611 Phuhet Marine Biological center special Publication 21(3): 611-612 (2000) INTRODUCTION TO NEOGASTROPODA Alan J. Kohn (Jniuersity of Washington, USA (TMMP) 672 Tlopical Marine Mollusc Programme INTRODUCTION TO As predators, neogastropods have a very NEOGASTROPODA good chemical sense - they generally detect a prey organism at a distance by chemical The Order Neogastropoda is very large, with signals emanating from it. The organ re- about 5,000 species. Almost all members of sponsible for distance chemoreception is the this order are marine, benthic, and carnivo- osphradium, a prominent, bipectinate struc- rous. A very few species have invaded fresh ture in the mantle cavity, Iocated on the in- water and are herbivorous, and the group ner surface of the mantle at the base of the includes some scavengers and parasites. siphon. The osphradium is richly ciliated Anatomically, neogastropods are much more and innervated, and it is arranged so that similar to mesogastropods than the latter water currents directed from the siphon pass are to archaeogastropods (Vetigastropoda + over it before reaching the ctenidium. In Patellogastropoda). The arrangement of archaeogastropods and most mesogastro- mantle cavity, ctenidium, nervous system, pods the osphradium is less weII developed, coelomic derivatives, gut, etc. are essentially usually an elongate ridge with a central similar, especially to the "higher" mesogas- groove parallel to the ctenidium. After de- tropods, e.g. the Ranellidae. The main dif- tection and recognition, many neogastropods ference is in the radula, which in the Neo- attack and capture prey using chemical and gastropoda is not taenioglossate (i.e. with 7 mechanical devices. These include acid sali- teeth/row). The neogastropod radula varies vary secretions, venoms, and the capability according to superfamily: of drilling through shells. Superfamily MURICOIDEA: Classification of the major neogastropod Radula with 3 teeth./row (stenoglossate) families (based on Ponder and War6n. 1988) Superfamily CANCELLARIOIDEA: Radula a row ofvery elongate central teeth Superfamily MURICOIDEA Muricidae Superfamily CONOIDEA. Buccinidae (including the formerly Radula with 2-5 teeth./row, marginal teeth separate families Buccinidae, Nassariidae enlarged (toxoglossate) and Fasciolariidae, according to Ponder and War6n, 19BB) Neogastropods are often the most conspicu- ColumbeIIidae ous gastropods in marine habitats, but the Volutidae group is more "conservative," that is it is Olividae more homogeneous and less diverse in its Harpidae habits and habitats, than the mesogastro- Marginellidae pods. Neogastropods are characterized by an Mitridae inhalent siphon in the front; it is actually Costellariidae an extension of the left side of the mantle. The siphon permits many neogastropods to Superfamily CANCELLARIOIDEA burrow in sand to a depth that completely Cancellariidae covers the she1l, but many species also oc- cupy hard substrates. In many, especially Superfamily CONOIDEA irr the Muricoidea and familyTurridae of the Turridae Conoidea, a long shell siphon protects the Terebridae inhalent mantle siphon. Conidae.