major Bowman, 1976 [cave waters; Jamaica]

Stygiomysis clarkei Bowman , IliOEe and Yager, 1984 [cave waters; Bahamas] Stygiomysis aemete Wagner, 1992 [phreatic waters; Dominican Republic] Stygiomysis cokei Kallmeyer and Carpenter, 1996 [cave waters; Yucatan, Mexico].

Three other undescribed species are known from the Salentine Peninsula (south Italy) ( Pesce, 1975), Quintana Roo, Mexico and Florida, USA (Bowman, in litt.).

The remarkable distribution of Stygiomysis undoubtedly points to a Tethyan origin, all the species of the genus being actually known from the Caribbean and surrounding areas, and south Italy.

Stygiomysis cokei is a large species, well characterized by the unusually long telson and very narrow uropodal protopods. This species was previously known only from caves near Tulum, Quintana Roo, Mexico. Our collections, therefore, considerably extend the range of S. cokei to include four cenotes in the state of Yucatan, located approximately 200 km west of Tulum on the opposite side of the Yucatan Peninsula .

Only minor morphological diOEerences were found in the present material as compared to the original description and illustrations of the species (body length, number of setae on mediodistal margin of the lamella of pleopods 3±5, armature of the uropodal protopod). However, so far little is known about the variability of the species of this genus, and the entire family appears to be remarkably uniform in many features ( Kallmeyer and Carpenter, 1996).

Habitat. Cenote Pabakal (`Mud Stains’) is located about 45 km south-east of Merida, near the village of Eknakan, Yucatan. From the 30-m wide, cave-like entrance to this cenote, a breakdown slope descends to a 30 m wide by 20 m long lake containing large, stalagmitic columns. The eastern passage splits and reaches a maximum depth of 23 m at 140 m penetration. The western passage descends to 30 m depth at 190 m penetration. Also collected from this cave were the cirolanid isopod Yucatalana robustispina Botosaneanu and IliOEe, 1999, copepods, amphipods and thermosbaenaceans.

Cenote San Eduardo is located near the village of Tecoh, 41 km south-east of Merida. This cenote is entered through a dry cave and contains two diOEerent and unconnected underwater caves. The largest of these begins from the main pool on the north side of the cave. From this 15 m wide by 5 m long pool, a breakdown slope ends at a depth of 24 m and penetration of 57 m. On the right side of the pool, a small tunnel continues past several sharp turns to a 30 m diameter, circular room, containing a large air bell at the top. A second pool lies to the south of the entrance. The underwater passage on this side of the cenote is shallower and less extensive.

Cenote Kankirixche (`Yellow Fruit Tree’) is located 49 km south of Merida , near the town of MucuycheÂ, Yucatan. A steep, 15 m entrance slope leads to a large underground lake. Water depths in the entrance area range from 5 to nearly 50 m, while the room is almost circular with a diameter of approximately 90 m. In the south-west corner of the cavern, a low but wide tunnel at 50±53 m water depths passes through a bedding plane that opens onto a chamber, about 90 m long and 45 m wide with a ¯oor to ceiling height of approximately 18 m. Two passages lead out of this room, one of which has been explored to a maximum penetration of 313 m and depth of 53 m. A halocline is present at 50 m depth.

Cenote Dzonot-ila is located 52 km south of Merida , near the town of AbalaÂ, Yucatan. The cenote entrance consists of a rectangular, 12 m deep well shaft, providing access to an underground lake. The largest section of the cave is a 40 m wide by 30 m high passage with a ridge of large breakdown blocks running down the centre and deepest depths along the walls. At the far end of this passage, a small restriction leads to a 30 m wide by 2 m high room containing numerous stalactites and stalagmites. Maximum water depth in the cave is 39 m.

Actun Ko is a large underwater cave system located between Playa del Carmen and Tulum, along the Caribbean coast of the Yucatan Peninsula. The entrance consists of a collapsed sinkhole with a pool running in a semicircle along the margins. This cave has several entrances and several kilometres of explored submerged passages. The halocline in this cave is at about 12±14 m depth.