Quantitative extraction of living Plathelminthes from marine sands

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Abstract
Quantitative extraction of soft-bodied meiofauna from marine sands has been an unsolved problem. The SMB-method (sewater, magnesium chloride, beaker) is described and tested, which combines several previously used methods. It yields high extraction efficiency for living Plathelminthes, when compared to both grain-method (equivalent to a thorough grain-by-grain inspection of the sample) and flask-method (based on anesthetization with MgCl2-solution). Tested first on eullittoral sand, the latter 2 methods revealed significant personal bias for the investigators, which for the SMB-method was avoided by adjusting the procedure of the technique in every detail. The sublittoral sets of samples subsequently studied proved the effectiveness of the SMB-method, which when tested against the grain-method did not differ significantly from it, either in overall examination or for single taxa of Plathelminthes. The SMB-method is recommended as a time-saving method with high extraction efficiency for living Plathelminthes from marine stands; it includes the following essential points: 4 initial seawater-washes to avoid damage to delicate specimens; application of hypertonic MgCl2-solution; at least 1 final ethanol-wash; use of a beaker of 1000 cm3; 1 or 2 gauzes with minimum mesh size 40 .mu.m; sample volume must not exceed 50 cm3 in a ratio of 1:5 with the supernatant fluid and multiple searches of Petri-dish contents. The 4 initial seawater-washes yielded 61% of the extracted plathelminthes. Addition of the MgCl2 wash and 2 brief seawater washes separated 97.3% of all individuals from the sediment. The final ethanol washes were required only for Proseriata. Caution must be advised as to species-specific extraction behavior in different sediments.