206 ELOPIFORM FISHES 



shelled invertebrates and the parasphenoid is equipped with large hemispherical 

 teeth which are opposed by similar teeth on the basibranchial plate. 



The pterothrissids have slightly enlarged, conical teeth on the parasphenoid, 

 endopterygoid, basibranchial and basihyal tooth plates. There are generally fewer 

 teeth than in other albuloids ; indeed in Pterothrissus the parasphenoid teeth, although 

 well developed, are confined to the region beneath the parasphenoid ascending wings. 

 The difference in dentition no doubt reflects a difference in diet between the families, 

 the albulids feeding essentially on molluscs and crabs while the Recent pterothrissids 

 prey on the thinner shelled crustaceans. Stomach contents of Pterothrissus gissu 

 taken off the coast of Japan (depth unknown) revealed an almost exclusive diet of 

 caridean malacostracans. 



Crushing dentition, of which one example is seen in the Albulidae, is of relatively 

 rare but repeated occurrence among actinopterygians. The condition is clearly 

 specialized and suited to fishes of a restricted ecological niche. Within the Chon- 

 drostei, such fishes as the Amphicentridae and the Bobasatraniidae have a crushing 

 dentition principally involving occlusion between the pterygoid and coronoid teeth. 

 Bobasatrania has a basibranchial plate with crushing teeth (Nelson 1969a). 



In the Holostei the Pycnodontiformes (and to a lesser degree the Semionotidae) 

 show a crushing dentition developed upon the dentary and the so called ' splenials ' 

 (held to be the result of fusion between the articular, coronoid and splenial, Nursall 

 1964). Unlike the chondrostean examples, the opposing dentition in pycnodonts 

 is borne by the enlarged vomer, which together with the parasphenoid is keyed to 

 the stout ethmoid. These fishes generally have short jaws. 



Among teleosts a crushing dentition is more often developed in various ways 

 within the buccal cavity and pharynx. In Albulidae, Phyllodontidae and Pletho- 

 dontidae the grinding dentition is upon the basibranchium and parasphenoid (some- 

 times also the endopterygoid). Such a development is the result of specialization 

 involving the basic or primary teleostean bite. Pristolepis is unique among acantho- 

 pterygians in showing a toothed parasphenoid opposed by a crushing dentition on the 

 basibranchial complex. However, here a secondarily enlarged basihyal is involved 

 (Nelson 1969a). 



Other teleosts exhibiting a grinding or crushing dentition show specialization of 

 the posterior gill arch elements. Thus, some cyprinids have molariform teeth on the 

 fifth ceratobranchials which work against a callus pad on the ventral surface of the 

 neurocranium. The labroids have opposed upper and lower pharyngeal plates. A 

 development of grinding teeth in the posterior part of the branchial arches is con- 

 comitant upon the possession of a protrusile jaw mechanism and mobile pharyn- 

 geals, the latter correlated with the development of retractores arcuum branchialium 

 muscles. All these features are found in fishes which have lost the primary teleostean 

 bite. 



A crushing dentition has therefore arisen several times and in each case the teeth 

 involved have been determined by the ' evolutionary grade ' ot the fishes concerned. 



Apart from the Phyllodontidae, about which very little is known, some of the 

 plethodonts have a dentition somewhat similar to the Albulidae. This similarity 

 has led to a suggested relationship between these two groups. Woodward (1901) 



