DEEP-SEA PROTOBRANCHIA (BIVALVIA) 



87 



robust shells with lunule & escutcheon 

 long broad continuous hinge 

 large adductors 



P.minuta 



Rfora 



R lenticula 



R abyssorum 



hind gut thru' 

 to left 



Y.curta- 



Y.veletta 



short hinges 



/. 



Y.inconspicua 

 Y.extensa 



Y.argentinea 



fragile shells without lunule & escutcheon 

 separate hinge plates 

 moderately large subequal adductors 



Y.fabula 



subrostrate 

 long hinges 

 small unequal adductors 



's' shaped hind guts 





Y.lucida 

 Y.obesa 

 Y.similiris 



Y.bilanta 



Y.hanna 



Y.capensis 



Y.sinuosa 



Y.blanda 



Y.biscayensis 



single 

 hind gut loop 



Y.perplexa 



Y.pseudolata Y.similis 



/ ovate 



Y.enata 

 Y. Jeffrey si 



1 

 Y.ella 



coils 



loops 



Y.americana 

 Y.subcircularis 

 Y. biguttata 

 Y. ovata 



1 



Y.insculpta 



multiple 

 hind gut loops 

 & coils 



increasing 

 shell height 

 &hind gut length 



Fig. 148 Diagram to show resemblances in shell form of the deep-sea species of the genus Yoldiella found in the Atlantic, arranged in 

 increasing length and complexity of the hindgut and each group of species arranged in increasing depth sequence. 



