The complete structure of the anterior sensory nervous system of the small nematode C. elegans has been determined by reconstruction from serial section electronmicrographs. There are 58 neurons in the tip of the head. Fifty-two of these are arranged in sensilla. These include six inner labial sensilla, six outer labial sensilla, four cephalic sensilla and two amphids. Each sensillum consists of ciliated sensory neurons ending in a channel enclosed by two non-neuronal cells, the sheath and socket cells. The amphidial channel opens to the outside as does that of the inner labial sensilla so that these probably contain chemoreceptive neurons. The endings of the other sensilla are embedded in the cuticle and may be mechanoreceptive. The cell bodies of all the neurons lie near the nerve ring and their axons project into the ring or into ventral ganglia. One of the ciliated sensory neurons in each of the six inner labial sensilla makes direct chemical synapses onto a muscle making these sensory-motor neurons. The anatomy of four isogenic animals was compared in detail and found to be largely invariant. The anatomy of juveniles is nearly identical to that of the adult, but males have four additional neuron processes.

Electron microscopical reconstruction of the anterior sensory anatomy of the nematode Caenorhabditis elegans.?2UU.

Publisher Summary Chemo-, thermo-, and hygroreceptors are primary sensory cells, which bear one or several modified cilia whose membranes are specialized to take part in the transduction process. These membranes must be exposed to the stimuli but also be protected against desiccation, mechanical, and other injury. Hence, a variety of structural specializations is found that serves these functions. In insects, chemo-, thermo-, and hygroreceptive sensory cells are located exclusively in sensilla, which are organelles built up by a definite number of characteristic cells. During development, the innermost enveloping cell produces a cuticular sheath (scolopale), which envelops the dendritic processes for varying distances along their course through the receptor lymph cavity. This sheath producing cell is surrounded by the trichogen cell, which is itself surrounded by the trichogen cell. These cells build up shaft and socket, respectively, of the cuticular outer structures during development. The perikarya of all cells of the sensillum are enclosed within the epidermis.

Ultrastructure of invertebrate chemo-, thermo-, and hygroreceptors and its functional significance.

A series of cladistic analyses assesses the status and membership of the taxon Polychaeta. The available literature, and a review by Fauchald & Rouse (1997), on the 80 accepted families of the Polychaeta are used to develop characters and data matrices. As well as the polychaete families, non-polychaete taxa, such as the Echiura, Euarthropoda, Onychophora, Pogonophora (as Frenulata and Vestimentifera), Clitellata, Aeolosomatidae and Potamodrilidae, are included in the analyses. All trees are rooted using the Sipuncula as outgroup. Characters are based on features (where present) such as the prostomium, peristomium, antennae, palps, nuchal organs, parapodia, stomodaeum, segmental organ structure and distribution, circulation and chaetae. A number of analyses are performed, involving different ways of coding and weighting the characters, as well as the number of taxa included. Transformation series are provided for several of these analyses. One of the analyses is chosen to provide a new classification. The Annelida is found to be monophyletic, though weakly supported, and comprises the Clitellata and Polychaeta. The Polychaeta is monophyletic only if taxa such as the Pogonophora, Aeolosomatidae and Potamodrilidae are included and is also weakly supported. The Pogonophora is reduced to the rank of family within the Polychaeta and reverts to the name Siboglinidae Caullery, 1914. The new classification does not use Linnaean categories, and the Polychaeta comprises two clades, the Scolecida and Palpata. The Palpata has the clades Aciculata and Canalipalpata. The Aciculata contains the Phyllodocida and Eunicida. The Canalipalpata has three clades; the Sabellida (including the Siboglinidae) Spionida and Terebellida. The position of a number of families requires further investigation.

Cladistics and polychaetes

Publisher Summary This chapter discusses basic concepts and advances of invertebrate immunity. In mammals and other higher vertebrates, a plethora of information exists on the origin, development, structure, and functions of the cells and tissues of the immune system. The cells of the invertebrate immune system can be subdivided into two main groups—namely, the freely circulating blood cells/coelomocytes and a variety of fixed cells. These latter cells may be either scattered throughout the tissues or localized together in hemopoietidphagocytic organs. In addition to these cell-mediated defenses, there are a number of chemical and mechanical barriers to parasite invasion. The chapter also explains the structure and classification of blood cells/coelomocytes. It provides a functional approach for blood cell classification and the cells are arranged into five main groups—namely, progenitor cells, phagocytic cells, hemostatic cells, nutritive cells, and pigmented cells.

