Kevin Halcrow

Modified pore canals in the cuticle of Gammarus (Crustacea : Amphipoda); A study by scanning and transmission electron microscopy

A novel type of pore canal is described from the cuticle of three species of Gammarus. Each canal passes from the epidermis vertically through the endocuticle and exocuticle, and in the most distal layers of the latter is slightly expanded. Before entering the epicuticle the canal narrows, forming a neck the base of which is encircled by an electron-dense collar. Several tubular structures arise from the collar and pass distally into the reticular innermost regions of the epicuticle. Within the neck and just below its opening at the cuticle surface, a rod-like structure is inserted; this protrudes a short distance from the pore. Each pore canal is connected to many necks; the openings of the latter are aligned in rows over the surface, the openings and rows being about 0.15 and 1.0 micron apart, respectively. Changes in the pore and canal contents are visible and their significance is discussed.

SCANNING ELECTRON MICROSCOPY OF SURFACE MICROSTRUCTURES OF SOME GAMMARIDEAN AMPHIPOD CRUSTACEANS

The cuticular surface of the head and second coxal plate of 124 species (104 genera) of Amphipoda has been examined by scanning electron microscopy. Most of the species examined possess a variety of microstructures that are presumed to be nonsensory, including numerous pores of different sizes and several types of cuticular projections (microtrichs). The microstructures frequently are distributed over the surface in highly ordered arrangements. The functional and phylogenetic significance of these features is discussed. In recent years some attention has been given to the variety of microstructures present on the surface of the integument of amphipod crustaceans. Among the structures described to date are those that appear, on the basis of their morphological organization and relatively restricted distribution, to be sensory. Thus, Mauchline and Ballantyne (1975) have identified by light microscopy several types of presumed sensilla projecting from the integumental surface of both hyperiid and gammaridean amphipods. The scanning electron microscope (SEM) investigations of Cuadras (1982), Holmquist (1982), Schwedhelm (1984), and Oshel (personal communication) on gammarideans provide more details of the morphology of some of these cuticular projections. In Schwedhelms report, a sensory role for the microstructure described is substantiated by demonstration of its innervation. In other instances, a sensory function is presumed from similarities between the external appearance of the microstructure in question and that of undoubted sense organs described from other arthropods. However, in addition to these putative sensilla there are several other microstructures in amphipods which occur extremely abundantly over much of the cuticular surface and which display other, morphological, characteristics that do not seem compatible with a sensory function. For example, the external opening of each of the very numerous pore canals of three species of Gammarus bears a peglike projection that is not innervated (Halcrow, 1978); these projections in an unstated species of Gammarus have been identified as sensilla and also as microtrichs by Cuadras (1982). According to Richards (1951), microtrichia are projections from the surface ofthe cuticle which may or may not contain a cytoplasmic filament extending from the underlying epidermis. This purely morphological definition of a microtrich is adopted in the present study without any connotations of a sensory function. Pores through the cuticular surface can be even more abundant than the microtrichs (Duncan, 1985; Halcrow, 1985; Moore and Francis, 1985). Several sizes of pores have been described, but it seems that most are the external openings of pore canals. The distinct morphology and ordered distribution of the microtrichs and pores of Gammarus spp. (Halcrow, 1978) suggested that they might be useful characteristics in the taxonomy of the Amphipoda and, particularly, the Gammaridea, a group in which the natural classification continues to be a source of much controversy (Bousfield, 1978; Bowman and Abele, 1982; Barnard and Karaman, 1983). Duncan (1985) has recently used an investigation of the cuticular microstructures of three species of terrestrial talitrid amphipods to speculate on the evolutionary history of this family.

Spinning a Marine Silk for the Purpose of Tube-Building

ABSTRACT Amphipod silk is a fibrous, self-secreted, adhesive substance employed in tube-building by amphipod species within the Corophiidea, Ampeliscoidea and Aetiopedidea. In the present study we provide a detailed characterisation of a novel, marine-based silk production system situated in pereiopods 3 and 4 in the corophioid Crassicorophium bonellii and the aorid Lembos websteri. The silk material is a mixture of protein and mucopolysaccharides. Ultrastructural and histological analyses revealed that silk in both species is produced in several rosette-type glands, presumed to be of two different types. These glands are distributed among all limb articles apart from the coxa but mainly in the basis and merus of pereiopods 3 and 4. Secretion commences in the basis and a thread-like secretion product leaves the glandular pereiopod through a cuticular pore near the dactylar tip. The silks physical and chemical properties most likely change while moving through the dactylar duct, which subdivides into several small ductules and terminates in a spindle-shaped chamber. This chamber, which communicates with the exterior, may be considered a silk reservoir in which the silk appears fibrous. For the first time an independently evolved, marine arthropod silk processing and secretion system is described.

