Fine Morphology of the Jaw Apparatus of Puncturella noachina (Fissurellidae, Vetigastropoda) Elena Vortsepneva, 1 * Dmitry Ivanov, 2 G€ unter Purschke, 3 and Alexander Tzetlin 1 1 Department of Invertebrate Zoology, Moscow State University, 119234 Moscow, Russia and White Sea Biological Station, Russia 2 Zoological Museum, Moscow State University, Bolshaya Nikitskaya Str. 6, 225009 Moscow, Russia 3 Zoologie, Fachbereich Biologie/Chemie, Universit€ at Osnabr € uck, 49069 Osnabr € uck, Germany ABSTRACT Jaws of various kinds occur in virtually all groups of Mollusca, except for Polyplacophora and Bivalvia. Molluscan jaws are formed by the buccal epi- thelium and either constitute a single plate, a paired formation or a serial structure. Buccal ectodermal structures in gastropods are rather different. They can be nonrenewable or having final growth, like the hooks in Clione (Gastropoda, Gymnosomata). In this case, they are formed by a single cell. Conversely, they can be renewable during the entire life span and in this case they are formed by a set of cells, like the forma- tion of the radula. The fine structure of the jaws was studied in the gastropod Puncturella noachina. The jaw is situated in the buccal cavity and consists of paired elongated cuticular plates. On the anterior edge of each cuticular plate there are numerous longitudinally ori- ented rodlets disposed over the entire jaw surface and immersed into a cuticular matrix. The jaw can be divided into four zones situated successively toward the anterior edge: 1) the posterior area: the zone of forma- tion of the thick cuticle covering the entire jaw and forming the electron-dense outer layer of the jaw plate; 2) the zone of rodlet formation; 3) the zone of rodlet arrangement; and 4) the anterior zone: the free scrap- ing edge of the plate, or the erosion zone. In the gen- eral pattern of jaw formation, Puncturella noachina resembles Testudinalia tessulata (Patellogastropoda) studied previously. The basis of the jaw is a cuticular plate formed by the activity of the strongly developed microvillar apparatus of the gnathoepithelium. How- ever, the mechanism of renewal of the jaw anterior part in P. noachina is much more complex as its scrap- ing edge consists not just of a thick cuticular matrix rather than of a system of denticles being the projec- ting endings of rodlets. J. Morphol. 000:000–000, 2014. VC 2014 Wiley Periodicals, Inc. KEY WORDS: Fissurellidae; Gastropoda; Puncturella noachina; ultrastructure of jaws INTRODUCTION Jaws of various kinds occur in virtually all groups of Mollusca except for two taxa: Polyplacophora and Bivalvia. Molluscan jaws are formed by the buccal epithelium and either constitute a single plate, a paired formation or a serial structure. The first type of jaw is found in Monoplacophora (Lemche and Wingatrand, 1959), Scaphopoda (Schaefer and Hasz- prunar, 1996), and Gastropoda (Patellogastropoda, opisthobranch Euthyneura), the second in Gastrop- oda (Opistobranchia), Aplacophora (Ivanov and Starobogatov, 1990), and Cephalopoda (Boletzky, 2007), and the third is restricted to Gastropoda (opisthobranch Euthyneura; Barker and Efford, 2002). In all molluscs, the jaw lies in the buccal cav- ity and occupies a lateral, dorsal, or dorso-lateral position. The lower jaw of Cephalopoda takes a ven- tral position and is regarded as not being homolo- gous to the jaws of other molluscs (Boletzky, 2007). Thus, the highest diversity in jaw morphology occurs in gastropods possessing single dorsal jaw plates (Patellogastropoda, occulinida), paired jaw plates situated on the dorso-ventral side (Nudi- pleura), and serial jaw plates on the dorsal side of the buccal cavity (opisthobranch Euthyneura). The presence of two separate symmetrical (paired) jaw plates in opisthobranch Euthyneura (Cephalaspidea, Thecosomata, Anaspidea, almost all Nudipleura) is suggested to be plesiomorphic for Euthyneura, whereas the absence of jaws (Cri- mora, many Cryptobranchia, e.g., Doris, Archido- ris, Austrodoris, and Sclerodoris, Dendrodorididae, Phyllidiidae) is regarded as apomorphic (Gosliner, 1994; Wagele and Willan, 2000). Two separated plates consisting of rod-like structures also occur in rhipidoglossate Gastropoda (Haszprunar, Contract grant sponsor: The Russian Foundation; Grant num- bers: N-3-119-10; 12-04-32293; Contract grant sponsor: The Ostpartnerschaften-Programm des Deutschen Akademischen Austauschdienstes. *Correspondence to: Elena Vortsepneva; Department of Inverte- brate Zoology, Moscow State University, 119234 Moscow, Russia and White Sea Biological Station, Russia. E-mail: vortcepneva@gmail.com Received 2 October 2013; Revised 14 January 2014; Accepted 19 January 2014. Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jmor.20259 VC 2014 WILEY PERIODICALS, INC. JOURNAL OF MORPHOLOGY 00:00–00 (2014)