Invertebrate Immunity: Basic Concepts and Recent Advances

Towards a phylogeny of gastropod molluscs: an analysis using morphological characters

Comparative studies on the segmental musculature of about seventy benthic polychaetes were conducted. The errant polychaetes comprise a central type and three radiating lines of evolution. It is suggested that those families with a complicated muscle system are a primitive stock.

Zur vergleichenden anatomie der segmentalen muskelsysteme und zur verwandtschaft der polychaeten-familien

The small cells of the midgut glands of Armadillidium vulgare, Oniscus asellus, Porcellio scaber, and Alloniscus oahuensis were examined by transmission electron microscopy, X-ray microanalysis, histochemistry, and atomic absorption spectroscopy. Inclusions containing large amounts of heavy metals were the most prominent feature of these cells. Various areas of the midgut glands exhibited large differences in storage capacity. Juveniles were free of lead.

Small cells in the midgut glands of terrestrial isopoda: Sites of heavy metal accumulation

Electron microscopy is an established diagnostic method in pathology of man as weIl as of vertebrate animals. During the last decade, ultrastructural studies have also been performed in invertebrates to elucidate cellular injuries caused by hazardous substances (BAYNE et al. 1985, MOORE 1985, STORCH 1988, HOPKIN 1989). The interest in invertebrates has increased due to their suitability to monitor environmental pollution. For example field and laboratory studies have been performed using the bivalve Mytilus edulis or the gastropod Littorina littorea as indicator of chemical contamination (AUFFRET 1988, CAJARAVILLE et al. 1989, CAJARAVILLE et al. 1990, MOORE 1988). Additionally, many invertebrates, such as aphids, grasshoppers, caterpillars or slugs are of significance as pest organisms in agriculture. Others, in most cases insects like the Ichneumonidae or Planipennia, are of increasing importance in biological or integrated pest control.

Invertebrate Cells as Targets for Hazardous Substances

Die komplizierten, bipektinaten Osphradien der NeogastropodenBuccinum undatum undNeptunea antiqua sind durch folgende Zelltypen gekennzeichnet: Die hochprismatischen Stutzzellen stellen den Hauptteil des mehrreihigen Osphradialepithels und sind durch ein reich ausgebildetes Villussystem sowie zahlreiche Pigmentgranula charakterisiert. Bisweilen tragen sie Zilien. Mindestens zwei Schleimzelltypen lassen sich unterscheiden. Den verschiedenen Sinneszelltypen lassen sich zwei Funktionen zuordnen: der Chemorezeption und dem Tastsinn. Die Funktion eines weiteren Typs mit stark ausgebildetem glattem endoplasmatischem Reticulum bleibt unbekannt.

The osphradium of the prosobranch gastropods Buccinum undatum L. and Neptunea antiqua

The contributions of ultrastructural research to the elucidation of invertebrate evolution are discussed by means of a number of selected examples. Studies of the fine structure of the integument of Aschelminthes and Platyhelminthes illustrate the method of interpretation. In addition, the following subjects and their significance for phylogeny are treated: annelid setae, sensilla of Pentastomida, choanocyte-like cells, epitheliomuscular cells, podocytes, gills of Polychaeta and lungs of Decapoda, and spermatozoa

Volker Storch

Papers

Zur vergleichenden anatomie der segmentalen muskelsysteme und zur verwandtschaft der polychaeten-familien

Small cells in the midgut glands of terrestrial isopoda: Sites of heavy metal accumulation

Invertebrate Cells as Targets for Hazardous Substances

The osphradium of the prosobranch gastropods Buccinum undatum L. and Neptunea antiqua

Contributions of Comparative Ultrastructural Research to Problems of Invertebrate Evolution