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Adult acanthocephalans are typically found in the intestine of vertebrates, where they can readily absorb nutrients. However, Corynosoma cetaceum has been frequently reported in the stomach of cetaceans from the Southern Hemisphere. The ecological significance of this habitat was investigated by examining data on number, sex ratio, maturity status, biomass, and fecundity of C. cetaceum in different parts of the digestive tract of 44 franciscanas Pontoporia blainvillei. Individual C. cetaceum occurred in the pyloric stomach (PS) and, to lesser degrees, in the duodenal ampulla (DA) and the main stomach (MS). Females outnumbered males in all chambers, although the sex ratio was closer to 1:1 in the MS; there also was a higher proportion of nongravid females, with a smaller biomass in the MS than in the PS and the DA. This evidence suggests that cystacanths are released from prey tissues in the MS, where entire prey are reduced to semi-fluid chyme. The 3 chambers harbored gravid females that did not differ significantly in mean biomass or fecundity. The maturity status of females was nearly identical between the PS and the DA. In the MS, the higher proportion of non-gravid females is probably due to the occurrence of newly recruited females to this site. Mean biomass and fecundity of gravid females covaried strongly and positively among chambers within hosts. These results suggest that there are no major differences between the 3 chambers with respect to the suitability for reproduction by C. cetaceum. However, although the MS is the largest chamber, it harbored the smallest number of gravid females. Interestingly, worms were largely restricted to the aboral portion of the MS, a sheltered region where a concentration of chyme, and thus nutrient availability, likely occurs. Linear distribution differences of gravid female C. cetaceum at increasing intensities suggest that reproductive females occupy chambers according to available space. In summary, the stomach should be considered the main habitat for C. cetaceum. The choice of this habitat is puzzling because other Corynosoma species occur in the intestine, and because the stomach of cetaceans is not an absorptive site.Adult acanthocephalans inhabit the digestive tracts of vertebrates (Crompton, 1973). The preferred site for most species is the intestine (especially the middle region [Petrochenko, 1956]), apparently due to their requirement for simple nutrients that can be absorbed across the body wall (Crompton, 1973;Starling, 1985). However, some species infecting fish have been recorded in the stomach (Petrochenko, 1956), possibly because the stomach of fish is known to be a region of nutrient absorption (Crompton, 1973). Within the groups of acanthocephalans infecting birds and mammals, only 2 species, both in the genus Corynosoma, have been reported as adults from the stomach. Corynosoma hamanni was mostly found in the duodenum of Antarctic seals, but about 3% of the component population was found in the pyloric region of the stomach (Zdzitowiecki, 1...

Adult acanthocephalans are typically found in the intestine of vertebrates, where they can readily absorb nutrients. However, Corynosoma cetaceum has been frequently reported in the stomach of cetaceans from the Southern Hemisphere. The ecological significance of this habitat was investigated by examining data on number, sex ratio, maturity status, biomass, and fecundity of C. cetaceum in different parts of the digestive tract of 44 franciscanas Pontoporia blainvillei. Individual C. cetaceum occurred in the pyloric stomach (PS) and, to lesser degrees, in the duodenal ampulla (DA) and the main stomach (MS). Females outnumbered males in all chambers, although the sex ratio was closer to 1:1 in the MS; there also was a higher proportion of nongravid females, with a smaller biomass in the MS than in the PS and the DA. This evidence suggests that cystacanths are released from prey tissues in the MS, where entire prey are reduced to semi-fluid chyme. The 3 chambers harbored gravid females that did not differ significantly in mean biomass or fecundity. The maturity status of females was nearly identical between the PS and the DA. In the MS, the higher proportion of non-gravid females is probably due to the occurrence of newly recruited females to this site. Mean biomass and fecundity of gravid females covaried strongly and positively among chambers within hosts. These results suggest that there are no major differences between the 3 chambers with respect to the suitability for reproduction by C. cetaceum. However, although the MS is the largest chamber, it harbored the smallest number of gravid females. Interestingly, worms were largely restricted to the aboral portion of the MS, a sheltered region where a concentration of chyme, and thus nutrient availability, likely occurs. Linear distribution differences of gravid female C. cetaceum at increasing intensities suggest that reproductive females occupy chambers according to available space. In summary, the stomach should be considered the main habitat for C. cetaceum. The choice of this habitat is puzzling because other Corynosoma species occur in the intestine, and because the stomach of cetaceans is not an absorptive site.

