Putative mating plugs of harvestmen (Opiliones, Laniatores)

Abstract

In many species of scorpions (Order Scorpiones) and spiders (Order Araneae), mating plugs (gel-like or sclerotized) are deposited in the female reproductive tract, minimizing the possibilities of further matings. Although harvestmen (Order Opiliones) have direct sperm transfer via copulatory organs (penis or spermatopositor in the male and ovipositor in the female), prior studies of the reproductive anatomy of these arachnids have not reported the occurrence of these structures. With the aid of scanning electron microscopy, we observed distinct masses of amorphous, gel-like material in the distal openings of the ovipositors of six different specimens including representatives of the families Cosmetidae (Cynorta marginalis and Flirtea picta), Gonyleptidae (Discocyrtulus bresslaui and Geraeocormobius sylvarum), Kimulidae (Kimula sp.) and Metasarcidae (Metasarcus clavifemur). Dissection of one of these structures from a specimen of the cosmetid harvestman C. marginalis revealed a detailed endocast of the internal surfaces of the female reproductive tract. Considerable interspecific variation in the relative sizes and shapes (smooth and rough) of the amorphous gel-like structures were observed, but evidence of sclerotized components (i.e., parts of the male genitalia) was not found. The location and morphology of the gel-like structures are consistent with observations of mating plugs in other arachnids. The composition, source (male, female or both) and function of these amorphous gel-like structures (i.e. effective matting plug) requires additional study.