FNZ 55 - Criconematina (Nematoda: Tylenchida) - Classification of the order Tylenchida
Wouts, WM 2006. Criconematina (Nematoda: Tylenchida). Fauna of New Zealand 55, 232 pages.
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ISSN 0111-5383 (print),
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Published 24 Mar 2006
ZooBank: http://zoobank.org/References/088E84BD-3DE3-4EA2-B6D9-C45BBC0A12F1
Classification of the order Tylenchida
Many systems have been proposed for the classification of the plant parasitic nematodes of the order Tylenchida. The majority of these classifications included the aphelenchs as a suborder. Siddiqi (1986, 2000) and Hunt (1993) removed the aphelenchs from Tylenchida, a move with which I concur.
The more recent classifications by Siddiqi (1986, 2000) and Maggenti el al. (1988) and Maggenti (1990) differ generally and are compared in the first 4 columns of Table 1. Only categories represented in New Zealand are included. Categories where the systems agree are placed at the same level. Differences in the classifications are apparent from blank spaces. In the order Tylenchida both Siddiqi (2000) and Maggenti (1990) accept the suborder Tylenchina. Siddiqi (2000) also recognises Criconematina and Hoplolaimina Chizhov & Berezina, 1988, suborders Maggenti considers superfamily and family respectively within Tylenchina. Both authors agree on many of the families, but Siddiqi accepts Tylodoridae (Paramanov, 1967) Siddiqi, 1976, Atylenchidae Skarbilovich, 1959, Meloidogynidae (Skarbilovich, 1959) Wouts, 1973, Hemicycliophoridae Skarbilovich, 1959, Sphaeronematidae (Raski & Sher, 1952) Geraert, 1966, and Paratylenchidae Thorne, 1949, taxa Maggenti either rejects or considers subfamilies, and Maggenti accepts Belonolaimidae (Whitehead, 1960) Siddiqi, 1970, which Siddiqi rejects.
At the genus level the two systems differ further but at this level only differences within Criconematina are considered here. In Criconematidae Siddiqi accepts Crossonema, Macroposthonia, and Criconemoides, genera that Maggenti considers to be synonyms or genus dubius. Siddiqi accepts Blandicephalanema, a taxon Maggenti considers to be subgenus. In Paratylenchidae, Maggenti considers Gracilacus Raski, 1962 to be a genus; Siddiqi considers it a subgenus.
The classification of Criconematina followed here is presented in column 5 and is basically the one proposed by Siddiqi (2000), modified by the results presented in this work.
THE SUBORDER CRICONEMATINA
Classification of the New Zealand taxa of the suborder Criconematina
Suborder CRICONEMATINA
Superfamily CRICONEMATOIDEA
Family Criconematidae
Subfamily Criconematinae
Genus Criconema
Subgenus Criconema
- Nothocriconemella
- Nothocriconema
= Ogma
= Pateracephalanema
= Syro
= Blandicephalanema
- Hemicriconemoidinae
= Hemicriconemoides
- Macroposthoniinae
= Macroposthonia
= Criconemoides
- Criconemoides
- Criconemella
- TYLENCHULOIDEA
= Tylenchulidae
- Tylenchulinae
= Trophotylenchulus
= Tylenchulus
= Sphaeronematidae
- Sphaeronematinae
= Sphaeronema
= Paratylenchidae
- Paratylenchinae
= Paratylenchus
- Paratylenchus
- Gracilacus
- HEMICYCLIOPHOROIDEA
= Hemicycliophoridae
= Hemicycliophora
The suborder Criconematina was proposed by Siddiqi in 1980 for Tylenchida with females in which the procorpus (= precorpus) of the oesophagus has amalgamated with the large muscular metacorpus (= postcorpus/median bulb); and the basal bulb, containing the 3 oesophageal glands, is small; and with males in which the oesophagus is degenerate.
