Seawater salinity and blood acid-base balance in the lugworm, Arenicola marina (L.).

The kinetics of variations in the blood acid base balance (ABB) were investigated in a moderately euryhaline osmoconformer, the lugworm Arenicola marina (L.), exposed to natural and experimental hypo- or hyperosmotic shocks. In natural as well as in experimental conditions, a hyposmotic shock induced a transient and essentially metabolic acidosis, probably linked to the ionic readjustments following the shock, which was rapidly overridden by a metabolic alkalosis. In field conditions, a new ABB equilibrium was then attained, the metabolic alkalosis being neutralized by the respiratory and metabolic acidosis occurring normally in the lugworm during low tide. Conversely, in the normoxic conditions of our laboratory experiments, a new ABB equilibrium was never reached. Under experimental conditions, a hyperosmotic shock always induced a respiratory and metabolic acidosis. In the field, this phenomenon must occur at the beginning of high tide and must help to restore normal blood ABB in lugworms submitted to a moderate hyposmotic shock during low tide. All the observed blood ABB variations reveal the complex intracellular processes through which the lugworm submitted to moderate osmotic shocks tentatively regulates, sometimes without any real success, its osmoticity and volume. Obviously, complementary physical, physiological and behavioral mechanisms allow the lugworm to live in sediments washed by almost fresh water during a 7-8 h 'low tide'.

Extracellular Hemoglobins of Hydrothermal Vent Annelids: Structural and Functional Characteristics in Three Alvinellid Species.

The polychaete annelids Alvinella pompejana, Alvinella caudata, and Paralvinella grasslei are strictly associated with deep sea hydrothermal vents. Each species possesses an extracellular hemoglobin, Hb, which has been studied and compared to that of a common intertidal polychaete, the lugworm Arenicola marina. The four Hbs exhibit very similar quaternary structures and spectral properties, and only small differences appeared in the gross polypeptide compositions after reduction and sodium dodecyl sulfate denaturation of the native molecules. Conversely, by a comparison of the effects of pH (6.6-7.6) and temperature (10-40{deg}C) on their intrinsic O affinities, Bohr factors, cooperativities, and apparent heats of oxygenation, lugworm Hb can be differentiated from that of the alvinellids, and the Hb of A. pompejana from that of A. caudata. The known biology of the lugworm and a further analysis of the data suggest several hypotheses concerning the in vivo O2 transport function of the alvinellid Hbs, the in vivo blood pH value in the two alvinellid species, their respective range of optimal temperature, and their ability to create a differentiated and stable external microenvironment.

Anatomical and ultrastructural study of the pharyngeal bulb in Protodrilus (Polychaeta, Archiannelida). I. Muscles and myo-epithelial junctions.

The pharyngeal bulb of Protodrilus is both a muscular and an epithelial organ whose function is the drawing up of food particles. The muscular system of the bulb is formed of tightly connected antagonistic muscles: the bulbus muscle and the sagittal and "grating plate" muscles. All of them are composed of obliquely striated fibers whose ultrastructural characteristics are similar to those of Hirudina and even more to those of epitokous forms of Nereidae and Syllinadae. Myo-epithelial cells do not exist in the pharyngeal bulb of Protodrilus contrary to what was previously thought; the muscles and the stomodeal epithelium are united by junction areas on both sides of the basal lamina. These myo-epithelial junctions may be compared of the myoepidermic junctions known in several Arthropods. A comparison of the ultrastructural features of the bulbus muscle fibers of Protodrillus (Protodrilidae) and Trilobodrilus (Dinophilidae) shows that the Protodrilus fiber clearly belongs to the obliquely striated type classically found in Polychaeta, while the Trilobodrilus fiber is a very peculiar type of obliquely striated fiber. These differences do not agree with Jägerstens hypothesis on the unity of the Archiannelida established on the basis of a structural similarity of the bulbus muscles.

Anatomical and ultrastructural study of the pharyngeal bulb in Protodrilus (Polychaeta, Archiannelida) II. The stomodeal and its cuticle.

The epidermal and stomodeal cuticles of Protodrilus are described then compared. The thin epidermal cuticle, the thickness of which is about the same over all the body, is characterized both by the absence of fibrils in its deepest part and by the extension of epidermal microvilli above the cuticle. The stomodeal cuticle, the thickness of which is as variable as that of the epithelium, presents two layers of fibrils comparable to the collagen fibrils described in the cuticle of other Annelida, as well as a relatively diversified supramicrovillous coating. The anterior cuticular thickening or grating plate, is characterized by the length of the epithelial microvilli, the thickness of the cuticular matrix and the superficial cuticular zone with supramicrovillous denticles supported by an axis of fibrous bundles. In the stomodeal cuticle, the fibrillar material seems to give to the cuticle best resistance to deformation during the pharyngeal bulb contraction, while an especially elaborated supramicrovillous coating is found in regions most exposed to friction. These features contrast with the relative simplicity of the epidermal cuticle.