GULF OF MEXICO 



383 



into the body cavity. As it often is impossible to 

 bring back the large individuals one can make a 

 note of their length and width, color, arrangement 

 of tube feet, papOlae, or other features, and 

 preserve some pieces of the skin with a tag tied to 

 it; one should take a skin sample from the dorsal 

 side as well as from the ventrum as the spicules 

 often are quite different in these two regions. 

 Formalin must never be used as it dissolves the 

 spicules and makes the tissue soft. 



The gross anatomical features can be found 

 listed in almost any zoological textbook. For ex- 

 amination of the spicules one places a small piece 

 of skin on a slide, noting whether it is from dox-sal 

 or ventral side, or elsewhere, and after most of 

 the alcohol has evaporated one adds a few drops 

 of fresh chlorox or zonitc or a similar chlorine 

 bleaching compound. It pays to follow the dis- 

 integration of the tissue to estimate the position 

 of the different types of spicules. Often one can 

 get the outer spicules off by placing the skin with 

 the outer side downward in the liquid for a short 

 time. This is of special advantage when the 

 external spicules are small or so few that they 

 easily disappear among those of the deeper layer. 

 Special preparations may often be made of the 

 tube feet to ascertain whether an end plate or a 

 trace of such is present, and how the walls are 



armed; many times juvenile spicules are retained 

 near the tip of papillae. In the dendrochirota the 

 introvert, the retractile thin-skinned part behind 

 the tentacles, contains usually characteristic 

 spicules, as do also the tentacles. The size of tlie 

 animal must be noted since there often is con- 

 siderable difference in the size and shape of the 

 spicules in the young and the aged individuals. 

 In some forms the spicules are reduced with age 

 and may become completely resorbed; in others, 

 they grow heavier and more complex. 



Extremely small individuals,a few millimeters 

 long, are often difficult to identify. Sometimes 

 they have still only simple perforated plates, and 

 when the first typical spicules appear they are 

 in many forms scaled down to the animal's size. 

 In some forms there is a period during which the 

 spicules are excessively large, and these spicules 

 may be foimd preserved near the tip of the papillae 

 when they have disappeared in other places. 



Permanent slides can be made by rinsing off 

 the chlorine solution with distilled water and 

 letting the slide go through alcohol-xylol-balsam. 

 Great care must be exercised not to have the slides 

 contaminated with spicules from earlier prepara- 

 tions. With important specimens it is wise to 

 use a new eye dropper and a fresh bottle of chlorine 

 solution. 



KEY TO THE ORDERS 



1. Animals with disk-shaped tentacles 2 



1 . Animals not with disk-shaped tentacles 3 



2. No respiratory trees present. Exclusively deep water forms 1. Elasipoda, p. 383 



2. Respiratory trees present. Shallow water to deep water forms 2. Aspidochirota, p. 384 



.3. Tentacles dendritic, 10 to 20 in number; numerous tube feet. Plankton feeders. Clings to the substratum or buried 



in mud or sand, except for the tentacles and the anal end 3. Dendrochirota, p. 394 



3. Tentacles not dendritic, feather-shaped or with few lateral digits 4 



4. Tentacles 15, small, in a terminal circle, with few digits. Tube feet reduced to anal papillae. Body barrel-shaped 



with a shorter or longer "tail." Burrows in mud 4. Molpadonia, p. 405 



4. Tentacles 10 (or 12-13) with few to many digits, sometimes feather-shaped. Tube feet totally lacking. Body 

 worm-like often able to contract transversely so the hind end drops off (may later be regenerated). Among coral 

 fragments or burrowing in sand or mud 5. Apoda, p. 406 



Order 1 ELASIPODA 



In the Gulf of Mexico only three representatives 

 have so far been taken of this remarkable order 

 which first became known when the Challenger 

 explored the deepest parts of the oceans in the 

 1870's. On the whole, one can say that the deeper 

 parts of the Gulf of Mexico represent a true 



"Mediterranean" type of water body, with few 

 species, but nevertheless one may expect almost 

 any species known from the Atlantic Ocean. In 

 case other species than those listed below should 

 be found, it will be necessary to consult more ex- 

 tensive reports, such as Mortensen's, The Echino- 

 derms of the British Isles, 1927, or Deichmann's 

 1930 and 1940 papers. 