Siddiqi (1986, 2000) further characterises the suborder as obligate plant parasites that show marked sexual dimorphism. The females may be slender, sausage-shaped or obese to spheroid, the males are always slender. The cuticle when coarsely striated generally has no lateral field but may have scales and spines or may be surrounded by a sheath. A finely striated cuticle is generally thin, and deirids and a lateral field may be present; phasmids are absent. The lip region of the female usually consists of 1–3, often modified, annules. The oral opening is a dorsoventral slit in a labial disc that is surrounded by 2 lateral and 4 submedian pseudolips, with no labial sensorial organs apparent. The cephalic framework is hexaradiate. The stylet of the female is of variable length and has well-developed knobs: large knobs are generally anchor-shaped. The procorpus is wide, surrounding the stylet base. The median oesophageal bulb is wide and muscular, containing a large valve. The isthmus is generally narrower than the basal bulb and very thin in some taxa. The orifice of the dorsal oesophageal gland is usually more than 4 µm from the base of the stylet and the oesophago-intestinal valve indistinct. In Tylenchulus Cobb, 1913 the secretory–excretory pore is located posteriorly and produces a gelatinous matrix in which the eggs are laid. The vulva is a transverse oval slit located posteriorly. The female reproductive system consists of a single anterior branch (monodelphic, prodelphic). The gonoduct consists of oviduct, spermatheca, and uterus with differentiated crustaformeria, or egg shell producing region, but without postvulval uterine sac. The spermatheca is offset laterally or ventrally, but is axial when distended with sperm. The vulval lips are open or closed, with or without the anterior lip overlapping the vulva. The slender males are monarchic, i.e., with a single anterior testis, and possess a stylet incapable of tissue feeding. The anus of the male is a small pore. The spicules are relatively long compared to those of other tylenchs, with a small head and slender shaft, often arcuate. The gubernaculum is straight or crescent shape. The caudal alae are not pronounced and may be absent. The cloacal lips are variable.
In these taxa locomotion may be assisted by the flexibility of the cuticle between the annules; and a cuticular sheath may be present in juveniles as well as in females. Submedian lobes may surround the oral disc; the length of the stylet shaft is independent of the length of the conus; and the intestine is syncytial, lacking a definite lumen.
Three superfamilies are recognised: Criconematoidea, Tylenchuloidea, and Hemicycliophoroidea.
CRICONEMATOIDEA: CRICONEMATIDAE
The superfamily Criconematoidea consists of the single family Criconematidae.
Females and juveniles of this family are spindle- or sausage-shaped, in the oesophagus the isthmus is wide relative to the width of the basal bulb, and the cuticle generally has retrorse annules that may bear scales or spines. The family Criconematidae consists of the subfamilies Criconematinae, Macroposthoniinae, and Hemicriconemoidinae.
CRICONEMATINAE
Criconematinae are characterised by the presence of spines or scales on the cuticle of both the females and the juveniles, except for Criconema in which only the juveniles have cuticular appendages and the females are smooth. In New Zealand Criconematinae is the best represented subfamily of the suborder Criconematina. Of the 7 genera recognised by Siddiqi (2000), Criconema, Blandicephalanema, Ogma, and Crossonema are present.
Criconema
Siddiqi (1986) recognises in the genus Criconema the subgenera Criconema, Notholetus, Nothocriconemella, and Paracriconema. In Paracriconema he places species with lip annules that are differentiated from the body annules. In 1984 Raski et al. redescribed C. giardi, the type species of Criconema, as a species with a differentiated lip region in the form of a single lip annule separated from the body annules by a constriction (collar). Siddiqi (2000), therefore, considered Paracriconema a synonym of Criconema.
The lip annule of C. giardi in some specimens indeed looks somewhat set off. Close examination, however, shows that it is not set off but very flexible. It may be retrorse or direct sideways or fold anteriad all in the same specimen, and directed anteriad it may look somewhat set off. In Fig. 4A Raski et al. (1984: 306) illustrate this very well. The lip annule drawn is retrorse and continuous with the body contour on one side of the animal but is directed forward and somewhat set off on the other side. The close-up of a normally occurring configuration of the head in their Fig 4B (p. 306) shows a regularly formed annule, not set off, and continuous with the body contour.
