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Species of Anisakis typically infect the stomach of cetaceans worldwide, often causing ulcerative lesions that may compromise the host's health. These nematodes also cause anisakiasis or allergic reactions in humans. To assess the risks of this emerging zoonosis, data on long-term changes in Anisakis infections in cetaceans are necessary. Here, we compare the prevalence and severity of ulcerative lesions caused by Anisakis spp. in five cetacean species stranded along the north-west Spanish coast in 2017-2018 with published data from 1991-1996. Open ulcers were found in 32/43 short-beaked common dolphins, Delphinus delphis; 3/5 striped dolphins, Stenella coeruleoalba; 1/7 bottlenose dolphins, Tursiops truncatus; and 1/3 harbour porpoises, Phocoena phocoena meridionalis; a single individual of long-finned pilot whale, Globicephala melas, was found uninfected. In common dolphins, the mean abundance of open ulcers per host was 1.1 (95% confidence interval: 0.8-1.3), with a maximum diameter (mean ± standard deviation) of 25.4 ± 16.9 mm. Stomachs with scars or extensive fibrosis putatively associated with Anisakis were detected in 14 and five animals, respectively. A molecular analysis based on the mitochondrial cytochrome c oxidase II gene using 18 worms from three cetacean species revealed single or mixed infections of Anisakis simplex sensu stricto and Anisakis pegreffii. Compared with the period 1991-1996, we found a strong increase of prevalence, abundance and extension of ulcerative lesions in most cetacean species. Anisakis populations could have increased in the study area over the last decades, although we cannot rule out that a higher environmental stress has also boosted the pathological effects of these parasites.

Dead specimens of Corynosoma cetaceum were used to describe the trunk musculature of this species and to infer the use of the trunk as a secondary holdfast. Inferences were based on trunk muscle arrangement, changes in trunk shape, size and distribution of spines, and geometry of tegument thickness. The foretrunk of C. cetaceum is swollen and forms a spiny disk that is bent ventrally. The disk is flattened by several groups of muscles not described previously, which seem able to finely adjust the disk surface over the substratum. Disk attachment appears to be accomplished by two dorsal neck retractor muscles specialized in pulling the anchored proboscis into the foretrunk. This mechanism has been described in other acanthocephalans, becoming surprisingly efficient when used with a flattened, armed foretrunk. The ventrally spined hindtrunk requires force to move downwards in order to attach. A single ventral neck retractor muscle seems specialized in pulling the posterior trunk forward, inducing a downward force due to the muscle's precise points of insertion. This mechanism necessarily generates ventral wrinkling that needs to be eliminated for the spiny surface to be functional. The trunk ventral muscles are apparently arranged so as to concentrate the "excess" of the tegument into a single fold, optimizing the use of the remaining surface for attachment. The size and distribution of spines, as well as the geometry of tegumental thickness, conform to these observations. Morphological changes, seemingly simple, such as structural bending, may have triggered a cascade of subtle modifications and new functions during acanthocephalan evolution, reflecting how morphological integration and novelty interact.

Richness and composition of gastrointestinal helminth communities of 54 loggerhead turtles, Caretta caretta, from the western Mediterranean were interpreted from patterns of helminth exchange at 2 host taxonomic scales: exchange between marine turtles and other marine hosts and exchange within turtles. We predicted exchange of the former to be unimportant ecologically and evolutionarily because of the host phylogenetic distance. The absence of records of successful exchange at this host taxonomic scale confirmed that host physiological barriers seem to prevent contemporary parasite transfer between marine turtles and other sympatric hosts. Marine turtles also seem to exhibit an evolutionary association with their parasites largely independent from that of other marine hosts. Therefore, the composition of gastrointestinal helminth communities of marine turtles is predictably restricted to digeneans, nematodes, and aspidogastreans specific to these reptiles. At the scale of host species, helminth exchange among marine turtle species was expected to be significant. This was suggested by reports indicating a high proportion of parasites common to all sea turtle species. Mediterranean C. caretta harbored only 4 digenean species typical of marine turtles, and immature individuals of 1 digenean species accidentally acquired. Further, no relevant parasite exchange with other marine turtles was expected to occur because C. caretta is the only sea turtle species abundant in the western Mediterranean. Therefore, a predictable composition coupled with low species richness in infracommunities might be accounted for partly by constraints on parasite acquisition at both host scales. Host factors limiting parasite recruitment (mainly ectothermy and a wandering behavior) may also contribute to depauperate and isolationist infracommunities.