| The archinemertean Procephalothrix simulus Iwata,1952, which is one of the most common intertidal nemerteans in Qingdao and vicinity, is selected as experimental animal to study its tolerance to salinity, temperature, pH and three heavy metals (Cu2+, Zn2+ and Cd2+), and the accumulation of three heavy metals.1. The salinity, temperature and pH tolerance of Procephalothrix simulus Iwata, 1952 were experimentally studied. In hypo-media, the nemerteans could survive 96-h in 3.3%o solution at 10℃ (median lethal salinity (LS50) was not determined at this temperature), and 96 h LS50S were 7.3%o and 13.5%o at 20℃ and 30℃ respectively. In hyper-media, 96-h LS50 values were 53.9%o, 47.1%o and 41.4%o at 10℃, 20℃ and 30℃ respectively. The trend of body weight changes in diluted media indicated that this nemertean is a volume regulator. During a 96-h exposure in media of 0℃ worms were thanatoid, but could recover if the temperature was gradually elevated to 20℃. In thermal tolerance experiments, the nemertean survived 96 h in seawater of 30℃, and worms suffered high mortalities when the temperature exceeded 32℃. Present results suggest that the interaction of temperature and salinity on the lethal effects on P. simulus is significant (P<0.01). Elevated temperature decreases the ability of salinity tolerance, and elevated salinity (salinity range 18-38‰) decreases the ability of thermal tolerance. The survival pH level for this nemertean is 5.00-9.20.2. The acute toxicity of three heavy metals (Cu2+, Zn2+ and Cd2+) with different concentrations to the nemertean Procephalothrix simulus Iwata, 1952 was experimentally studied. The results showed that in 24h, 48h, 72h and 96h, the LC50S of Cu2+ were 10.980, 0.498, 0.174 and 0.141mg/L respectively; the LC50S of Zn2+were 24.620, 17.170, 12.507 and 9.152mg/L respectively and the LC50s of Cd2+ were 143.230, 35.150, 15.220 and 10.870mg/L. The toxicity of the three heavy metals to this nemertean species was , Cu2+>Zn2+>Cd2+. The tolerance to heavy metals declined with the time of exposure, and in the first 24h, the tolerance was the strongest, then abruptly dropped. From 24h to 48h, 48h to 72h and 72h to 96h, the LC50 changed much slowly. When exposed in metal solutions, the nemertean showed a series of reactive behaviors including the eversion of the proboscis, autotomy and mucus secretion.3. The accumulation of heavy metals by the nemertean Procephalothrix simulus Iwata,1952 were studied. The result showed that the metal concentrtion in whole body tissues was significantly increased (P<0.05) after worms were exposed in 15μg/L Cu2+ solution for 6 d, in lmg/L Zn2+ solution for 3 d and in lmg/L Cd2+ solution for 6 d. The tissue concentration of three heavy metals increased with the increase of exposure time. During depuration experiment, the nemerteans exposed to Cu2+ and Zn2+ solution recovered much well than those exposed to Cd2+ solution. The result showed that the nemertean had a high capability of accumulation and satisfied a series of the needs for biomonitors, so the nemertean can be regarded as an efficient biomonitor.
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