21 an Illustrated Guide to the Genera Of
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- 21 AN ILLUSTRATED GUIDE TO THE GENERA OF THE LAND MOLLUSCA OF NEW ZEALAND. by W. F. Ponder and T. P. Warren. INTRODUCTION Where Land Mollusca Live. The majority of N. Z, land snails are restricted to the isolated remnants of native bush. The bush is called a macrohabitat but the places where the individual animals live are referred to as microhabitats. These can be made into a very lengthy list, but for our purposes the more important microhabitats only will be mentioned. The bush consists essentially of three layers: - trees, bushes and shrubs, and the ground cover. The former provides a home for relatively few snails, though by beating the foliage some species may be found, while others hide beneath loose bark and in the dead leaves nestling between branches. Shrubs and bushes provide a similar habitat to trees. Palms (the nikau) harbour snails in the large leaf bases. The ground cover is, however, the richest habitat, both in the variety of species encountered and in the diversity of microhabitats available. Small ferns, mosses and creeping plants provide shelter for some species while others prefer the dampness and protection found beneath rotting logs on the forest floor. Leaf litter is a rich habitat providing a subaquatic environment for many tiny snails and other animals. Not only the native bush provides a habitat for snails. Coastal scrub and flax is often rich in species and a few are found in tussock grassland and others beneath sand dune plants. Subfossil land snails are occasionally encountered in limestone caves or on sand dunes. Several subspecies of the large land snail Placostylus ('Maoristylus) ambagiosus Suter are known only as subfossils. How to Collect and Store Land Mollusca. Only simple equipment is needed to become a student of land molluscs, though to study small forms adequately a microscope is needed. A pair of forceps, a small paint brush, stoppered tubes and labels are all that is required. A torch may come in handy as light is often very poor in the bush. To collect foliage - living species, a piece of white cloth spread out on a wire frame is all that is needed. This is held beneath a tree while the branches and foliage are shaken or beaten with a stick. A bag of leaf mould sorted under magnification yields many of the small species that one would not normally see in the field. Other debris involving a lot of fine material should be treated in a similar manner. Slugs should be drowned in fresh water to extend them and then preserved in 75% ethyl alcohol or in 5% neutralised formalin. Snails can be preserved by the same method, or after relaxing, the animal 22 - can be removed from the shell. The large Paryphanta and Placostylus should not be left too long as air bubbles may form under the perlostracum of the shell. Paryphanta shells should be plugged with cotton wool to prevent their collapse when dried out. The smaller species can be preserved as above, or, if only the shell is required, soaked for a day or two in 75% alcohol and then dried. Some ribbed or bristled species may be covered in dirt. This can be easily removed by stirring them in a dish containing 1-1 mixture of alcohol and water, and then drying on clean blotting paper. Large snails should be kept in trays with a label giving the species name, locality, date, data about the habitat, etc. Small shells are best kept in glass vials or short lengths of glass tubing plugged at both ends with cotton wool, not corks. Lables (as above) should be placed inside the tube. Dissection of the animal is an important part of the study of land snails, but it is too large a topic to be discussed here. The morphology of the jaw; and radula can, however, be studied without much difficulty, and observations of the external features of the living animal present few problems. The radula and jaw can be either dissected out of the head, or the buccal mass can be heated in a 10% solution of caustic potash to dissolve away all non-chitinous material. The radula should then be mounted in a suitable medium (e. g., glycerine jelly or polyvinyl lactophenol) after staining (if necessary) with a suitable dye or chemical (e. g., picric acid). The jaw can usually be examined without mounting and staining, but if this is necessary a similar method can be used as for the radula. History. The New Zealand terrestrial molluscs have attracted the attention of malacologists for over a hundred years. The early workers in the field, such as Gray, Pfeiffer, and Reeve, were men who lived in Europe and studied material collected by several pioneer explorers to New Zealand. Much valuable work was done locally in the latter half of last century by Hutton, Suter, Cheeseman, Webster and Murdoch. In more recent years the tradition has been carried on chiefly by Iredale, Powell, Dell, Cumber and Burton. Part of the studies of Hutton, Suter, Webster and Murdoch concerned the