Abstract
Two new species of the family Selachinematidae Cobb, 1915 from an intertidal sandy flat in the East China Sea are described. Both species are distinct rapacious nematodes, preying on other nematodes. Gammanema magnum sp. nov. is characterized by its leaf-like labial setae, large loop-shaped amphideal fovea in the male and small spiral ones in the female, an anterior buccal cavity reinforced by 12 rhabdia, each rhabdion with about six denticles, and two unequally long spicules. Gammanema magnum sp. nov. is a striking species, exhibiting extreme sexual dimorphism in the amphideal fovea, but lacking a gubernaculum or precloacal supplements, all features by which it can be differentiated from congeneric species. Synonchium caudatubatum sp. nov. is characterized by a posterior buccal cavity, with three mandibles each with a large tooth flanked by three smaller teeth on both sides, a transverse oval-shaped multispiral amphideal fovea, and a bluntly rounded tail with a protuberant caudal duct. Synonchium caudatubatum sp. nov. is unique in the genus in having a protuberant caudal duct in the tail end. Furthermore, it differs from its congeners by its mandibles, which have seven teeth each. Synonchium caudatubatum sp. nov. lacks a gubernaculum and a precloacal supplement, both features present in congeners except S. depressum Gerlach, 1954.
Highlights
Within the order Chromadorida Chitwood, 1933, the family Selachinematidae Cobb, 1915 is distinctly characterized by a large buccal cavity divided into two compartments
Gammanema magnum sp. nov. is characterized by its leaf-like labial setae, large loop-shaped amphideal fovea in the male and small spiral ones in the female, an anterior buccal cavity reinforced by 12 rhabdia, each rhabdion with about six denticles, and two unequally long spicules
Gammanema magnum sp. nov. is a striking species, exhibiting extreme sexual dimorphism in the amphideal fovea, but lacking a gubernaculum or precloacal supplements, all features by which it can be differentiated from congeneric species
Summary
Within the order Chromadorida Chitwood, 1933, the family Selachinematidae Cobb, 1915 is distinctly characterized by a large buccal cavity divided into two compartments. Many of them are repeatedly reported as predators of other nematodes, and may play a key role in the ecosystems of coarse sandy sediments given their high diversity and high numbers (Okhlopkov 2003; Tchesunov & Okhlopkov 2006). The taxonomy of Selachinematidae was revised by Gerlach (1964) based on the classification of the buccal cavity structure. Gerlach & Riemann (1973) differentiated two subfamilies within the Selachinematidae based on buccal cavity and cuticular structures. The subfamily Choniolaiminae Schuurmans-Stekhoven & Adam, 1931 is characterized by a buccal cavity reinforced by cuticularized rhabdia in both compartments: six well-developed rhabdia in the broad cup-shaped anterior chamber and three weaker rhabdia in the cylindrical posterior chamber (Tchesunov & Okhlopkov 2006). 15 genera are included in the family Selachinematidae (Vanaverbeke 2015)
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