Towards identification of the ecological lifestyle in nektonic squid using statolith morphometry

Abstract

Nine morphometric parameters of statolith parts were studied in eight nektonic squid having different lifestyles: Berryteuthis magister, Berryteuthis anonychus, Gonatus berryi, Gonatus fabricii, Gonatopsis borealis (all Gonatidae), Loligo gahi (Loliginidae), Todarodes sagittatus (Ommastrephidae) and Moroteuthis ingens (Onychoteuthidae). Five parameters (indices of the free part of the rostrum, wing length and width, rostrum width relative to total statolith length and total statolith length relative to mantle length) were found to be specific for near-bottom versus pelagic species in all families studied; one parameter (index of dorsal dome length) was highly conservative among all gonatids. Possible reasons for such patterns among the indices are discussed based on current understanding of statolith function. Analysis of both morphological and morphometric parameters of statoliths allows inferences to be made about the ecological lifestyle of both Recent and extinct species of squid belonging to the same family. Using these parameters, it is suggested that an extinct species of Berryteuthis identified from Pliocene deposits in California had a lifestyle intermediate between the near-bottom B. magister and its more pelagic counter-part B. anonychus. Statoliths of another extinct squid, Moroteuthis addicotti, resembled both in shape and size those of young B. magister, suggesting the possibility that M. addicotti is a synonym of Berryteuthis sp.