Two new families of amphiboloid gastropods were recently erected, largely due to the very distinct structural and functional configurations of their distal reproductive systems. The spermovipositors in monaulic Salinator spp. (Amphibolidae) are functionally unique in Gastropoda, and it is suggested that they perform both oviposition and sperm transfer/receipt during non-reciprocal copulation. In contrast, the remarkably complex penises in syntremous diaulic Phallomedusa spp. (Phallomedusidae) are used exclusively for sperm transfer during reciprocal copulation. The phallomedusid penis is structurally unique among gastropods because it is protruded by pivoting around a fixed point rather than extending by eversion, and bears elaborate appendages to improve traction during copulation. The complex and functionally ambiguous distal reproductive structures of Maningrida (Maningrididae) differ from other amphibolids in the arrangement and structure of their prostate and copulatory structures. Genital armature of varying complexity occurs in all amphiboloidean families. There may be a correlation between the absence of a long-term sperm storage structure (spermatheca) and the evolutionary diversification of copulatory structures in these gastropods.
Keywords: monauly; non-reciprocal copulation; genital armature; sexual selection