The type species C. giardi, therefore, has a regularly formed discus-shaped single lip annule, a character I have here recognised as characteristic for the subgenus Criconema.
Loof et al. (2001) recognise C. guernei as type species of Criconema, instead of C. giardi. As C. giardi and C. guernei were then considered synonyms this had no effect on the definition of the genus. As I explain in Appendix 1 I consider C. guernei a valid species. Criconema guernei and C. giardi both have the same head configuration and on the basis of that characteristic belong to the same subgenus Criconema. The change of type species, therefore, would not affect the definition of that subgenus. The presence of longitudinal rows of scales on the cuticle of C. guernei, however, profoundly changed the perception of both the genus and the subgenera. The scales make C. guernei identical to Ogma terrestris Raski & Valenzuela, 1987, as explained in appendix 1. O. terrestris is closely related to C. spinicaudatum (Raski & Pinochet, 1976) Raski & Luc, 1958. The 2 species differ only in that C. spinicaudatum has scales on the posterior part of the body, whereas in O. terrestris all body annules bear scales, and should belong to the same genus and subgenus. Their head configuration resembles that of several other Criconema species. These species are here combined in the subgenus Criconema. This new criterion for the subgenus Criconema allows the placement in it of species recognised by Siddiqi (2000) in the subgenus Notholetus. Criconema species with differentiated lip annules include C. annuliferum (de Man, 1921) Micoletzky, 1925, the type species of Nothocriconema De Grisse & Loof, 1965, the most senior and here recognised valid subgenus name for this group of species. Species with more than 1 undifferentiated lip annule are retained in the subgenus Nothocriconemella. Notholetus and Paracriconema are not recognised as valid subgenera.
Subgenus Criconema
This subgenus Criconema is characterised by a single, not distinctly set off, unmodified, somewhat discus-shaped lip annule, which is narrower than the 1st body annule, a rather high labial region, and a conically pointed, set off tail. The subgenus, and the 8 species from New Zealand considered to belong to it, are discussed in Appendix 1. Other species considered to belong to this taxon are: C. giardi; C. cardamomi (Khan & Nanjappa, 1972) Raski & Luc, 1985; C. racemispinosa Mehta, Raski & Valenzuela, 1982 new combination; and C. spicatum (Ebsary, 1981) Raski & Luc, 1985.
All these species have been described from the Southern Hemisphere, with the exception of C. cardamomi (India) and C. spicatum (Hawaii) which may have also originated from this region. The only known host of C. cardamomi is Eletteria cardamomum (L.) Maton (Zingiberaceae), a commercially grown plant that may not be its original host. Criconema spicatum was described from 2 females from moss packing material which may have originated somewhere in the Southern Hemisphere. Both species were described as having 2 lip annules, but in the illustration of C. cardamomi only 1 lip annule is present, and in that of C. spicatum the head is distorted, which may account for the apparent 2nd annule. The Southern Hemisphere occurrence suggests that these species have originated in Gondwanaland.
Other subgenera of Criconema
The subgenera Nothocriconemella Ebsary, 1981 and Nothocriconema De Grisse & Loof, 1965, contain species with females that lack ornamentation on the cuticle. Nothocriconemella species have 2 undifferentiated lip annules and the diameter of the anterior annule is not greater than that of the posterior annule. Nothocriconema species have 1 or 2 differentiated lip annules and the 1st lip annule may has a greater diameter than the 2nd. Like Criconema, Nothocriconemella is well represented in New Zealand. The subgenus Nothocriconema is poorly represented.
Ogma
The genus Ogma is characterised by females that have differentiated lip annules and coarse body annules. The body annules, on their posterior edge, bear outgrowths of different shapes varying from smooth spines and scales to ornate palmate structures arranged in longitudinal rows.
