Egg-laying patterns and in vivo egg production in the monogenean parasites Heteraxine heterocerca and Benedenia seriolae from Japanese yellowtail Seriola quinqueradiata.

Egg-laying patterns and egg production in Heteraxine heterocerca from the gills and Benedenia seriolae from the skin of Japanese yellowtail Seriola quinqueradiata in Japan were investigated in vivo. Eggs were collected every 3 h from sexually mature H. heterocerca and B. seriolae infecting 3 S. quinqueradiata kept individually over 3 consecutive days and exposed to alternating periods of illumination and darkness (LD 12:12; light on 06.00, light off 18.00) and maintained at 23.8 +/- 0.1 degrees C and 35 ppt salinity. A well-defined egg-laying rhythm was demonstrated for H. heterocerca while B. seriolae was shown torelease eggs continuously. A total of 114,000 H. heterocerca eggs was collected and of these, 45.4 (42.5-49.9)% were collected during the first 3 h period following dark at 18.00 h. A total of 662,857 B. seriolae eggs was collected and these were distributed over each 3 h period ranging from 11.1 to 14.1% of the daily egg output. All eggs extracted from the uterus of each H. heterocerca were joined together forming an 'egg-string'. The contrasting egg-laying patterns of H. heterocerca and B. seriolae suggest that each species makes use of a different infection strategy to infect the same host species, S. quinqueradiata.

Experimental infections, using a fluorescent marker, of two elasmobranch species by unciliated larvae of Branchotenthes octohamatus (Monogenea: Hexabothriidae): invasion route, host specificity and post-larval development.

The infection biology of Branchotenthes octohamatus (Monogenea: Hexabothriidae) from the gills of the southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae), was studied using the fluorescent dye, 5(6)-carboxyfluorescein diacetate N-succinimidyl ester (CFSE). This is the first use of this technique on a monogenean species with unciliated larvae and the first for any monogenean larva infecting an elasmobranch host. CFSE-labelled post-larvae were recovered from gills of T. fasciata within 30 min of exposure to the host, providing strong evidence that larvae invade host gills directly and do not migrate after initial attachment elsewhere. The rapidity with which larvae settled suggests that the mode of infection may deliver larvae directly to the gills via the host's inhalant respiratory current. The specificity of B. octohamatus was investigated by exposing a sympatric rhinobatid host species, the western shovelnose ray, Aptychotrema vincentiana, to B. octohamatus larvae newly emerged from eggs laid by adult parasites from gills of T. fasciata. Experimental exposure of A. vincentiana to freshly hatched B. octohamatus larvae resulted in a persistent infection, indicating that B. octohamatus may not be strictly host specific. Post-larval development charted on these experimentally infected A. vincentiana specimens was slow. Parasites appeared to be sexually mature at 91 days at 21-25 degrees C. Branchotenthes octohamatus larvae bear only 4 pairs of hooklets on the haptor whereas all other hexabothriid larvae described so far have 5 hooklet pairs. Ontogenetic changes to the haptor revealed that it is probably hooklet pair III that is lost from B. octohamatus prior to larval development.

The oncomiracidium of Nasicola klawei (Monogenea: Capasalidae: Capsalinae).

The oncomiracidium of the capsaline Nasicola klawei (Monogenea: Capsalidae), adults of which were collected from the nares of the yellowfin tuna Thunnus albacares (Scombridae) caught off Nelson Bay on the east coast of Australia, is described. This is a new locality record for N. klawei. This is the first description of an oncomiracidium of a Nasicola species and only the third time the larva of a capsaline species has been documented. The oncomiracidium of N. klawei is distinguished from others in the subfamily by the distribution of the body pigment and large distinct refringent (lipid?) droplets in the body and the prominent, posteriorly directed pointed process on the guard of each of the 14 hooklets. Oncomiracidia of the other two described Nasicola species, N. hogansi and N. brasiliensis, should be examined to determine whether these characters have generic or species-specific significance.

Three unrelated species, 3 sites, same host--monogenean parasites of the southern fiddler ray, Trygonorrhina fasciata, in South Australia: egg hatching strategies and larval behaviour.

The southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae), is parasitized by 3 monogenean (platyhelminth) species from 3 families on 3 different sites of the host: Calicotyle australis (Monocotylidae) from the cloaca, Pseudoleptobothrium aptychotremae (Microbothriidae) from the skin and Branchotenthes octohamatus (Hexabothriidae) from the gills. Cues that promote egg hatching were investigated for each species and the behaviour of their larvae was also documented. Eggs were laid by parasites in vivo and maintained at 22 degrees C. Three different egg hatching and host finding strategies were discovered. Calicotyle australis eggs hatched spontaneously with a strong diurnal rhythm that is likely to be under circadian control. The larva is ciliated, photo-responsive and can survive for up to 24 h at 22 degrees C after hatching. Pseudoleptobothrium aptychotremae may have a 'bet-hedging' strategy. Some eggs hatched spontaneously and rhythmically. However, since the hatching success was low, it is possible that other eggs require a different cue provided by the host. The larva is also ciliated but shows no photo-response and was observed to remain active for <4 h at 22 degrees C after hatching. Branchotenthes octohamatus has a 'sit-and-wait' strategy that depends on mechanical disturbance to stimulate hatching. The larva is unciliated, shows no photo-response but may survive for more than 2 days at 22 degrees C after hatching. The implications of hatching strategy, larval behaviour and morphology in the goal to find a host are discussed for each species.

The precocious oncomiracidium of Neoentobdella parvitesticulata (Monogenea: Capsalidae: Entobdellinae).

The oncomiracidium (larva) of the entobdelline Neoentobdella parvitesticulata (Monogenea: Capsalidae), adults of which parasitise the skin of the stingray Himantura fai (Dasyatidae) at Heron Island, Great Barrier Reef, Queensland, Australia, is described. The larva undergoes precocious development (progenesis) in the freely deposited egg. At >600 microm long, the fully embryonated, free-swimming oncomiracidium is more than twice as long as the larva of the related species N. diadema. Furthermore, the larva of N. parvitesticulata has a total of 60 flame bulbs compared with only 18 in N. diadema. The anterior hamuli in the oncomiracidium of N. parvitesticulata have well-developed distal hooks and may already be functional for secure attachment whereas those of N. diadema are rod-shaped, have no distal hook and would be unable to function in this way in newly attached larvae.

Effects of temperature, salinity, desiccation and chemical treatments on egg embryonation and hatching success of Benedenia seriolae (Monogenea: Capsalidae), a parasite of farmed Seriola spp.

The effects of temperature and salinity on the embryonation period and hatching success of eggs of Benedenia seriolae were investigated. Temperature strongly influenced embryonation period; eggs first hatched 5 days after laying at 28 degrees C and 16 days after laying at 14 degrees C. The relationship between temperature and embryonation period is described by quadratic regression equations for time to first and last hatching. Hatching success was >70% for B. seriolae eggs incubated at temperatures from 14 to 28 degrees C. However, no B. seriolae eggs embryonated and hatched at 30 degrees C and <2% of eggs hatched when incubated at 24 degrees C after transfer to 30 degrees C for 48 h. Embryonation period was similar for eggs incubated in sea water at 25, 30 and 35 per thousand salinity, but increased for eggs incubated at higher or lower salinities. When incubated at salinities ranging from 25 to 45 per thousand, more than 70% of B. seriolae eggs embryonated and hatched. Hatching success was lower at 20 and 50 per thousand salinity and few or no eggs hatched at 10 and 15 per thousand. Hatching of B. seriolae eggs can be prevented by desiccation for 3 min, by immersion in water at 50 degrees C for 30 s or by treatment with 25% ethanol for 3 min.

Mechanism of adhesion and detachment at the anterior end of Merizocotyle icopae (Monogenea: Monocotylidae) including ultrastructure of the anterior adhesive matrix.

The anterior adhesive mechanism was studied for Merizocotyle icopae (Monogenea: Monocotylidae). Adult anterior apertures can open and close. In addition, duct endings terminating within the apertures are everted or retracted depending on the stage of attachment. Adhesive in adults is synthesized from all 3 secretory types (rod-shaped, small and large spheroidal bodies) found within anterior apertures. All exit together and undergo mixing to produce the adhesive matrix, a process that depletes duct contents. A greater number of ducts carrying rod-shaped bodies is depleted than ducts containing spheroidal bodies which changes the ratio of secretory types present on detachment. Detachment involves elongation of duct endings and secretion of additional matrix as the worm pulls away from the substrate. The change in secretory type ratio putatively modifies the properties of the secreted matrix enabling detachment. Only after detachment do ducts refill. During attachment, individual secretory bodies undergo morphological changes. The larval and adult adhesive matrix differs. Anterior adhesive in oncomiracidia does not show fibres with banding whereas banded fibres comprise a large part of adult adhesive. The data suggest that this is the result of adult spheroidal secretions modifying the way in which the adult adhesive matrix forms.

