Two moults occur during larval development in the eggs of Anisakis simplex (Rudolphi, 1809) and Pseudoterranova decipiens (Krabbe, 1878) from the North Atlantic. Live larvae forced out of eggs in sea water by coverslip pressure shortly before spontaneous hatching were surrounded by the thin cuticle of the first-stage larva. Infective larvae from naturally hatched eggs are loosely ensheathed in the thick cuticle of the second-stage larva. Thus, it is the third-stage larva that emerges from the egg of both species and not the second-stage larva as previously believed. The thin, smooth, fragile cuticle of the first-stage larva remains in the egg. The striated, cocoon-like cuticle of the second-stage larva of A. simplex may increase the buoyancy of the third-stage larva. The tail tip of the cuticle of the second-stage larva of P. decipiens is sticky and adheres the sheathed third-stage larva to the substrate.
During a parasitological survey of Leucoraja erinacea, L. ocellata, Malacoraja senta and Amblyraja radiata from Passamaquoddy Bay and waters surrounding the West Isles of the Bay of Fundy, NB, Canada, seven species of cestodes were recovered. Examination of these skates revealed the presence of two distinct species of Pseudanthobothrium Baer, 1956: one was retrieved from M. senta and A. radiata, identified as P. hanseni Baer, 1956 and redescribed herein; the other was retrieved from L. erinacea and L. ocellata and differs from previously described species. The new species is described herein as P. purtoni n. sp. on the basis of the degree of apolysis, the maximum width of the strobila, the length of the cirrus-sac and the number of testes. Additionally, the distinctiveness of both species of Pseudanthobothrium is supported by the characterisation of a 643 base-pair nuclear marker, which includes most of the D2 variable region of the large subunit ribosomal DNA (LSU). The recovery of two different tetraphyllidean species, each from two different host species, challenges the oioxeny (strict host-specificity) of echeneibothriine cestodes and can be explained, at least in part, by the similarities in diet and substrate preference within each host pair.
The mature cysticercoid of Ophryocotyle insignis, from Patella vulgata, was examined using transmission electron microscopy. Eight different types of microtriches were present over the tegument of the larval body and microvilli covered the caudal bladder, or cercomer. Rounded, modified microtriches were present on the external surface of the bladder enclosing the cysticercoid. Microtriches lining the retraction chamber ranged from small triangular projections having an electron-dense ridge along the anterior margin but having no shaft, to more typically shaped, larger microtriches having a cytoplasmic base, electron-dense shaft, and an electron-dense ridge along the anterior margin of the base. The scolex tegument had large robust microtriches which, in transverse section, had many projecting flanges. The microtriches on the rostellum were long and slender. Long, thin microtriches were present amongst the small spines on the suckers and short microtriches were found on the unspined areas of the suckers. Possible functions for the different types of microtriches are suggested and the significance of microvilli on the cercomer is discussed.
The mature spermatozoa from Bothrimonus sturionis (Pseudophyllidea), Pseudanthobothrium hanseni (Tetraphyllidea), and Monoecocestus americanus (Cyclophyllidea) were examined using transmission electron microscopy. Transverse sections of the sperm of B. sturionis indicate that the number of sperm axonemes varies from one to eight, with approximately one-third of the sperm containing two axonemes. Likewise, the number of peripheral microtubules lying just within the external plasma membrane varies from 12 to 20. The nucleus is electron lucent and fibrous in appearance. The spermatozoa of B. sturionis show great variation in the material examined and the majority of them are believed to be aberrant. The spermatozoon of P. hanseni contains a single axoneme with the nucleus wrapped in a crescent around it in the anterior region of the sperm. The posterior portion of the spermatozoon is characterized by a helical flange which projects from the main body of the sperm. The spermatozoon of M. americanus is elongate and slender, containing a single axoneme with an electron-dense nucleus coiled around it in the anterior one-third of the sperm. Electron-opaque bodies, which may be glycogen, fill the cytoplasm. The spermatozoa of all three species contain neither an acrosome nor mitochondria. The flagella of all the spermatozoa have a 9 + "1" arrangement of microtubules. The importance of the ultrastructure of spermatozoa in the phylogeny and taxonomy of cestodes is discussed.
A parasitological survey in the Bay of Fundy, Canada, resulted in the recovery of mature specimens from 5 species of phyllobothriid tapeworms (Cestoda: Tetraphyllidea) from 4 rajid skates: Echeneibothrium canadensis and E. dubium abyssorum specimens from Amblyraja radiata; E. vernetae and Pseudanthobothrium n.sp. from Leucoraja erinacea and L. ocellata; and P. hanseni from A. radiata and Malacoraja senta. Partial sequence data of a variable region (D2) from the large subunit ribosomal DNA (LSU) were used here to determine the host distribution of immature specimens for 4 of these 5 species (E. d. abyssorum was not included in the analyses). Immature specimens from both Pseudanthobothrium spp. were identified in the same hosts as recorded previously for mature specimens, thus suggesting that there are mechanisms that prevent the attachment of the parasite in an 'unsuitable' host species. Immature E. canadensis specimens were recovered exclusively from A. radiata, whereas immature E. vernetae specimens were recovered from L. erinacea and A. radiata, despite the latter host species not harbouring mature E. vernetae specimens. Their presence in the latter host species may be explained by host restriction or resistance, which allows the attachment of the parasites in the 'wrong' host species, but not establishment or development.
Bothrimonus (= Diplocotyle) is described from six species of teleost fishes and three species of gammarids from various geographical locations: Apeltes quadroons from Newfoundland; Microgadus tomcod from Massachusetts; Oncorhynchus gorbuscha from Attu Island in the Pacific Ocean; Pseudopleuronectes americanus from St. Andrews, New Brunswick; Salvelinus alpinus from Greenland; Salmo salar from Newfoundland; Gammarus océaniens from Newfoundland; Marinogammarus finmarchicus and M. pirloti from St. Andrews, Scotland. The synonymy and morphological variation of Bothrimonus is discussed and all the material examined is considered to be B. sturionis Duvernoy, 1842.
An integrated account of the ecology and life cycle of Bothrimonus is synthesized from the literature, experiment, and observation of larval and adult stages of the parasite. Bothrimonus has a circumpolar distribution in boreal or subarctic conditions. As an adult it is found in a wide variety of fish hosts which feed in littoral or estuarine waters. Adult worms have a short life-span in the fish host and occur only seasonally. A single intermediate host appears to be involved in the life cycle and this is most commonly a brackish-water gammarid. The operculate eggs, which contain unciliated larvae, possess characteristic polar filaments which have an adhesive function. Entry is almost certainly by ingestion of eggs by the gammarid host; the larval forms often attain sexual maturity within the gammarid host with accompanying production of apparently normal eggs. Although it has been possible to infect fish hosts experimentally with larval stages, it has not yet been possible to infect gammarids with eggs obtained either from neotenic individuals in gammarids or from adults in the fish host.The life cycle of Bothrimonus indicates closer affinities of the Cyathocephalidae with caryophyllaeid than with other pseudophyllidean tapeworms. Distribution is discussed in terms of its evolution and a freshwater origin in the Ponto–Aralo–Caspian province is proposed.
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