The ornamentation of the female cuticle should have facilitated the definition of the genus, but it has not. In the previous section Ogma terrestris, a species with an undifferentiated lip annule, was transferred to Criconema. Also the distinction between Ogma and other related genera is not at all clear. In Ogma the outline of the cuticle in cross-section appears wavy due to the presence of longitudinal ridges with spines and scales. Especially long and palmate scales form very distinct ridges with the anterior and posterior end views of specimens resembling cogwheels (Wouts et al. 1999). When the number of scales increases to more than 12 the ridges they form become less pronounced, the spaces between them become shallower, and the end view gradually changes to a more regular outline of continuous scales as is considered characteristic of Crossonema. The exact point where the ridges of Ogma make way for the continuous fringe of scales of Crossonema, however, is difficult to establish. Siddiqi (2000) puts the limit at 21. Species with more than 21 rows of spines are considered to have a continuous fringe and regular outline and to belong to Crossonema. In species with more than 14 scales, however, this number per specimen within the species becomes variable and makes this criterion unreliable and difficult to apply. The demarcation between Ogma and Crossonema, therefore, is not distinct. The 2 genera are here considered synonyms and their species are combined in the genus Ogma.
Categorising the subgenera within Ogma has been difficult too. In 1987 Siddiqi recognised 7 subgenera in Ogma (Ogma, Blandicephalanema, Pellipecten Siddiqi, 1986, Croserinema Khan, Chawla & Saha, 1976, Homogma Siddiqi, 1986, Pateracephalanema Mehta & Raski, 1971, and Seriespinula). In 2000 he only retained 4 of these (Ogma, Pateracephalanema, Croserinema, and Seriespinula), and added 2 new subgenera (Orphreyus Siddiqi, 2000 and Macrocriconema Minagawa, 1986).
Only Croserinema (with alternating scales) and Seriespinula (with continuous scales) are further discussed here. Pateracephalanema is recognised as a valid genus and Orphreyus and Macrocriconema do not occur in New Zealand.
To evaluate the significance of alternating scales it is important to know how scales generally appear on the cuticle of the nematode. In the genus Ogma it seems that the annules immediately behind the lip region are smooth or lobed and that further down the body the lobes gradually become longer and form a continuous fringe of spines. This fringe then subdivides and transforms into scales. That in different species this transformation of the fringed edge into rows of scales takes place on different parts of the body is best observed in the otherwise identical species Ogma palmatum (Siddiqi & Southey, 1962) Siddiqi, 1986 and O. civellae (Steiner, 1949) Mehta & Raski, 1971. In O. palmatum the fringe of short spines on the lip region transforms to scales immediately below the lip region. Because the palmate scales of O. palmatum are unique within Ogma in that they alternate in position on the annules, Siddiqi (1996, 2000) placed it as only species in the subgenus Croserinema. In O. civellae the fringe of spines does not organise into ridges of scales until the postvulval region. To place species in which this process takes place over the first 5–10 body annules in a different genus or subgenus than those in which this process takes place near the postvulval region seems unjustified.
Mehta & Raski (1971) were the first to point this out. Mindful of the shared habitat of the 2 species, they wrote: “the juveniles of both are similar, if not identical. Cuticular markings of the adult head and tail region (when palmate in civellae) are similar in both. All other data (stylet length, total body annules, head annule size, total length, etc.) are well with agreement with each other. The major difference between these species is the type of markings on most of the body annules. However, the fact that sometimes unusually large numbers of single spines occur in palmatum brings them closer yet. Whether they are the same species, or closely related but distinct species is not certain. But due to this close relationship they are placed under the same genus”.
