Four New Nematode Species From the Bothnian Bay, Northern Baltic Sea, With a Redescription of Microlaimus Globiceps De Man, 1880 (Nematoda)

Four free-living nematodes from the Bothnian Bay, the northern part of the Baltic Sea, are described as new to science. A key to the genus Eleutherolaimus Filipjev, 1922, is given. Eleutherolaimus schneideri sp. n. is characterized by unequal cephalic setae and subcephalic setae, subcephalic setae shorter than the head diameter, amphid position in junction of buccal cavity and oesophagus, long cardia and short spicules. Microlaimus limnophilus sp. n. belongs to the group of small microlaimids (shorter than 0.5 mm) and is characterized by very small teeth (dorsal tooth about 0.5 μm long) and wide body annules (2.5-3.0 μm in midbody). Prismatolaimus paraprimitivus sp. n. has a slender body (a = 56-65), outer labial setae and cephalic setae in separate circles, wide amphid (2/3 of corresponding body diameter), precloacal supplements confined to posterior body region and long tail. Halalaimus dimorphus sp. n. is recognized by long amphid, posteriorly narrow oesophagus, setose inner labial sense organs, well-separated head setae, swollen, blunt tail end. The reproductive system of Halalaimus dimorphus sp. n. is unique in showing both sperm and egg dimorphism; the spermatozoa have longitudinal striations. Microlaimus globiceps de Man, 1880 is redescribed.