| The present paper embodies two studies: faunal analysis of aquatic oligochaeta in Zhongshan, South China, and environment gradient analyses of zoobenthos in 13 Yangtze shallow lakes. Environment-indicating functions of zoobenthos were preliminarily constructed. The results are mainly as follows:1. Altogether 31 species of aquatic oligochaetes belonging to 16 genera and 4 families were identified. Among them, Aulophorus flabelliger (Naididae) is recorded from China for the first time.2. Aquatic oligochaetes were unevenly distributed in Zhongshan waters and species numbers in various habitats were significantly different. There were a lot of taxa in heterogeneous habitats, but few in homogeneous habitats.3. It is shown that Zhongshan has more thermophilus species than northern areas of China. Among the fauna, Branchiodrilus simperi and Aulophorus flabelliger are tropical species, distributed in Guangdong and Guangxi of South China and around the tropics of India, East Africa, Australia and USA.4. The relationships between zoobenthos and environment variables in 11 Yangtze-isolated lakes were revealed by Canonical Correspondence Analysis (CCA). Water depth and Secchi depth were found to be the most important environmental factors regulating the distributions of zoobenthos. Niche differentiations occurred among 32 species in water depth and Secchi depth. Ten species including Rhyacodrilus sinicus, Aulodrilus pluriseta, Nais inflata, Cricotopus, Limnoperna lacustris, Alocinma longicornis etc., had significantly positive correlations with water depth; 18 species including Polypedilum, Hippeutis umbilicalis, Procladius, Microchironomus etc., had significantly positive correlations with Secchi depth; Four species, Limnodrilus sp., Chironomus, Glyptotendipes and Tanypus, had significantly negative correlations with depth and Secchi depth. Based the optimum value of each species, a zoobenthos-water depth indicatory function was generated as y=-0.8+1.22x, and a zoobenthos- Secchi depth indicatory function was generated as y=-0.67+1.77x. The validation results showed that the observed and predicted values were significantly correlated (r=0.78 and r=0.81 respectively, n=58, p<0.001).5. The relationships between zoobenthos and environment variables in 2 Yangtze-connected lakes were revealed by CCA. Water velocity and water depth were found to be the most important factors regulating the distributions of zoobenthos. Niche differentiations occurred among 29 species in Secchi depth, water velocity and water depth. Four species including Alocinma longicornis, Parafossarulus striatulus, Oncomelania hupensis and Clinotanypus, had significant positive correlations with Secchi depth; 18 species including Polypedilum, Limnodrilus hoffmeisteri, Limnodrilus sp., Stenothyra glabra, Limnoperna lacustris etc., had significant negative correlations with water velocity; 12 species including Stictochironomus, Chironomus, Einfeldia, Rhyacodrilus sinicus, Bellamya, Semisulcospira amuremis, Semisulcospira cancellat etc., had significant negative correlations with water depth. Based on the optimum value of each species, a zoobenthos-water depth indicatory function was generated as y=3.32+0.097x, and a zoobenthos-water velocity indicatory function was generated as y=0.16+0.21x. The validation results showed that the observed and predicted values were significantly correlated (r= 0.83 and r= 0.79 respectively, n=24, p<0.001).At the end of this summary, the author presents diagnoses of the new record species.Aulophorus flabelliger Stephenson, 1931 (Fig. 2-7- A, B, C)Material: IHB GD2005006a-b, two whole-mounted specimens; IHB GD2005006c-d, two glycerine-mounted specimens; GD2005006e, one specimen in 10% formalin; all from plant zoots in Beitaiyong stream (22°26′29.7″N, 113°22′34.9″E) of Zhongshan. The specimens are deposited in the Institute of Hydrobiology (IHB), Chinese Academy of Sciences, in Wuhan, China. Description: Five complete preserved specimens about 3mm long, 0.18mm wide, 21-26 segments. Body transparent. No eyes. Dorsal chaetae from VI onwards. 1 hair per bundle, 72-76μm long. 1 palmate needle per bundle, 44-48μm long, 2.7-2.9μm thick, with nodulus distal; teeth strongly diverging, maximally 12μm wide, distal one 12μm long and proximal 10μm long, with web and 20-25 intermediate teeth. Ventral bifids of II-V 3-5 per bundle, 90-102μm long, 2.4-2.5μm thick, longer and thinner than the rest, with nodulus proximal; distal tooth 5.0μm long and proximal 2.9μm long. Those following 3-4 per bundle, 44-52μm long, 1.9μm thick, with nodulus distal; distal tooth much shorter and thinner than proximal (1.5μm : 2.9μm in length, 0.7μm : 2.1μm in base thickness). Branchial fossa with 3 pairs of long, cylindrical gills, and a pair of finger-like parallel palps. Portable tube about 4 mm long, 0.24 mm wide, delicate and transparent.Remarks:This tropical species was originally described from Kenya (Stephenson, 1931), and subsequently reported also from Somalia (Ercolini, 1970), Australia (Brinkhurst & Jamieson, 1971), India (Kalpana & Naidu, 1979) and southern USA (Brenneman, 1980). Our material conforms to the previous descriptions (Stephenson, 1931; Ercolini, 1970; Brinkhurst & Jamieson, 1971; Kalpana & Naidu, 1979; Brenneman, 1980) in most aspects, but needles are different to some extent (Table 2). Under an oil immersion objective, needles of our specimens were found to have numerous intermediate teeth, which have not been mentioned before. The forms of Somalia and India were reported to have web indentations near distal teeth of needles, and those of Kenya, Australia and USA near proximal teeth. The authors are of the opinion that the difference in needles is a matter of observation, for the numerous teeth are rather difficult to be distinguished from the web; under a 40×objective, the needles of Zhongshan worms were similar to the published drawings. In addition, hairs and needles of the present specimens are somewhat shorter than those in the previous descriptions.Distribution and habitat: Zhongshan of south China (new record), India, East Africa (Kenya, Somalia), Australia, and USA (Louisiana); all tropical and subtropical regions (31°N-29°S). Decomposing roots of water-plant in ponds and streams.
|
PDF Full Text Request