Two New Tapeworm Species Revealed in Endemic Balinese Shovelnose Rays

Hidden inside the spiral intestines of two rare shovelnose rays found only in Indonesian waters, scientists have uncovered a surprisingly rich community of parasitic tapeworms, including two species entirely new to science. The discovery, published in the journal Acta Parasitologica, doubles the known diversity of these parasites in any single region where the ray genus Rhinobatos has been studied, and it offers an unexpected window into what these threatened animals actually eat.

An international team led by Xaver Neitemeier-Duventester and Harry Wilhelm Palm of the University of Rostock, together with colleagues from Udayana University in Bali, examined twenty-three rays purchased at the Pasar Ikan Tradisional Kedonganan fish market on Bali’s southern coast between November 2018 and September 2021. Twelve of the specimens belonged to Rhinobatos jimbaranensis, a species recorded so far only from the eastern Indian Ocean off southern Bali and listed as threatened on the IUCN Red List. The remaining eleven were R. penggali, an endemic relative known from the southern coasts of Java, Bali, and Lombok. Both rays live on inner island shelves at depths of one to sixty meters and were described to science only in 2006.

The researchers focused on the order Trypanorhyncha, one of the most species-rich groups of marine cestodes and a group whose members are distributed worldwide. These tapeworms are prized by parasitologists as biological indicators because their life cycles weave through the marine food web: larvae develop in invertebrates or fish, and adult worms settle in the intestines of sharks and rays. By cataloguing which tapeworm species infect a host, scientists can infer details about its diet, migration, and zoogeographic distribution without directly observing the animal at sea.

Using standardized dissection and a gut-wash technique to flush every worm from the stomach and spiral valve, the team recovered twelve trypanorhynch species in total, ten from R. jimbaranensis and eight from R. penggali. Six species infected both ray species: Dollfusiella spinosa, Parachristianella indonesiensis, Parachristianella monomegacantha, Prochristianella clarkeae, Pseudochristianella jimbaranensis sp. nov., and Trygonicola macropora. Four species appeared only in R. jimbaranensis, including Dollfusiella hemispinosa, an unidentified Dollfusiella, the new Prochristianella bicki sp. nov., and Proemotobothrium linstowi. Two others, Dollfusiella michiae and Kotorelliella jonesi, were found exclusively in R. penggali. In all, the survey established thirteen new host records and eight new locality records.

The two new species were diagnosed through a combination of classical morphology and cutting-edge imaging. Specimens were stained with Mayer-Schuberg’s acetic carmine, cleared in eugenol, and mounted permanently in Canada balsam for light microscopy. The team then turned to confocal laser scanning microscopy at the University of Rostock, using Leica DMI6000 CS and Stellaris 8 instruments to build three-dimensional reconstructions of the tentacles and their hook armatures, and to scanning electron microscopy at the Rostock University Medical Centre, where critical-point-dried specimens coated with gold revealed surface details at the micrometer scale.

Prochristianella bicki sp. nov., named in honor of Dr. Andreas Bick, former supervisor of the lead author, is a small worm measuring roughly 1.3 to 1.9 millimeters in length, found in the spiral valve of R. jimbaranensis. Its tentacle armature is heteroacanthous and heteromorphous, with solid hooks arranged in ascending half spirals of nine to ten hooks. A distinctive feature is that the first pair of hooks disappears beyond the eleventh or twelfth metabasal row, leaving only a rudimentary hook in row twelve. The species also carries a characteristic basal armature with four rows of enlarged billhook-shaped hooks on the basal swelling, and it lacks the prominent microtriches visible in several of its closest relatives. Its nearest morphological counterpart, Prochristianella mooreae, can be distinguished by its ten to twelve hollow hooks per half spiral, compared with the nine to ten solid hooks of the new species.