radula, genitalia and other anatomical details, which has proved a valuable basis for later workers to continue from Much, however, remains to be done on the anatomy of the smaller species particularly and a rich field of research is available here. At the present time there are 56 genera and subgenera recognised in New Zealand and these contain some 373 species and subspecies. Further revision and research will undoubtedly lead to increases in both of these figures. HOW TO USE THE GUIDE In the illustrated guide to the native New Zealand terrestrial molluscan genera, each genus is briefly described under its appropriate family. Rather than use the more common types of key for this rather difficult group, a pictorial guide is considered by us to be more generally useful. A specimen should be readily placed in a genus by comparing it with the figures and checking with the appropriate description of the genus. Specific identification can then be attempt• ed by referring to the checklist in "Shells of New Zealand" by A. W. B. Powell. This reference will give sources for full descriptions of each species. The most useful reference in this respect is Suter's "Manual of the New Zealand Mollusca". The shells are described and figured, the approximate maximum size given, The distribution, and number of species noted for each genus. The animal, radula, and jaw are described only when shell characters are considered inadequate for positive identification. In most cases the species illustrated is the type species for the genus, though other members are also figured in those instances where there is a wide range of variation within the genus. Few of the figures are original, the majority being taken from Suter (1915). The following guide concerns the native snails and slugs but there are also a number of introduced snails and slugs that may be encountered, most of which have originated from Europe. A list of these species can be found in Suter's Manual (p. 1071). Class GASTROPODA Order PROSOBRANCHIA Suborder ARCHAEOGASTROPODA Superfamily NERITACEAE Family HYDROCENIDAE Animal with no gill, but a pulmonary chamber. Tentacles short, large, eyes prominent and at the outer bases of the tentacles. Foot oval, short. Radula rhipidoglossan - formula » + 1 + (1 + 1 + 1) + 1 + «. Shell imperforate, conic and globular. Whorls convex, spire short. Columella callous. Operculum calcareous, ornamented with concentric striae. Inner side with a prominent apophysis. - 24 - Genus OMPHALORISSA Iredale, 1913 (Georissa multilirata Brazier). Shell minute, imperforate, translucent. In very moist and dark parts of the bush. North and South Islands. 2x1 mm. Fig. l, Omphalorissa purchasi (Pfeiffer); A, operculum. Suborder MESOGASTROPODA Superfamily LITTORINACEA Family CYCLOPHORIDAE Animal with long, cylindrical tentacles, the eyes at their outer bases on short peduncles. Foot long, attentuate behind. No gill, but a pulmonary chamber. Jaw reticulate, radula taenioglossan (2+1+1+1+2). Shell conical or depressed, usually covered with a horny periostracum, aperture circular, peristome simple or reflexed. Operculum spiral, testaceous or horny with many to few whorls. Genus CYTORA Kobelt and Moellendorff, 1897 (Cyclophora cytora Cray) (= Murdochia Ancey). Shell small, umbilicated, with 5-6 whorls. Protoconch 2 whorls, first smooth, second spirally striate. Moist parts of the bush among fallen leaves and fronds. 3. 25 x 5 mm. Three Kings, North and South Islands, Stewart Island. 18 species and subspecies. Fig. 2, Cytora cytora Gray, 2A, Cytora pannosa (Hutton), operculum Family LIAREIDAE Animal with long cylindrical tentacles, eyes at their outer bases. Foot elongate, tapering behind. No jaws, radula taenioglossan with multicuspate teeth. Shell of moderate size, tall spired, smooth or vertically ribbed, body whorl often angled or keeled. Aperture oval, peristome continuous, often flanged. Operculum horny, spiral. Genus LIAREA Pfeiffer, 1853 (Realia egea Gray). Shell small, subperforate, operculate, often with zig-zag markings. Protoconch of 2 smooth whorls. peristome continuous, with a labial flange. Mostly under decaying leaves of Bielschmedia taraire. Adult shell (7-9 whorls) approx. 3x9 mm. 12 species and subspecies. North Island, mainly North Auckland. Fig. 3, Liarea egea tesselata Powell, 3 A, Liarea turriculata (Pfeiffer), operculum. 25 Subclass PULMONATA Order STYLOMMATOPHORA Suborder HOLOGNATHA Superfamily ENDODONTACEA Family OTOCONCHIDAE Animal elongate, much too large to withdraw into the shell. Mantle extended over shell. No posterior mucous gland. Jaw distinctly furrow• ed. Shell very flat, transparent, partly external, of few rapidly increasing whorls. Genus OTOCONCHA Hutton, 1884 (Vitrina dimidiata Pfeiffer). Shell very thin, pale yellow, with minutely striated growth lines, whorls 2£r. Protoconch of 1_- smooth whorls. Base of shell completely cut away. Animal sluglike, yellowish mottled brown with large anterior visceral hump containing the shell.