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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



great depths in more southern waters, and for 

 this reason some of the papers cited may be of 

 use in identification of species in the Gulf region. 

 The littoral and very shallow water ostracods of 

 the Gulf of Mexico have scarcely been studied, 

 but judging from the small amount of work which 

 has been done on this ecological realm (Tressler 

 1940; Tressler and Smith, 1948), the so-called 

 "barren zone" of Rothwell, lying between the 

 strand and about 20 meters depth, should furnish 

 many species. 



ECOLOGY 



With the limited data available little can be 

 said of the ecological relationships of the species 

 known from this region, and most of this is 

 dependent upon Rothwell's information which he 

 has kindly placed at the author's disposal. 



Only 56 species of marine ostracods have been 

 reported from the Gulf of Mexico proper and 19 

 additional species from the West Indies, Carib- 

 bean Sea, and adjacent areas. Most of these 

 species have been reported from the northwest 

 sector of the Gulf. 



Rothwell divided the region of the Gulf in 

 which he was working into five zones based upon 

 depth and on the nature of the shelf area, as 

 follows: (1) a Barren Zone between 10 and 24 

 meters depth, (2) the Marginal Shelf Zone be- 

 tween 24 and 68 meters, (3) the Upper Conti- 

 nental Slope between 68 and 190 meters, (4) the 

 Lower Continental Slope between 190 and 1,250 

 meters, and (5) the Deep Sea Zone beyond 1,250 

 meters depth. If we examine the ostracods for 

 which depth data are available, we find that 10 

 out of the 12 species reported from near Tortugas 

 are in the "Barren Zone." This anomaly may 

 be explained by the fact that Rothwell's samples 

 were all taken with small-diameter punch coring 

 devices or by small bottom samplers; sampling by 

 means of a dredge over a greater area of the 

 bottom would undoubtedly have recovered as 

 many species of ostracods in the shallower water 

 as were found in the beach samples at Beaufort 

 (Tressler 1940) and in shallow water at Solo- 

 mon's, Maryland (Tressler and Smith, 1948). 

 The species fount! in the barren zone included 

 Cytherura lineata, Loxoconcha ekijanft, Cytherideis 

 silicula and Paradoxstoma ensiforme in the north- 

 west sector and the following from Tortugas: 

 Cypridina .squamosa, Astenrpe mariae, Anterope 



elliptica, Cyclasterope tripla, Cyclasterope sphaerica, 

 Pontocypris intermedia, Macrocypris africana, Mac- 

 rocypris schmitti, Nesidea cushmani, Xestoleberis 

 punctata. 



No species was found exclusively in the Mar- 

 ginal Shelf Zone, but a number of forms were 

 found only in this region and in the adjacent 

 Upper Continental Slope down to 190 meters. 

 These included Paracytherois jlexuosa, Cytherella 

 polita, Macrocypris similis, Paradoxstoma ensi- 

 forme, and Cytherei.s .silicula. 



Ostracoda which were found in the two preced- 

 ing zones and in the Lower Continental Slope 

 Zone as well as down to a depth of 1,250 meters 

 included Anjilloecia cylindrica, Macrocypris decora, 

 Cytherella obtusata, and Cythereis margaritifera. 



Five species were confined to the Lower Con- 

 tinental Slope and the Deep Sea Zones. These 

 are Ne.sidea mctrix, Krithe tumida, Pontocypris 

 trigonella, Xe.stoleberis expan-sa, and Cypridina 

 fialus. Four species were found only in the Deep 

 Sea area: Nesidea ovata, Bythocypris bosquetiana, 

 Macrocypris tumida, and Pseudocythere caudata. 



The deepest station at which ostracods were 

 collected was 3,630 meters located southeast of 

 B'-ownsvillc; two species were found here, Krithe 

 tumida and Xestoleberis expansa. Several species 

 were, however, found at depths below 3,000 

 meters. These included, besides the two men- 

 tioned above, Cythereis echinata (3,157 meters), 

 Cythereis erica (3,220 meters), Cythereis stolonifera 

 (3,246 meters), Cythereis dictyon (3,475 meters), 

 and Cytheropteron mucronalatum (3,431 meters). 



With the exception of the genus Conchoecia, rep- 

 resented by one species, C. atlantica from Tortu- 

 gas, and the males of the genus Asterope {A. 

 mariae and A. elliptica) also from Tortugas, all 

 the ostracods so far reported from the Gulf of 

 Mexico are bottom-dwelling forms. Conchoecia is 

 a true pelagic species and one of the very few 

 found among the Ostracoda. The females of the 

 genus Asterope keep close to the bottom, whereas 

 the males are active swimmers and ascend to the 

 surface where they are often taken in plankton 

 catches. The nature of the bottom sediments on 

 which the Ostracoda of the Gulf of Mexico are 

 found varies considerably with the area, depth, 

 and the species of ostracod, but unfortunately, for 

 security reasons this subject cannot be discussed 

 within the limits of this report. 



