Ultrastructural studies of the cephalosome of some marine and estuarine calanoid copepods

The ultrastructure of the integument, sensory, neurosecretory and digestive systems are described from the marine calanoid copepods, Calanus helgolartdicus (Claus) and Labidocera cervi Krämer and the estuarine calanoid copepods, Sulcanus conflictus Nicholls and Gladioferens pectinatus (Brady). The Integument The ultrastructure of the epidermal cells and the very well developed tegumental glands are described. The possible functions of the tegumental cells are discussed. The ultrastructural architecture of the cuticle is described. Modified cuticle such as the lens of the Pontellidae, Labidocera and sites of muscle attachment to the cuticle are also treated. The Sensory System Nauplius Eye: The ultrastructure of the apparently specialized moveable eye of Sulcanus is described and briefly compared to those seen in other copepods. The eye consists of two lateral ocelli and one median ocellus. The median ocellus is different from the lateral ocelli in the arrange ment and organization of the retinular cells. The median ocellus has a two-tiered arrangement of rhabdoms and it is suggested that the median ocellus functions like the Pecten (Mollusca) eye, with an \on\" \"off\" response. The Dorsal Frontal Organs: The dorsal frontal organs are shown to be present in the Copepoda. The micromorphology of the dorsal frontal organs of the estuarine calanoid copepod Sulcanus are described. The organs are probably photoreceptors as indicated by the presence of the phaosomes and the rhabdomeric-like \"tubular bundles\". It is suggested that the dorsal frontal organs may act as a switch involved in the perception of seasonal changes. Mandibular Sensilla: The ultrastructure of the sensory receptors in the mandibles of Gladioferens are described. These sensilla which also occur in the other appendages of the cephalosome are probably chemo- and mechanoreceptors. There are also ttchloride cells\" in the mandibles and it is possible that associated with these are osmoreceptors. The functional significance of these sensilla with respect to the animals' feeding behaviour is discussed. The Neurosecretory System The ultrastructure of Claus's organ and the X-organ associated with the frontal filaments are described from the marine calanoid copepod Calanus and from the estuarine calanoid copepod Sulcanus. Claus's organs are apparently closely associated with the X-organ and may be considered as part of the X-organ complex. Claus's organ may be a neurosecretory baroreceptor. The X-organ complex probably constitutes the sensory pore X-organ and is comparable to those seen in the peracaridian Malacostraca. The Digestive System The Labral Glands: The ultrastructure of the labral glands of Gladioferens are described. The glands show similarities to the goblet cells of mammalian stomachs and probably secrete mucus. This is supported by histo-chemical tests. The gland is highly organized with well developed valves. The significance of the glands with respect to the filter feeding mechanism of the animal is discussed. The Mid-gut Diverticulum: The ultrastructure and histochemistry of the mid-gut diverticulum of Calanus are described. This part of the gut appears to be associated with some form of active transport as seen in the presence of so-called mitochondrial pumps. It appears unlikely that the mid-gut diverticulum is involved in the secretion of enzymes as there is an absence of rough endoplasmic reticulum. Appendix This is a section consisting of electron micrographs (with appropriate legends) on the eye and other organs from species of copepods other than those treated in the main part of the thesis. It is intended for comparative studies."