I agree that these 2 species belong to the same genus and even the same subgenus Ogma. A similar example of almost identical species, differing only in the organisation of the scales on the cuticle, presents itself in 2 new species from a subalpine region of the South Island, described in this contribution. In one species the fringe of spines breaks up into rows of scales on the anterior part of the postvulval region. In the other species it starts on the first 2 or 3 body annules, so that scales are present along the length of the body. As observed by Mehta & Raski (1971) for O. civellae and O. palmatum, these new species, too, share their habitat, and it could be argued that they are the same species. They are obviously closely related. Again, I accept them as independent species in the genus and subgenus Ogma.
The shared habitat of the species in each example may be an indication of their recent development from each other.
The above examples seem to indicate that scaled species developed from fringed ones. If the transformation from a fringe of spines to palmate scales is a random process, one would expect that it could take place anywhere along the body. Forms intermediate between O. civellae and O. palmatum, with a change at mid-body for instance, might be expected. But this does not seem to occur. Scale change seems to be restricted to the lip region and the vulval region. That it does not have to take place in a regimented fashion is clear from the more or less alternating configuration of the scales of O. palmatum and of one of the new species described in this contribution. The restricted number of such species described compared to the overwhelmingly large number of nominal species with scales in regular rows, indicates that in the evolution of the species the arrangement in rows is the most successful. If scaled species develop from fringed species then, potentially, many more Ogma species exist in New Zealand, in the form of yet undiscovered, fully fringed predecessors of the longitudinally scaled, recently described, new species.
Within the genus Ogma, species with similar scales, either alternating (formerly subgenus Croserinema) or in longitudinal rows (formerly subgenus Seriespinula), seem more closely related than species with dissimilar scales. Scale type, therefore, seems to be the appropriate character to define subgenera. To organise all Ogma species in subgenera accordingly would require a thorough comparison of all species described. The inclusion of molecular data would be invaluable and would reinforce a phylogenetic classification. Such a comprehensive review, however, is not within the scope of this contribution and Ogma is here not subdivided.
The genus Ogma is well represented on native vegetation in New Zealand (Wouts et al. 1999) and Australia (Reay & Davies 1998). Especially common are species with palmate scales located on distinct ridges usually running from the base of the head to the tail region with a reduced number running through to the tail terminus. Ogma species with such scales include O. campbelli, O. crenulatum, O. paucispinatum, O. polyandra, O. semicrenatum, and O. sexcostatum. In these species the direction of the scales is posteriad. On contracted females the scales lie flat against the body, but they direct progressively further outward when the female body relaxes, and stand almost perpendicular to the axis of the body on fully extended females and on empty cuticles of decomposed specimens. The body of the female is generally curved gently ventrally, tapering anteriorly from the base of the stylet, posteriorly approximately from mid-body, and more acutely from the level of the vulva. The lip region is truncate and has 2 distinct annules. The anterior annule is generally directed anteriorly and surrounds the pseudolips. The oral opening is a dorsoventral slit located on an oval oral plate. The amphidial apertures are elongate, located on the lateral side of the oral plate and are surrounded by lateral pseudolips. The 2 dorsolateral and 2 ventrolateral pseudolips complete the lip region. The cephalic sclerotisation looks distinct in face view. The stylet is rigid. The vulva is distinct and closed and may be covered with a drop of resinous substance.
The body of the male is typical for the family. The body annules are distinct. The head is dome-shaped and has 5 or 6 more or less distinct annules. The region immediately surrounding the cloaca is irregularly annulated and distinctly protruding from the contour of the body, forming a platform where the cloaca is located, with the body acutely narrowing posterior to this region. The lateral field, with 4 incisures, protrudes from the body contour. The tail is slender.
