The antioxidant enzyme activity and malondialdehyde(MDA) content of Cephalothrix hongkongiensis were studied to assess variations in the biochemical/physiological parameters of nemerteans under heavy metal stress.Worms were exposed to copper,zinc and cadmium solutions at different concentrations,and the activity of three antioxidant enzymes,catalase(CAT),superoxide dismutase(SOD),and glutathione peroxidase(GPX),and MDA content were measured.The results show that the activity of each enzyme changed immediately after exposure to heavy metals.CAT was invariably inhibited throughout the experimental period,while the SOD activity was significantly elevated by exposure to Cu^(2+) for 48h,but then decreased.SOD was inhibited by Zn^(2+) during the first 12h of exposure,but activated when exposed for longer periods.Under Cd^(2+) stress,SOD activity decreased within 72h.GPX activity varied greatly,being significantly increased by both Cu^(2+) and Zn^(2+),but significantly inhibited by Cd^(2+) in the first 12-24h after exposure.MDA content increased on Cu^(2+) exposure,but normally decreased on Zn^(2+) exposure.MDA content followed an increase-decrease-increase pattern under Cd^(2+) stress.In conclusion,the antioxidant system of this nemertean is sensitive to heavy metals,and its CAT activity may be a potential biomarker for monitoring heavy metal levels in the environment.
We performed a karyotype analysis on four species from Phylum Nemertea using regenerating somatic cells. Two palaeonemertean species, Cephalothrix hongkongiensis and Cephalothrix sp., had the same chromosome number （2n=28）, but different karyotypes （16 m＋10 sm＋2 st, NF=54 and 22 m＋4 sm＋2 st, NF=54, respectively）. The karyotypes of the two heteronemerteans, Notospermus geniculatus and Ramphogordius sanguineus were 2n=38, 30 m＋6 sm＋2 sm/st （NF=76/74） and 2n=56, 48 m＋4 sm＋4 sin/st CNF=112/108）, respectively.
