otoconia From Four New Zealand Chimaeriformes 



K. P. Mulligan, R. W. Gauldie, and R. Thomson 



ABSTRACT: A scanning electron microscopy and 

 x-ray diffraction investigation of chimaeriform oto- 

 liths shows densely packed and strongly bound ag- 

 gregations of otoconia in the form of aragonitic 

 spherulites. Characteristic sizes, shapes, and sur- 

 face features are described for each of the four 

 species investigated. Otoconial diameters differ 

 among species, but the chimaeras are nonetheless a 

 uniform group in terms of otoconia type and otolith 

 shape. 



Members of the Class Chondrichthyes (elasmo- 

 branchs and Chimaeriformes) are known to have 

 otoliths composed of otoconia bound in a protein 

 matrix (Stewart 1903; Iseltoger 1941; Carl- 

 strom 1963; Barber and Emerson 1980). The 

 use of the term otolith in reference to chondrich- 

 thyan fish requires some clarification. There are 

 difficulties in establishing chemical or crystalline 

 homologies between aggregated otoconia and 

 otoliths proper as they occur in teleosts. How- 

 ever, they are similar in being semirigid or rigid 

 structures supported on a hair cell pad and in- 

 volved in sound transduction in both elasmo- 

 branchs and teleosts (Popper and Fay 1977; Fay 

 1983). When homologies are established, a gen- 

 eral term for a crystalline, calcium carbonate 

 structure associated with sound transduction 

 may appear, but until then we will persist in 

 using the term otolith in a more general sense 

 than its derivation implies. 



Studies on the otolith of the chimaera Callor- 

 hynchus milii (Callorhynchidae). which is found 

 in inshore waters of New Zealand, showed that 

 it was composed of fused spherulitic otoconia 

 (Gauldie et al. 1987). Spherulite otoconia were 

 one of three differing forms of otoconia, which 

 were found in the Australian lungfish Neocerato- 

 dusforsteri (Gauldie et al. 1986a), and were sim- 



K. P. Mulligan, Fisheries Research Division, P.O. Box 297, 



Wellington, New Zealand. 



R. W. Gauldie, (to whom reprint requests should be sent). 



Fisheries Research Division, P.O. Box 297, Wellington, New 



Zealand. 



R. Thomson, S.E.M. Facility, V.U.W., Wellington, New 



Zealand. 



ilar to the type of free otoconia found in conjunc- 

 tion with the otoliths of some teleosts (Dale 1976; 

 Gauldie et al. 1986b) and described in some shark 

 species (Carlstrom 1963). 



Spherulitic otoconia fused into otolichs have 

 also been described in humans, occurring in asso- 

 ciation with hereditary deafness (Johnsson et al. 

 1981). Humans normally have only calcitic 

 otoconia similar to those occurring in the lung- 

 fish, but apparently there are still human genes 

 that will code for the spherulitic otoconia. It is 

 tempting to see the widespread distribution of 

 spherulitic otoconia as an indication that they are 

 the most primitive kind of crystalline calcium 

 carbonate secreted by the vertebrate ear. There 

 are strong similarities between the shapes and 

 anatomical arrangement of the otoliths in the 

 chimaera C. millii and the lungfish A^. forsteri, 

 as well as in some of their constituent otoconia. 

 These observations support the suggestion (Pat- 

 terson 1965; Romer 1968) that the modern 

 chimaeras might be descended from ptyctodont 

 placoderms. Thus, apart from the issue of 

 chimaera affinities within the elasmobranchs 

 (Zangerl 1973), the spherulitic otoconia of the 

 chimaeras may hold some clues to the funda- 

 mental mechanism of otolith deposition. 



Several species of deep-water chimaeras occur 

 in New Zealand's waters. Otolith form and struc- 

 ture from the two families Rhinochimaeridae 

 {Harriotta raleighana and Rhinochimaera sp.) 

 and Chimaeridae (Hydrolagus novaezelandiae 

 and Chimaera sp.) are investigated in this 

 paper. 



MATERIALS AND METHODS 



Three specimens of each species — H. ra- 

 leighana, Rhinochimaera sp., H. novaeze- 

 landiae, and Chimaera sp. — were caught in a 

 deep-water trawl survey of the Chatham Rise 

 area, December 1985. Heads were placed in a 

 10% neutral buffered formalin solution for 24 

 hours and transferred to 109c isopropanol until 

 dissection. The preservative solutions remained 

 alkaline during storage time, but after more 



Manuscript accepted February 1989. 

 Fishery Bulletin, U.S. 87: 923-934. 



923 



