瓢形蛤类的系统分类问题

REMARKS ON THE TAXONOMIC POSITION OF MODIOMORPHIDS (BIVALVIA )

瓢形蛤目(Modiomorphoida)系Newell(1969)所建,被置于古异齿亚纲(Palaeo—heterodonta),包括两个超科:瓢形蛤超科(Modiomorphacea)和圆壳蛤超科(Cyclocon-chacea)。Newell当时就承认此目是异源的,显然包括了许多不同类群的祖先,只是为了方便才将它们放到一起。后来片齿蛤科(Lamellodontidae)被证明是腕足类。

There is apparently no consensus on the definition and taxonomic composition of the Modiomorphidae. The more traditional view has been to unite Devonian Modiomorpha with Ordovician modiolopsids so that the family name Modiolopidae has been rejected as a junior subjective synonym of the Modiomorphidae (LaRocque and Newell ,1969;Bailey, 1983,Pojeta et al. , 1986;Carter, 1990;Johnston,1993;Liljedahl, 1994). However,Fang and Morris(1996) were of quite different opinion. Here some problems concerning the separation of Modiomorpha from the Modiolopsacea and of the Modiomorphidae from the Carditacea are discussed.The Modiomorphidae,under the name Permophoridae has long been placed in the super-family Carditacea of the Heterodonta and postulated as the ancestor of carditids, while the genus Modiomorpha has been assigned to another subclass owing to inadequate information about its internal features,especially the ligament structure. This is why the investigation of the relationships between them was long hindered. The Devonian Modiomorpha and such like occupy and intermediate morphological position between the Ordovician Modiolodontidae and the post -Devonian Permophoridae,but has closer relations with the latter.The similarity of the Modiomorphidae( = Permophoridae)to the Carditidae is apparently superficial and may be due to convergence. In brief, it is difficult to discern close phylogenctic relationship between carditids and modiomorphids. The true relationship of the latter is with the Anomalodesmata (Morris , 1978; Waller, 1990; Morris et al. , 1991; Johnston, 1993; Fang and Morris, 1996).