R. A. Hammond

Bio: R. A. Hammond is an academic researcher from Cardiff University. The author has an hindex of 1, co-authored 1 publications receiving 30 citations.

The fine structure of the trunk and praesoma wall of Acanthocephalus ranae (Schrank, 1788), Lühe, 1911.

Abstract: The wall of the trunk, that of the praesoma, and the lemnisci of Acanthocephalus ranae have been studied by electron microscopy. Striations visible in sections of the body wall under the light microscope do not correspond with the ‘striped layer’ revealed by the electron microscope.A new region, the ‘canal layer’, has been described. This contains canals running into the body wall from cuticular pores.Structurally the wall of the trunk and that of the praesoma are similar. The lemnisci resemble the ‘inner layer’ of the praesoma wall. However, it is suggested that the wall of the trunk differs physiologically from that of the praesoma, and from the lemnisci. The possible roles of the wall of the praesoma and the lemnisci in fat excretion or uptake have been discussed.The body wall of A. ranae has been compared with that of the other acantho-cephalans studied with the electron microscope.Grateful acknowledgement is made to D.S.I.R. (now S.R.C.) for a research grant to the Department of Zoology for the purchase of a Huxley ultramicrotome, a vacuum coating unit, and an AEI EM 6 electron microscope.I am grateful to Dr D. A. Erasmus for reading and criticizing the manuscript, and to Mr T. Davies for valuable technical assistance.

Host-parasite interactions in Acanthocephala: a morphological approach.

Abstract: In this review recent morphological and histochemical descriptions have been compiled of (mainly outer) features of all developmental stages of the Acanthocephala as well as what is known about the host's defence measures directed against these worms. From acanthors, for intance, it is documented how they escape melanization inside the haemocoel of a suitable intermediate host after they have been activated and released from their eggshell enclosure in the gut of the arthropod. Acanthors possess a complex set of eggshell-envelopes and interstices that fulfill different tasks. While the sequence of events inside the intermediate host's haemocoel is rather well known, what happens in paratenic hosts has been little studied. In final hosts the host-parasite interactions depend on the systematic affiliation of the parasite as well as the host and on the depth of penetration of each acanthocephalan species in the intestinal wall of the host. The mode of attachment also influences the microhabitat preference inside the gut. Mammals often reveal symptoms of high morbidity when infected with acanthocephalans, while fish seem to tolerate high intensities of worms deeply penetrating into their intestinal wall without showing pronounced symptoms of disease. The review also treats the subjects of host specificity, nutrient uptake and metabolism of the worms as well as their absorbance of metals and other elements. The high absorbance capacity for heavy metals suggests the usefulness of acanthocephalans as bioindicators.

Ecological and Physiological Aspects of Helminth-Host Interactions in the Mammalian Gastrointestinal Canal

Abstract: Publisher Summary This chapter discusses interaction of helminths and their hosts within the alimentary canal and, especially the stomach and intestines. Many such parasites live in the gastro-intestinal canal while others penetrate into the wall of the canal and a few invade organs, such as the liver and pancreas. The dynamic relationship between parasite and host is clearly shown and a good example set for future researchers. First, there is a study of the parasite–host interface, including the various kinds of organs of attachment, the varied nature of the lumen and the mucosa of the gastrointestinal canal, the nature of adhesion, and absorptive surfaces of the helminth and the host. The chapter describes the ecology of helminth site selection by trematodes, cestodes, and nematodes and matters concerning concurrent infections, transplantation, and migration. The chemical and physical characteristics of the intestinal lumen ionic and osmotic characters, microbial ecology, enzymes, bile acids and dietary fats, nutritive gradients, and matters of luminal homeostasis are discussed. The functional gradients in the gastrointestinal tract, bearing on the absorption of electrolytes and nonelectrolytes, water absorption, and malabsorption are also discussed.

The structure of the helminth cuticle.

Abstract: Publisher Summary This chapter discusses the structure of helminth cuticle. The following groups and species are considered: Turbellaria (Kronborgia amphipodicola), Monogenea (various species), Digenea (Fasciola hepatica and various other species), Cestodaria (Gyrocotyle urna), Cestoda (various species), Nematoda (various species), and Acanthocephala (Polymorphus minutus). In the Digenea, the change from miracidium to sporocyst also involves shedding of the ciliated epidermal cells and the formation of a syncytial epidermis from cells, which lie below the muscles. Cestodaria are either monogeneans or occupy a phylogenetic position between the monogeneans and the cestodes. The development of the epidermis of adult cestodes still needs much work to clarify the situation, especially from the embryological point of view. The epidermis of adult cestodes has been confirmed as an outer cytoplasmic syncytial epidermis, which is covered with microvilli bearing electron-dense spine-like tips, and in cytoplasmic continuity with nucleated cell-like bodies in the parenchyma. The cuticle of many different stages and species of nematode is examined with the electron microscope, and a certain type of cuticle structure appears to be common to most larval nematodes and also to some adults. Several examples of moulting in nematodes have been described, and it would appear that moulting differs in different types of nematode and sometimes in different stages of the life cycle. The body wall of some larval stages of two acanthocephalans has been described by means of electron microscopy and shown to be rather similar to that of the adult.

The biology of the acanthocephala.

Abstract: Publisher Summary This chapter discusses the biology of the acanthocephala. The morphology, functional anatomy, histology, cytology, ultrastructure development, biochemistry, host-parasite relationships, epidemiology, and medical and veterinary helminthology of acanthocephala are briefly discussed. A combination of experimental physiology and histology has given a clearer understanding of how the uterine bell apparatus and proboscis work in comparison to work based on earlier purely histological studies. The movement of the acanthor is also elucidated. The fine structure of acanthocephalan spermatozoa is given. The relationship between acanthocephala and cestoda can now be better understood as a result of advances in knowledge of biochemistry and fine structure. Other comparisons between these two groups are made in relation to intermediary metabolism and finally there is a phylogenetic explanation of peculiarities of acanthocephalan embryonic and larval development.

The absorptive surface of Moniliformis dubius (Acanthocephala). I. Fine structure.

Abstract: The fine structure of the syncytial epidermis of Moniliformis dubius (Acanthocephala) was examined with emphasis on the Streifenzone. Numerous crypts elaborate the area of the absorptive surface. Surface architecture is supported by a tripartite filamentous terminal web consisting of a 100 A sheet underlying the plasma membrane, a more extensive and diffuse inner region surrounding the crypts and a differentiated cytoplasmic annulation encircling each crypt neck. Inclusions and organelles described include filaments, microtubules, glycogen, lipid droplets, vesicles, mitochondria, Golgi complexes, endoplasmic reticulum and five lysosomal types. The eutelic nuclei contain little beterochromatin and have unusual nucleolar features.