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Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of

1-1970

System Analysis and Phylogeny

Armand R. Maggenti University of California - Davis

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Maggenti, Armand R., "System Analysis and Nematode Phylogeny" (1970). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 102. https://digitalcommons.unl.edu/parasitologyfacpubs/102

This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. J Nematol. 1970 January; 2(1): 7–15.

System Analysis and Nematode Phylogeny

A. R. MAGGENTI 1

The purpose here is to suggest a method The available fossils represent only a small which will permit understanding of the fraction of the former plant and life phylogenetic relationships of contemporary on earth. That enormous numbers of representatives of the phylum Nematoda and plants, important to the evolution of without fossils. It is not my intent to again contemporary forms, must have existed and (14) offer a phylogeny for the Nematoda. declined to extinction without leaving a trace To say that no real benefit or knowledge of is illustrated by an observation in recent phylogeny or evolution is possible without historical times. Of the millions of buffalo fossils is succumbing to apathy. One cannot (American Bison), some estimates in excess deny or ignore that all systems, morphologi- of 100 × l0 s, strewn over the Great Plains cal, biological and chemical manifested in scarcely three generations ago, today there modern forms developed by evolutionary is hardly a trace. The skeletons have now sequence. It is true that with a complete largely disappeared and the bones are dissolv- fossil record the rates of evolution and de- ing and crumbling into dust under the attack velopmental pressures could be accurately of weather. Without conservation of the re- evaluated. However, in the absence of a maining limited numbers, practically the only fossile record evolutionary relations and other evidence of their occurrence would be developmental tendencies can be assessed "buffalo wallows." Without supplementary by the use of direct or corollary system knowledge of the buffalo, however, these analysis. Taxonomists must not overlook would not be identifiable. systems and their analysis. The advent of sophisticated instrumenta- Obviously, confidence would be much tion has permitted new research avenues more complete in the presence of a complete heretofore impossible or impractical. Com- fossil record. The fossil record provides (in puters, electron microscopes, and the myriad addition to verification of existence) knowl- of instruments available to the biochemist edge of time of existence, rates of develop- and physiologist have facilitated significant ment, and to some extent distribution and contributions to our store of knowledge. The abundance. The latter have proven to be impact of this rapid development of method- more accurate for marine life than terrestrial ology, technology and instrumentation has fauna and flora. Though often assumed, led into an era of apparently divergent tax- frequency of occurrence of fossils is rarely onomic schools. Taxonomists are categorized correlated with former population density or as numerical phenetic, cladistic or phyloge- distribution but rather indicates areas and netic. It is indeed unfortunate that, perhaps time periods favoring preservation together through faulty communication, each school with optimum predisposal to fossilization. seems to lack appreciation for the others' attempt to attain the same goal from another Received for publication 5 September 1969. point of view. Among the various schools 1 Department of Nematology, University of California, Davis, California 95616. the phylogenetic approach has been termed 7 8 Journal of Nematology, Vol. 2, No. 1, January 1970

