Kearn G C
School of Biological Sciences, University of East Anglia, Norwich, U.K.
Int J Parasitol. 1994 Dec;24(8):1227-71. doi: 10.1016/0020-7519(94)90193-7.
The evolutionary expansion of the monogeneans has taken place in parallel with the diversification of the fish-like vertebrates. In this article the main trends in monogenean evolution are traced from a hypothetical skin-parasitic ancestor on early vertebrates. Special consideration is given to the following topics: early divergence between skin feeders and blood feeders; diversification and specialization of the haptor for attachment to skin; transfer from host to host, viviparity and the success of the gyrodactylids; predation on skin parasites and camouflage; colonization of the buccal and branchial cavities; diversification and specialization of the haptor for attachment to the gills; phoresy in gill parasites; the development of endoparasitism and the origin of the cestodes; the success of dactylogyroidean gill parasites; the uniqueness of the polyopisthocotyleans; ovoviviparity and the colonization of the tetrapods. Host specificity has been the guiding force of coevolution between monogeneans and their vertebrate hosts, but the establishment of monogeneans on unrelated hosts sharing the same environment (host-switching) may have been underestimated. Host-switching has provided significant opportunities for evolutionary change of direction and is probably responsible for the establishment of monogeneans on cephalopod molluscs, on the hippopotamus and possibly on chelonians. There are indications that host-switching may be more common in monogeneans that spread by direct transfer of adults/juveniles from host to host. A limitation on the further expansion of monogeneans is the need for water for the dispersal of the infective larva (oncomiracidium).
单殖吸虫的进化扩张与鱼类样脊椎动物的多样化同时发生。在本文中，单殖吸虫进化的主要趋势是从早期脊椎动物上一种假设的皮肤寄生祖先开始追溯的。特别关注以下主题：皮肤取食者和血液取食者的早期分化；用于附着在皮肤上的钩的多样化和特化；从一个宿主转移到另一个宿主、胎生以及三代虫科的成功；捕食皮肤寄生虫和伪装；口腔和鳃腔的定殖；用于附着在鳃上的钩的多样化和特化；鳃寄生虫的携播；内寄生现象的发展和绦虫的起源；指环虫科鳃寄生虫的成功；多后盘吸虫的独特性；卵胎生和对四足动物的定殖。宿主特异性一直是单殖吸虫与其脊椎动物宿主之间协同进化的指导力量，但单殖吸虫在共享相同环境的不相关宿主上的定殖（宿主转换）可能被低估了。宿主转换为进化方向的改变提供了重要机会，并且可能是单殖吸虫在头足类软体动物、河马以及可能在龟类上定殖的原因。有迹象表明，宿主转换在通过成虫/幼虫从一个宿主直接转移到另一个宿主传播的单殖吸虫中可能更为常见。单殖吸虫进一步扩张的一个限制是感染性幼虫（纤毛幼虫）的扩散需要水。
