ORIGINAL PAPER Morphology of the jaw apparatus in 8 species of Patellogastropoda (Mollusca, Gastropoda) with special reference to Testudinalia tesulata (Lottiidae) Elena Vortsepneva • Dmitry Ivanov • Gu ¨ nter Purschke • Alexander Tzetlin Received: 11 February 2013 / Revised: 17 June 2013 / Accepted: 20 June 2013 / Published online: 26 July 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The fine structure of the jaw apparatus was studied by scanning electron microscopy in eight species of Patellogastropoda. The jaw apparatus is an unpaired two- layered dorsolateral structure with anterior and posterior wings attached to the odontophore by muscles. The jaw of Testudinalia tesulata (O.F. Mu ¨ller, 1776) is a derivative of the cuticle typical for the foregut. The tissue forming the jaw is a specialized foregut epithelium (gnathoepithelium), consisting of a special type of cells called gnathoblasts. The jaw grows in areas of the epithelium characterized by high concentration of electron-dense vesicles, ER and long microvilli that penetrate deep into the jaw plate. This indicates that the gnathoblasts take an active part in jaw growth. In most cases, these areas of the gnathoepithelium are highly folded. The main differences between the spe- cies studied are form and thickness of the frontal edge of the jaw. These differences do not correlate with the sys- tematic position of the species studied but likely depend more on the feeding mode. The transmission electron microscopy studies yielded new morphological criteria for comparison between various gastropod species and other members of Trochozoa, in particular, Annelida. The jaws of Annelida are cuticular structures formed on the surface of specialized epithelial cells, often also called gnatho- blasts. The jaw of Patellogastropoda can be attributed to the first type of annelid jaw formation characterized by an epithelium with long microvilli and continuous growth. Keywords Patellogastropoda  Testudinalia tesulata  Lepeta  Lottia  Ultrastructure  Jaws Introduction Hard-cuticle jaws are known in all groups of mollusks except Polyplacophora and Bivalvia. These jaws are formed by the buccal epithelium and comprise a single solid plate in Monoplacophora (Lemche and Wingstrand 1959), Patello- gastropoda, and Pulmonata (Gastropoda) (Ivanov and Sta- robogatov 1990) but are paired plates in Opisthobranchia, Scaphopoda (Cyclobranchia), Aplacophora, and Cephalo- poda (Ivanov and Starobogatov 1990) or serial structures in Pulmonata (Barker and Efford 2004). The jaw located in the buccal cavity either has a lateral, a dorsal or a dorso-lateral position. Paired jaws of Cephalopoda are in a dorso-ventral position and are assumed to be non-homologous to the other mollusk jaws (Boletzky 2007). The jaw apparatus of Gastropoda is a solid structure of cuticular ectodermal origin lying at the posterior border of the buccal cavity. The general structure of the jaws is quite diverse and is known for all larger gastropod taxa. Fretter and coauthors (Fretter et al. 1981) were the first who indicated that the structure of jaws is different in different gastropod groups (an unpaired jaw in patellogastropods and a paired jaw in non-patellogastropod groups, including Neomphalus McLean, 1981). Later Haszprunar (1988) suggested using the jaw morphology as a character in reconstruction of the phylogeny of Gastropoda; and Communicated by A. Schmidt-Rhaesa. E. Vortsepneva (&)  D. Ivanov  A. Tzetlin Department of Invertebrate Zoology, Moscow State University, 19899 Moscow, Russia e-mail: vortcepneva@gmail.com E. Vortsepneva  D. Ivanov  A. Tzetlin White Sea Biological Station, Moscow, Russia G. Purschke Zoologie, Fachbereich Biologie/Chemie, Universita ¨t Osnabru ¨ck, 49069 Osnabru ¨ck, Germany 123 Zoomorphology (2013) 132:359–377 DOI 10.1007/s00435-013-0199-y