intuitive because it relies upon the Schuurmans Stekhoven and De Coninck (20) experience and the judgment of the observer proposed a scheme based on amphidial to determine significance of characters. Some shapes; Steiner (21) utilized the excretory significance must be attached to the fact that system. The difficulty with a single gross the fundamental ideas of the traditional phy- morphological character analysis is the un- logenetic taxonomists have often been con- certainty whether the evolved scheme is firmed by the opposing schools. progressive or regressive. Filipjev (8), Chit- The literature suggests that all too much wood (3), Maggenti (14), Platonova (19) time is spent in argument about the theoreti- and Gerlach (9) proposed phylogenies utiliz- cal merits of the various methods of approach ing several systems for which the most in- rather than the compatibility and significance formation was available. The parasitologists of the results. Comparison of the findings of have supplemented these criteria by a cor- the various approaches and argument over relation of parasite characteristics with host areas of noncorrelation would seem to be biology and evolution. much more fruitful. As in all methodology, Goodey (10) states, "classification of any different techniques have different inherent group of organisms is a matter of conven- limitations. Therefore, it would behoove the ience" and that the "collection and catalogu- taxonomists to recognize the restricting prem- ing of have not yet progressed far ises of each particular school. It would enough for their interrelationships to be seri- then be advantageous to combine the efforts ously studied." It is essential for the growth of each system, thereby increasing the level and progress of this science that we do not of confidence in any phylogenetic conclu- allow ourselves to be deceived by this type sions. It is axiomatic in science that the of reasoning. The best classification accord- realness of any determination should be sup- ing to Mayr (16) is not that which guarantees ported by multiple evaluation using different rapid unambiguous identification but that techniques. which has the highest predictive value. Thus In attempting to form a classification of nematode taxonomists must decide to accept higher categories into phylogenetic units we the limitations enforced by the lack of a must accept certain limitations. We are al- fossil record and attempt to formalize a ways faced with insufficient knowledge of the phylogeny on the basis of tested evolutionary phylogenetically important characters of principles and methods for evolutionary many groups. In classification, phylogenies resolution or forego the phylogenetic concept must be presented in a linear sequence of of classification and replace it with a "practi- species, genera, families and so forth, while cal" classification permitting rapid identifica- the phylogenetic tree, more than a classifica- tion. tion, has the added dimension of time. There- I do not accept Goodey's philosophy; fore, no classification could be an exact therefore, the proposal here is to describe representation of the phylogeny, even if all a means whereby alternate phylogenetic the facts were known. schemes based upon thorough detailed sys- The phylogenies and the evolutionary re- tem and character group analysis can be lationships of nematodes that have been compared; the regions of superimposition proposed have usually utilized gross mor- would then suggest the most probable line of phology of a single character group. For descent. The approach is not original; it example, De Coninck (5) employed the dis- has been tested and utilized successfully in tribution of cephalic setae and papillae; other disciplines. The basic idea is to utilize SYMPOSIUM" SYSTEM ANALYSIS PHYLOGENY • Maggenti 9

diverse systems of all types, morphological, mon to all except in the systems of excretion. hormonal, chromosomal, immunological, bio- The reason for this will become obvious logical, physiological or biochemical. The when the system is discussed. In other than effectiveness of the system is predicated upon a model system many more features of each each system being analyzed independently system would have to be discussed. How- and objectively. The confidence in determi- ever, for simplicity in illustrating the feasi- nations by approaches used heretofore is bility of the approach, these were kept to a limited by the subjective decision-making minimum. These particular systems were requisite in character selection and estimation chosen because of their variability through- of profundity at each successive level. That out the Nematoda. taxonomy can and should require the use of Within Nematoda other systems have value supplemental systems and properties other at different levels of investigation. The stoma, than the gross morphology of simple char- for instance, is of little value in system analysis acters has been well established. Nadler (17) because it is likely to be greatly influenced by employed chromosomal characters in his environment. Analysis of this feature rapidly study of the taxonomy of ground squirrels; reduces to circumlocution; however, this does Kelly (12) used comparative endocrinology not negate its usefulness at lower category in his investigation of the evolution of in- levels of investigation. The same may be said vertebrates and vertebrates; and Barrington of the amphid, even though it appears to be (1) utilized comparative hormone studies in more conservative and less susceptible to his book on evolution. Within nematology, environmental influence. Until we know more immunology has been used in the systematic about amphidial structure and function this studies of both plant parasitic and free living organ does not lend itself to analysis. An nematodes by Bird (2), Lee (13), and EI- important aspect of system study is to recog- Sherif and Mai (7). nize those features which analyze in a linear Without an analysis such as employed by fashion. The position and form of cephalic the numerical taxonomists there is danger of setae and papillae is such a case. The pattern subjective bias. The model scheme being of progression is toward cephalization and presented here could be quantitatively ana- reduction in setal size with the eventual lyzed. However, for the purpose of discussion replacement by papillae (15). This de- and in order to illustrate the approach, this velopment is useless for main dichotomic technique has not been applied. Each system separation but extremely useful in confirming was analyzed independently with deliberate the progression in any dichotomic line. The effort not to weight the characteristics within female reproductive system was not utilized each system, to estimate evolutionary signifi- in this study because of the clarity of the cance, or to relate one system to another. features of the male system as well as the The features selected were the esophagus, the obvious complementary development of these male reproductive system and the systems of systems. However, it should be emphasized excretion. Characteristics for each major that for a thorough analysis as many systems group were listed and organized according as possible need to be included. to order of frequency of occurrence so that The diagrammatic illustration of the anal- the initial features are common to large ysis of the esophageal system is shown in groups of nematodes, then each progresses Figure 1. The category names are not indi- to features present in select groups. No at- cated; the concern at this time is analysis of tempt was made to define the feature com- the system. This discussion is not being 10 Journal o[ Nematology, Vol. 2, No. 1, January 1970

