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; Page 70 THE VELIGER Vol. 8; No. 2 The Mitridae of Fiji BY WALTER OLIVER CERNOHORSKY Vatukoula, Fiji (Plates 13 to 23; 11 Text figures; 1 Map) Table of Contents The actual occurrence of mitrid species in Fiji is rather difficult to evaluate from unillustrated faunal lists, or Introduction 70 accounts which lack bibliographic annotations. A species Habitat and variation 70 may have been interpreted by subsequent authors in a Diagnostic characters 72 different way than was actually intended by the original The animal 72 describer. The collection of additional material, however, Genera of Mitridae 75 may very well contain species presently treated as uncon- Taxonomy 75 firmed reports. Bibliography 76 The majority of species have an Indo-West Pacific Methods and observations 77 distribution, ranging from the Red Sea and Persian Gult Acknowledgments 78 throughout the Indian and Pacific Oceans to Polynesia Index of species 79 and Hawaii ; only a few species are confined to the Pacific, Description of species of Mitra 81 while two species reach as far as Clipperton Island. Description of species of Strigatella . .109 Notes on the geography of the Fiji Islands and other Description of species of F^;ifz7/w7n 115 pertinent data have been given in a previous publication Description of species of Pusia 142 (Cernohorsky, 1964). Description of species of Pferyozfl 151 Description of species of Imbricaria 153 Description of species of Swainsonia 154 HABITAT AND VARIATION Unconfirmed reports of Mitridae from Fiji . 156 Members of the family Mitridae are mostly tropical, and Fossil records of Mitridae from Fiji 157 species of the various generic groups occupy a distinct Conclusion 157 ecological niche in Fiji waters, and possibly elsewhere. Literature cited 158 About 45% of all species recorded from Fiji are sand- burrowers, inhabiting sand banks and sandy lagoons with an average amount of sea-weed substrate. The INTRODUCTION remaining species are found under coral boulders, exposed This faunal study is an attempt to record all species or partially buried in sand, or in crevices of solid reef flats. of Mitridae from Fiji waters to date, and to list pertinent The large species of Mitra, Vexillum, Pterygia and Swain- data on ecology, variability and distribution, and to supply sonia become active at the turn of the incoming tide; morphometric measurements and animal descriptions they move one-half inch to one inch below the surface, wherever known. and leave well-defined tracks which are rarely straight. All the material available for study has been obtained Ecologic intertidal zonation is evident in some species. through dredging in shallow and deeper water to about Strigatella paupercula (Linnaeus) lives near the high- 1 7 fathoms, and hand-collecting and dredging in the inter- tide mark in large colonies, in crevices of basalt boulders. tidal zone. The majority of specimens has been gathered Variation within the species of Mitridae has been from the coastal reefs of Viti Levu and outlying islands, greatly underrated. Intrapopulation and ecophenotypic while smaller lots were collected at the Yasawa group and variants of some species may be pronounced to such an the Lau Islands. Only specimens collected by local resi- extent as to create the false impression that one is dealing dents and the author have been taken into consideration with two distinct species. Specimens of Vexillum deshayesi sf>ecies reported by other authors from Fiji have been (Reeve) inhabiting areas of clean sand substrate grow shown under a separate heading. approximately 35% larger than their counterparts from Page 71 Vol. 8; No. THE VELIGER Vol. 8: No. 2 Page 72 THE VELICER feature, since this number can vary from to 20 in a series muddy sand localities. They also differ in colour and of shells of a species. number of axial ribs. Specimens of Mitra (Cancilla) form and sculpture of the whorls have been found clathrus (Gmelin) from shallow water, are appreciably The to be fairly reliable characteristics in a good many species, larger in size than those from deeper water. Examination but by no means in all. In certain species the sides of the of a long series of shells of any given species will make it whorls were flattened in some individuals, but moderately appear obvious that no single individual conforms to tire convex in others; the whorls were either rounded at the type concept. Tliese individuals are rather representatives sutures or even subangulate. of a given population of a species, with all its inherent or The number of fully formed whorls may vary up to 4 acquired variabilities of colour, sculpture and size. whorls in adult shells, while the nuclear whorls were found Although most species of Fijian Mitridae have been to vary by 2 at the most. collected over a number of years, no structural shell sculpture is generally a fairly