Mechanism of adhesion and detachment at the anterior end of Neoheterocotyle rhinobatidis and Troglocephalus rhinobatidis (Monogenea: Monopisthocotylea: Monocotylidae).

The anterior adhesion and detachment mechanisms observed for Neoheterocotyle rhinobatidis and Troglocephalus rhinobatidis (Monogenea: Monocotylidae) appear similar to those observed for the two other monopisthocotylean monogenean species with anterior apertures for which published data are available. This supports the theory that monogeneans with apertures may utilise a common mechanism. Adult anterior apertures can open and close and duct endings can evert during the adhesion phase and retract during detachment and searching behaviour. The adhesive is comprised of two secretory types, rod-shaped and spheroidal bodies, found within anterior apertures. These exit together and undergo mixing to produce the adhesive matrix in which elongate membranes from rod-shaped bodies are seen intermixed with a granular electrondense matrix. The morphology of the adhesive matrix differs from that found for some other monogenean taxa. Anterior detachment by these monocotylids appears to involve a depletion of rod-shaped bodies in ducts and mechanical withdrawal of the anterior end.

A preliminary phylogenetic analysis of the Capsalidae (Platyhelminthes: Monogenea: Monopisthocotylea) inferred from large subunit rDNA sequences.

Phylogenetic relationships within the Capsalidae (Monogenea) were examined using large subunit ribosomal DNA sequences from 17 capsalid species (representing 7 genera, 5 subfamilies), 2 outgroup taxa (Monocotylidae) plus Udonella caligorum (Udonellidae). Trees were constructed using maximum likelihood, minimum evolution and maximum parsimony algorithms. An initial tree, generated from sequences 315 bases long, suggests that Capsalinae, Encotyllabinae, Entobdellinae and Trochopodinae are monophyletic, but that Benedeniinae is paraphyletic. Analyses indicate that Neobenedenia, currently in the Benedeniinae, should perhaps be placed in a separate subfamily. An additional analysis was made which omitted 3 capsalid taxa (for which only short sequences were available) and all outgroup taxa because of alignment difficulties. Sequence length increased to 693 bases and good branch support was achieved. The Benedeniinae was again paraphyletic. Higher-level classification of the Capsalidae, evolution of the Entobdellinae and issues of species identity in Neobenedenia are discussed.

A comparison of the anterior adhesive system in the oncomiracidium and adult of the monogenean parasite Menizocotyle icopae (Monocotylidae).

The anterior adhesive system of the oncomiracidium and adult of Merizocotyle icopae (Monogenea: Monocotylidae) were compared. The oncomiracidium has one ventrally placed aperture on either side of the head near the anterior extremity. In the adult, there are three ventrally placed apertures on either side of the head region. Both systems have three types of electron-dense secretory bodies opening into each aperture. A rod-shaped secretion (S1) and a small electron dense ovoid secretion (S2) are common to larvae and adults. The third secretion type differs: in adults, it is a large, spherical (S3) type but in larvae, it is an ovoid (S4) body. S4 bodies do occur in adults, but appear to be secreted as a general body secretion. An additional anteromedian secretion (S5) is also present in the oncomiracidium, but is not secreted into the anterior apertures. Homology and function of secretions are discussed.

Invasion of the shovelnose ray (Rhinobatos typus) by Neoheterocotyle rhinobatidis and Merizocotyle icopae (Monogenea: Monocotylidae).

This study examined the route of infection by free-swimming larvae of 2 monocotylid monogeneans that inhabit the gills (Neoheterocotyle rhinobatidis) and the nasal tissue (Merizocotyle icopae) of the shovelnose ray, Rhinobatos typus, from Heron Island on the Great Barrier Reef, Australia. Larvae of N. rhinobatidis and M. icopae attached directly to the gills and the nasal tissue of the ray, respectively, and did not first settle on the skin. Initial development of the post-oncomiracidium of N. rhinobatidis was rapid and hamuli formed between 6 and 24 h p.i. at a mean temperature of 26 degrees C. However, growth then slowed markedly and was variable; only 2 fully mature individuals were found 20 days p.i. at a mean temperature of 24.5 degrees C. Development of M. icopae was slow and variable throughout; hamuli did not appear until 10 days p.i. and no mature individuals were obtained even 22 days p.i. at a mean temperature of 24.5 degrees C. No character could be found as an indicator of parasite age for N. rhinobatidis or M. icopae due to the high variability in development in both species.

