IO = intromittent
organ; DCT = dense connective tissue; LCT = loose connective tissue; FR = fin ray.
They are morphologically quite similar--the primary character distinguishing them is differences in the male genitalia, specifically the aedeagus, or intromittent
"Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent
organ is also reversed," Kazunori Yoshizawa from Hokkaido University in Japan said.
Male genitalia/gonopods are intromittent
organs which are widely used in taxonomy on the grounds that they exhibit species-specific characters (Song & Bucheli 2010).
In male teleosts, androgens are an important output of the BPG axis because they stimulate gonadal development, initiate spermatogenesis, provide biofeedback regulation of the BPG axis and regulate the expression of secondary sexual characteristics such as nuptial color changes, behavior, and intromittent
organs (Blazquez et al., 1998; Kodric-Brown, 1998; Grober and Bass, 2002; Yamaguchi et al., 2005; Parikh et al., 2006a; Yamaguchi et al., 2006).
In males, the reproductive system features epididymis, responsible for temporary spermatozoa storage, and intromittent
organs (penis) to transfer gametes to the body of females (ROMER; PARSONS, 1985).
Fertilization is internal and the transfer of sperm may occur indirectly through spermatophores in representatives of the suborder Cyphophthalmi, or directly by means of a long and fully intromittent
male genitalia in the suborders Eupnoi, Dyspnoi, and Laniatores (Machado & Macias-Ordonez 2007).