Ultrastructural Analysis of the Pleopod Tegumental Glands in Male and Female Lobsters, Homarus Americanus

We have examined the ultrastructure of the glands in pleopods of mature male and of juvenile and sexually mature female lobsters. Glands are present in both sexes but are most abundant in sexually mature females with well-developed ovaries. The glands are comprised of three cell types (secretory cells, a central cell, and a canal cell) which are arranged in rosettes. There are two types of secretory cells: one produces homogeneous granules and the other honeycombed granules. The central cell has peripheral and central lobes; the central lobes interdigitate with narrow apical projections on the secretory cells. The canal cell possesses a thin ductule which opens into the lumen of the gland and appears to convey secretory material from the lumen to the surface of the pleopod cuticle. Scanning electron micrographs of the pleopod surface reveal that exudate is usually present in the ductule openings; this suggests that the glands secrete continually. Because of their ultrastructural features, we propose that these glands be referred to as "pleopod tegumental glands." Our data suggest that the pleopod tegumental glands have functions beyond attachment of fertilized eggs to the ovigerous setae. The first description of the glands in the pleopods of American lobsters (Homarus americanus) was provided by Herrick (1893). Various terms, including cement glands, pleopod glands, abdominal glands, and tegumental glands, have since been used to describe these glands (Aiken and Waddy, 1982). For reasons given below in Results, we refer to these glands as "pleopod tegumental glands." The glands in crustacean pleopods are organized in rosettes (Herrick, 1893, 1895, 1909; Yonge, 1932, 1937), and, at the light microscope level, resemble tegumental glands which are present ubiquitously beneath cuticular surfaces of arthropods. Tegumental glands in the eyestalk of Homarus americanus (Arsenault et al., 1979), in the gills of Palaemonetes pugio (Doughtie and Rao, 1982), and in the head and mouth parts of Porcellio scaber (Gorvett, 1946) are organized in rosettes consisting of a canal cell and a cluster of secretory cells which are radially arranged around a central cell (Herrick, 1895; Yonge, 1932; Gorvett, 1946; Arsenault et al., 1979; Aiken and Waddy, 1982; Doughtie and Rao, 1982). A small ductule passes through the center of the canal cell and conveys secretory product from the lumen of the gland to the exterior surface of the cuticle (Yonge, 1932; Doughtie and Rao, 1982). This arrangement of cells is quite similar to class IIItype epidermal exocrine glands of insects as defined by Noirot and Quennedy (1974). Pleopod tegumental glands in female H. americanus and other macrurans are generally considered to cycle in phase with the ovary and not with molting (Herrick, 1895; Yonge, 1932, 1937; Aiken and Waddy, 1982). It has been clearly established that as the ovary develops, the pleopod tegumental glands become engorged with an opaque white substance (Herrick, 1893, 1895, 1909; Yonge, 1937; Stephens, 1952; Lowe, 1961; Cheung, 1966; Waddy and Aiken, 1980). The function of the pleopod glands is unresolved, but because they cycle with the ovary, and because of their location near the ovigerous setae, they are thought to be involved in the attachment of fertilized eggs to the ovigerous setae (Braun, 1875, 1876; Herrick, 1893; Yonge, 1937; Silberbauer, 1971; Fisher and Clark,