SUMMARYThe life-cycles of two closely related cephalobaenid pentastomids, Raillietiella gehyrae and Raillietiella frenatus, which utilize geckos as definitive hosts and cockroaches as intermediate hosts, have been investigated in detail. Early development in the fat-body of cockroaches involves 2 moults to an infective, 3rd-stage larva which appears from 42–44 days post-infection. Complete development in geckos involves a further 5 moults in the case of males and 6 for females. Males mature precociously and copulation is a once-in-a-lifetime event which occurs around day 80 post-infection when both sexes are the same size but the uterus of the female is undeveloped. Sperm, stored in the spermathecae, is used to fertilize oocytes which slowly accumulate in the developing saccate uterus. Patency commences when the uterus carries approximately 4000–5500 eggs but only 25–36 % of these contain fully developed primary larvae. Since only mature eggs are deposited, we postulate that the vagina (?) of the female must be equipped with a selective filter that allows through large eggs but retains smaller, immature eggs. Thus the only limit on fecundity is the total number of sperms in the spermathecae and this is precisely the same factor that constrains egg production in the advanced order Porocephalida.

Three large Raillietiella species have been described from a number of snakes in Africa, South East Asia and the Philippine Islands, although the criteria used to distinguish the species are variable and overlapping. As a consequence several authors have expressed doubts concerning the validity of these species. By using more reliable diagnostic criteria, namely hook dimensions and the form of the male copulatory spicule, we show that all three species are valid. They are redescribed and the host lists are amplified and amended. Evidence about the life-cycle is assessed and it is suggested that two or three vertebrates may be involved. Autoreinfection, which was thought to be important in natural transmission, may be linked with pathology of the host induced by trauma associated with captivity.

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Four previously established Raillietiella spp. are redescribed. Two of these, R. kochi and R. shipleyi from African monitor lizards, cannot be reliably separated, R. shipleyi is regarded therefore as a synonym of R. kochi. A new species R. cartagenensis from South American geckos and a skink is differentiated from other sharp-hooked species on the unique form of the male copulatory spicule.The entire genus is assessed in the light of recent evidence and a new set of taxonomic groupings is proposed which is based primarily on host differences. However, 14 species, infecting small insectivorous lizards, are subdivided into two groups because of marked differences in the morphology of the posterior hook, an idea originally outlined by Self (1969). Appropriate combinations of body length, annulus number, posterior hook dimensions and the form of the male copulatory spicule provide adequate diagnostic criteria.Certain species infect a large number of hosts which have a wide range of diet. Since vertebrate intermediate hosts may be involved in the life-cycle it may subsequently transpire, when more sophisticated diagnostic techniques appear, that several species have been grouped together. The genus embraces 24 well characterized species and at least seven others await confirmation.

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