Descriptions of Eumonhystera borealis n. sp., Sphaerolaimus occidentalis n. sp., and a Redescription of S. gracilis de Man 1876 (Nemata) from Bothnian Bay, Baltic Sea.

The free-living nematodes Eumonhystera borealis n. sp., Sphaerolaimus occidentalis n. sp., and S. gracilis de Man 1876 from Bothnian Bay in the northern Baltic Sea are described and illustrated. Eumonhystera borealis n. sp. differs from other species by its small body size (314-393 μm), narrow body (a = 37-49), and large anterior amphids. In Sphaerolaimus occidentalis n. sp. the amphids are posterior to the buccal cavity, and it differs from other similar species by having two sclerotized rings in the posterior part of the buccal cavity. An intersex is reported for S. gracilis. Sphaerolaimus gracilis is cannibalistic or a predator of other species, with a preference for E. borealis n. sp. Sphaerolaimus occidentalis n. sp. coexists with S. gracilis at depths of 80 m but not at 12 m.