Cellulase Activity in Gammarus Oceanicus Segerstrale (Amphipoda)

[Es werden Messungen uber die Aktivitat der Cellulase des Verdauungstrakts von Gammarus oceanicus vorgelegt. Bei Amphipoden, die 3-4 Wochen hungerten, ist die Cellulase-Aktivitat nur halb so hoch wie bei Individuen, die mit der Alge Fucus vesiculosus oder mit tierischem Gewebe (Kiemen- und Mantelgewebe der Muschel Mya arenaria) gefuttert wurden. Ausgehungerte und dann mit Muschelgewebe gefutterte Individuen zeigen eine gesteigerte Aktivitat gegenuber ungefutterten Individuen. Experimente mit Antibiotika legen nahe, dass Bakterien fur einen Teil der nachgewiesenen Cellulase-Aktivitat verantwortlich sind. Es ist ferner moglich, dass die Aktivitat dieses Enzymes jahres-zeitlichen Schwankungen unterliegt., Es werden Messungen uber die Aktivitat der Cellulase des Verdauungstrakts von Gammarus oceanicus vorgelegt. Bei Amphipoden, die 3-4 Wochen hungerten, ist die Cellulase-Aktivitat nur halb so hoch wie bei Individuen, die mit der Alge Fucus vesiculosus oder mit tierischem Gewebe (Kiemen- und Mantelgewebe der Muschel Mya arenaria) gefuttert wurden. Ausgehungerte und dann mit Muschelgewebe gefutterte Individuen zeigen eine gesteigerte Aktivitat gegenuber ungefutterten Individuen. Experimente mit Antibiotika legen nahe, dass Bakterien fur einen Teil der nachgewiesenen Cellulase-Aktivitat verantwortlich sind. Es ist ferner moglich, dass die Aktivitat dieses Enzymes jahres-zeitlichen Schwankungen unterliegt.]

Ultrastructural diversity in the pore canal systems of amphipod crustaceans

Transmission electron microscopy was used to analyze the structure and organization of the intracuticular pore canal system in 34 species of amphipod crustaceans. Pore canals were detectable in all species, including those that, from scanning electron microscopy, had been considered to lack them. Canal structure ranges from simple transcuticular passages of uniform diameter to more elaborate systems with distal canal dilatations variously equipped with electron dense collars, tubular filaments, single or multiple channels leading to the surface and transverse partitions separating canal contents of different electron densities. Considerable branching between tubular elements of the canal system is evident in many species. In most species the canals communicate with the outsidevia epicuticular channels. Even in those species in which this communication was not established, their epicuticle generally contains abundant cavities with external pores. Although some consistency in structure and organization is present among a few groups of taxonomically related species, pore canal characteristics generally could not be correlated with habitat or life style. It is suggested that the structural and organizational variety present reflects a considerable array of functions among amphipod pore canal systems.

CELL DIVISION IN THE CARAPACE EPIDERMIS OF DAPHNIA MAGNA STRAUS (CLADOCERA)

Cell division frequency in the carapace epidermis of D. magna declines with increasing animal size. Cell division is not necessarily one of the activities of premolt. During any particular intermolt the dividing cells are larger than those that do not divide but their size is also related to animal size, the cells in small animals dividing at a smaller average size than in larger individuals. Cell abundance following mitosis and prior to ecdysis consequently is not fixed but depends on animal size. The synthesis of an ephippium appears to be accompanied by cell division frequencies much higher than those occurring contemporaneously in other regions of the carapace.

Dynamics of Shape and Location in Epidermal Cells of Gammarus Oceanicus (Amphipoda)

ABSTRACT Polygonal patterns on the surface of epimeral plates of adult Gammarus oceanicus were compared in matched areas of exuvial and postmolt cuticle samples. The patterns, which record dimensions and locations of epidermal cells at premolt, were used to analyze shape and size distributions, shape and location changes during premolt, and the relative abundances of dividing cells. The degree of similarity of epidermal cell shape and location between exuvial and postmolt samples is very close, particularly in regions that lack dividing cells. It is hypothesized that conservation of shape and location originates from a sustained attachment of epidermis to cuticle throughout an intermolt of several weeks. Incidences of cell division were relatively consistent within multiple samples from individual animals and ranged from 0-24% between animals. However, cell division might be underestimated because of cell loss, which was evident directly, by pattern matching, or indirectly, by unchanged cell numbers, in identical sample pairs in which cell division was seen to have occurred.

The Effects of Reduced Salinity on Endocuticle Deposition in Gammarus oceanicus Segerstrale

ABSTRACT The deposition of endocuticle by postmolt Gammarus oceanicus Segerstrale maintained in either 10% or 100% seawater was examined at intervals for 12 days following ecdysis. After an initial inhibition or slowing of cuticle formation when the animals were transferred to 10% seawater, the frequency of lamella formation was similar in both experimental groups. Dilution of the external medium was also without persistent effect on the rate of increase in endocuticle thickness during the period of observation. Although crustacean osmoregulation is a topic of sustained interest, little attention has been given to the effects of salinity change on the molt cycle. The few data available suggest that molting in euryhaline forms is relatively insensitive to salinity change. For example, the molt frequency of the amphipod Corophium volutator varies only slightly over a wide range of salinities, decreasing only at extremely low and high salinities (McLusky, 1967). Moreover, Haefner and Schuster (1964) maintained female Callinectes sapidus, collected from one locality, at three salinity ranges and could not detect any significant differences between the postmolt increases in linear dimensions of individuals in the three groups. However, the possibility that salinity changes during proecdysis and postmolt might compromise an animals ability to produce a new cuticle has not yet been considered. Disruptions of amino acid metabolism and distribution in salinity-stressed marine invertebrates have been documented frequently (Gilles, 1979). Such disruptions, imposed on a crustacean epidermis undergoing striking changes in rates of protein synthesis, correlated with progress through the molt cycle (Stevenson, 1972), might be reflected in the rate of cuticle deposition. This possibility is investigated in Gammarus oceanicus, an abundant marine littoral amphipod often found in regions of the shore subject to freshwater run-off. A description is given of some of the effects of diluted seawater on endocuticle deposition by G. oceanicus placed in this medium following ecdysis.