First published record of the pathogenic monogenean parasite Neobenedenia melleni (Capsalidae) from Australia.

The monogenean Neobenedenia melleni (MacCallum, 1927) Yamaguti 1963 is a well-known and virulent pathogen in culture conditions recorded from the skin of many teleost fish species worldwide. Until now, N. melleni has not been reported from wild or cultured fish in Australian waters. This study documents a recent outbreak of N. melleni that occurred on Lates calcarifer (barramundi) cultivated in sea cages in Hinchinbrook Channel between Hinchinbrook Island and mainland Queensland, Australia, which resulted in the loss of 200,000 fish (50 tonnes). The origin of this outbreak is unclear because N. melleni has not been recorded from any wild host species in Australia and strict quarantine regulations exclude the possibility of its introduction on imported fish. We propose that N. melleni occurs naturally on wild populations of some teleost species in Australian waters and that the few surveys of wild fish conducted along the east coast have failed to report this species. The possibility that uncharacteristically low water temperatures led to the outbreak is discussed.

Phylogenetic analysis of the Monocotylidae (Monogenea) inferred from 28S rDNA sequences.

The current classification of the Monocotylidae (Monogenea) is based on a phylogeny generated from morphological characters. The present study tests the morphological phylogenetic hypothesis using molecular methods. Sequences from domains C2 and D1 and the partial domains C1 and D2 from the 28S rDNA gene for 26 species of monocotylids from six of the seven subfamilies were used. Trees were generated using maximum parsimony, neighbour joining and maximum likelihood algorithms. The maximum parsimony tree, with branches showing less than 70% bootstrap support collapsed, had a topology identical to that obtained using the maximum likelihood analysis. The neighbour joining tree, with branches showing less than 70% support collapsed, differed only in its placement of Heterocotyle capricornensis as the sister group to the Decacotylinae clade. The molecular tree largely supports the subfamilies established using morphological characters. Differences are primarily how the subfamilies are related to each other. The monophyly of the Calicotylinae and Merizocotylinae and their sister group relationship is supported by high bootstrap values in all three methods, but relationships within the Merizocotylinae are unclear. Merizocotyle is paraphyletic and our data suggest that Mycteronastes and Thaumatocotyle, which were synonymized with Merizocotyle after the morphological cladistic analysis, should perhaps be resurrected as valid genera. The monophyly of the Monocotylinae and Decacotylinae is also supported by high bootstrap values. The Decacotylinae, which was considered previously to be the sister group to the Calicotylinae plus Merizocotylinae, is grouped in an unresolved polychotomy with the Monocotylinae and members of the Heterocotylinae. According to our molecular data, the Heterocotylinae is paraphyletic. Molecular data support a sister group relationship between Troglocephalus rhinobatidis and Neoheterocotyle rhinobatidis to the exclusion of the other species of Neoheterocotyle and recognition of Troglocephalus renders Neoheterocotyle paraphyletic. We propose Troglocephalus incertae sedis. An updated classification and full species list of the Monocotylidae is provided.

Phylogenetic analysis of the Monocotylidae (Monogenea) inferred from 28S rDNA sequences.

