University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 1-1979 The Role of Cuticular Strata Nomenclature in the Systematics of Nemata Armand R. Maggenti University of California - Davis Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs Part of the Parasitology Commons Maggenti, Armand R., "The Role of Cuticular Strata Nomenclature in the Systematics of Nemata" (1979). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 98. https://digitalcommons.unl.edu/parasitologyfacpubs/98 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. 1979 January; 11(1): 94–98. The Role of Cuticular Strata Nomenclature in the Systematics of Nemata A. R. MAGGENTI 1 Abstract: A system of cuticular nomenclature based on the strata observed in Enoplia is proposed. Nematode cuticle is divided into four fundamental strata: epicuticle, exocuticle, mesocuticle, and endocuticle. Application of this system allows the correlation of complementary strata throughout Nemata. The major taxonomic categories within Nemata are differentiated on the basis of their cuticular strata as compared with the Enoplia model cuticle. Key Words: cuticle, Enoplia. classification. Systematists have long utilized external have chemical or functional relationships modifications and specialized organs of the that prove them homologous within cuticle to separate species, genera, families, Nemata. In fact, such relationships have etc. Even today, with our improved knowl- not been proved, and superimposition of edge of internal structures and organs, the this terminology throughout is misleading. external cuticle remains a basic character Bird (3) pointed out that "the diversity in to the taxonomist. Perhaps the importance Nomenclature of the various layers of the given cuticle in taxonomy is justified by the nematode cuticle has resulted in some con- fact that tile hypodermis is a remnant of fusion." embryological ectoderm, retaining tile prim- After a review of cuticular studies I itive potential of the tissue. That potential believe that the laminated strata and their is shown in diverse integumental organs sequential order can bave significance and functioning in secretion, excretion, and sen- correlation throughout Nemata if an sation. Furthermore, the glands of the body enoplid cuticle model is used. There is and the cuticle of body invaginations are little purpose in attempting any under- appreciated more fully if they are recog- standing of cuticular strata following nized as derivitives of ectoderm. current nomenclature. One simply cannot Since the external modifications and talk about or see an orderly sequence manifestations of the cuticle have played a among Nemata for the "so-called" median major role in our systematic concepts, it (homogeneous matrix) layer or the basal seems plausible that the internal structuring layer. Recent reviews attempting to do that of nema integument could be useful in have broken down because current concepts examination of current systematic concepts. based on Ascaris do not allow for compari- Nematode cuticle is commonly de- son, primarily because of the assumption scribed as a laminated noncellular elastic that all nema cuticles have the complete secretion of the hypodermis. Although complement of cortical, median, and basal numerous studies have been conducted layers (3, 4). It is my premise that continu- with light microscopy, TEM, and SEM, we ing to view cuticle on that basis will impede continue to have little understanding of correlation of cuticular characteristics with this complex organ that interfaces the nema our understanding of nematode systematics. with its external environment. Furthermore, Hinz (9) finds no justification Studies of ascarid cuticle with the Iight for designating the cortical, fibril, and microscope and TEM (3, 6, 10, 22) serve homogeneous (= median) layers in Para- as the basis for contemporary interpreta- scaris equorum as separate strata, and he tions of nematode cuticle. Tile model treats them as substrata of the cortical layer. ascarid cuticle has nine layers distributed A topographic system of nomenclature among three strata designated as tile utilizing an enoplid for reference is pre- cortical, matrix (median), and basal layers. sented here. Of the nematodes studied, It has been assumed that these same strata Denontostoma of Enoplia offers the most occur in all Nemata and the terms have complete sequence of cuticular strata. The been used in a manner that implies they toponyms are all based on the noun 'cuticle' modified by adjectives connoting relative Received for publication 8 June 1978. positions and, as such, the integument is 1 Nematologist. Division of Nematology, University of Cali- fornia, Davis 95616. divided into four fundamental strata: 94 Cuticular Strata Nomenclature: Maggenti 95 epicuticle, exocuticle, mesocuticle, and layer appears also to be triple-layered. endocuticle. Exocuticle: This stratum is subdivisible Fig. 1 applies the toponyms to the rec- into two or more sublayers. In Enoplida it ognized strata in Deontostoma (21). This contains two substrata: an outer lamina- concept correlates cuticular strata through- tion composed of a finely granular dense out Nemata with an Enoplia model and substance. The inner substratum, common allows for the absence of certain strata to much of Nemata, consists of fine radially depending upon the cuticle under consid- oriented striae, which at higher resolu- eration. For example, in the cuticle of tion appear to be formed from two Ascaris only three strata are recognized: electron-dense plates separated by an epicuticle, exocuticle and mesocuticle; electron-transparent core. Body wall canals current studies show no evidence of endo- may extend through the exocuticle. cuticle. Mesocuticle: This stratum is composed Applying this system, based on Enoplia, of organized rods, fibers, plates, or struts. to the Nemata we can recognize differences In the enoplid model this stratum consists between Adenophorean and Secernentean of fibrous layers arranged obliquely at 45 to cuticle. We can further differentiate, on the 55 ° from each other. The number of sub- basis of the nature of tile strata, Enoplia strata is variable. from Chromadoria. In Secernentea it is Endocuticle: The substrate of this layer possible to distinguish among Rhabditida, is poorly defined. The substratum often Spirurida, Strongylida, and Tylenchida. appears to be penetrated by hypodermal Therefore, our major taxonomic divisions extensions and muscle attachment. In TEM aml phylogenetic concept are confirmable photos and reconstructions of the endo- by this system. That cannot be done with cuticle it sometimes appears to have a systems based on cortical, median, and basal feathery fibroidal consistency. layers. For instance, tile "basal" layer of Among Enoplia the presence of all strata Ascaris (22) is not the same stratum as the is remarkably constant. The mesocuticle "basal" layer of Meloidogyne (2) or the varies by the number of fiber layers, their "basal" layer of Xiphinema (19). In fact, direction, and angular relationship. The those are different strata in each of the evolutionary trend (Fig. l) seems to be genera named. In the system proposed here, reflected in a reduction of the number of the "basal" layers of those genera are rec- substrata and oblique fibers (I, 8, 11, 15, ognized as exocuticle in Meloidogyne, 17, 18, 19, 21). The thickness of endocuticle mesocuticle in Ascaris, and endocuticle in is also variable, showing strong develop- Xiphinema. ment in tile insect parasite Mermis (15). Fig. l, utilizing diagrams based on TEM The structure of the cuticle of Trichodorus studies, illustrates the application of this (18) has been poorly resolved and currently concept and its conformity to our current has as a distinct stratum only the epicuticle. taxonomic concepts. To show strata iden- Chromadoria are distinguished by the tifications the diagrams are scaled, where striking modifications of the mesocuticle feasible, to Enoplia; the thicknesses of (16, 23, 24), which may be platelike or a strata do not represent actual measure- combination of oblique fibers and a "fluid" ments. For purpose of simplification the substratum with structural struts. cuticles diagrammed are based on main Tile similarity in cuticular structure of body cuticle studies; anterior and caudal dcanthonchus (24), Chrornadorina (16), cuticles are excluded. and Caenorhabditis (7, 25) lends circum- The characteristics of the four funda- stantial evidence to the hypothesis that mental strata derived from an enoploid Secernentea arose from chromadorid-like model are as follows: ancestors. The literature indicates that the Epicuticle: The outermost stratum, endocuticle occurs only in Rhabditida (7, typically tri-laminate and consisting of two 25). Filarids, Ascarida, Spirurida, and electron-dense layers separated by an Strongylida are characterized by the pres- electron-transparent zone. In at least two ence of only three strata: epicuticle, nematodes, Meloidogyne iavanica and Tri- exocuticle, and mesocuticle