Pateracephalanema
Pateracephalanema Mehta & Raski, 1971 originally included species with females with either 1 or 2 lip annules. Siddiqi (1986) synonymised the genus with Ogma, as a subgenus with females with a single lip annule and imbricate scales, restricting it to species described by Colbran in the 1960s. Criconema pectinatum Colbran, 1962, the only Pateracephalanema species with 2 lip annules was transferred to the new subgenus Pellipecten. Siddiqi (2000), without changing the definition, returned C. pectinatum to the subgenus Pateracephalanema. He may have assumed that C. pectinatum, too, had a single lip annule. Colbran (1962) in the original description mentions a single annule and his illustration only vaguely indicates a second one. Mehta & Raski (1971), however, in their drawing of the head clearly indicate the presence of a second annule. Criconema pectinatum is, therefore, here removed from Pateracephalanema, but retained in Ogma. Pateracephalanema is removed from Ogma and reinstated as the valid genus for the Australian species with a single lip annule and imbricate scales.
Syro
Orton Williams (1985) proposed the genus Syro for a new species from New Guinea, with females with a single lip annule and more than 12 rows of low scales, with or without spines, on the body annules; the number of scales on the dorsal side of the body differing from that on the ventral side; branched appendages trailing posterior to the tail terminus; and a postvulval region wider than long. Heat-relaxed females were further characterised by a rather thick, typically curved body. Seven species were included “that do not resemble each other closely”. Siddiqi (2000) synonymised Syro with the subgenus Ogma (Pateracephalanema). I feel this does not do justice to the unique characteristics of the species in either of the taxa. With the discovery of 2 new species that very closely resemble the type species, Syro vexillatrix Orton Williams, 1985, the distinct single lip ring of Syro species, unique among scaled species, together with its curved body shape and low scales, justify recognition of Syro as an independent genus.
Blandicephalanema
The genus Blandicephalanema Mehta & Raski, 1971 was proposed for species from New Zealand characterised by females with a lip region consisting of a high lip ring that gradually tapers to a rounded anterior end, supported by a narrow base-ring, altogether giving the lip region a narrow, dome-shaped appearance. The 4 species known in the genus, B. serratum, B. pilatum, and 2 new species, are all from Australia and New Zealand, a further indication of the common origin and long and close geographical association between these 2 countries.
The genus Amphisbaenema Orton Williams, 1982 resembles Blandicephalanema. It was erected to accommodate A. paradoxiger Orton Williams, 1982 from [Western] Samoa (Orton Williams 1982). Raski & Luc (1985) synonymised Amphisbaenema with Criconema, but Decraemer et al. (1996) reinstated it as a valid genus. Decraemer & Geraert (1992) reported A. paradoxiger from Papua New Guinea. According to them Blandicephalanema differs from Amphisbaenema by the strong but low head sclerotisation being restricted to the 2nd lip annule, and the different structure of head and body cuticle.
Because of the flexibility of the cuticle of Criconematidae the significance of the sclerotisation covering 1 or 2 annules within a genus is far from clear. The main differences between the 2 taxa, therefore, seem to be head and cuticle structure. The structure of the head and cuticle, however, are influenced strongly by the extracuticular layer present in the two taxa.
Decraemer et al. (1996) give a detailed description of this layer in Amphisbaenema. Between the annules it resembles more or less polygonal scales cemented to the surface like interlocking pieces of a puzzle forming a coarse paving. This is quite different from the extracuticular layer of Blandicephalanema. But within Blandicephalanema there is considerably variation between species. It is a loose layer with scales and other outgrowths on B. serratum, but a fairly persistent, continuous layer of imbricate scales about as long as wide grown together in B. pilatum, very similar to that described by Decraemer et al. (1996) for Amphisbaenema juveniles.
The main difference between Blandicephalanema and Amphisbaenema seems to be that in Amphisbaenema the extracellular layer is more persistent. Because of this the configuration of the lip region has been interpreted differently.
