Characters in Stylommatophora (Mollusca) 269 Сборник трудов Зоологического музея МГУ им. М.В. Ломоносова Archives of Zoological Museum of Lomonosov Moscow State University Том / Vol. 54 Cтр. / Pр. 269–297 FUNCTIONAL INTERRELATIONS BETWEEN CONCHOLOGICAL AND ANATOMICAL CHARACTERS IN STYLOMMATOPHORA (MOLLUSCA, GASTROPODA) Anatoly A. Schileyko Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences; [email protected] Parameters of shells (shape, size) of stylommatophoran mollusks are determined by the history of the group, peculiarities of their food and con- ditions of life in different geological periods, as well as genetic nature. The history of Stylommatophora since the Paleozoic is briefl y discussed. It is assumed that one of the important factors determined the historical development of stylommatophorans were peculiarities of their food. The aperture is the main channel of communication of a mollusk with the outside world and any elements of the apertural structure are related, directly or indirectly, with the adaptation of animals to their environment. Therefore, special attention is paid in the article to the morphofunctional analysis of apertural structures. The main results of this analysis may be summarized by six basic conclusions. 1. The teeth in the aperture are represented by two categories that are designated as superfi cial and immerged. Superfi cial teeth are local thi cke- nings of the lip; immerged ones are natural result of narrowing of the last whorl at the fi nal stages of the shell formation. 2. Superfi cial teeth and lip serve basically for squeezing mucus from the mantle collar and the epiphragm formation. 3. Superfi cial teeth there are mostly in mollusks, that dig themselves into the soil to survive of dry season. 4. The main function of immerged teeth is providing an optimal orien- tation of shell with visceral sack with respect to the cephalopodium and improvement of management of high shell. 5. With increase of aridity, amplifi cation of the superfi cial teeth and weakening of immerged teeth is observed. This trend is clearly seen in the species that live openly and survive the drought by gluing to the substrate using the aperture. 6. Snails inhabiting steppe, desert and semi-desert areas often lack ape- rtural teeth and well developed lip. In such species, a wide lapel of the aperture is often developed, contributing to tight contact of the aperture to the substrate. © A.A. Schileyko, 2016. 270 A.A. Schileyko In several families persisting in the current geological time, there is a clear trend toward shell reduction leading to the formation of a slug mo rphotype, with all reduction stages being observable over their mem- bers. Reduction of shell stimulates perfecting of the nervous system and improvement of physiological features of mollusks, as well as growing complexity of their behavior. From this a forecast follows that this trend will be intensifi ed in the course of further evolution of Stylommatophora. ФУНКЦИОНАЛЬНЫЕ ВЗАИМОСВЯЗИ КОНХОЛОГИЧЕСКИХ И АНАТОМИЧЕСКИХ ПРИЗНАКОВ У STYLOMMATOPHORA (MOLLUSCA, GASTROPODA) Анатолий A. Шилейко Институт проблем экологии и эволюции им. А.Н. Северцова РАН; [email protected] Параметры раковины (форма, размеры) стебельчатоглазых моллю- сков (Stylommatophora) определяются историей развития группы, осо- бенностями их питания и условиями существования в разные геоло- гические периоды, а также эпигенетическими ограничениями. Кратко анализируется история развития стиломматофор начиная с палеозоя. Предполагается, что одним из важных факторов, опреде- ливших развитие стебельчатоглазых моллюсков, были особенности их пищевых объектов. Устье есть основной канал связи моллюска с внешним миром и любые элементы строения устья так или иначе связаны, прямо или опосредованно, с приспособлениями животных к условиям внешней среды. Поэтому особое внимание в статье уделено морфофункцио- нальному анализу устьевых структур. Основные результаты этого ана- лиза сводятся к шести базовым положениям. 1. Зубы в устье представлены двумя категориями, которые обо- значаются как поверхностные и погружённые. Поверхностные зубы представляют собой местные утолщения губы; погружённые часто появляются как естественный результат более или менее ярко выра- женного сужения последнего оборота на заключительных этапах он- тогенетического формирования раковины. 2. Поверхностные зубы и губа служат в основном для выжимания слизи из края мантии и формирования эпифрагмы. 3. Поверхностные зубы имеются большей частью у моллюсков, за- рывающихся в почву на сухой сезон. 4. Основная функция погружённых зубов — обеспечение опти- мальной ориентации раковины с висцеральным мешком по отноше- нию к цефалоподиуму и совершенствование управлением высокой раковиной. 