Shark spiral intestines may operate as Tesla valves

Looking to nature for inspiration has led to many diverse technological advances. The spiral valve intestine of sharks has provided the opportunity to observe the efficiency of different valve systems. It is supposed that the spiral intestine present in sharks, skates and rays slows the transit rate of digesta through the gut and provides increased surface area for the absorption of nutrients. In this investigation, we use a novel technique—creating three-dimensional reconstructions from CT scans of spiral intestines—to describe the morphology of the spiral intestine of at least one species from 22 different shark families. We discuss the morphological data in an evolutionary, dietary and functional context. The evolutionary analyses suggest that the columnar morphology is the ancestral form of the spiral intestine. Dietary analyses reveal no correlation between diet type and spiral intestine morphology. Flow rate was slowed significantly more when the two funnel-shaped spiral intestines were subjected to flow in the posterior to anterior direction, indicating their success at producing unidirectional flow, similar to a Tesla valve. These data are available to generate additional three-dimensional morphometrics, create computational models of the intestine, as well as to further explore the function of the gastrointestinal tract of sharks in structural and physiological contexts.

Host relationships and geographic distribution of species of Acanthobothrium Blanchard, 1848 (Onchoproteocephalidea, Onchobothriidae) in elasmobranchs: a metadata analysis

Species of Acanthobothrium have been documented as parasites of the spiral intestine of elasmobranchs. Results of a metadata analysis indicate that 114 species of elasmobranchs have been reported as hosts of 200 species of Acanthobothrium. The metadata analysis revealed that 3.7% of species of sharks and 14.9% of species of rays that have been reported as hosts to date; some species are parasitized by more than one species of Acanthobothrium. This work provides a Category designation, as proposed by Ghoshroy and Caira (2001), for each species of Acanthobothrium. These Category designations are a tool to facilitate comparisons among members of Acanthobothrium for descriptions of new species in the future.

Site specificity and attachment mode of Symcallio and Calliobothrium species (Cestoda: “Tetraphyllidea”) in smoothhound sharks of the genus Mustelus (Carcharhiniformes: Triakidae)

Previous studies suggest that cestodes (i.e., tapeworms) of the sister genera Symcallio and Calliobothrium attach in different specific regions of the spiral intestine of their triakid shark hosts, with species of Symcallio attaching in the anterior region of the spiral intestine and species of Calliobothrium attaching with a broader distribution centered around the middle of the spiral intestine. In the present study, we tested the generality of this pattern of site specificity in two additional species pairs: Symcallio peteri and Calliobothrium euzeti in Mustelus palumbes and S. leuckarti and C. wightmanorum in M. asterias. Finding that these cestodes also exhibit the aforementioned pattern, we investigated a series of functional explanations that might account for this phylogenetically conserved pattern of site specificity. The mucosal surface of the spiral intestine of both shark species was characterized, as were the attachment mechanisms of all four cestode species. Although anatomical differences in mucosal surface were seen along the length of the spiral intestine in both shark species, these differences do not appear to correspond to the attachment mode of these cestodes. We find that while species of Symcallio, like most cestodes, attach using their scolex, species of Calliobothrium attach with their scolex and, to a much greater extent, also with their strobila. Furthermore, attachment of Calliobothrium species appears to be enhanced by laciniations (flap-like extensions on the posterior margins of the proglottids) that interdigitate with elements of the mucosal surface of the spiral intestine. The role of proglottid laciniations in attachment in species of Calliobothrium helps reconcile a number of morphological features that differ between these two closely related cestode genera.