The current classification of the Monocotylidae (Monogenea) is based on a phylogeny generated from morphological characters. The present study tests the morphological phylogenetic hypothesis using molecular methods. Sequences from domains C2 and D1 and the partial domains C1 and D2 from the 28S rDNA gene for 26 species of monocotylids from six of the seven subfamilies were used. Trees were generated using maximum parsimony, neighbour joining and maximum likelihood algorithms. The maximum parsimony tree, with branches showing less than 70% bootstrap support collapsed, had a topology identical to that obtained using the maximum likelihood analysis. The neighbour joining tree, with branches showing less than 70% support collapsed, differed only in its placement of Heterocotyle capricornensis as the sister group to the Decacotylinae clade. The molecular tree largely supports the subfamilies established using morphological characters. Differences are primarily how the subfamilies are related to each other. The monophyly of the Calicotylinae and Merizocotylinae and their sister group relationship is supported by high bootstrap values in all three methods, but relationships within the Merizocotylinae are unclear. Merizocotyle is paraphyletic and our data suggest that Mycteronastes and Thaumatocotyle, which were synonymized with Merizocotyle after the morphological cladistic analysis, should perhaps be resurrected as valid genera. The monophyly of the Monocotylinae and Decacotylinae is also supported by high bootstrap values. The Decacotylinae, which was considered previously to be the sister group to the Calicotylinae plus Merizocotylinae, is grouped in an unresolved polychotomy with the Monocotylinae and members of the Heterocotylinae. According to our molecular data, the Heterocotylinae is paraphyletic. Molecular data support a sister group relationship between Troglocephalus rhinobatidis and Neoheterocotyle rhinobatidis to the exclusion of the other species of Neoheterocotyle and recognition of Troglocephalus renders Neoheterocotyle paraphyletic. We propose Troglocephalus incertae sedis. An updated classification and full species list of the Monocotylidae is provided.

The Calicotyle conundrum: do molecules reveal more than morphology?

Partial large subunit 28S rDNA sequences were obtained for specimens of Calicotyle (Monogenea: Monocotylidae) from eight different host species distributed worldwide to test the validity of some species and to address the question of host-specificity in others. Sequences obtained for Calicotyle specimens identified as C. kroyeri based on morphological methods from the type-host Raja radiata (Rajidae) and an additional host R. clavata, both from the North Sea, were identical. However, 'C. kroyeri' from the cloaca of R. naevus from Tunisia, Raja sp. A from Tasmania and R. radula from Tunisia differed from C. kroyeri from R. radiata by five (0.51%), 21 (2.13%) and 39 (3.96%) base pairs, respectively, over 984 sites. Therefore, it is likely that the specimens from Raja sp. A, R. radula and perhaps even from R. naevus are not C. kroyeri. Molecular results determined that the calicotylines from the cloaca of Urolophus cruciatus and U. paucimaculatus (Urolophidae) from southern Tasmania identified previously as C. urolophi are indeed identical. Large subunit 28S rDNA sequences of C. palombi and C. stossichi collected from the cloaca and rectal gland, respectively of Mustelus mustelus (Triakidae) from the coast of Tunisia differ sufficiently for these calicotylines to be considered separate and valid species. Our results indicate that some species of Calicotyle are not strictly host-specific, but that C. kroyeri may not be as widely distributed in rajids as was believed previously. Calicotyle specimens from rajids must be re-examined critically to determine whether there are morphological differences indicative of specific differences that may have been overlooked previously.

Euzetia occultum n. g., n. sp. (Euzetiinae n. subf.), a monocotylid monogenean from the gills of Rhinoptera neglecta (Rhinopteridae) from Moreton Bay, Queensland, Australia.

Euzetia occultum n. g., n. sp. (Monogenea: Monocotylidae) is described from the gills of the Australian cownose ray Rhinoptera neglecta Ogilby collected in Moreton Bay, Queensland, Australia. Euzetia has one central and ten peripheral loculi, which is similar to species in Decacotyle Young, 1967. However Euzetia is distinguished from other genera in the family by the presence of an additional loculus on either side of the central loculus. Because Euzetia does not fit into any of the six existing subfamilies in the Monocotylidae Taschenberg, 1879, as currently recognised, we propose the Euzetiinae n. subf. to accommodate the new genus. Euzetia occaltum is described and illustrated fully. This is the first published record of a monocotylid from a species of Rhinoptera Cuvier.

Dendromonocotyle colorni sp. n. (Monogenea: Monocotylidae) from the skin of Himantura uarnak (Dasyatididae) from Israel and a new host record for D. octodiscus from the Bahamas.

Dendromonocotyle colorni sp. n. (Monogenea: Monocotylidae) is described from the dorsal skin surface of two specimens of Himantura uarnak (Forsskål) kept at the Eilat Underwater Observatory in Israel. Dendromonocotyle colorni is distinguished from the other eight species in the genus by the morphology of the terminal papillar sclerite on the haptor, the distal portion of the male copulatory organ and the morphology of the vagina. The development of the male copulatory organ is detailed for D. colorni and the adaptations of species of Dendromonocotyle to life on the dorsal skin surface of rays are discussed. Dendromonocotyle octodiscus Hargis, 1955 was identified from the dorsal skin surface of the southern stingray Dasyatis americana Hildebrand et Schroeder off Bimini, Bahamas and represents a new host record.

