Etienne Geraert

Morphometric relations in nematodes.

In descriptions of nematodes it is often customary to use the ratio between two well-defined distances rather than the absolute measurements of the same distances. The most widely used ratios are a, b, c, V and T. Examinations have proved that it is advisable to discard some of them; details are mentioned under Conclusions, p. 182.

COMPARISON OF THE HEAD PATTERNS IN THE TYLENCHOIDEA (NEMATODA)

The first comparative study of head patterns in tylenchs was that of Sher & Bell (1975). De Grisse (1911) and Coomans & De Grisse (1981) srudied rhe underlying nervous system. The new information added since then is reviewed in this paper to see if the various patterns are characteristic of higher groupings (e.,9. families) within the Tylenchoidea. Therefore I used published and unpublished scanning electron micrographs (sEM) to produce schematized drawings. Comparing the photographs it was obvious that variation was found in the expression of pattems and sensilla. The schematized drawings give the maximum infbrmation obtained: e.g. whatever sensillum, distinct on a single photograph of a species or genus, was added on the drawing. In contrast to other nematodes there are no distinct lips in tylenchs. The head is an amalgamated lip region, internally strengthened by a cephalic framework and often including annuli, perhaps derived from ones formerly part of the body. The head can be continuous with the body, or variously offset but is always small to very small and unspectacular. It bears the mouth opening, which is nlinute and situated apically and centrally. There are two consecutive openings: the mouth opening seen at the outside is the prestoma opening: small, rounded to oval in Tylenchoidea and Aphelenchina, dorso-ventral slit to I-shaped slit in Criconematoidea. The stoma opening is found less than a micrometer to the

Comparative morpho-anatomical studies of the female gonoduct within the Pratylenchidae (Nematoda: Tylenchina)

Summary ‐ The cellular morphology of the gonoduct of six Pratylenchus species, three Pratylenchoides species, Radopholus similis , Zygotylenchus guevarai, Hirschmanniella looe and Nacobbus aberrans was revealed by dissection and light microscopy. Except for Nacobbus aberrans , all studied species show an overall similarity in gonoduct construction, i.e., an ovary often ending with a ring of cells, an oviduct formed from two rows of four cells and a 12-celled spermatheca followed by a tricolumella containing 16-24 cells. Pratylenchoides magnicauda and Z. guevarai did not diverge from the other Pratylenchidae in this respect, although their gonoduct differs from that of Amplimerlinius and Meloidogyne , both formerly postulated as related genera. The spermatheca structure observed in N. aberranshas not been reported elsewhere in the Nematoda, although the uterus is similar to that reported within the Heteroderinae and Meloidogyninae and the uterus comprises more than 300 cells, enlarging from a tricolumella to a polycolumella. Transmission electron microscopy of Z. guevarai revealed details of the cytoplasmatic contact between epithelial cells and the germ cells; a e ngerlike ovarian wall cell extension was found penetrating the oocyte. The oviduct lacks a preformed lumen and comprises eight cells with highly plicated cell membranes. The spermatheca is constructed from e attened wall cells and is followed by columnar uterus cells where evidence of eggshell formation was demonstrated.

The cellular structure of the female reproductive system within the Heteroderinae and Meloidogyninae (Nematoda)

Gonads from living young females, representing 23 different species, were extracted to study the cellular structure of the female genital structure within the Meloidogyninae and Heteroderinae. All genera studied can be characterised by their cellular spermatheca morphology. Within Meloidogyne a spherical spermatheca is found with lobe-like protruding cells, most species having 16 to 18 spermatheca cells with interlaced cell boundaries while M. microtyla and M. ichinohei have more spermatheca cells with different cell boundaries. Heterodera and Globodera reveal a comparable gonad structure. The spermatheca cells of Heterodera are columnar and arranged in a restricted number of rows, whereas in Globodera the spermatheca cells are squarish to rounded, depending on the species. The gonad morphology of Afenestrata koreana is clearly different from what would be expected based on the related genera Globodera and Heterodera. The apparently simplest genital system was found in Meloidodera floridensis where the uterus has a limited number of cells. In the other genera studied a large and variable cell number was found.

