The Digestive System of Porcellio Scaber Latreille, 1804 (Isopoda, Oniscoidea): Histology and Histochemistry

THE DIGESTIVE SYSTEM OF PORCELLIO SCABER LATREILLE, 1804 (ISOPODA, ONISCOIDEA): HISTOLOGY AND HISTOCHEMISTRY

ROGER L. LANE Ashtabula Campus, Kent State University, Ashtabula, Ohio, 44004, U.S.A.

ZUSAMMENFASSUNG Das Lumen des Ösophagus wird von einer Intima aus Chitin und sauren Mucopolysac- chariden ausgekleidet. Die kurze säulen- bis würfelförmige Mucosa des Ösophagus deutet einige Phosphatase-Aktivität an. Innere und äußere Muskelfasern sorgen für den Nahrungstransport zu Cardia und Pylorus. Die Cardia zeichnet sich durch sklerotisierte Proteinplatten aus. Die E-Zellen am distalen Ende eines jeden Mitteldarmdivertikels stellen in histochemischer Hinsicht keine Besonderheit dar. Die F-Zellen und die R-Zellen verhalten sich histochemisch sehr ähnlich und scheinen einen einheitlichen Zelltyp zu repräsentieren. Beide spielen eine Rolle bei Enzymsekretion, Absorption von Nahrungsstoffen, Exkretion und Glykogenspeicherung. Die R-Zellen enthalten zusätzlich Lipidtröpchen. Phosphatase-Aktivität zeigt bedeutende Absorptionsvorgänge in der Mucosa des Enddarms einschließlich der Zellen der Typhlosolis an. Die Muscularis ist dünn, und ein deutlicher Schließmuskel ist vor dem kurzen, schlecht erkennbaren Rektum vorhanden.

INTRODUCTION

Among the Crustacea members of the Isopoda have been the subject of many investigations regarding digestive anatomy (fig. 1), histology, ultrastructure, and physiology. Comprehensive overviews of the alimentary canal and its associated structures in terms of histology and histochemistry are few in number, however. The purpose of this investigation is to present such an over- view, together with statements on the functional significance of the informa- tion presented, for the digestive system of a terrestrial isopod, Porcellio scaber Latreille, 1804. McMurrich (1897) provided one of the earliest descriptions of the histology of the hindgut of Armadillidium Brandt, 1830, Porcellio Latreille, 1804, and Oniscus Linnaeus, 1758. Unfortunately, the species of these genera were not identified. Later, Murlin (1902) described the histology of the hindgut and hepatopancreas of five terrestrial isopods, including P. scaber. After a void of more than sixty years, studies of adult terrestrial isopod digestive systems resumed with a brief report on the carbohydrates and enzymes in the digestive tract of Oniscus asellus Linnaeus, 1758, by Hartenstein (1964) and the more extensive investigations of the histology of the gut of Armadillidium vulgare (Latreille, 1804) and A. nasatum Budde-Lund, 1885, by 114

Fig. 1. Diagrammatic representation of the digestive anatomy of Porcellio scaber Latreille, 1804. CS, cardiac stomach; ESO, esophagus; HG, hindgut; HGS, hindgut sphincter; HPC, hepatopancreas; PS, pyloric stomach; RE, rectum; TYP, typhlosole.

Schmitz & Schultz (1969) and of Porcellio laevis Latreille, 1804 by Alikhan (1969a, 1969b). In subsequent studies more attention was focused on the ultrastructure of cells, particularly of the hepatopancreas, from a variety of terrestrial species (Smith et al., 1969; Clifford & Witkus, 1971; Holdich & Mayes, 1975; Moritz et al., 1973; Hryniewiecka-Szyfter, 1972; Vernon et al., 1974, and Storch, 1982). One of the few investigations that took a more comprehensive approach was that of Hassall & Jennings (1975) on Philoscia muscorum (Scopoli, 1763) in which the histology, histochemistry, and enzyme constitution of the gut are presented. The present study will describe the histology and histochemistry of the esophagus, cardiac and pyloric stomachs (proventriculus, gastric mill), the hepatopancreatic caeca (midgut or digestive caeca), and the hindgut. Whether or not the midgut caeca should be termcd hcpatopancreatic caeca has been debated by Van Weel (1974) and Gibson & Barker (1979). Despite agreement