The geographic distribution of echiurans in the Atlantic Ocean (Phylum Echiura) Author Biseswar, Ramlall text Zootaxa 2009 2222 17 30 journal article 10.5281/zenodo.190138 5a2b24d7-5527-4650-96a4-1404035191d2 1175-5326 190138 Key to the species of Thalassema from the Atlantic Ocean 1 Gonoducts two pairs ................................................................................................................................................... 2 - Gonoducts one pair ..................................................................................................................................................... 3 2 Gonostome fan-shaped; papillae arranged in transverse series in middle region of trunk .................. T. philostracum - Gonostomal lips semicircular and frilled, papillae largest and most densely packed in posterior region of trunk, not arranged in transverse series ................................................................................................................ T. thalassemum 3 Anal vesicles lacking; microscopic papillae located only in middle region of trunk ............................ T. antarcticum - Anal vesicles present .................................................................................................................................................. 4 4 Gonostomal lips folded or crumpled; rectal caecum absent ........................................................................ T. elapsum - Gonostomal lips not folded or crumpled .................................................................................................................... 5 5 Interbasal muscle absent; gonostomes large; papillae more closely packed at anterior and posterior ends of trunk .... .............................................................................................................................................................. T. arcassonense - Interbasal muscle present ............................................................................................................................................ 6 6 Integument thin and transparent; papillae small white specks scattered over trunk, more closely arranged at posterior end; rectal caecum absent ......................................................................................................................... T. diaphanes - Integument opaque; papillae prominent, unequal in size, the larger ones scale-like and bent forwards; rectal caecum present ...................................................................................................................................................... .. T. hartmani