ESOPHAGEAL SYSTEM J I I NUCLEI SEGREGATED NUCLEI NONSEGREGATED I I I RADIAL NUCLEI IST MARGINALNUCLEI IST I I I I NO SPECIALIZED WITH SPECIAL I I I POINTS OF MUSCLE POINTSOF MUSCLE I ATTACHMENT ATTACHMENT TUBOFD NONTUBDID TUBOID NONTUBO ID I I t MUTACORPUB METAEDRPUS I : DEVELOPED UNDEVELOPED GLANDS ENCLOSED STICHOSOME I IN ESOPHAGUS GLANDS EXPOSED i I I GLANDS NOT ENCLOSED GLANDSENCLOSED IN IN VALVED POBTERLOR VALVEDPOSTERIOR BULB I I BULB CYLINDRICAL CORPUS CYLINDRICALCORPUS PYRIFORM GLANDULAR ELONGATEDGLANDULAR I REGION ORIFICE DORSAL ORIFICE DORSAL ESOPHAGEAL GLAND ESOPHAGEALGLAND IN HEAR S~OMIA NETACDRPBS

NONOVERLAPPING OVERLAPPING NONOVERLAPPING OVERLAPPING GLANDS GLANDS GLANDS GLANDS

FIo. 1. Analysis of morphologic and histologic characteristics of esophagi in Nematoda. presented as an exhaustive analysis of the appear in the esophagus. Each of these selected systems; it has been kept intention- groups can be further subdivided on the ally brief in order to facilitate an understand- presence or absence of tuboid endings on ing of the approach. the esophageal radii of the corpus. Those Form and function of any cell, tissue, or esophagi having segregated nuclei, radial organ is determined by its nuclear compo- nuclei first and tuboid endings on the radii nents, and nuclear distribution within the define two other subdivisions: those with esophagi of nematodes falls into two groups. and those without muscular development of In one group the nuclei are dispersed the metacorpus. Coincident with metacorpal throughout the esophagus, whereas in the development is the increased development of other the nuclei segregate anteriorly and esophageal glands. Where these glands open posteriorly. The latter is extremely interest- into the esophagus identifies another dichot- ing because such a condition supplies the omy, that is, whether the dorsal gland opens foundation for the specialization of the into the corpus or into the metacorpus. As diverse characteristics exhibited in nematode glandular volume increases there is a pro- esophagi. It is also in the segregated esoph- gressive reduction in posterior musculature agus that the so-called isthmus is manifested. which eventually results in the glands over- Continuing down the left hand dichotomy, lapping the intestine. The latter character is nuclear arrangement can be further divided useful only in individual taxa. as to type of nuclei, their order of appear- Returning to the right hand of the scheme ance, and coincident structure. Thus basi- presented in Figure 1 it will be seen that in cally two groups segregate on the position of the case of non-segregated nuclei within the radial or marginal nuclei being the first to esophagus that musculature and glands seem SYMPOSIUM: SYSTEM ANALYSIS PHYLOGENY ° Maggenti 1l

I 1 2 TESTES WITHOUT 2 TESTES WITH EJACULATORY MUSCLE EJACULATORY MUSCLE

r i ! I 2 TESTES 2- TESTES WITH GLANDS WITHOUT GLANDS I I | i I 2 TESTES 2 TESTES WITH GLANDS WITHOUT GLANDS 2 TESTES 1 TESTIS

I I I TESTIS 2 TESTES 1 TESTIS WITH GLANDS

MALE REPRODUCTIVE SYSTEM

Fro. 2. Analysis of the male reproductive system in Nematoda. to lend themselves to further analysis. On little information concerning the testis itself; the basis of musculature esophagi segregate however, we do recognize many features into those forms without specialized areas of associated with the male reproductive system. the lumen for muscle attachment and those The divergence expressed by the presence or forms with specialized areas of attachment. absence of ejaculatory muscles manifests in It is among the latter group that esophagi both branches an interesting dichotomy of with more than three glands can be found. the presence or absence of ejaculatory glands. In some the development goes so far as to be It is interesting to note that ejaculatory glands described as a stichosome, that is, a multiple are associated with terrestrial nemas of exposed glandular structure on one or both widely divergent types. In the left-hand sides of the esophagus. Because a well de- group of Figure 2 no nematode is known fined dichotomy does not present itself, this with two testes plus ejaculatory glands; this section is connected by a broken line. The is indicated in the diagram by a broken line. last dichotomy is really a manifestation of Discrepancies and gaps in available informa- the external form of the posterior bulb of tion are readily recognized. If the analysis the esophagus. is correct then predictions can be made as to Figure 2 illustrates the analysis for the what areas need further investigation for male reproductive system. Nematodes fall additional knowledge or unsuspected species, into two groups, each with consistent char- It must be realized that in many instances acteristics and each with two testes. It is not the extinction of an animal may forever ex- assumed here, however, that the primitive clude the completion of our knowledge. nematode had two opposed testes. We have The right hand dichotomous branch of 12 Journal of Nematology, Vol. 2, No. 1, January 1970

