The volume changes caused by coupled temperature and moisture variations in early-age concrete elements lead to formation of stresses. If a restraint exists along the contact surface of mature concrete against which a new concrete element has been cast, generated stresses are mostly of a restraint origin. In engineering practice a wide range of externally restrained concrete elements can be distinguished such as tank walls or bridge abutments cast against an old set foundation, in which early-age cracking may endanger their durability or functionality. Therefore, for years methods were being developed to predict early-age stresses and cracking risk of externally restrained concrete elements subjected to early-age thermal-moisture effects. The paper presents the comparative study of the most recognised analytical approaches: the method proposed in EC2, the method proposed by ACI Committee 207 and the method developed at the Luleå University of Technology.

The paper comprises the review of all 23 known valid species along with synonyms and polytomic keys based on morphological features. Mature specimens of 8 species occur in fishes, 4 in birds, 11 in mammals. Each species settles in a definite section of the digestive tract. The structure of a population is dependent upon the time which has passed since the moment of invasion and the intensity of infestation. Acathocephalans can be found in hosts all the year round, but incomplete seasonality of the occurrence of 2 fish parasites has been recorded. Fish parasites show wide specificity in relation to the hosts mentioned while bird and mammal parasites specificity is narrow. The majority of acanthocephalan species have circumpolar distribution but only 3 have been found inside the polar circle and the other 7 are common in the environs of subcontinental archipelagoes. Acanthocephalans do not yield precedence as far as the diversity of species and infestation intensity are concerned in the Antarctic to other groups of parasite helminths. Their great importance results from their mass occurrence in the vertebrates which are the focus of. man's practical interests — fishes, seals and whales.