ECHINODERIDA OF THE GULF OF MEXICO 



By B. G. Chitwood, formerly. Department oj Biology, The Catholic University of America 



These are small (0.2-1.0 mm. long) worms pre- 

 senting a gross similarity to crustaceans, but the 

 body cavity corresponds to a blastocoele. The 

 body is ventrally flattened, covered with a cuticu- 

 lar exoskeleton consisting of 13-14 segments. 

 Segmentation also extends to the musculature and 

 nervous system. The cuticle bears large, seg- 

 mentally distributed, nonretractile setae and 

 minute spines in scattered or regular arrangement. 

 The mouth is terminal; alimentary canal straight, 

 consisting of mouth, pharjTix, esophagus, mid-gut, 

 rectum, and terminal anus. The first segment of 

 the body takes the form of a retractile proboscis 

 armed with hooks and spines. The pharynx has 

 a round lumen, cuticular lining, low cuboidal 

 cellular layer, and external layer of cii-cular 

 muscles; esophagus and mid-gut are simple, non- 

 ciliated; small salivary glands are attached to the 

 esophagus. 



The body musculature is rather complex, circu- 

 lar muscles being present only in the second 

 zonite. In the remainder of the body the muscles 

 extend from zonite to zonite through the body 

 cavity, usually being attached only at the ends. 

 The nervous system consists of a bilobed dorsal 

 ganglion, paired commissures, and a double ven- 

 tral nerve trunk with segmentally arranged 

 ganglia. The body cavity is without epithelium. 

 The excretory system consists of a single pair of 

 simple protonephridia opening on the tenth zonite. 

 Gonads are paired, sac-like, with paired sex open- 

 ings on the thirteenth zonite. Sexes are separate. 



Specialized copulatory bristles are present in the 

 male. Development includes minor changes in 

 external structure and at least one molt. 



These organisms are found in bottom sand 

 feeding on algae or in the slime on crabs and 

 mollusks. Remane (1936) has given a thorough 

 summary of our knowledge of this group. 



Systematically, they present an interesting 

 paradox since they show similarities to nematodes, 

 gordiid larvae, gastrotrichs, and Crustacea. They 

 are usually placed with the unsegmented worms 

 (i. e., Subkingdom Scolecida, or Vermes Amera) on 

 the assumption that they are pseudo-segmented . 

 More thorough study of the embryology and 

 post-embryonic development would appear war- 

 ranted. 



Only four species have been reported from 

 North America. These include Pycnophges Jre- 

 quens, Trachydemus mainensis, and Echinoderella 

 remanei reported by Blake (1930) from Maine and 

 Echinoderella steineri reported by the writer (1951) 

 from Aransas Bay, Texas. 



LITERATURE CITED 



Blake, C. H. 



1930. Three new species of worms belonging to the Order 

 Echinodera. Publications of the Biol. Survey of The 

 Mount Desert Region, 10 pp. 

 Chitwood, B. G. 



1951. Echinoderella steineri new species {Scolecida 

 echinodera). Texas Jour. Sci. 3 (1): 113-114. 

 Remane, A. 



1936. Kinorhyncha. Bronn's Klassen u. Ordnung des 

 Tierreichs 4 (2) : 242-385. 



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