HYPODERMIS I i I CANALS PLUS NON-CANALED S INUS CELL SINUS CELL PLUS HYPOOERMAL GLANOS I OCCAS IONAL LOBED SINUS CELL NON-LOBED SINUS CELL PLUS HYPODERMAL GLANDS PLUS HYPODERMAL GLANDS

i I CANALS POSTERIOR CANALSPOSTERIOR AND ANTERIOR I I BACILLARY BAND I i SINGLE CANAL TWO CANALS I POSTERIOR ANTERIOR POSTERIORANTERIOR I HYPOOERMAL GLANDS HYPODERNAL GLANDS PRERECTUM PRERECTUM SINUS CELL

EXCRETORY SYSTEM FIG. 3. Analysis of the excretory systems in Nematoda.

Figure 2 is also based on the presence or The system without true canals is by far absence of glands associated with the testes. the most interesting. In most forms with the The final dichotomy separates those forms simple sinus cell there is generally a corre- with either one or two testes. sponding development of other hypodermal The third system to be analyzed here is glands. J~igerski61d (11) associated the exis- that of excretion, Figure 3. Vital processes tence of sublateral hypodermal glands with are less susceptible to subjective interpreta- degeneracy of the excretory system in Adeno- tion than their morphological manifestation. phorea. The term sinus cell is used The analysis begins with the hypodermis. throughout in order to maintain consistency All alleged excretory systems in Nematoda between Adenophorea and Secernentea. The are derived from hypodermal tissue. How- diagram also illustrates that in some instances ever, all processes of excretion are not the simple sinus cell may be modified by necessarily hypodermal in origin. For lack posterior lobes; and in others these are well of critical information the initial division is developed and extend posteriorly for a con- determined by whether or not the specialized siderable distance. When no sinus cell is hypodermal cell (rennete, sinus cell, ventral present, the hypodermal glands are often gland) is associated with a canal system or well developed and in some forms are mani- not. If it is, then the position and number fested in bizarre structures such as the bacil- of canals is to be considered, that is, whether lary band in trichurids. Furthermore, an they are found both posterior and anterior additional important feature of some nem- to the sinus cell or only posterior. Among atodes with the simple sinus cell is the pres- those forms possessing canals both anteriorly ence of a pre-rectum. It is found in forms and posteriorly we note that the canals may with hypodermal glands and presumed sinus be present on both sides of the body or cells, as well as in the absence of the sinus confined to only one side. cell. It is also worth noting that when the SYMPOSIUM: SYSTEM ANALYSIS PHYLOGENY ' Maggenti 13

?

1111111111 In

EUTERATOC EPHALUS ? CHROMADORIA ENOPLIA

AD ENOPHOREA Mlllmll ~ CHROMADORIDA TRIPYLIDAE I IRONIDAE TERATOC EPVAL IDAE ~ ~ CHROMADORA ARAEOLAIM IDA DESMOSCOLECIDA

DORY L~'~'~w'w'~c~lx'wT~ KHABDIT (NA CEPFIALOBIDAE ~x.~.x>;~,.x~,~v~ TRICHUROIDEA

