中国南沙海区全新世小孔亚目(苔藓虫唇口目)的古生态研究

PALAEOECOLOGY OF HOLOCENE ASCOPHORA (CHEILOSTOMATA,BRYOZOA) FROM THE NANSHA ISLANDS,CHINA

本文简要叙述南沙海区全新世小孔亚目苔藓虫群体形状和生态环境的关系,对非附着生长的类型进行了初步的分类。

Thirty-five bryozoan samples collected from the Nansha Islands during 1984 through1988 yielded a total of 64 species of Ascophora belonging to 29 genera. The samples may begrouped into 4 geographic divisions, namely the northeastern, southeastern, south-centraland southwestern areas, based upon the abundance and composition of taxa and theirecological environment. Area Ⅰ is situated to the south of Liyue Tan (Reed Bank), whereonly a few genera are present and the bryozoans are characterized by branch colonies simi-lar to dendroid corals. Area Ⅱ is near Palawan Trough, water depth about 150m (maxi-mum 200m); five samples from this area yielded 26 Ascophoran species of 13 genera; Fami-ly Conescharellinidae are well developed. Area Ⅲ extends from Zengmu Ansha (ZengmuShoal) to Nankan Ansha (Nankan Shoal) with water depth not exceeding 100m, theascophorans from 20 spots are very abundant and diversified in variety of species (61); onlyOsthemosia is absent here. Area Ⅳ is located on the northeastern slope of Natuna Archi-pelngo with a water depth between 100--145m, 6 samples yielded 41 ascophoran species,but Holoporella and Tubucellaria were not found here. The Holocene Ascophora from the Nansha Islands vary in zoarial shapes and ingrowth methods, including incrusting, plate-like, lamellar, bilamellar, bifoliate,hollow-ramose, ramose, dendroid, cylindrical, mushroom-like, reticulated,mammillae-surfaced-pillar, nodular, conical, discus-like, wheel-shaped, fan-shaped, gin-ger-like, hemispherical and spherical forms; some of these are large and thin and live infixed position, but others are small, free, inlaid, floating, trundling or paved. Three largegroups of zoarial shapes were recognized based upon their ecology. The creeping group occupies about 1 / 4 of total collection and be subdivided into 4kinds; (1) stable forms, they lie steadily on substrata, such as Schizoporella unicornis,Arthropoma cecilli, Dakaria granulosa, Perigastrella sp., Schizomavella lepralioides andParasmittina glomerata; they stably attach their rounded colonies to bivalves; others suchas all Petraliella and Adeona, directly lie on the sea bottom. (2) instable forms, they are at-tachcd to bivalves or rocks, including Parasmittina trispinosa nitida, Holoporella erectorostris, Hippoporina elegans and Cosciniopsis fallax, but they may also lie on corals orsome other Ascophora, such as Retepora and Adeonella. Among them, P. trispinosa nitidaappears plate-like on rocks but encrusting or subnodular on bivalves or on Retepora; H.elegans appears encrusting on bivalves but subramose on corals. (3)abnormal forms, suchas Coleopora lagena Lu is fixed on small pebbles at its infancy stage but its colony ishemispherical at their adult stage, so that there are free and paved zoaria with their rootlets.(4) alternating forms, for example, Hippoporina elegans appears encrusting, plate-like andsubramose, found from different water depths. The erect group occupies about 1 / 5 of total collections with solid body only and atta-ched its proximal parts to sea bottom or other substrata. They grow upward, usually in aslightly high energy and shallow water region. Consequently some encrusting Ascophoraenclose entirely crinoid stems, sponge spines, worm-tubes, etc., forming hollow ramosecolonies, such as Coleopora sp., Cellepora sp. and some Parasmittina; they are solid, growupward, but do not attach its proximal parts to sea bottom. In the study area, another hol-low-ramose species Parasmittina crasslandi vacuramosa lacks substratum in zoarial center;it is directly attached to the sea bottom. The free group is represented mostly by family Conescharellinidae, accounts for about1 / 2 of the total individuals and consists of nodular, conical, hemispherical or sphericalforms, mostly inlaid in cavity of coral or sponge, some spreading on sea bottom directlywith their rootlets, but few floating such as circular form Flabellopora planata and sphericalform Costazia radiata (trundle). The Nansha Islands Holocene Ascophora belong to a clearly euryhaline, shallow andtropical bryozoan po