reliable modifications were apparent which would be attributable The interstitial feature, but also subject to changes in certain species. In to seasonal influences. A moderately short life-cycle of some Vexillum species the interstitial transverse grooves Mitridae is suspected, but the actual life-span was impos- may be short in some individuals, but continuous and sible to determine. overriding axial ribs in others; the same applies to shells Juvenile shells are appreciably diflFerent in form than with a sculpture consisting of axial ribs or striae. are adults, and have a far greater width-index. The body The width, colour and placement of pattern stripes are whorl is more bulbous, the outer lip is thin and unformed, a variable feature in species bearing such ornamentation. and convexly rounded. The protoconch is usually well The colour and pattern of Mitridae are of course highly preserved in ju\'eniles, and averages one to one and variable; it should be pointed out, however, that three- one-half more nuclear whorls than in fully grown adults; quarters of the species recorded from Fiji were rather consequently the number of fully formed whorls is smaller variable in colour, the remainder were surprisingly con- in juveniles than in adult shells. stant in this respect. The sculpture of the outer lip is the only constant DIAGNOSTIC CHARACTERS character which can be relied upon with confidence. Adult Certain morphological characters are less reliable for specimens of species with a smooth outer lip wiU never specific identification than others, while some are subject include individuals with a crenulate lip, and vice versa. to changes in individuals of certain species. The general The reliability of interpretation of one or several diag- shape and form of the shell is more constant in Vexillum nostic features will depend solely on the individual species, species than it is in species of the genus Strigatella. The whose particular characters may be of a fairly constant ratio of width to length, expressed in percent, will gener- nature, or highly variable. ally vary from 4 to 7 per cent in Vexillum species, but as In contrast to the Cypraeidae, juvenile shells of Mit- much as 14 per cent in certain species of Strigatella. The ridae when only one quarter of the size of the adults have length of aperture in relation to spire length can differ by a completed colour pattern, sculpture and columellar as much as 18 per cent; certain species will be represented folds; the latter, howe\er, are sharper, more elevated and by individuals whose aperture may be equal in length to less callous than is the case in adults. Statistics compiled that of the spire, or considerably longer than the spire. from Fiji specimens have shown that the number of axial One hundred years ago it was not unusual to name a ribs does not increase nor decrease with maturity. This is specimen as a new species if it possessed two more also the case with the ratio of aperture height to spire columellar folds than a similar species already named. height, which remains unchanged throughout develop- Considerable confusion has been created by writers who ment from juvenile to adult. Although the aperture in believed the number of columellar folds to be constant; juveniles is generally wider and more convexly rounded, some writers were even less particular in counting the the spire is also proportionately shorter, with a flatter number of folds, and often omitted to include the last apical angle. two anterior folds which may have been weakly developed. The number of columellar folds is possibly the least THE ANIMAL reliable feature of the shell, as it will generally vary =t 1 fold from the mean, or up to 3 folds in individuals of the The structure of the animal is similar to that of other same species. gastropods, consisting of a body and foot, siphon, tentacles, The number of labral lirae, in species where they are eyes, proboscis, sexual and internal organs; an operculum usually present, is another highly unreliable diagnostic is absent. Page 73 Vol. 8; No. 2 THE VELIGER substrate broad and Mitridae may be grazing on detritus layers of the The foot is generally oval or cylindrical, and encrusting animals. truncated anteriorly, narrowing posteriorly. Locomotion species have, size for size, a the foot, and The sand-living Vexillum is achieved by waves of contractions along somewhat larger foot than coral-dwelling Mitra species; directed anteriorly; this rapid undulating rippling of the to envelop and smother their of the foot. they have been observed foot is also visible on the anterior dorsal part prey with the foot, very much in the same fashion as the The speed of forward movement on sand substrate is Olividae. moderately rapid; specimens one inch in length covered a distance of 32 mm in 10 seconds. at the EYES TENTACLES The siphon is either long or short, and smooth SHELL distal end.