OIPLOGASTER IOAE RHABD IT IDAE °]P~THEROpHDROIDEA DORYLAIMOIDEA

TYL ENCHOIDEA APHELENCHOIOEA

;;///yD/.~///k>/> V/.// TYLENCH IDAE HETERODER ID¢~E PARApHELENCH IDAE APRELENCHOID IDAE EXCRETDRY SYSTEH I

CORRELATION OF SYSTEMS FIG. 4. Correlation of systems: superimposition of analyses of nematode esophagi, male reproduc- tive system, and systems of excretion. pre-rectum is extensive the hypodermal ought to be. Furthermore this uncertainty glands are not and conversely a shorter pre- would suggest that a closer inspection of rectum is found with well developed hypo- their internal relationships is in order. Any dermal glands. The origin or function of the phylogeny or classification with these as pre-rectum in nematodes has not yet been foundation groups should be subjected to established. The circumstantial implication severe scrutiny. Unfortunately this criticism that it may be important in the function of applies to all the classifications widely used excretion in the nematodes in which it is today. found should not be ignored. Of additional interest is the position of The final step is the superimposition of the trichurids. Only the male reproductive sys- individual models to detect correlation, dis- tem in Figure 4 shows a distinct dichotomy crepancies or lack of information, Figure 4. with the Dorylaimida. The other two systems Category names have been included for analyzed, though not so clearly, also indicate better orientation. As one might have ex- a closeness to Dorylaimida, as was sug- pected the highest degree of correlation is gested by Chitwood (3). found in the Secernentea, enoplids and The superimposition further indicates the among the dorylaims. The apparent discrep- all too apparent lack of information concern- ancy among the Monhysterida, Araeolaimida ing the relationship of the secernentean and Chromadorida would indicate that these excretory system and male reproductive sys- groups are not as well understood as they tem to those of the adenophoreans. Perhaps, 14 Journal o/ Nematology, Vol. 2, No. 1, January 1970

when fully described, a nematode like Euter- The four major classifications available at atocephalus may clarify many questions in present are Filipjev (8), Chitwood (3), this region. Goodey (10) and De Coninck (6). Goodey's In Figure 4 the division of the nominal classification, as he clearly states, makes no classes Adenophorea and Secernentea is in- effort to reflect relationship; therefore, it is dicated. The scheme, however, would indi- irrelevant to this discussion. His classification cate that three groups are evident: the first is predicated on convenience, economic im- in very broad terminology embraces enoplids, portance, and consequently lacks the funda- the second chromadorids and the third rhab- mental phylogenetic property, predictability. ditids. If classes are accepted in Nematoda Each of the remaining three classifications then it is apparent from the analysis illus- has strong features well worth considering. trated in Figure 4 that the conventional class Filipjev proposed a classification that pres- division as it is currently accepted is not ent knowledge would lead us to conclude sufficient. This scheme corroborates the was extremely perceptive. He reviewed the subclass division of Chromadoria and Enoplia then known nematodes as representative Pearse (18). specimens and was unbiased by relative The analytical separation of Chromadorida abundance, economic importance or bulk of does not lend any confidence to the assump- information on specific nematodes. His con- tion that they are basic members of Chroma- clusions were formulated from observation of doria. The systematics of this whole group total morphology. He recognized the overall should be carefully investigated. Any such basic features of and accepting the investigation will necessarily involve much Leptosomatidae as primitive he built his more than just the single character of amphid classification. Filipjev, however, rejected the shape. For instance in the Monhysterida we idea of nematodes being subdivided into find forms with smooth cuticle without lateral classes. In addition to Filipjev, Maggenti fields, undivided esophagi with wide stomatal (14) and Platonova (19) also proposed attachment, a lack of specialized areas for phylogenies based on Leptosomatidae as muscle attachment and with the cephalic primitive. setae in two sublabial circles of six and four. Chitwood's published phylogeny and clas- These are nearly the same characters that sification has Rhabditis and Plectus as con- could be listed for Enoplia. Yet they are dis- temporary representatives of the foundation cussed as advanced Chromadoria that have group. From Rhabditida there is progression undergone regression. There is no evidence toward the other Secernentea, however, from for such a premise; futhermore, none is Plectus there is regression away from the necessary. It would seem rather important remaining Adenophorea. Most important to but overlooked that the marginal nuclei are this discussion of Chitwood's (4) classifica- the most anterior nuclei in the esophagus of tion is his establishment of the two classes Monhysterida. The transition from marginal Adenophorea and Secernentea. In addition nuclei to radial nuclei anteriormost (Chro- to the class divisions Chitwood had an un- madorida and Secernentea) and then back usual grasp of the organization of the again requires too many unwarranted as- Secernentea; aside from category modifica- sumptions. Accepting and working with the tions his basic organization of Secernentea systems and morphology as expressed in has stood sound and workable for thirty contemporary species is more objective and years. the resulting scheme more feasible. Pearse (18) made the important contribu- SYMPOSIUM: SYSTEM ANALYSIS PHYLOGENY • Maggenti 15

