Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 24-25. 2007. (Budapest, 2007)
6 Dui Hills (BlTNER 1990). This locality was interpreted as shallow water kelp assemblage (HOFFMAN et al. 1978). The brachiopod fauna also consists of these two species in the oyster bioherm at Zdziechowice, but A. cuneata is dominant (BlTNER 1990). Very similar brachiopod assemblages were found at Radwanówka (BlTNER 1990), Ohrid, Bulgaria (BlTNER 1993) and Niechobrz (BlTNER & PlSERA 2000), with the dominance of A. cordata. However, there are two additional species in negligible amounts at the last three localities. All of these localities were interpreted as shallow ,A. water environments. BlTNER & KAIM (2004) reported the same two Argyrotheca species, with the dominance of A. cordata (89%), from an atypical fades: dark grey sandy—silty deposits of the intra-Carpathian Nowy Sacz Basin. They suggested that this assemblage might be transported basinward from a shallower setting. These three species (M. detruncata, A. cuneata, A. cordata) commonly occur together in the Recent Adriatic Sea (LOGAN 2003), as well as in the whole Mediterranean Sea (LOGAN 1979), mainly in the shallow water environments. Palaeoecological review of megathyridids Previously, the paedomorphic family Megathyrididae have been generally considered primitive, but nowadays most authors consider them advanced, rapidly evolved neotenous forms (ASGAARD 1986). Megathiris and Argyrotheca are known from the Late Cretaceous and are widely distributed in modern seas, and most species are continental shelf dwellers. Megathiris and Argyrotheca are common in coralligenous biocoenoses (LOGAN 1979). They also inhabit small crevices and interstices, or the walls of submarine cliffs and caves. M. detruncata has been observed attached to rocks and stalagmites in the deepest recesses of a submarine cave, under conditions of virtually no water movement and light (LOGAN 1979). Elsewhere within the shallow part of the coralligenous biocoenosis small brachiopods may be found attached to almost any hard substrate, including shells, rocks and man-made objects. Both Argyrotheca species are very small and have simple, bilobed schizolophe lophophores, regarded less effective for food extraction (RUDWICK 1970). Megathiris is only slightly 7 larger and ptycholophous, the lophophore never developing beyond a four-lobed stage (LOGAN 1979). The small forms with simple, less efficient lophophore prefer shallow-water regions, where particulate organic matter is more plentiful (LOGAN 1979). Recent brachiopods generally have wide depth ranges, therefore we can use fossil brachiopods as depth indicators with great uncertainty. LOGAN (1979) divided the Recent Mediterranean brachiopods into two depth groups: shallow water (typical of the infralittoral and circalittoral zone) and eutybathic species. Both Argyrotheca and Megathiris belong to the shallow water group (shelf species ranging down to 200m), but sometimes occur at deeper environments on coralline algae bottoms and gravels, too. The maximum occurrence is from 20 to 60m for A. cuneata and A. cordata, and 20—120m for M. detruncata. All shallow water species show patchy distributions, with isolated high densities of several hundreds specimens per square meter being occasionally recorded (LOGAN 1979). Members of the shallow water group are all small in size, inhabiting protected, lightpoor environments, such as caves. Extant representatives of Megathiris and Argyrotheca exhibit mainly cryptic mode of life in shallow depth in light-poor environments (crevices, caves, undersides of boulders). Argyrotheca is known from cryptic habitats in Recent reef environments (e.g. LOGAN 1975). TOSCANO & SORGENTE (2002) reported these two Argyrotheca species from maerl deposits and molfuscan— bryozoan assemblage of the rhodalgal-bryomol temperate carbonates of the Apulian Shelf. According to TADDEI RUGGIERO (1987, 1990) A. cordata often lives in association with living thalli of Peyssonelia rosa-marina. LOGAN (1975) gave a detailed ecological study on A. hermudana from the Bermuda platform. The specimens usually attached by the pedicle to the underside of foliaceous and encrusting corals or underside of boulders. The shell is normally oriented in an almost vertical position. The distribution of individuals is patchy, probably resulting from late release of brooded larvae, rapid settlement and post-setdement competition with other organisms (LOGAN 1975). JACKSON et al. (1971) mentioned that A. johnsom from Jamaican fore-reef slopes increased in density with depth, and suggested that density can be correlated with low light intensity. The competition for living space may also be an important limiting factor. Colonization of cryptic habitats enables brachiopods to avoid the intense competition for space, which occurs on more exposed surfaces. The presence of firm substrate for attachment is regarded as the main limiting factor. Water energy and light operate mainly in the larval stages prior to settlement (LOGAN 1979). According to SlMOES et al. (2004) A. cf. cuneata is more common in the shelf than in the coastal samples of Brazilia. They recognized three distinct brachiopod associations; one of them is the Terehratulina—Argyrotheca fauna, which is common at depths ranging between 100— 200 m. Experiments on the settlement patterns of Argyrotheca cordata and Argyrotheca cuneata in the eastern Mediterranean confirm their preference for cryptic habitats within crevices and fractures of blocks of rocks (ASGAARD & BROMLEY 1991). The larvae settle late in the autumn and their lifespan does not exceed two years. A major limiting factor in brachiopod colonization in shallow water may be the grazing pressure from chitons and echinoids. VALENTINE & JABLONSKI (1983) showed that nonplanktotrophic groups, such as the articulate brachiopods, have relatively few offsprings and some species of Argyrotheca protect the larvae in brood pouches. Cryptic habitats aid the reproductive and developmental strategy of these low-energy species with a low fecundity 7 . Argyrotheca probably pursued r-selected life-strategies, small, short-lived organisms generated by slow growth (HARPER et al. 1995).
