MULLIGAN ET AL.: OTOCONIA FROM FOUR NEW ZEALAND CHIMAERIFORMES 



otoconia may have been due to incremental 

 growth. It was similar to the layered appearance 

 of the lungfish otoconia (Gauldie et al. 1987) and 

 to the layered appearance of statoconia in some 

 mollusc species (Geuze 1968). If there was incre- 

 mental growth of the otoconia, it indicates that, 

 even at the most primitive level, the calcium 

 metabolism of the inner ear has a definite perio- 

 dicity. However, there is a major difference be- 

 tween the growth process of otoconia in the 

 chimaera and that of statoconia in the mollusc 

 (Kuzirian et al. 1981): the aragonitic otoconia of 

 the chimaera obviously grows (and fuses into an 

 otolith) in situ. The otoconia of the chimaera 

 otolith often showed small surface crystals that 

 apparently fuse together, implying continuous 

 growth in situ, which is characteristic of teleost 

 otoliths. 



It can be assumed that a rigid otohth is re- 

 quu'ed if the otohth functions as a sound trans- 

 ducer (Fay 1983) and that, in contrast, a loose 

 aggregation of otoconia serves as a tilt, or 

 angular momentum detection mechanism 

 (Marmo 1983). The otoliths of the four species 

 described here are rigid in comparison to those 

 of C. milii (Gauldie et al. 1987), less rigid than 

 the lungfish otoliths (Gauldie et al. 1986), and 

 much more rigid than the loose and friable ag- 

 gi'egations of otoconia that occur in most sharks 

 and rays (Mulligan and Gauldie 1989). One might 

 therefore conclude from our observations that 

 the otoliths of chimaerids were functionally at a 

 stage between a rigid sound transducer of the 

 teleost type (which is found also in the lungfish) 

 and an angular momentum detection mechanism. 



The presence of spindle-shaped aragonite 

 crystals in the otolith oi Chimaera sp. is a partic- 

 ularly interesting observation because boih 

 spindle-shaped and spherule-shaped aragonite 

 otoconia occur together with calcite crystals in 

 the lungfish otolith. "Aragonite spherule" 

 otoconia have also been described for the primi- 

 tive shark Heptanchus cinereus (Nishio 1926) 

 and have been observed (Mulligan and Gauldie 

 1989) in the related Heptranchias perlo of New 

 Zealand waters. Furthermore, aggregated 

 spherulitic otoconia have been observed in 

 humans with congenital hearing disorders 

 (Johnsson et al. 1981) and are difficult to distin- 

 guish visually from otoconial aggregations in 

 chimaeras and some teleosts (Gauldie et al. 

 1986b). 



It is tempting to see parallels between the 

 otoconia of chimaeras, lungfish, and primitive 

 sharks. However, the nature of evolutionary 



processes (particularly convergence processes) 

 does not allow simple extrapolation of "primi- 

 tive" features, and hence phylogenetic recon- 

 struction, from modern species (Cain 1983). This 

 is particularly true when the physiological ef- 

 fects of otoconia types on inner ear function are 

 completely unknown. However, it is clear that 

 the spherulitic otoconia and otic organization of 

 chimaeriform fish have chemical and anatomical 

 parallels with the inner ear of teleost fish in the 

 orders Cheilodactylidae, Moridae, Gadidae, 

 Balistidae, and Gempylidae; with some sharks; 

 and, rarely, with humans. The occurrence of 

 spindle shaped aragonite otoconia in conjunction 

 with spherule otoconia has a parallel in the oto- 

 conia of the lungfish. Such similarities makes it 

 very difficult to assign any taxonomic value to 

 otoconia types. Perhaps spherulitic otoconia rep- 

 resent one of very few successful calcium carbon- 

 ate matrix/mineralization systems which con- 

 verge in so many vertebrates simply because 

 there are so few alternatives. 



ACKNOWLEDGMENTS 



We are indebted to Brent Fry of the New 

 Zealand Geological Survey for his assistance 

 with x-ray diffraction. 



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