Labral glands in Centropages typicus (Copepoda, Calanoida). I. Sites of synthesis

Abstract

In Centropages typicus the labrum contains two symmetric gland clusters on the right and left sides. Each cluster comprises two principal elements: a vast unit (AU) located in the anterior, distal area and a dozen smaller units (LPU) in the lateral, posterior area. All these glandular units empty through several pores situated on the labrum. In addition, other secretory units (LDU) are observed in a more dorsal and posterior zone at the level of the perioesophageal nerve ring, and hence outside the labrum itself; these LDU probably secrete through the dorsal side of the stomodeum. All the glandular units (i.e., AU, LPU, and LDU) are organized in syncytia. They have the typical ultrastructural features of a secretory system (rough endoplasmic reticulum, numerous dictyosomes, and secretory granules, the latter amassed at one pole), and several stages of activity may be characterized. The biochemical composition of the products synthesized by rough endoplasmic reticulum and Golgi apparatus is probably very complex. Mucopolysaccharides and glycoproteins both appear to be contained in a single type of grain. The mucopolysaccharides would cause agglutination of food particles carried up to the stomodeum by water currents. The glycoproteins would consist of different enzymes functioning in a preliminary digestive phase occurring before the aliments enter the midgut.

Ducts of the labral glands ofLeptestheria dahalacensis (Crustacea: Branchiopoda: Spinicaudata)

“…We observed by TEM a direct contact between each pair of gland cells and the accessory cell, and between the latter and the duct cell. A similar situation has been observed in some nonmalacostracan Crustacea (Cephalocarida, Copepoda, and Mystacocarida) (Gharagozlou-Van Ginneken, 1977;Arnaud et al, 1988a;Elofsson et al, 1992;Herrera-Alvarez et al, 1996).…”

“…In some cases, as in our samples, it has a filamentous appearance (Rieder, 1977;Doughtie and Ranga Rao, 1982;Arnaud et al, 1988b). We believe that this material is produced by the accessory cell, as hypothesized by Arnaud et al (1988a) for Centropages typicus. Although few micrographs clearly document the process, this hypothesis appears to be supported by certain ultrastructural features of the cytoplasm in the accessory cell (see Fig.…”

“…Furthermore, different locations of the external duct pores in A, B, and C-type gland cells on the dorsal surface of the labrum indicate differing functions in the feeding process. Varied, multiple functions have been suggested in other Crustacea (Fryer, 1962;Gharagozlou-Van Ginneken, 1977;Arnaud et al, 1988a;Elofsson et al, 1992;Martin, 1992;Schmitz, 1992;Wä gele, 1992;Bannister, 1993;Herrera-Alvarez et al, 1996). On the basis of scanty histochemical data concerning the labral glands of other nonmalacostracan Crustacea (Sterba, 1957;Dornesco and Steopoe, 1958;Pochon-Masson et al, 1975;Gharagozlou-Van Ginneken, 1977;Zeni and Franchini, 1990;Zeni and Zaffagnini, 1992), the secretions produced by these glands have, at least, a dual function: 1) as a viscous or mucous substance (glycosaminoglycans) able to agglutinate the food particles carried towards the feeding groove by the thoracopods (a role perhaps performed by the secretion of B-type and C-type gland cells, products of which-given their location-are the first to come into contact with food); and 2) as a proteinaceous substance involved in an initial digestive stage (enzymes or proenzymes) (a role perhaps carried out by the secretions from the A-type gland cells, which are introduced subsequently once the agglutinated food particles, broken up by the mandibles, reach the buccal opening and are ingested).…”

The distribution of exocrine glands in Lepeophtheirus salmonis and Caligus elongatus (Copepoda: Caligidae)

“…Mauchline, 1977;Briggs, 1978;Gharagozlou-van Ginnekcn, 1979;Arnaud, Brunet, & Mazza, 1988a; 1988b; Dumont & Silva-Briano, 1997). Unfortu-nately the few detailed studies which have been undertaken serve only to highlight our lack of understanding of these structures, their secretions and their significance to the biology and ecology of these animals.…”

A comparison of the labrum-paragnath complex in five species of calanoid copepods

“…The labrum may contain glandular outlets that discharge into the buccal cavity (Arnaud et al, 1988). It provides the housing that protects the oral opening as well as the operations of the mandible gnathobases, and helps to retain food prior to ingestion.…”