Ruthenica, 2007, 17(1-2): 33-41. ©Ruthenica, 2007

Anatomy of accessory rhynchodeal organs of Veprecula vepratica and Tritonoturris subrissoides: new types of foregut morphology in Raphitominae ()

A. E. FEDOSOV

A.N. Severtzov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninsky prospect 33, Moscow, 119071, RUSSIA

ABSTRACT. Anatomy of anterior part of digestive The opposite tendency of foregut transformation system in two representatives of the subfamily Raphi- is the origin of specialised accessory organs, usually tominae, Veprecula vepratica and Tritonoturris sub- constituting outgrowths of rhynchodaeum. Forma- rissoides has been studied. V. vepratica possesses full tion of these organs has been observed in mollusks set of foregut organs while the foregut of T. subrisso- ides is highly reduced — radula, venom apparatus, possessing a full set of foregut organs as well as in proboscis and salivary glands are absent. In both spe- mollusks demonstrating full loss of foregut complex cies there is an additional foregut organ, lacking in [Taylor, 1990]. other studied representatives of Raphitominae but ha- Loss of radula in representatives of Turridae is ving analogues in representatives of other groups of an extraordinary event and in both known cases a Conoidea. The foregut morphology of V. vepratica and complete reduction of foregut organs is accompani- T. subrissoides, apparently representing new types of ed by appearance of special rhynchodeal structures. foregut organization for Raphitominae is described, These organs are pyriform gland of Zemacies excel- and the possible functioning of these organs is discus- sa [Medinskaya, Sysoev, 2003] and distinct tongue- sed in comparison to analogous structures found in other conoideans. shape muscular outgrowth in some species of Ho- raiclavus [Fedosov, Kantor, in press]. These organs have developed in representatives of two subfami- lies, Zemaciinae and Crassispirinae, independently. Some representatives of the family Terebridae Origin of special foregut complex, consisting of also possess a special rhynchodeal organ [Taylor, highly modified radula and venom apparatus and Miller, 1990]. The presence of this organ, named underlying the unique feeding mechanism of Cono- APS (accessory proboscis structure), does not cor- idea, was a crucial step in evolution of the group. It relate with the state of reduction of other foregut allowed their rapid radiation, unusual diversity and organs. It sporadically appears in both radulate and doubtless evolutional success [Taylor et al., 1993]. radula-less terebrids. High effectiveness of this mechanism, consisting in Family , particularly the subfamily Rap- usage of separate radular teeth held at the tip of the hitominae, is characterized by unusually high diver- proboscis for stabbing and envenomation of the prey, sity of foregut morphology exceeding that in other allowed Conus to become one of the most species- groups of Conoidea [Kantor, Taylor, 2002]. Raphi- rich genera among invertebrates. Moreover, mol- tominae include most of described radula-less rep- lusks of this are a rare example of invertebrates having developed fish-hunting [Duda, Palundi, resentatives of Conoidea [Kantor, Sysoev, 1989; 2003]. Nevertheless, in representatives of some gro- Kantor, Taylor, 2002, our unpublished data]. Despite ups of Conoidea the foregut complex providing this this great morphological diversity, additional foregut effective feeding mechanism, undergoes significant structures have never been found in representatives transformations. of Raphitominae, as well as in other Conidae. In some evolutionary advanced lineages of Co- While studying anatomy of anterior part of di- noidea a clear tendency to the reduction or complete gestive system in representatives of the subfamily loss of radula has been noticed [Taylor et al., 1993, Raphitominae, two new types of the foregut which Oliverio, 1995; Kantor, Taylor, 2002]. Usually the include different rhynchodeal outgrowths, were loss of radula is accompanied by a reduction of found in Veprecula vepratica Hedley, 1903 and Tri- proboscis, venom apparatus and, sometimes, saliva- tonoturris subrissoides Hervier, 1897. They are des- ry gland, i.e. the other foregut organs employed in cribed below together with the discussion of possible the classical conoidean mode of feeding. functioning of these organs.