摘要:

AbstractBased on a compatative study of the system of lateral line grooven on the paranmchal plate ofArctonemasp. from the Devonian of Spitsbergen and some of the holonematids and cocontents, the conclusion is reached that in these forms, one may have a pontiot “pit‐line” complex coresponding to that developing onlogenelically inPretoptenusamong the dipnoans. Observations on the lateral line system of various ptyctodontids include the following. In Chehophonus the lateral lines of the anterior part of the hend presumably possessed regularly spaced dilatation, resembling those of the corresponding lines in some recent holocephallane In cremurella, where also some new lateral line system components are put on record, the infraorbital canal was in front of the “marginal” plate enclosed in a bony tube, arisen by the fusion of ring‐like elements. In cremurella there is even reason to believe that ontogenetically, the component of the dermal bones formed as series of bony ring‐like elements, similar to they accompansing the lateral lines in fossil and recent holocephalians. In some forms as Chehophonus and Rhynchodus, a distinelly developed profundus lateral line has been identified. The holotype of “Lpipetalu” Gross is refigured and referred to n new ptyctodontid genus,

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1971.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractA small sample of freshwater triclads from streams and pools of the Gebel Marra volcanic massif in the Western Sudan was examined by the author. All specimens showed the general features characteristic of triclads within the “arrow‐headed”Dugesiagroup. The specimens serially examined show a number of less conspicuous features not agreeing with those described in otherDugesiaforms reported from African localities. A description has been given and as a new species nameDugesia sudanicahas been proposed. The new species would, according to the author, represent a further “microspecies” within the “superspecies”Dugesi

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1971.tb00711.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

AbstractBecause the types of hooks are so similar in the oncosphacra/procercoid ef cestodes and in several groups of monogenclic trcmatodes and because the exterior of a procercoid with the hooks in a cercomer is so suggestive of a monogenetic nematode, the development of the procercoids of threeDiphyllobothriumspecies was studied. The intention was to determine whether or not the procercoid protonephridial system would have a developmental stage when its type is similar to, or identical with that type which characterizes the monogeneans. Such a conformity would greatly support the theory of a common origin of monogeneans and ceslodes. However, it has emerged that no similar developmental stage exists. The ontogeny revealed a thorough metamorphosis from a very simple primary protonephridial system (identical with that of the miracidium larva in digeneans) to a secondary system, which develops into the system of the adult tapeworm. This fact may be interpreted as an argument against the supposed inter‐relalionships between monogeneans and cestodes. However, the type of hooks and the procercoid cercomer still indicate common ancestors. An analysis of the miracidium, the oncosphaera and the oncomiracidium (the monogenean larva) with reference to their different developmental stages when hatching, gave rise to my interpretation of the fundamental structure of both the miracidium and the oncosphaera as primitively simple and not reduced, Especially the identical type of protonephridial system indicates. in my view, that digeneans and ceslodes originally had a common larva type. If the ceslodes and the monogeneans have common ancestors, then the procercoid may be interpreted as the ontogenetic recapitulation of a common hook‐armed ancestor, here namedhexucanthoid. This rhabdocoelan creature with six hooks in the cercomer and adapted to an ectocommensalic/ectoparasitic mode of life, is thought to have given rise to the monogeneans, the gyrocotylideans, the amphilinideans and the cestodes. The monogeneans were found to have two fundamentally different types of marginal hooks, and on this basis ihe existence of two different lines of evolution in Monogenea is indica

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1971.tb00712.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY