Zool. Anz. 237 (1998): 43-58 ZOOLOGiSCHER © by Gustav Fischer Verlag ANZEIGER Possible Homologies in the Proventriculi of Dicondylia (Hexapoda) and Malacostraca (Crustacea) Klaus-Dieter KLASS Ludwig-Maximilians-Universitat, Zoologisches Institut, Miinchen, Germany Abstract. Striking similarities were found between the armarial part of the proventriculus of Lepismatidae (Hexapoda: Dicondylia: Zygentoma) and the cardia of Decapoda (Crustacea: Malacostraca: Eucarida). These in­ clude a similar shape and arrangement of the sclerites and denticles, a similar pattern of apodemes, and similar sym­ metry relations. The armarium of Dicondylia and the cardia of Malacostraca may, therefore, be homologous, and the similarities between Lepismatidae and Decapoda may belong to the ground-plan of Mandibulata. On the other hand, the distribution of the structural features of these organs within Tracheata and within Crustacea is inconsistent with this assumption and may indicate that this similar morphology was developed independently in Dicondylia and in Malacostraca. The homology question cannot yet be definitely resolved. Key words. Zygentoma, Decapoda, Mandibulata, gizzard, stomach, armarium, cardia, phylogeny, homoplasy, ground-plan, symmetry. 1. INTRODUCTION images, and the same is true for two ventrolateral scle­ rites/denticles; these paired elements have an intrinsic Many Hexapoda Dicondylia (Zygentoma + Pterygota) asymmetry. The primary function of this armature is have the posterior part of the ectodermal, cuticle-lined certainly mastication. foregut differentiated into a strongly muscular proven­ Many Crustacea Malacostraca also have the posterior triculus (gizzard). Its morphology and function are very part of the foregut differentiated into a masticatory- and diverse in the individual orders. The proventricular wall filtering organ called stomach or proventriculus. It has a usually has longitudinal folds (plicae), which often bilateral symmetry, and it is composed of an anterior car­ form sclerotised structures in the anterior part (armar­ dia and a posterior pylorus, both of which may have a ium). Based on a comparison of Lepismatidae (Zygen­ complicated cuticular morphology with many sclerites. toma), Blattidae (Dictyoptera), and nymphs of Corduli- Some cardia sclerites bear denticles. As in Dicondylia, idae (Odonata), the ground-plan of the proventriculus the morphology of this organ varies strongly within the of Dicondylia was reconstructed (KLASS 1998). This Malacostraca. Morphological descriptions are numer­ ground-plan is very similar to the proventricular mor­ ous. SIEWING (1952,1954, 1956) gives a comparative ac­ phology of Lepismatidae. In the armarium, six large count throughout the Malacostraca; PATWARDHAN (1934, sclerites, each with a strong denticle, are present in an 1935a-e) and SCHAEFER (1970) survey the Decapoda; essentially hexaradial arrangement. Hexaradial symme­ HAFFER (1965) surveys mainly the Peracarida. try is overlain by a distinct bilateral symmetry estab­ So far, no detailed comparison was made between the lished by individual differentiation of the sclerites and proventriculi of Dicondylia and Malacostraca, and, to denticles: A dorsal and a ventral sclerite/denticle lying my knowledge, no homology relations have been sus­ in the plane of bilateral symmetry are single (unpaired pected. The organs are generally regarded as having de­ elements) and have an intrinsic bilateral symmetry. veloped independently in Dicondylia and Malacostraca Two dorsolateral sclerites/denticles are a pair of mirror- (e.g. SIEWING 1956; GRUNER et al. 1993). 44 K.-D. KLASS 2. MATERIAL AND METHODS za apodeme along dorsomedian margin of zygocardiac ossicle 2.1. Species investigated and preparation zco zygocardiac ossicle The cuticular elements of the armarium of Ctenolepisma li- neata (Fabricius, 1775) (Hexapoda: Zygentoma: Lepismati- 3. CARDIAC/ARMARIAL MORPHOLOGY dae) and those of the cardia of Carcinus maenas (Linnaeus, 1758) (Crustacea: Decapoda: Brachyura: Portunidae) were OF CARCINUS AND CTENOLEPISMA investigated. Hereafter, these species are referred to by the generic name alone. The specimens were stored in 4% form­ 3.1. Carcinus maenas aldehyde. The soft tissues were removed by treatment with The cuticular morphology and the muscles of the 10% KOH, and the remaining cuticle was washed in distilled proventriculus are described in COCHRAN (1935) for the water and stored in 70% isopropanol. closely related Blue Crab, Callinectes sapidus Rathbun When data from previous studies are referred to, the names of (Decapoda: Brachyura: Portunidae), and in PATWARD- the respective taxa, mostly species, are specified as completely as in the original papers (specification often incomplete). HAN (1934) for the freshwater crab Paratelphusa guerini Milne-Edwards (Decapoda: Brachyura: Telphu- sidae). The cuticular morphology of the crab Cyclo- 2.2. Abbreviations grapsus punctatus Milne-Edwards (Decapoda: Brachy­ (Single small letters: compare in chapter 3) ura: Grapsidae) is described by SCHAEFER (1970). The cardiac morphology of Carcinus, Callinectes, Paratel­ acp anterolateral cardiac plate phusa, and Cyclograpsus is very similar. ap apodeme on primary armarial sclerite (numbered 1-6) The terminology of COCHRAN (1935) and PATWARDHAN at tooth/denticle bearing "lateral accessory teeth" ca apodeme on posterolateral cardiac plate (1934, 1935a-e) is largely adopted here; additionally, cl lobe formed by posterior part of cardiopyloric valve abbreviations are used. As a general difference from cpv cardiopyloric valve Ctenolepisma, most cardiac sclerites are encrusted with D position of dorsal side of whole animal calcite. COCHRAN and PATWARDHAN refer to them as da apodeme anterior to denticle mt "ossicles" or "plates". Some sclerites form bulges pro­ dcp dorsal cardiac plate jecting into the cardiac lumen. COCHRAN and PATWARD­ dp primary armarial denticle (numbered 1-6) HAN call these bulges "teeth"; I call them, as in Cten- ea apodeme along anterior margin of exopyloric ossicle lepisma, "denticles". Many sclerites form apodemes, epo exopyloric ossicle which are in most cases low, massive ridges along the fp primary armarial plica (numbered 1-6) sclerite's epidermal face, and which are usually seen as ia plate-like posterior part of apodeme on inferolateral shallow grooves on the opposite face of the cuticle. cardiac ossicle These apodemes are not named in COCHRAN or in PAT­ ico inferolateral cardiac ossicle ip primary interplicium = interspace between two neigh­ WARDHAN. The abbreviations used here for the sclerites boring primary plicae fp: ip2-3 between fp2 and fp3; comprise three lower case letters; those for the denticles ip5-6 between fp5 and fp6 comprise two lower case letters, with "t" in the second la anterior apodeme of prepectineal ossicle position; those for the apodemes comprise two lower It lateral tooth/denticle case letters, with "a" in the second position. (Only some mco mesocardiac ossicle apodemes are named; in Fig. 1 the line along which the mt median tooth/denticle apodeme infolds, i.e. the apodeme base, is labeled with pa posterior apodeme of prepectineal ossicle, extending the abbreviation of the apodeme.) Some further con­ onto pectineal ossicle spicuous elements are designated by single lower case pco pterocardiac ossicle letters. Two elements forming a pair (see below) have pep posterolateral cardiac plate the same name. Setae, very important for the function peo pectineal ossicle of the cardia but not for the scope of this comparison, poo postpectineal ossicle ppo prepyloric ossicle are omitted from the figures although some are men­ pro prepectineal ossicle tioned in the description. The heaviness of sclerotisa- pyo pyloric ossicle tion or calcification is, with some exceptions, not repre­ sdo subdentary ossicle sented in the figures. The following description pro­ sp primary armarial sclerite (numbered 1-6) ceeds mainly from dorsal to ventral. ta apodeme along ventral and posterior margins of pecti­ Cardiac symmetry is purely bilateral (Fig. 1). The plane neal ossicle of symmetry coincides with that of the whole animal ua U-shaped apodeme on zygocardiac ossicle • (dorsal side = D, ventral side = V in Fig. 1). Most ele­ uco urocardiac ossicle ments are paired, i.e. represented by two mirror-image V position of ventral side of whole animal counterparts in the left and the right half of the cardia. va median apodeme of cardiopyloric valve Proventriculus Homologies in Hexapoda and Malacostraca 45 Some elements in the dorsal or ventral midline lie in the rated from mco by a deep membranous cleft a. Each plane of symmetry and are unpaired. pco has an apodeme aa along its posterior margin. The The dorsal wall of the cardia is occupied by a T-shaped longitudinal T-bar is composed of the urocardiac ossi­ group of sclerites (Fig. 1). The transverse T-bar is cle uco (its anterior part, (mco) in Fig. 1, is the meso­ formed by the pair of pterocardiac ossicles pco, with cardiac ossicle sensu COCHRAN, which is by no means the unpaired mesocardiac ossicle mco (sensu PATWARD- demarcated from the posterior part) and the roughly tri­ HAN) between them. The pco are only posteriorly sepa- angular prepyloric ossicle ppo - both unpaired. The \ Id J 2C0 C ' ^' ua \ peo ' ' /' / uc° m ej , zco \ Kit .' ,/ ' *fe py° k ^ -x*\J' 7 rpoo /' r .- h ' . J..^ ^H- - t i Figs. 1,2. Entire internal view of cardia/armarium. The cardia (Carcinus) or armarium (Ctenolepisma) is shown, cut longitu­ dinally and spread out. Undulate lines are cutting