LIFE HISTORY OF THE FREE-LIVING MARINE NEMATODE CHROMADORITA TENUIS (NEMATODA: CHROMADORIDA)
, BY
PREBEN JENSEN Marine Biological Laboratory, University of Copenhagen, Strandpromenaden, DK-3000 Helsingor, Denmark
The life history of the free-living marine nematode Chromadoritatenuis was studied in the laboratory at 2°C, 10°C and 18°C in agar plates based on 6°/ooS seawater. The duration of all developmental stages was temperature-dependent and increased with decreasing temperature; fecundity decreased with decreasing temperature. Juveniles of C. tenuis as well as three other chromadorids studied have a replacement tooth behind the dorsal tooth. The cuticularized lin- ings of the buccal cavity and the oesophagus are renewed during the moulting process; the old lining is passed into the intestine, whereas the body cuticle is shed into the medium. The number of generations produced annually by C. tenuisis estimated at 8-10 under temperature and salinity conditions prevailing in the Baltic Sea. Keywords:Embryology, development time, temperature, Baltic Sea.
Free-living nematodes are the most diverse, abundant and widespread metazoan group in the benthos (Glowacka et at. , 1976; Fenchel, 1978; Platt & Warwick, 1980; Jensen, 1983). Kinne (1977) reviewed information on the life cycles of these animals. Subsequent information has been presented by Tietjen & Lee (1977), Bergholz & Brenning (1978), Heip et al. (1978), Alongi & Tietjen (1980), Schiemer et al. (1980), Smol et al. (1980), Vranken et al. (1981), Warwick (1981a and b). For longer-lived species, the number of generations produced annually may be estimated from field studies (e.g. Smol et al., 1980). For shorter-lived species this is almost impossible because their generations mostly overlap. In order to obtain ecological information for shorter-lived species, laboratory experiments that cover the annual range of variables normally encountered by these organisms are necessary. The present paper gives information on the influence of temperature on the reproductive potential of the nematode Chromadorita tenuis (G. Schneider, 1906), living on the submerged vegetation of brackish waters (Jensen, 1983). Observations on embryonic development and the moulting process in C. tenuis and related species are also presented. C. tenuis has been much studied in the Baltic Sea (Jensen, 1979; 1981; 1982a and b; 1983) where the salinity is stable at 6°/0o S. Another paper on food consumption and growth of C. tenuis is being prepared. Von Thun (1968) also studied C. tenuis in the laboratory at 15°/0o S, some of his results being summarized by Gerlach (1971 and 1972). 336
This study is part of a project on the behaviour and ecology of Baltic Sea nematodes carried out at the Tvarminne Zoological Station, University of Helsinki, Finland and the Marine Biological Laboratory, University of Copenhagen, Denmark.
MATERIALS AND METHODS
The 2°C, 10 ° C and 18 ° C laboratory conditions, in which the animals were raised, were selected as representative of local conditions during winter (November-May), spring and autumn (June and September-October) and summer (July-August) respectively (Fig. 1). Chromadorita tenuis as well as
Fig. 1. Monthly water temperature (mean and range) at 2 m depth close to Tvarminne Zoological Station, southern archipelago of Finland. No measurements between February and May 1979.
Chromadorita,fennica,Jensen, 1979, Hypodontolaimus balticus (G. Schneider, 1906), Ptycholaimellus ponticus (Filipjev, 1922), Punctodora ratzeburgensis (Linstow, 1876), Chromadorina erythropthalma (G. Schneider, 1906) and Prochromadora orleji (De Man, 1880) from submerged vegetation and the benthos were raised in the laboratory in 87 mm Petri dishes containing 0.8% agar, 6°/0o S seawater and inoculated with the pennate diatom Nitzschia palea var. debilis (Kütz.) Grunow (as Nitzschia sp. in Jensen 1982a and b). Cultures of C. tenuis were observed repeatedly during 18 months (May 1980-October 1981), with transfers to new