Pseudochristianella jimbaranensis sp. nov., named after both the type locality and the type host, proved to be the most common parasite in the study. Seventy-three specimens were recovered from R. jimbaranensis and thirty-five from R. penggali, giving it a prevalence of 83.33 percent in the former and 90.91 percent in the latter, the highest recorded in either host. The worm bears four to six proglottids, roughly forty-eight to fifty-two testes, and a metabasal armature of fifteen solid hooks per half spiral that reduces to thirteen toward the tip. Its defining trait lies in the basal armature: two rows of enlarged slender uncinate hooks, followed by four rows of small spiniform hooks, and approximately thirty-five to thirty-six billhooks arranged on the external surface of the basal swelling, a configuration that clearly separates it from the three previously described species of the genus.

Beyond the taxonomy, the parasite community told a story about feeding ecology. Most of the recorded trypanorhynchs belong to the superfamily Eutetrarhynchoidea, whose larvae typically develop in crustaceans, consistent with the known diet of both rays, which feed primarily on small bottom-dwelling invertebrates. But two of the recovered worms belong to families with fish intermediate hosts. Kotorelliella jonesi, a tentaculariid, was found only in R. penggali, a species already suspected of eating small bony fish based on stomach content analyses. More intriguingly, Proemotobothrium linstowi, an otobothriid whose plerocercus larvae have been documented in teleosts, appeared only in R. jimbaranensis. That finding suggests that this ray, like its congener, also occasionally includes fish in its diet, a behavioral nuance that stomach sampling alone had not confirmed for the species.

The study also revealed patterns of parasite community structure. Species of Parachristianella and Pseudochristianella showed high prevalences and abundances in both ray hosts and appear to function as core species in Balinese Rhinobatos, while the four Dollfusiella species, despite their taxonomic richness, occurred at low intensities and are best regarded as non-core members of the community. The dominance of eutetrarhynchoid tapeworms mirrors patterns seen in other Rhinobatos species worldwide, from R. productus in the Gulf of California to R. planiceps in Chile and R. rhinobatos in Tunisia, all of which host parasite assemblages dominated by the genera Dollfusiella, Prochristianella, Parachristianella, and Pseudochristianella.

The findings carry weight beyond parasitology. Indonesia hosts the richest elasmobranch fauna on Earth, with 221 species of sharks and rays, and once operated the world’s largest chondrichthyan fishery, landing more than 100,000 tonnes annually in the early 2000s. Today, roughly forty percent of shark species face extinction risk from habitat loss, prey depletion, and overfishing. Because parasites like trypanorhynchs encode ecological information about their hosts, documenting them can support conservation planning for species such as R. jimbaranensis, whose range is among the most restricted of any ray. The authors note that knowledge of the trypanorhynch fauna of Bali remains scarce, with only a handful of published surveys, and they call for further studies to explore the full species diversity of these tapeworms in Balinese waters. Holotype and paratype specimens of both new species were deposited in the Zoological Museum Bogor in Indonesia, with additional paratypes held at the Berlin Natural History Museum, ensuring the material remains accessible in the country of origin.

Subject of Research: Trypanorhynch tapeworm diversity and feeding ecology of endemic Rhinobatos rays from Bali, Indonesia

Article Title: Trypanorhyncha (Cestoda) from Endemic Rhinobatos Species (Elasmobranchii: Rhinobatidae) from Bali, Indonesia, with the Description of Two New Species

Article References: Neitemeier-Duventester, X., Suryaningtyas, E. W., Riegert, J. W., Damriyasa, I. M., Arthana, W., & Palm, H. W. (2026). Trypanorhyncha (Cestoda) from Endemic Rhinobatos Species (Elasmobranchii: Rhinobatidae) from Bali, Indonesia, with the Description of Two New Species. Acta Parasitologica, 71(5), Article 227. https://doi.org/10.1007/s11686-026-01365-3

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01365-3

Keywords: Trypanorhyncha, Cestoda, Rhinobatos jimbaranensis, Rhinobatos penggali, Bali, Indonesia, new species, parasitology, feeding ecology, elasmobranchs, confocal laser scanning microscopy, marine biodiversity