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Position of Pharyngeal Gland Outlets in Monhysteridae (Nemata)

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Position of Pharyngeal Gland Outlets in Monhysteridae (Nemata) Journal of Nematology 28(2): 169-176. 1996. © The Society of Nematologists 1996. Position of Pharyngeal Gland Outlets in Monhysteridae (Nemata) A. COOMANS, I A. EYUALEM, 1'2 AND M. C. VAN DE VELDE 1 Abstract: In this study an attempt was made to determine the position of the outlets and nuclei of the pharyngeal glands in four monhysterid genera. Five Eumonhystera spp., seven Monhystera spp., and eight Monhystrella spp. were studied under the light microscope. Longitudinal sections of an undescribed Monhystera sp. and cross sections of Geomonhystera ckisjuncta were also studied under the scanning and transmission electron microscope, respectively. The results of the light microscopic studies were inconclusive about the position of the outlets but showed a number of nuclei in the basal part of the pharynx. The scanning and transmission electron microscopic studies revealed five pharyngeal glands and their outlets; their position was as follows: dorsal gland outlet at the base of buccal tooth, first pair of ventrosublateral gland outlets halfway along the pharynx, and second pair of ventrosublateral gland outlets close to the base of the pharynx. It is concluded that at least three, and possibly five, nuclei are in the basal part of the pharynx. This pattern, in the position of the outlets and nuclei, is similar to that in Caenorhabditi6 elegans (Maupas, 1900) Dougherty, 1953 and may well be the basic plan in the Class Chromadorea (including Secernentia as a subclass). Key words: Geomonhystera, Monhystera, Monhysterida, morphology, nematode systematics, pharyn- geal gland outlet, pharynx, scanning electron microscopy, transmission electron microscopy, ultra- structure. The number, shape, and position of near the base of the stoma; the ventrosub- pharyngeal glands, and especially the po- lateral (="subventral") glands never open sition of their nuclei and outlets, are im- at the anterior end of the pharynx. This portant features to establish phylogenetic arrangement is in contrast to Enoplida, relationships among nematodes at several where a pair of ventrosublateral glands of- taxonomic levels (2,4,5,10,13). Typically, ten opens through teeth in the stoma or at nematodes have three or five pharyngeal the anterior end of the pharynx, as the glands (one dorsal and one or two pairs of dorsal gland does. ventrosublateral glands). Maggenti (12) Monhysterida are usually classified as an considered the five glands to be an ances- order in Chromadoria (11,12). Chitwood tral character found in Enoplia and the and Chitwood (2) presented diagrams on presence of only three glands in Chroma- the position of pharyngeal nuclei in five doria (including Monhysterida) as derived. monhysterid genera (Desmolaimus de Man, Three glands in Secernentea was also con- 1880, Siphonolaimus de Man, 1893, Ter- sidered derived. However, he further schellingia de Man, 1880, Theristus Bastian, stated that five glands might be derived 1865, and Tripylium Cobb, 1920). The nu- from three glands by duplication of the clei of one dorsal and one pair of ventro- subventrals in some Chromadoria and Se- sublateral glands were shown in the poste- cernentea. On the other hand, examples rior region of the pharynx; the outlets of exist in some taxa, e.g., Dorylaimida, these glands were depicted at or close to where five glands have been reduced to the base of the stoma for the dorsal gland three (Longidoridae) (14). (all five genera), and close to the nerve ring According to Chitwood and Chitwood for the ventrosublateral glands (in Ter- (2), Chromadoria, such as Monhysterida, schellingia, Theristus, and Tripylium). This have only the dorsal gland opening at or pattern agrees with that of Chromadoria in general. Received for publication 15 May 1995. Riemann (13) described the pharyngeal 1 Zoology Institute, Ledeganckstraat 35, 9000 Gent, Bel- glum, and 2Bahir Dar Teachers' College, Addis Ababa Uni- glands of Linhomoeidae, a family of Mon- versity, Personal P.O. Box 223, Bahir dar, Ethiopia. hysterida. In Paralinhomoeus de Man, 1907 The authors acknowledge the technical assistance of R. V. Driessche for processing the samples, mounting the slides, and Anticyclus Cobb, 1920, the orifices of and making sections. one dorsal and two ventrosublateral glands 169 170 Journal of Nematology, Volume 28, No. 2, June 1996 are situated in the stoma region. In the positions of S1N (at level or just poste- Eleutherolaimus Filipjev, 1922, an addi- rior to nerve ring) and S2N (near base of tional pair of ventrosublateral glands with pharynx). orifices at the level of the nerve ring was described. Riemann (13) referred to a pa- MATERIALS AND METHODS per by zur Strassen (17) in which the latter Specimens for light microscope (LM) author described ventrosublateral gland and scanning electron microscope (SEM) openings