Key to species of Neohexostoma (modified from Millemann [21] and Zambrano [35]):

1. Non-existent separation between the termination of testes and the anterior of haptor........ ... ... ... ... ... ... .... .........2

Remarkable separation between the termination of testes and the anterior of haptor.. .... ..... ... ... ... ... ... .... ......3

2. Clamps similar in size.. ... ... ... ... ........ N. kawakawa

Clamps decreasing backwards in size.. ... .... N. mochimae

3. A strong constriction before haptor.. ... ... ... ... ... ....4

No constriction before haptor.. ... ... ... ... ... ... .... ......5

4. Haptor with a split in its posterior margin.. ... ... ... ... ... ... .... .... .... ...... ... ..... N. gymnosardae

Haptor with a short lappet.. ... ... ... ... ... .... N. thunninae

5. Most posterior pair of clamps approximately one-half the size of anterior pairs.. ... ... ... ... ........ N. extensicaudum

Most posterior pair of clamps slightly smaller than anterior three pairs ..... ... ... ... ... ... ... ... ... ... ... ... ... .... ......6

6. Eggs with two short polar filaments.. ..... N. robustum

Eggs with two long polar filaments.. ... ... ... ... ... .......7

7. Lateral sclerites of clamps straight.. ... ... ..... N. pricei

Lateral sclerites of clamps double-pronged.. ... ... ... ... .... ..... ... ... ... ... ... .... ............ N. euthynni