THE HOLOTHURIANS OF THE GULF OF MEXICO 



By Elisabeth Deichmann, Museum of Comparative Zoology, Harvard College 



The holothurians constitute one of the smaller 

 groups of Recent echinoderms. They occur 

 widespread in the sea, ranging from the shores of 

 the Arctic to the greatest depths of the ocean and 

 particularly abundant in the tropical shallow 

 waters, especially in the coral reef zone. They 

 are predominately bottom forms, though a few 

 are adapted for an exclusive pelagic mode of life, 

 and some have been observed actively swimming. 



Except for the larger members of the order 

 they are less likely to be noticed than other 

 echinoderms. For one thing they have thoroughly 

 masked their original five-rayed structure by 

 developing a secondary bilaterality, with a strong 

 muscular system and reduction — in most forms — 

 of the calcareous skeleton; hence they can con- 

 tract into shapeless lumps or seek shelter in narrow 

 crevices or burrow in sand or mud. In addition, 

 many species dissolve into slime when taken out 

 of water, so it is certain that many specimens 

 never reach the museum collections, even if a 

 careful collector has succeeded in capturing them. 

 It is sometimes difficult to give good description 

 of these forms as their bodies so often are con- 

 torted when preserved; also, the number of tube 

 feet frequently increases with age, and the spicules 

 in the skin are apt to undergo profound changes 

 during the animal's life. One finds, therefore, 

 the older literature cluttered with worthless 

 species, based on poorly preserved specimens or 

 immature or aged individuals. 



The West Indian region is considered one of the 

 best explored in the world, but our knowledge of 

 the distribution of the holothurians there is still 

 incomplete, and this is particularly true of the 

 northern section — the Gulf of Mexico. In some 

 respects this is an advantage as the worker can 

 begin with a clean slate, free from old records of 

 species which impossibly could have been col- 

 lected there. 



During the last 20 j'ears there has been an 

 increasing interest in the biology of the Gulf area. 



and material of holothurians has steadily been 

 coming in to the Museum of Comparative Zoology, 

 Harvard College, for identification. It may be 

 worth noting that the only new shallow water 

 dendrochirote added to the West Indian fauna 

 since 1930 came from Louisiana; also, that the 

 Atlantis expeditions around Cuba have added a 

 number of new species (or species new to the 

 region), and some of these extend their range into 

 the Gulf area along the north coast of Cuba. 



Biologically, one can roughly divide the area 

 under consideration into two zones: the shallow 

 water zone, from shore down to about 200 fath- 

 oms — about as deep as one possibly can dredge 

 with a small boat — and the deep water zone which 

 demands a specially equipped vessel with compli- 

 cated collecting apparatus. The shallow water 

 zone can again be divided into the southern part 

 with coral reefs, that is, the southern part of 

 Florida, the north coast of Cuba, and Yucatan — 

 with a comparatively rich and diversified holothu- 

 rian fauna — and the barren sandy or muddy 

 stretches along the eastern shores of Mexico, the 

 Gulf States, and most of the western coast of 

 Florida. This region is characterized by an im- 

 poverished fauna of burrowing forms which in 

 suitable sheltered localities may occur in large 

 numbers. For the whole shallow water area one 

 can predict that the fauna may change locally 

 from year to year as it undoubtedly does in other 

 parts of the West Indies. The hurricanes may 

 play havoc with large areas both in the southern 

 coral reef region and along the endless stretches 

 of mud flats and sand bars which festoon the 

 northern part of the Gulf, and it may take several 

 years before larvae from individuals living at 

 greater and more secure depths have been able 

 to settle down and re-populate a denuded area 

 again. 



The deep water zone will probably prove to 

 consist of two areas, the vast muddy expanses, 

 mostly inhabited by Elasipoda which are adapted 



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