close to the anterior end of the observations were fixed with hot (--+60 °C) pharynx in Siphonolaimus. On the basis of 4% formaldehyde. Nematodes were ex- these observations, Riemann (13) pro- tracted with centrifugal flotation from posed classifying Linhomoeidae and Si- freshwater sediment of Lake Tana, Ethio- phonolaimidae in Siphonolaimoidea and pia. Ludox (50% silicasol [SiO2] colloid so- to differentiate this superfamily from lution) was used as an extraction agent. Monhysteroidea by the position of the For SEM, nematodes were hand-sectioned pharyngeal gland outlets, among other longitudinally under a binocular micro- characters. This proposition was accepted scope; the longitudinal sections then were by Lorenzen (11). dried with the critical point drying proce- Jacobs et al. (9) described three pharyn- dure and attached to self-adhesive tape, geal gland cells (one dorsal and a pair of coated with gold, and studied under SEM, ventrosublateral) in Diplolaimella dievenga- according to the procedures of Eyualem tensis Jacobs, Van de Velde, Geraert & and Coomans (6). Nematodes for trans- Vranken, 1990, occurring at the base of mission electron microscopy (TEM) were the pharynx. The ventrosublateral nuclei isolated from "Sluice Dock" Ostend, a were referred to as S2N 1 and S2N 2 in the man-made marine lagoon near the Belgian text (p. 9-10) as well as on the illustration coast, and cultured according to Vranken (Fig. 10H,J) (9). Another pair of smaller et al. (16). Specimens were picked from but still prominent nuclei were located just petri dishes, cooled in an ice-bath to behind the nerve ring. These nuclei were stretch, and then killed and fixed in an ice- referred to as SIN 1 and SIN 2 in the text (p. cooled fixative composed of 1.5% acrolein, 10), where it was mentioned that "these 3% glutaraldehyde, and 1.5% paraformal- were first interpreted as gland nuclei"; but dehyde in 0.2 M sodium cacodylate buffer. SIN s and S1N 2 were still explained as "an- After fixation and rinsing, the specimens terior set of ventrosublateral gland nuclei" were post-fixed in 2% osmium tetroxide, in the legend to Fig. 10. Thus, there re- followed by en bloc staining in 2% uranyl mains some ambiguity about the ventro- acetate. Other details of the procedures of sublateral nuclei. nematode preparation for TEM were Jacobs and Heyns (7) described five pha- those described in Van de Velde and ryngeal glands in Monhystera coomansi Ja- Coomans (15). cobs & Heyns, 1992: one dorsal gland with nucleus (DN) at the base of the pharynx RESULTS and the outlet (DO) at the base of the Light microscopic observations on dif- stoma, a first pair of ventrosublateral ferent Monhysterids, viz. Monhystera cf. glands with nuclei (SiN)just in front of the gabaza Joubert & Heyns, 1980; M. somereni nerve ring and outlets ($10) at the base of Allg~n, 1952; four undescribed Monhystera stoma, and a second pair of ventrosublat- spp.; Monhystrella macrura (de Man, 1880) eral glands with nuclei (S2N) between level Andr~ssy, 1981; M. lepidura altherri (Juget, of DN and nerve ring and outlets ($20) at 1969) Jacobs, 1987; six undescribed Mon- level of nerve ring. Jacobs et al. (8) rede- hystreUa spp.; Eumonhystera dispar (Bastian, scribed three Monhystera species and gave 1865) Andr~issy, 1981; E. filiformis (Bas- the same interpretation as Jacobs and tian, 1865) Andr~issy, 1981; E. pseudobul- Heyns (7), with the only difference being bosa (yon Daday, 1896) Andr~ssy, 1981; E. Pharyngeal Gland Outlets in Monhysterids: Coomans et al. 171 mwerazii (Meyl, 1957) Andr;issy, 1981; and f E. vulgaris (de Man, 1880), Andr/tssy, 1981, did not yield conclusive evidence about the exact position of the pharyngeal DO -- -- "'-~ gland outlets and nuclei. The dorsal gland I nucleus (DN) is situated near the base of the pharynx, and the cell extends to the stoma region. The ventrosublateral sectors are often vacuolar, which makes it difficult to locate the gland nuclei. However, a pair of nuclei in sublateral to lateral position was found in most specimens slightly be- hind the level of DN. A second pair of such nuclei was seen, though less frequently, anterior to the level of DN at less than two pharynx widths from pharynx base. Still other nuclei occur and, apart from DN, it is impossible to decide whether the above- mentioned nuclei are really S2N and S1N. Glandular tissue in the ventrosublateral sectors was observed up to the nerve ring (Fig. 1). -- -- f-,.,-,lmD Scanning electron microscopy of longi- $10 f " J tudinal sections of an undescribed Monhys- A tera sp. revealed five outlets (Fig. 2). The l ' dorsal outlet (DO) is a small (about 0.7- I Ixm-long) slit just behind the small dorsal I a tooth (Fig. 2B). A first pair of ventrosub- t f # lateral gland outlets ($10) occurs at 52- | I !-. 54% of the pharynx length, at the level of I the nerve ring (Fig. 2A,C); a second pair I ($20) occurs at 83-85% of the pharynx S1 " length (Fig. 2A,D). $10 and $20 are about S20-- t t 1-~m-long slits (Fig.
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