A technique for preserving pigmentation in some capsalid monogeneans for taxonomic purposes.

A technique is described to preserve the pigment found in the bodies and the intestine of some brightly coloured and darkly pigmented benedeniine capsalid monogeneans. Previous studies of these pigmented capsalids have proven difficult because the pigmentation usually disappears when the worms are fixed using preservatives containing concentrations of formalin over 5% and/or ethanol, acetic acid, chromic acid, picric acid and mercuric chloride. The technique developed here uses a fixative comprising glycerol, acetone and formalin (GAF). After fixation under light coverslip compression for three minutes, specimens are transferred to absolute acetone for three minutes and cleared in a mixture of nine parts cedar wood oil and one part absolute acetone before mounting in Canada balsam. Processing must be carried out quickly, as these chemicals will cause the pigments to fade if the specimens are exposed to them for too long. Pigmented benedeniines processed using this technique retain the distribution, intensity and colour observed in live worms. The colour and distribution of pigmentation in monogeneans may be of taxonomic importance and this technique aids preparation of whole-mounts suitable for registration as type-material.

Adhesive secretions in the Platyhelminthes.

This review is the first to draw together knowledge about bioadhesives secreted by a group of parasites. Mechanisms of mechanical attachment are well known among parasites, but some can also attach to host surfaces by chemical means using a thin layer of adhesive material secreted at the parasite-host interface. Attachment by adhesives to living surfaces has not been studied in detail previously. A significant volume of research has determined much about the chemistry and nature of bioadhesives secreted by various marine macroinvertebrates from different phyla for attachment to inert substrates. Mussels and barnacles are sessile and adhere permanently, whereas starfish display temporary but firm adhesion during locomotion, feeding and burrowing. We focus on the Platyhelminthes that comprises the largely free-living Turbellaria and the wholly parasitic Monogenea, Cestoda, Digenea and Aspidogastrea. The term tissue adhesion is introduced to describe attachment by adhesives to epithelial surfaces such as fish epidermis and the lining of the vertebrate gut. These living layers regenerate rapidly, secrete mucus, are a site for immune activity and are therefore especially hostile environments for organisms that inhabit them, presenting a significant challenge for adhesion. Not all platyhelminths adhere to living surfaces and types of adhesion to inert substrates by the free-living turbellarians are also reviewed. Tissue adhesion is particularly well exemplified by monopisthocotylean monogeneans, parasites that are especially mobile as larvae, juveniles and adults on the epidermis of the body and gill surfaces of fish. These monogeneans secrete adhesives from the anterior end when they move from site to site, but some have secondarily developed adhesives at the posterior end to supplement or replace mechanical attachment by hooks and/or by suction. The temporary but tenacious anterior adhesives of monogeneans display remarkable properties of instant attachment to and detachment from their host fish surfaces. In contrast to the mobility of turbellarians and monopisthocotylean monogeneans and the simplicity of their direct life cycles, the largely endoparasitic Cestoda and Digenea are considered to be less mobile as adults. The complex cestode and digenean life cycles, involving intermediate hosts, place different demands on their various stages. Diverse, mostly anterior, gland cells in larvae, metacestodes and adults of the true tapeworms (Eucestoda), and in larval and adult Gyrocotylidea and Amphilinidea are reviewed. Conspicuous gland cells, mostly but not exclusively at the anterior end, in miracidia, cercariae and adults of digeneans and in cotylocidia and adults of aspidogastreans are also reviewed. Unlike turbellarians and monogeneans, accounts of unequivocal adhesive secretions in the Cestoda, but especially in the Digenea and Aspidogastrea, are relatively rare. The primary purpose of many conspicuous glands in the different stages of these mostly endoparasitic flatworms is for penetration into, or escape from, different hosts in their life cycle. We provide a detailed review of current knowledge about adhesion (in the sense of a thin layer of chemical material) in the Platyhelminthes including uses among eggs, larval, juvenile and adult stages. Information on structure, morphology and ultrastructure of the various adhesive systems that have been described is reviewed. Application of the 'duo gland' model is discussed. Comparisons are made between the little that is known about the chemistry of flatworm adhesives and the significant knowledge of the chemical nature of other invertebrate bioadhesives, especially those from marine macroinvertebrates. The potential importance of adhesives in parasitism is discussed. (ABSTRACT TRUNCATED)