Two new species of Acanthobothrium Blanchard, 1848 (Onchobothriidae) in Narcine entemedor Jordan & Starks, 1895 (Narcinidae) from Acapulco, Guerrero, Mexico

Two species ofAcanthobothrium(Onchoproteocephalidea: Onchobothriidae) are described from the spiral intestine ofNarcineentemedorJordan & Starks, 1895, in Bahía de Acapulco, Acapulco, Guerrero, Mexico. Based on the four criteria used for the identification of species ofAcanthobothrium,A.soniaesp. nov.is a Category 2 species (less than 15 mm in total length with less than 50 proglottids, less than 80 testes, and with the ovary asymmetrical in shape).Acanthobothriumvidalisp. nov.is a Category 6 species (more than 15 mm in total length with more than 50 proglottids, fewer than 80 testes, and the ovary is asymmetrical). The new species differ from similar species from the Pacific Ocean by total length, the number of proglottids, diameter of the accessory sucker, the length of the cirrus sac, the number of testes per proglottid and the measurements of hooks. With the recognition ofA.soniaesp. nov.andA.vidalisp. nov., 42 species ofAcanthobothriumhave been reported from the Pacific coast of the Americas. This is the first report of species ofAcanthobothriumfrom a member ofNarcinefrom Mexico and it brings the number of species reported from elasmobranchs from the Pacific Coast of Mexico to 13.

Expression of a novel isoform of Na+/H+ exchanger 3 in the kidney and intestine of banded houndshark, Triakis scyllium

Na+/H+ exchanger 3 (NHE3) provides one of the major Na+ absorptive pathways of the intestine and kidney in mammals, and recent studies of aquatic vertebrates (teleosts and elasmobranchs) have demonstrated that NHE3 is expressed in the gill and plays important roles in ion and acid-base regulation. To understand the role of NHE3 in elasmobranch osmoregulatory organs, we analyzed renal and intestinal expressions and localizations of NHE3 in a marine elasmobranch, Japanese banded houndshark ( Triakis scyllium). mRNA for Triakis NHE3 was most highly expressed in the gill, kidney, spiral intestine, and rectum. The kidney and intestine expressed a transcriptional isoform of NHE3 (NHE3k/i), which has a different amino terminus compared with that of NHE3 isolated from the gill (NHE3g), suggesting that NHE3k/i and NHE3g arise from a single gene by alternative promoter usage. Immunohistochemical analyses of the Triakis kidney demonstrated that NHE3k/i is expressed in the apical membrane of a part of the proximal and late distal tubules in the sinus zone. In the bundle zone of the kidney, NHE3k/i was expressed in the apical membrane of the early distal tubules known as the diluting segment. In the spiral intestine and rectum, NHE3k/i was localized toward the apical membrane of the epithelial cells. The transcriptional levels of NHE3k/i were increased in the kidney when Triakis was acclimated in 130% seawater, whereas those in the spiral intestine were increased in fish acclimated in diluted seawater. These results suggest that NHE3 is involved in renal Na+ reabsorption, urine acidification, and intestinal Na+ absorption in elasmobranchs.

Distribution patterns and interactions of cestodes in the spiral intestine of the narrownose smooth-hound shark, Mustelus schmitti Springer, 1939 (Chondrichthyes, Carcharhiniformes)

The distribution patterns and the cestode species interactions within the spiral intestine of 20 specimens of Mustelus schmitti from coastal waters off Mar del Plata, Argentina were studied. Six cestode species were found: Tetraphyllideans Calliobothrium barbarae, C. australis, C. lunae and Orygmatobothrium schmittii, diphyllidean Echinobothrium notoguidoi and trypanorhynch Eutetrarhynchus vooremi. The most common number of parasite species per host was 3. Brillouin’s diversity index ranged from 0.1 to 1.2 Berger-Parker dominance index indicated that C. barbarae was the dominant species, followed by O. schmittii and C. australis. Calliobothrium barbarae, C. australis and O. schmittii presented a broad distribution along the spiral intestine, whereas C. lunae, E. notoguidoi and E. vooremi showed a more restricted niche breadth. In general, the Renkonen’s index showed no evidence of niche overlap in the range of distribution of the different species. In most of the infracommunities, intraspecific aggregation was stronger than interspecific aggregation, indicating that competition may play a little role. The distribution patterns of the Calliobothrium specimens concurs with the predictions of attachment sites for Calliobothrium species made by previous authors.