5. С возрастанием аридности условий наблюдается усиление по- верхностных зубов и ослабление погружённых. Эта тенденция хоро- шо прослеживается у видов, живущих открыто и переживающих за- суху, приклеиваясь устьем к субстрату. Characters in Stylommatophora (Mollusca) 271 6. Улитки, обитающие в степных, полупустынных и пустынных местностях, часто лишены устьевых зубов и хорошо развитой губы. У таких видов часто развит широкий отворот края устья, способству- ющий плотному прилеганию устья к поверхности субстрата. В настоящее геологическое время в пределах нескольких семейств чётко прослеживается тенденция к редукции раковины, приводящая к становлению морфотипа слизней. В современной фауне прослежи- ваются все этапы утраты раковины. Редукция раковины стимулирует совершенствование нервного аппарата и физиологических характери- стик моллюсков, а также усложнение их поведения. Из этого следует прогноз, согласно которому в ходе дальнейшей эволюции стебельча- тоглазых эта тенденция будет усиливаться. 1. Introduction characters of molluscs should be considered Superorder Stylommatophora is a large fi rst of all, which look like adaptations to the (at least 25000 species) and diverse (about 90 conditions existing in arid zones. Morpho- families, 2600 genera and subgenera) group functional analysis often allows to advance of terrestrial pulmonate mollusks spread all a hypothesis on the adaptive signifi cance of over the continents (absent in the Antarc- this or that character. tic only, although present in sub-Antarctic The systematic study of terrestrial pul- islands). Although initially stylommato- monate mollusks constituting superorder phorans are moisture-loving animals, many Stylommatophora began, naturally, from of them have mastered almost all types of descriptions of their shells. Start of a broad biotopes and often form large aggregations. study of the internal organization of ter- Causes of prosperity (or, on the contrary, restrial pulmonate mollusks was laid in the oppressed state) of a group depend on 1855, when two fundamental publications external factors (climate, soil, topographic have been issued by a German priest Adolf features, geologic history of the region, hu- Schmidt and a French naturalist Alfred Mo- man activities) as well on the peculiarities of quin-Tandon. These studies have demonstrat- the organization of the animals themselves. ed the existence of a wide variety of char- Although the “peculiarities of the orga- acters, mainly those related to the structure nization” may include not only morphologi- of reproductive tract. Since that time, the cal, but also physiological, biochemical, and anatomical method began to be widely used ethological properties of organisms, here are in studies on the systematics and phylogeny considered predominantly morphological of pulmonate mollusks. characters, the adaptive signifi cance of which As a result, to date a vast array of infor- is the subject of the present discussion. mation about the internal structure of stylom- Main and permanent danger threatening matophorans has been accumulated, fi rst of land mollusks living in conditions of dry cli- all concerning reproductive tract and radula. mate (or in regions where the rainy periods However, the functional signifi cance of are regularly replaced by dry seasons) is the the structural features of these animals is danger of dehydration. Nevertheless, there rarely discussed. One of many examples of is a large number of species living and even ignoring the functional role of certain char- prospering in arid areas. Therefore, those acters is the division of Stylommatophora 272 A.A. Schileyko into four large taxa of ordinal rank according reproach their author in anthropomorphism. to the structure of the excretory apparatus However, any formulated and published hy- (Orthurethra, Sigmurethra, Mesurethra, and pothesis is a matter for further discussion, Heterurethra) proposed by Pilsbry (1900) during which it will be either confi rmed or and supplemented by Baker (1955). Actually, improved, or rejected and replaced by a more these four names describe, or characterize, correct interpretation of the known facts. In the four states of the excretory system, and any case, nomination of a hypothesis serves the most perfect condition (sigmurethria) can as an impetus to further analysis and/or al- occur independently in different evolutionary ternative interpretation of these facts and is branches of Stylommatophora (Schileyko, targeted to the obtaining of new ones. 1975, 1978a). Abbreviations used in the fi gures thro u- It should be noted that paleontologists, in ghout the article are as following: H – heart; contrast to zoologists, use very effectively the K – kidney; LL – left lobe of mantle collar; method of phylogenetic reconstructions based MC – mantle