Species of Balaenophilus are the only harpacticoid copepods that exhibit a widespread, obligate association with vertebrates, i.e., B. unisetus with whales and B. manatorum with marine turtles and manatees. In the western Mediterranean, juveniles of the loggerhead sea turtle, Caretta caretta are the only available hosts for B. manatorum, which has been found occurring at high prevalence (>80%) on them. A key question is how these epibionts are transmitted from host to host. We investigated this issue based on experiments with live specimens of B. manatorum that were cultured with turtle skin. Specimens were obtained from head-started hatchlings of C. caretta from the western Mediterranean. Hatched nauplii crawled only on rough substrates and lacked the ability to swim. Only copepodites IV and V, and adults, were able to perform directional swimming. Legs 2, 3 and 4 played a major role in swimming and were only well-developed in these stages. Nauplii reared in wells with turtle skin readily fed on this item. Late copepodites and adults also fed on turtle skin but did not consume other potential food items such as fish skin, baleen plates or planktonic algae. Evidences suggest that the transmission of B. manatorum should rely on hosts’ bodily contacts and/or swimming of late developmental stages between spatially close hosts. The possibility of long-ranged dispersal is unlikely for two reasons. First, all developmental stages seem to depend on turtle skin as a food resource. Second, the average clutch size of ovigerous females was small (< 70 eggs) for free-living phases to successfully contact turtles that occur at very low densities (< 0.6 turtles·km−2) in the western Mediterranean. The high prevalence of B. manatorum in loggerhead turtles in this area raises the question whether these turtles have contacts, or tend to closely aggregate, more than is currently believed.

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Each individual cetacean is an ecosystem itself, potentially harboring a great variety of animals that travel with it. Despite being often despised or overlooked, many of these epizoites have been proven to be suitable bio-indicators of their cetacean hosts, informing on health status, social interactions, migration patterns, population structure or phylogeography. Moreover, epizoites are advantageous over internal parasites in that many of them can be detected by direct observation (e.g., boat surveys), thus no capture or dissection of cetaceans are necessary. Previous reviews of epizoites of cetaceans have focused on specific geographical areas, cetacean species or epibiotic taxa, but fall short to include the increasing number of records and scientific findings about these animals. Here we present an updated review of all records of associations between cetaceans and their epibiotic fauna (i.e., commensals, ecto- or mesoparasites, and mutualists). We gathered nearly 500 publications and found a total of 58 facultative or obligate epibiotic taxa from 11 orders of arthropods, vertebrates, cnidarians, and a nematode that are associated to the external surface of 66 cetacean species around the globe. We also provide information on the use as an indicator species in the literature, if any, and about other relevant traits, such as geographic range, host specificity, genetic data, and life-cycle. We encourage researchers, not only to provide quantitative data (i.e., prevalence, abundance) on the epizoites they find on cetaceans, but also to inform on their absence. The inferences drawn from epizoites can greatly benefit conservation plans of both cetaceans and their epizoites.

BackgroundThird-stage larvae of the Pseudoterranova decipiens species complex (also known as sealworms) have been reported in at least 40 marine fish species belonging to 21 families and 10 orders along the South American coast. Sealworms are a cause for concern because they can infect humans who consume raw or undercooked fish. However, despite their economic and zoonotic importance, morphological and molecular characterization of species of Pseudoterranova in South America is still scarce.MethodsA total of 542 individual fish from 20 species from the Patagonian coast of Argentina were examined for sealworms. The body cavity, the muscles, internal organs, and the mesenteries were examined to detect nematodes. Sealworm larvae were removed from their capsules and fixed in 70% ethanol. For molecular identification, partial fragments of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) were amplified for 10 isolates from 4 fish species. Morphological and morphometric data of sealworms were also obtained.ResultsA total of 635 larvae were collected from 12 fish species. The most infected fish was Prionotus nudigula, followed by Percophis brasiliensis, Acanthistius patachonicus, Paralichthys isosceles, and Pseudopercis semifasciata. Sequences obtained for the cox1 of sealworms from A. patachonicus, P. isosceles, P. brasiliensis and P. nudigula formed a reciprocally monophyletic lineage with published sequences of adult specimens of Pseudoterranova cattani from the South American sea lion Otaria flavescens, and distinct from the remaining 5 species of Pseudoterranova. A morphological description, including drawings and scanning electron microscopy photomicrographs of these larvae is provided. Sealworms collected from Argentinean fishes did not differ in their diagnostic traits from the previously described larvae of P. cattani. However a discriminant analysis suggests that specimens from P. nudigula were significantly larger than those from other fishes. Most of the sealworms were collected encapsulated from the muscles and, to a lesser degree, from the mesenteries and the liver.ConclusionsWe provided the first molecular identification, morphological description and microhabitat characterization of sealworm larvae from the Argentinean Patagonian coast. We also reported the infection levels of sealworms on 20 fish species in order to elucidate the life cycle of these nematodes in this area.