Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 88. (Budapest 1996)
Dulai, A.: Taxonomic composition and palaeoecological features of the Early Badenian (Middle Miocene) bivalve fauna of Szob (Börzsöny Mts, Hungary)
LIFE HABIT The life habit is very varied at bivalves. Some groups of them are epibenthic, a bigger part of bivalves belong to the infauna and a few groups live at the interface of the water and the sediment (semiinfauna). From the point of view of movement bivalves may be attached, vagile or free-lying. At some groups the life habit is changing during the life. The high variability of life habit of bivalves is clearly reflected in the Szob material. Several life habit groups are represented by the following genera in the examined material: — vagile infauna: Nucula, Nuculana, Linga, Megaxinus, Parvilucina, Myrtea, Lucinoma, Diplodonta, Cardiocardita, Cyclocardia, Glans, Megacardita, Crassinella, Parvicardium, Laevicardium, Lutraria, Ervilia, Tellina, Solecurtus, Venus, Circomphalus, Gouldia, Callista, Pelecyora, Paphia, Timoclea — free-lying semiinfauna: Anadara — free-lying infauna: Limopsis, Glycymeris — attached semiinfauna: Pinna — attached infauna: Corbula — boring infauna: Xylophaga — tube-dwelling infauna: Clavagella — vagile epifauna: Amusium, Chlamys, Pecten — attached epifauna: Barbatia, Striarca, Arcopsis, Plicatula, Anomia, Cubitostrea, Chama, Card i ta At the life habit there is a characteristic difference between the two collections (Fig. 5). Namely, the percentage of the epifaunal elements is nearly three times smaller at the washed material (15.58% in the museum collection and 6.03% in the washed material). Life habit groups are also showed in Figure 6 but in more detail. In order to show a clear picture the free-lying infauna and free-lying semiinfauna as well as attached infauna and attached semiinfauna are figured as a single group. For the same reason the poorly represented boring infauna and tube-dwelling fauna are missing in the figures. As it can be seen not only the percentage of infaunal elements increased on the account of epifaunal elements, but the rates changed among infaunal groups, too. In spite of the high diversity of vagile infaunal elements, the infauna is dominated by attached corbulids. The spatial distribution of vagile infaunal forms is very varied in the sediment, therefore presumably the competition for space was moderate. Nucula, cardiids and Lutetia live very near to the sediment-water interface. Nuculana, Laevicardium and Ervilia are shallow burrowers, Venus and Circomphalus can be found at intermediate depths, while Linga, Lucinoma and Parvilucina. are deep burrowers. Corbula gibba lives shallowly buried in the sediment, attached to gravel or shell fragments with a single byssus thread. Taking the eight most frequent species into consideration (Fig. 3) it can be seen that Chlamys scabrella is epifaunal element (on the surface or in the water mass), Anadara diluvii lives at the sediment-water interface, Corbula gibba, Corbula carinata and Ervilia miopusilla are shallow burrowers, Venus multilamella and Circomphalus subplicatus are intermediate burrowers, while Parvilucina dentata is deep burrower. In spite of