Decraemer et al. (1996), using scanning electron microscopy, found that pseudolips are not present in A. paradoxiger. Unfortunately, as suggested by Raski & Luc (1985), by not first removing the extra cuticular layer that obscures all characteristics of the lip region, they may have overlooked the pseudolips. Not only does the extracuticular layer obscure the lip region, it also holds it tightly together which makes both the basal lip annule and the pseudolips very difficult to observe. With the extracuticular layer present the head of Blandicephalanema “can consist of a single large dome-shaped annulus as long as the sclerotisation and offset from the first body annule” exactly as described for Amphisbaenema (Decraemer & Geraert 1992). In the absence of the extracuticular layer the head seems to open up, with the basal lip somewhat enlarging and becoming more distinct and the pseudolips becoming recognisable as individual lobes, or as Decraemer & Geraert (1992) describe it for Amphisbaenema “the head region is formed by 2 annuli more or less amalgamated, with a dome-shaped first annulus and a wider second annulus with rounded outline”. The 2nd annulus can be considerably wider and distinctly set off from both the 1st lip annule and the 1st body annule. The 1st lip annule may be long (Decraemer & Geraert 1992). Decraemer & Geraert (1992) photographed an Amphisbaenema head with the extracuticular layer present. In that state as in Blandicephalanema with the extracuticular layer present, the pseudolips are indistinct. In the absence of the extracuticular layer the Amphisbaenema head would have shown pseudolips.
The shape of the female head and body of Blandicephalanema and Amphisbaenema, therefore, are the same. In both taxa an obvious extracuticular layer is formed and they originate from the same general geographic region. They are here considered to belong to the same genus. The genus Amphisbaenema is synonymised with Blandicephalanema.
Jairajpuri & Southey (1984) compared the extracuticular layer of their new species Nothocriconema shepherdae (Jairajpuri & Southey, 1984) Raski & Luc, 1985 with the subcrystalline layer of heteroderids. In heteroderids this layer seems to form from excess sugars, excreted by the nematode female, converted by a yeast-like fungus to long-chain fatty acids. Changed to their calcium salt they form the subcrystalline layer. The origin of this layer in N. shepherdae is quite different. Jairajpuri & Southey (1984) indicate that although bacterial cells may be present on the outside of the layer, there is no evidence of fungi or other organisms beneath the layer. In Blandicephalanema this layer has scales and spines and other structures associated with it and is obviously part of the cuticle formed during moulting. In N. shepherdae, Macroposthonia hymenophorum (Wouts & Sturhan, 1999) Siddiqi, 2000, Criconemoides lamellatum Raski & Golden 1966, Neolobocriconema braziliensis (Raski & Pinochet) Hashim, 1984, Criconema amicorum (Orton Williams, 1982) Raski & Luc, 1985, and Criconema (Criconema) psephinum (Bernard, 1982) Raski & Luc, 1985, all with an extracuticular layer, this is probably similarly the case.
MACROPOSTHONIINAE
Macroposthoniinae are characterised by the absence of scales and spines on the cuticle of both the females and the juveniles. In New Zealand Macroposthonia xenoplax and M. rustica have only been found associated with grasses, weeds, and crops and must be considered introduced species; Criconemoides (Criconemella) parvus Raski, 1952 has been regularly encountered associated with native vegetation and could be considered endemic. Its worldwide distribution, however, is an indication not that it is endemic, but that its wide host range includes some of our native plant species. Together with a new species from Campbell Island these 3 are the only species representing this subfamily in New Zealand.
HEMICRICONEMOIDINAE
Hemicriconemoidinae are characterised by a double cuticle, formed by a sheath of round body annules, that surrounds the body. Only Hemicriconemoides cocophillus represents this subfamily in New Zealand. Although fairly widely spread in New Zealand its worldwide distribution precludes it from being considered endemic.
TYLENCHULOIDEA
This superfamily is characterised by having females and juveniles that have a thin cuticle with fine transverse striae and an oesophagus with a narrow isthmus. The 2nd stage juvenile, hatching from the egg, is the infective stage. For the New Zealand species it has been the stage most frequently encountered. In moist soil at 15oC, juveniles of the citrus nematode Tylenchulus semipenetrans Cobb, 1913 survive without a host for up to 2.5 years (Baines 1950). For further development and long-term survival of the species host roots in the soil are required. Citrus nematodes have been observed to survive, after their host trees were removed, for up to 9 years on roots that survived deep in the ground for that period of time (Baines et al. 1962).
