The ‘Hyena Female’ of Tardigrades and Descriptions of Two New Species of Megastygarctides (Arthrotardigrada: Stygarctidae) from Saudi Arabia

Abstract

From the ARAMCO Northern Area Intertidal Sampling Program in 1982, the authors have studied 22 small vials with tardigrades collected in the Arabian Gulf of Saudi Arabia, revealing a rich tardigrade fauna with a large proportion of currently undescribed species. In total, 12 species of heterotardigrades were recorded from 4 intertidal stations. All specimens were interstitial in sandy intertidal sediments. The recorded Arthrotardigrada comprise 11 species in 3 families and the Echiniscoidea are present with 1 species. This study presents the descriptions of Megastygarctides christinae n. sp. and Megastygarctides gerdae n. sp., two new species of arthrotardigrades displaying unique female genital structures not previously ascribed to tardigrades. The genital ducts of the two seminal receptacles are extended out of the body. In one of the new species, M. christinae n. sp., the extensions consist of two hollow penile-shaped spines with a terminal pore; in the other new species M. gerdae n. sp. the extensions consist of two ovoid cuticular structures, which overlap the six-lobed rosette of the female gonopore. The function of these two structures, located lateral to the female gonopore, is still mysterious, but they may be involved in both copulation and in the insemination of the spermatozoa through the eggshell. The name suggested for this type of female in tardigrades is the ‘tardigrade hyena female’ because of the abnormal size of the external genital structures. The male has a typical heterotardigrade gonopore consisting of a small oval papilla with a crescent-shaped opening, which may not have a function in the insemination of the female with spermatozoa. The two new species are compared with the known species of Megastygarctides.