Identification key for the Western Atlantic species of Acarnus

(Details of spicule set in Table 4)

1a. Three types of megascleres............................................................................. 2

1b. Four or more types of megascleres........................................................................ 3

2a. Megascleres as styles, tylotes, cladotylotes................................................................. 5

2b. Megascleres as tylotes, cladotylotes I and acanthostyles.............................................. A. radovani

3a. Megascleres as styles, tylotes, cladotylotes and acanthostyles.................................................. 4

3b. Megascleres as styles, tylotes, cladotylotes and tylostyles................................ Acarnus tupiniquim sp. nov.

4a. Two categories of cladotylotes.......................................................................... 6

4b. A single category of cladotylotes................................................................. A. souriei

5a. Cladotylotes I spined.................................................................................. 7

5b. Cladotylotes I smooth...................................................................... A. innominatus

6a. Two types of microscleres (toxas and chelae)............................................................... 8

6b. Three types of microscleres (toxas, chelae and microxeas).......................................... A. microxeatus

7a. Two categories of toxas................................................................................ 9

7b. Three categories of toxas........................................................................ A. toxeata

8a. Palmate isochelae <21µm (14.4–21µm)........................................................... A. nicoleae

8b. Palmate isochelae> 21µm (29.2–39.9µm).............................................. Acarnus hooperi sp. nov.

9a. Toxas I (accolada) and II (deeply-curved) present..................................................... A. tortilis

9b. Toxas II (deeply-curved) and III (oxhorn) present.................................................. A. deweerdtae