Koerneria sudhausi n. sp. (Nematoda: Diplogastridae); a hermaphroditic diplogastrid with an egg shell formed by zygote and uterine components

Abstract

AbstractA new hermaphroditic species belonging to the diplogastrid taxon Koerneria is described. Although Koerneria sudhausi n. sp. displays all known apomorphies of Koerneria, it shares apomorphic characters with Mononchoides colobocercus (originally described as Diplenteron colobocercus). I assume that the apomorphic features of Koerneria exist in M. colobocercus too and were overlooked in the original description. Consequently M. colobocercus is transferred from Mononchoides to Koerneria, becoming Koerneria colobocerca n. comb. Koerneria sudhausi n. sp. and its sister species, K. colobocerca, together form the Diplenteron species group within Koerneria. Characteristic features of K. sudhausi n. sp. are the species group-specific prerectum in combination with a short but pointed tail in both sexes. In K. sudhausi n. sp. a stoma dimorphism between stenostomatous and eurystomatous morphs occurs. Eurystomatous K. sudhausi n. sp. hermaphrodites lack two denticles in the armature of the left subventral stegostomatal sector. All adults possess pore-like amphids. Although K. sudhausi n. sp. is hermaphroditic, a considerable frequency of males (up to 16.6%) occurs. In cultures of K. sudhausi n. sp. males are functional. In K. sudhausi n. sp. males, the phasmid is situated between caudal papillae v6 and v7. The formation of a secondary egg shell by a uterine shell gland is described. Koerneria sudhausi n. sp. possesses an exceptionally high number of intestine cells, an inexplicable dimorphism in egg length, and a dauer juvenile that lacks the oily substance usually found in diplogastrid dauers.