Diplolaimella dievengatensis sp. n. was sampled from the Dievengat, a thalassic water pond situated near Knokke in North Western Belgium. The different juvenile and adult stages are described in detail. The male of D. dievengatensis is characterised by the length of the spicules ( > 25 μm), the prominence of the gubernacular apophyses and the presence and position of five pairs of equal and prominent post-cloacal genital papillae. The female is characterised by the sclerotizations of the vaginal cuticle and the absence of a postvulval uterine sac.

This study deals with five species (two of them new) of the family Monhysteridae belonging to three genera and identified as: Monhystera uncigubernaculum sp. n., M. magnacephala, Eumonhystera sudanensis sp. n., Monhystrella paramacrura and M. hastata. Females of M. uncigubernaculum sp. n. are characterized by the presence of large coelomocytes in the region of the uterus; two to the right side of its posterior part and several on the left side of its anterior part, the presence of two large postvulval gland cells, large uterus and long anteriorly bent vagina. Males are characterized by the presence of large amphidial apertures, long slender spicules and the presence of a unique, long, hook-like, posteriorly directed gubernaculum. E. sudanensis sp. n. is characterized by the presence of perioral platelets, the more posterior position of amphidial apertures with clear amphidial canals and pouches, the presence of refractive ocellus-like bodies, clear outlets of pharyngeal glands and excretory pore and with shorter tail length compared to vulva-anus distance. The genus Monhystera is discussed. Eumonhystera crassa is differentiated from E. dispar. S.E.M. photo's are given for three species.

The genus Monhystrella Cobb, 1918 is redefined and an up‐to‐date list of its species is given. Illustrated keys to both females and males of the species are provided, including the description of the most important characteristics for each species.

The type of material ofMonhystrella parvella (Filipjev, 1931) comb.n. from Abyssinia (Ethiopia) is redescribed and figured in detail. Data on the genital system and the ontogeny of this species are given. Monhystera filiformis sensu Gerlach, 1951 nec Bastian, 1865 of the Black Sea at Pomorie (Bulgaria) is synonymised with M. parvella. The Black Sea specimens have a shorter pharynx, a longer tail and differ also from the Abyssinian specimens in the shape of the tail and the spinneret outlet.

During the past three decades, much attention has been given to free-living nematodes and, in particular, to the species of the African continent. Despite the current absence of evidence for the existence of planktonic species, several conditions are suggested that could lead to intrusion of the planktonic habitat, e.g. turbulent shallow waters, high food densities and preadaptations such as swimming ability and negative geotaxis. A new and more practical ecological classification of the inland free-living nematodes is proposed to avoid further incoherency in this regard. All the free-living inland aquatic species described in Africa are presented here in a checklist, including notes on their ecology and distribution. Many of the cosmopolitan species, included in the checklist, are now increasingly being recognized as conglomerates of species, each species of which occupies a restricted area. Finally the distribution of free-living inland aquatic species in Africa is discussed and some preliminary notes are presented.