in described on the basis of eight syntype specimens (six atokous and two heteronereis) collected in Bahia Chetumal, Mexican Caribbean coast, and the variability in the paragnath numbers in the pharynx is established using 180 specimens; paragnath numbers are I:10(SD=1.9); 11:30 (SD=2.6); III:41 (SD=5.2); IV:29 (SD=3.5), V:I, VI:4, VII-VIII: >30.
Syntypes were deposited as follows: two atokous specimens in the Museum National d'Histoire Naturelle, Paris, one atokous specimen in The Natural History Museum, London, one atokous specimen in the Zoological Museum of the University of Copenhagen, one atokous specimen in the Naturhistorischen Museum, Vienna, and three specimens (one atokous and two heteronereis) in the Reference Collection of ECOSUR.
Material examined: Mexico, Mexican Caribbean toast, Bahia Chetumal, 24 September 1999, eight syntypes: six atokous and two heteronereis. Another 180 complete specimens were studied in order to evaluate the variability in paragnath numbers in the pharynx, they were collected in the same locality in different dates (26 in June, 21 in July, 20 in August, 26 in September, and 87 in October).
Description heteronereis: male syntype complete, female incomplete (ECOSUR NERE-S000), both with everted pharynx; male is 9.2 mm long, 2.3 mm wide, with 67 setigers, female is 15 mm long, 2.1 mm wide, with 61 setigers; body cream with pigmentation over the anterior one-third of the body.
Heteronereis were found during April, May, June, September and October.
Even in heteronereis, these species differ as shown in table 3.
pelagica I 6-16 9-18 1-2 III 41 36-68 11-19 V 1 1 0 VII-VIII 2 lines 2 lines 3 lines VII-VIII cones Large Medium size Large and medium Ligules Blunt Subtriangular Globose Tentacular Setiger 9-12 Setiger 3-10 Setiger 5 cirri reaches TABLE 3 Differences between the heteronereis stage of N.