Some Species of Dorylaimoidea Found in Belgium

Four species of monodelphic Dorylaiminae, belonging to three different genera were collected from meadow and arable land in Belgium. Additional specimens of Eudorylaimus monohystera from the Netherlands and Germany and of Pungentus silvestris from the Netherlands and England have been included in our study. One of us (E.G.) studied the Pungentus sp. more extensively, but as both species have been extensively described in the literature, a complete redescription is not presented here.

Structure of the Female Reproductive System in Some Dorylaimida and Enoplida (Nematoda)

A detailed study of the female reproductive system in the nematode orders Dorylaimida and Enoplida showed that the structure of ovary and oviduct was largely similar, whereas that of the uterus varied, depending on the species. The wall of the ovary at the germinal end is formed by many small cells; the oviduct consists of a single row of disc-like cells without a distinct central lumen. The oviduct starts closer to the germinal end of the ovary in enoplids, about the middle of the ovary in mononchs and closer to the end where the eggs ripen in dorylaims. A spermatheca is always absent. Trichodorids (usually considered as dorylaims) show such important dissimilarities in the structure of the female reproductive system that their current position within the Dorylaimida and even within the Enoplia becomes questionable.

Description of Hemicriconemoides Para Taiwanensis Sp.N. (Criconematidae) and Four Other Hemicriconemoides Species From Papua New Guinea With a Consideration of Variability in the Genus

Hemicriconemoides populations from Papua New Guinea contained H. parataiwanensis sp. n. (differing from H. taiwanensis in head shape, stylet length and RVan value), H. mangiferae, H. cocophillus, H. gaddi and H. obtusus. H. mangiferae was represented by two populations, so different from each other that their inclusion in the same species could only be concluded after comparison with some twenty populations from the literature. This study of variability demonstrated that the number of body annuli is correlated to body length, suggesting that annulus width is constant in Hemicriconemoides species; other correlations found are between number of body annuli and stylet length and between body annuli and vulva position. SEM study of the en face view revealed four different types of head structure: the most common one shows a narrow oral disc and two large, but covered, amphidial openings; a second type shows a large raised oral disc with an outer rim with amphids sometimes indistinct; while third and fourth types are represented only by one Australian species each.

Growth and Form in Nematodes: Iv. Tail Length and Vulva Position

During post-embryonic growth tail length can increase, remain constant or even decrease. Usually, such changes cannot be explained as populations of the same species may behave differently. The differences in length between males and females is based, I suggest, on the mechanics of mating and on requirements for defaecation. The constant position of the vulva is probably not essential functionally but may arise from the cell-constancy of the nematodes and equal elongation of epidermal cells in front of and behind the vulva. The position of the vulva is usually expressed as a percentage of the entire body length but, in several long tailed tylenchs, it is better to calculate it as a percentage of the distance between the top of the head and the anus.

Phasmids in Tylenchulidae (Tylenchida: Criconematoidea)

Light-microscope studies revealed the presence of phasmids in the mid-tail region in species of the genera Tylenchulus, Trophotylenchulus (syn. Trophonema), Sphaeronema and Meloidoderita in Tylenchulidae. Scanning electron microscopy studies on Sphaeronema species verified these observations. Absence of phasmids or phasmid-like structures was confirmed for genera placed in Paratylenchinae and Tylenchocriconematinae in the same family, and for other taxa of Criconematoidea. This first record of phasmids in the superfamily Criconematoidea requires reconsideration of the systematic position of Tylenchulidae and of the relationships of the genera currently placed in this family. Presence of phasmids, deirids and other morphological characters place Tylenchulidae in a basal position in Criconematoidea.

Four rotylenchus from Iran, with a key to the species

A Rotylenchus species, temporarily identified as R. basiri, has males with degenerate stylet and oesophagus, a character not yet found in the genus. The species has been studied by SEM, together with R. agnetis and R. glabratus. The common R. buxophilus is also present in Iran. A tentative key for the 74 nominal species revealed that several of them are difficult to distinguish.