Thalassema

Biseswar, Ramlall, 2009, The geographic distribution of echiurans in the Atlantic Ocean (Phylum Echiura), Zootaxa 2222, pp. 17-30 : 22

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