tion of further dividing the Adenophorea into 7. EL-SHERIF, M., and M. F. MAI. 1968. The use of immunodiffusion in nematode iden- two subclasses: Chromadoria and Enoplia. tification. Nematologica 14:593-595. De Coninck (6) recognized this division but 8. FILIPJEV, I.N. 1934. The classification of termed the categories infra-classes. It would the freeliving nematodes and their relation to the parasitic nematodes. Smithson. Misc. be difficult to argue with his knowledge and Collect. 89:1-63. interpretation of the individuality of the 9. GERLACH, S. A. 1966. Bemerkungen zur Chromadoria. A disturbing fact, however, Phylogenie der Nematoden. Mitt. biol. BundAnst. Land-Forstwirt. 118:25-39. is that the internal arrangement of the group 10. GOOOEY, T. 1963. Soil and Freshwater Chromadoria is based almost solely on the Nematodes. (2nd ed. revised by Goodey, amphidial form. J. B.). Wiley & Sons, Inc., New York. The model system analysis presented here Pp. 544. 11. JA.GERSKIOLD,L.A. 1901. Weitere Beitriige indicates that further in-depth analysis of all zur Kenntnis der Nematoden. Kgl. Svenska systems would reveal a phylogeny consistent Vetenskapsakad. Handl. (Stockholm) 35: 1-80. with the manifested development of con- 12. KELLY, G. F. 1968. Comparative Endo- temporary representatives. From this phy- crinology and Evolution. Bios 39:147-157. logeny it should be possible to devise a sound 13. LEE, S. H. 1965. Attempts to use im- classification that will in all probability re- munodiffusion for species identification of Meloidogyne. Nematologica 11:41 flect the best qualities of the classifications (Abstr.). of Filipjev, Chitwood, and Pearse, i.e. the 14. MAGGENTI, A.R. 1963. Comparative mor- organization of Filipjev, the classes of Chit- phology in nemic phylogeny. Pp. 273-282 In Dougherty, et al. The Lower Metazoa, wood, and the subclasses of Pearse. I have comparative biology and phylogeny. Univ. no doubt that given this foundation we can of Calif. Press. construct a sound classification based upon 15. MAGGENTI, A. R. 1965. Morphology of somatic setae: Thoracostoma californicum phylogeny and therefore manifesting inherent (Nemata: Enoplidae). Proc. Helminthol. predictability. Soc. Wash. 31 : 159-166. 16. MAYR, E. 1965. Numerical phenetics and LITERATURE CITED taxonomic theory. Syst. Zool. 14:73-97. 17. NADLER, C. F. 1966. Chromosomes of 1. BARRINGTON,E. J.W. 1964. Hormones and Spermophilus [ranklini and taxonomy of evolution. D. Van Nostrand Co., Inc., the ground squirrel genus Spermophilua. New York. 154 p. Syst. Zool. 15:199-206. 2. BIrtD, A. F. 1964. Serological studies on 18. PEARSE, A. S. 1942. An Introduction to the plant parasitic nematode, Meloidogyne Parasitology. Charles C. Thomas, Balti- javanica. Exp. Parasitol. 15:350-360. more. 375 p. 3. CH1TWOOD, B. G., and M. B. CHITWOOO. 19. PLATONOVA,T.A. 1964. Die Familie Lep- 1950. An introduction to Nematology. tosomatidae (Enoplida) die primitiviste See. 1, Anatomy. (Revised ed.) Monu- Gruppe der Nematoden. Material zur mental Press, Baltimore. 213 p. wissenschaftlichen Konferenz der gesam- 4. CHITWOOD, B.G. 1958. The designation of trussischen Gesellschaft fiir Helmintholo- official names for higher taxa of inverte- gie. Moskva. 2:64-67. brates. Bull. Zool. Nomencl. 15:860-895. 20. SCHUURMANSSTEKHOVEN, J. H., and L. A. DE 5. DE CONINCK, L.A. 1942. De symmetrie- CONINCK. 1933. Morphologische Fragen verhoudingen aan het vooreinde der (vrij- zur Systematik der freilebenden Nemato- levende) nematoden. Natuurwetensch. den. Verb. Deut. Zool. Ges. (Graz) 35: Tijdschr. 24:29-68. 138-143. 6. DE CONINCK, L. A. 1965. Syst6matique 21. STEINER, G. 1920. Betrachtungen zur Des N6matodes. Pp. 586-731. In P.-P. Frage des Verwandtschafts-verh~iltnisses Grass6 (ed.) Trait6 de Zoologic, Masson der Rotatorien und Nematoden. Festschr. et C *~, Paris. Zschokke, Basel 31. Pp. 15.