Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 87. (Budapest 1995)

Dulai, A.: Middle Miocene (Badenian) lunulitiform Bryozoa from Szob (Börzsöny Mts., Hungary)

Remarks: BALUK & RADWANSKI (1984a) described the new genus Reussirella for the members of COOK'S (1965a) Cupuladria owenii group on the basis of closed central zooecia. According to the describers this genus contains five species i.e. R. haidingeri (REUSS), R. reussiana (MANZONI), R. muliispinata (CANU et BASSLER), R. doma (D' ORBIGNY) and R. owenii (GRAY). The closed central zooecia refer to the relationship between Reussirella and Discoporella; for this reason, BALUK & RADWANSKI (1984a) described the family Discoporellidae containing the two former genera. The calcareous lamina covering the central zooecia are interpreted as a passive excurrent chimney by BALUK & RADWANSKI (1984b). This species was described from the Vienna Basin by REUSS (1847) and it is known only from the European Neogene deposits, so it is an extinct endemic species. According to some authors, it may be only badly preserved Discoporella umbellata (DEFRANCE) but it is not a real assumption. This species can frequently be found together with Cupuladria vindobonensis BALUK & RADWANSKI and/or Discoporella umbellata (DEFRANCE). In sections it can be seen that kenozooecial chambers are absent within the basal pad (Fig. 26). Autozooecia sometimes descend near to the basal surface. There are nearly 40 more or less complete specimens in the Szob material but the majority of the specimens are fragmentary. The regeneration of the colonies is well visible in some specimens but the fragments of primary colonies are absent at the basal surfaces, in contrast to the Korytnica material (BALUK & RADWANSKI 1977b). The irregular or elongated shape of the colony and the arrangement of the zooecia refer to regeneration (Figs 17-18, 20-22, 24). Most of the complete specimens are rather small but the biggest fragment is 4.5 mm which refers to a size of about 9-10 mm in diameter. Measurements on Reussirella haidingeri (REUSS) were given by REGUANT (1993). The length of zooecia in the Szob specimens is very similar to the Spanish material, however the width of zooecia and the length of vibracular opesia are smaller than in REGUANT'S Pliocene specimens (Table 7). Distribution: This species is known from the European Miocene and Pliocene sediments. In the area of Central Paratethys it was mentioned from the Vienna Basin (summarized by BALUK & RADWANSKI 1984a), Transylvanian Basin (MANZONI 1877), Carpathian Foredeep (MALECKI 1951), Korytnica Basin (BALUK & RADWANSKI 1977b, 1984b) and Pannonian Basin (MANZONI 1877). Over and above these Badenian localities this species was found in Austrian Eggenburgian sediments by VÁVRA (1977). Other occurrences of Reussirella haidingeri outside the Central Paratethys: Mallorca, France, Italy, Germany (Miocene) and Mallorca, France, Belgium, the Netherlands, Great Britain, Portugal, Tunesia (Pliocene). LIFE MODE OF LUNULITIFORM BRYOZOA At the end of the free-swimming larval stage a fine-grained, sandy bottom below the wave base is ideal for settlement. The larva settles on a small grain (foraminifers, quartz-grains). During a quick metamorphosis takes shape the ancestrular triplet, namely three zooecia form at the same time from the larval stage (HAKANSSON 1973). From that moment the colony develops by radial budding (LAGAAIJ 1963). During growth the colony expands beyond the grain and becomes free-living. The developing colonies form a flattened cone, which shape hampers sinking of the colony in the soft sediment. Lunulitiform species well adapted themselves to life on soft sediments, where they may be the dominant elements among Bryozoa. The investigations of recent species in aquarium and in natural marine environments confirm that the colonies lie on the bottom in apex-up position (GREELY 1967, 1970). Recently at the Guyana shelf the density of lunulitiform Bryozoa somewhere may be around 15,500 specimens/m (CADÉE 1975). On the other hand, GREELY (1967) mentioned 10 specimens/trT from Mississippi Sound.