The superfamily Tylenchuloidea consists of 3 families, Tylenchulidae, Sphaeronematidae, and Paratylenchidae.
TYLENCHULIDAE
Tylenchulidae are characterised by having swollen females that are not spherical or subspherical, but have a distinct postvulval region. The secretory–excretory pore is located some distance behind the oesophageal region and produces a gelatinous matrix in which the eggs are laid.
The family is represented in New Zealand by the genera Tylenchulus and Trophotylenchulus Raski, 1957. These are each represented by a single species that is rarely encountered.
In Tylenchulidae the feeding 2nd, 3rd, and early 4th stage juveniles (J4) are ectoparasites and do not swell. For sustained feeding the adult female needs a permanent feeding site of transformed cortical cells. In Tylenchulus the female forms the feeding site — nurse cells with hypertrophied nuclei. In Trophotylenchulus it seems the J4 establishes the feeding site — a syncytium. Once a feeding site is established the nematode becomes sessile, starts swelling, and transforms into a mature female.
The body seems to swell primarily dorsally and anterior to the vulva, because the ventral side of the swollen female is generally concave, the postvulval region is distinct, and beyond the anus a tail-like extension is present. Tylenchulus semipenetrans, the only representative of the genus in New Zealand, is a cosmopolitan pest of citrus. Present in large numbers, especially under the warm climatic conditions of Southern California, they can cause considerable growth reduction and yield loss. In New Zealand this species is rare and damage has so far only been recorded on grape vines. Lack of damage may be due to the generally low soil temperatures and the fact that the majority of commercial citrus trees are grafted on resistant Poncira trifoliata rootstock. It is an introduced species present only on introduced hosts.
SPHAERONEMATIDAE
Sphaeronematidae are characterised by the spherical or subspherical female lacking a postvulval region and with the secretory–excretory pore located in the oesophageal region.
Sphaeronematidae is a small family represented in New Zealand by the genus Sphaeronema. Specimens of Sphaeronema are rarely encountered. Sufficient material for identification was present only for a single species. For sustained feeding the preadult and adult female need a feeding site, a syncytium, formed of pericycle and phloem cells. The feeding site is probably initiated by the early J4. Once a feeding site has been established the J4 gradually increases in size and transforms into a somewhat swollen preadult female in about 7 days. The posterior part of the body remains exposed outside the root. In the last moult the tail is lost and the adult sessile female swells symmetrically and becomes an almost spherical body, with minute terminally located vulval lips. The eggs are laid in a gelatinous matrix.
PARATYLENCHIDAE
Paratylenchidae are characterised by having vermiform females with a stylet usually more than 20 mm long. There are more than 100 described species worldwide. In New Zealand the family is represented by the genus Paratylenchus Micoletzky, 1922. Like tylenchulids and sphaeronematids, female paratylenchs are small. Paratylenchs do not develop a specialised feeding site and remain slender. They are not rare in New Zealand, but they have not been studied in detail and will not be described individually. They are distinguished in a key (p. 79). Some species have been found associated with native vegetation but they are generally not considered endemic.
HEMICYCLIOPHOROIDEA
The superfamily Hemicycliophoroidea is characterised by females and juveniles that have an elongate, vermiform body with a thick cuticle with more than 200 rounded annules lacking spines or scales, and an oesophagus with a wide isthmus.
Type and only family present in New Zealand: Hemicycliophoridae
HEMICYCLIOPHORIDAE
The family Hemicycliophoridae is characterised by the thick body sheath of the female and juveniles and the strongly arcuate shape of the spicules of the male.
Hemicycliophoridae are well represented on native vegetation and some species may be endemic. The species collected in New Zealand have not been studied in detail and will therefore be represented in this paper only by the 2 species described by Yeates (1967, 1978). The other populations will be discussed briefly and their characters listed.