Stygiomysis holthuisi ( Gordon, 1958 )

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 : 271-272

Stygiomysis holthuisi ( Gordon, 1958)

(®gures 5, 6)

Material examined. Quintana Roo, Mexico: Cenote Maya Blue , Tulum; 13 March 1994, one immature specimen (female?) collected with vial from the water column in 15±20 m depths. Casa Cenote , Tulum; 14 January 1996; one female (7.1 mm) collected with plankton net from 6±8 m depths (halocline at 7 m). Yucatan, Mexico: Cenote MucuycheÂ, MucuycheÂ; 4 July 1999; eight females (5.5±6.7 mm), three males (4.5 ±5.9 mm) and three juveniles collected with plankton net from water column in 20±37 m depths.

Remarks. Described by Gordon (1958) to accommodate material from groundwaters of Devil’s Hole ( St. Martin, Lesser Antilles), Stygiomysis holthusi has been successively collected from several localities in the Caribbean, namely Puerto Rico ( Bowman, 1976), Anguilla ( Botosaneanu, 1980) and Grand Bahama Island ( Bowman et al., 1984). The present discovery in Yucatan ( Mexico) greatly extends the known distribution range of the species. Two of the Yucatan collection sites are located along the Caribbean coast, while another is from near the opposite side of the Peninsula in the state of Yucatan.

The material from Yucatan shows good agreement with Gordon’s description and illustrations, as well as with the other descriptions from Puerto Rico, Anguilla, and Grand Bahama, with respects to the main characters that distinguish S. holthuisi from the other congeners.

In the following description only the main diOEerences as compared to the original and the subsequent descriptions are reported. Telson slightly longer than wide (®gure 5) (vs nearly as wide as long in Gordon’s description; slightly longer than wide in specimens from Anguilla, Grand Bahama and Puerto Rico); two to four short spines ®ll the gaps between lateral and median apical spine groups (vs four to ®ve spines in Gordon’ s description; three in specimens from Anguilla, Grand Bahama and Puerto Rico).

Antennal ¯agellum 13- or 14-segmented (vs 16±18 in Gordon’s description; no information is available for material from other localities); antennular ¯agella subequal in length, both inner and outer ¯agella 17- or 18-segmented (vs inner ¯agellum 28-segmented, outer ¯agellum 16/18-segmente d).

Male second pleopod less setulose than in the original and following descriptions and ®gures.

Backward prolongation of the uropod protopod (®gure 6) with ®ve strong apical and subapical spines and two to three thin setules on the outer margin; inner margin armed with two to three spinules and four strong spines (vs the same margin armed with row of spinules interrupted by one or two stouter spines in Gordon’s description and ®gures; more spines on the same margin and lacking the outer subapical setula in specimens from Grand Bahamas).

The propod of uropod armature and the construction and spinulation of the telson could justify recognition of the specimens from Yucatan as a distinct species or subspecies. However, until enough material is available to determine the variability of S. holthuisi , we consider the Yucatan, Anguilla, Grand Bahama, Puerto Rico and St. Martin specimens to be conspeci®c. Planned DNA work on these populations could better determine their eOEective reproductive and genetic separation.

Habitat. Cenote Mayan Blue is located about 5 km inland from the Caribbean coast, about 3 km south of Tulum Pueblo, Yucatan. Primary orientation of this 15.5 km long cave is perpendicular to the coast suggesting that it serves as a major freshwater drainage conduit to the sea. Cave passages are predominantly developed at the halocline in 15 m water depths where mixing corrosion between fresh and salt water occurs. Water above the halocline averages less than 2 g /l salinity, while below the abrupt halocline at 18 m depth, salinity is 35 g /l. Shrimp [ Typhlatya spp. and Creaseria morleyi ( Creaser, 1936) ], remipedes ( Speleonectes tulumensis Yager, 1987 ), ostracods ( Danielopolina mexicana Kornicker and IliOEe, 1989 and Spelaeoecia mayan Kornicker and IliOEe, 1989), thermosbaenaceans ( Tulumella unidens Bowman and IliOEe, 1988), mysids ( Antromysis cenotensis Creaser, 1936 ), amphipods ( Tuluweckelia cernua Holsinger, 1990 ), isopods [ Bahalana mayana Bowman, 1987 and Creaseriella anops ( Creaser, 1936) ] and ®sh [ Ogilbia pearsei (Hubbs, 1938) ] inhabit the cave (IliOEe, 1993).

Casa Cenote is located about 10 km north of Tulum Pueblo, Yucatan. It connects directly to the Caribbean Sea and is the resurgence for Systema Nohoch Nah Chich, one of the longest underwater caves in the world. Haloclines in this cave are at about 8±10 m depth.

Cenote Mucuyche is located within the ruins of a hacienda in the village of MucuycheÂ, Yucatan. The crescent-shaped sinkhole entrance is approximately 30 m long by 15 m across. A breakdown slope with a ¯ight of steps descends to a 30 m long by 10 m wide, gravel and rock ¯oored pool. Against the far bedrock wall, a narrow hole at 5 m depth opens into a 50 m long, 10 m wide breakdown chamber that angles diagonally down to 30 m depth. At this point, a vertical breakdown shaft ascends to 15 m depth before choking oOE. Also collected from the cave were copepods, mysids ( Antromysis cenotensis ), thermosbaenaceans, amphipods and isopods [ Creaseriella anops ( Creaser, 1936) ].