The scale of the undertaking is remarkable. Scientific observers from the Mexican Institute for Sustainable Fisheries and Aquaculture measured and weighed a total of 8852 specimens representing eleven species from eight families of elasmobranchs, the class of cartilaginous fishes that includes all sharks and rays. The animals were captured during 55 trawling hauls conducted by commercial shrimp vessels between April 2013 and August 2017, across the continental shelf stretching from the mouth of the Río Bravo and the coast of Veracruz in the west to the Tabasco–Campeche Basin in the southeast. Each haul, conducted at night at depths between 9.1 and 90 meters, lasted between 1.8 and 7.0 hours as the nets dragged across the seafloor.

Why does such basic measurement work matter so much? Length–weight relationships, or LWRs, are among the most routinely used yet essential elements in fisheries science. They allow scientists to estimate biomass from length data alone, converting the average length of fish in a sample into the average weight, which is far more laborious to measure directly. They also let researchers convert length-based growth equations into weight-based ones and compare the physical condition of the same species across different regions or seasons. In practice, these equations are a critical component of stock assessment models, the analytical engines that determine how many fish can be sustainably harvested and how threatened populations might recover.

The mathematical foundation of the study is elegantly simple. The researchers fitted the classic power model, in which weight equals a constant times length raised to an exponent b, by regressing log-transformed weight against log-transformed length using the least-squares method. The constant a acts as a body shape coefficient, while the exponent b describes the type of somatic growth. When b equals exactly 3, growth is isometric, meaning the animal maintains its proportions as it grows. When b falls below 3, growth is negatively allometric, with the animal becoming more slender as it lengthens; when b exceeds 3, growth is positively allometric and the animal becomes stockier with size. Confidence intervals around b revealed which growth types could be statistically distinguished from isometry.

The results delivered a comprehensive picture of growth patterns across the southern Gulf’s demersal elasmobranch community. The allometric parameter b ranged from 2.5 to 3.2, entirely consistent with the expected range for fishes. Of the 23 estimations reported across pooled and sex-specific analyses, fifteen showed negative allometry, six showed isometry, and only two showed positive allometry: females of the butterfly ray Gymnura lessae and pooled samples of the bonnethead shark Sphyrna tiburo. Coefficients of determination, a measure of how well the model fits the data, exceeded 0.950 for every single species, meaning that weight can be predicted from length with remarkable accuracy.

Among the standout findings were four completely novel length–weight relationships for the lesser electric ray Narcine bancroftii, the skate Dipturus olseni, the roundel skate Rostroraja texana, and the guitarfish Pseudobatos lentiginosus. None of these species had ever had their length–weight relationship published before. In addition, the study provided the first Gulf of Mexico estimates for the southern stingray Hypanus americanus, G. lessae, the cownose ray Rhinoptera bonasus, the Atlantic angel shark Squatina dumeril, and the smooth dogfish Mustelus canis, while extending the known range of estimates for the bonnethead and the Gulf smoothhound Mustelus norrisi from the northern Yucatan Peninsula to the western Gulf.

Perhaps the most biologically intriguing discovery concerns the differences between the sexes. Using analysis of covariance, the researchers tested whether males and females of the six most abundant species followed the same growth curve. Five of the six species showed significant sexual dimorphism: females of R. texana, G. lessae, N. bancroftii, P. lentiginosus, and S. dumeril all carried more weight per unit of length than males, producing higher b parameters. Only the southern stingray bucked the trend, and the authors attribute this anomaly to a sampling quirk rather than biology. Larger female H. americanus exceeding 110 centimeters are less susceptible to shrimp trawling because turtle excluder devices fitted to the fleet’s nets tend to exclude the biggest individuals, blurring the expected pattern in the data.

The trawl fishery itself proved an unlikely but valuable scientific instrument. Because bottom trawls are poorly selective for species and size, especially for dorsoventrally flattened demersal animals like rays, the bycatch provided an unusually broad and representative size range for each species. The data covered eleven of the sixteen elasmobranch species known to occur in the shrimp trawl bycatch, which collectively account for roughly 3 percent of the total catch. Rays dominate this incidental harvest, contributing 82.4 percent of the bycatch biomass and 94.8 percent of its abundance, while sharks make up the smaller remainder. For most species the sample sizes were robust, exceeding 250 individuals, though five rarer species were represented by fewer than 100 specimens each.

Beyond the equations themselves, the study recorded new maximum sizes for two species, with female Rostroraja texana reaching 66.5 centimeters in total length, males 65.0 centimeters, and female Pseudobatos lentiginosus reaching 81.5 centimeters. Such records matter because maximum size constrains the upper bounds of population models and signals the demographic health of a species. The b values obtained for seven of the species were consistent with prior estimates from other parts of the Caribbean, the east coast of the United States, northeastern Brazil, and the Yucatan Peninsula, suggesting that these growth patterns are geographically stable and that the new parameters slot credibly into the broader Atlantic dataset.

The wider significance of this work lies in the conservation crisis facing sharks and rays. Elasmobranchs are among the most vulnerable marine taxa worldwide because their slow life histories, late maturity, and low reproductive rates make them acutely sensitive to fishing mortality. The Western Central Atlantic, including the Gulf of Mexico, has been identified as one of three global hotspots of threat to elasmobranch biodiversity, hampered by insufficient biological information and historical fishery data that lack taxonomic resolution. In Mexico, several of these species support artisanal fisheries, while others die unseen in trawl nets. By supplying the first biometric conversion factors for four species and the first Gulf-wide estimates for five more, the study directly serves Mexico’s research priorities under the Gulf of Mexico Fisheries Management Plan, giving managers the quantitative foundation they need to convert simple length observations into the weight estimates on which every modern stock assessment depends.

Subject of Research: Length–weight relationships of eleven demersal elasmobranch species from shrimp trawl bycatch in the southern Gulf of Mexico

Article Title: Length–weight relationships of eleven demersal ray and shark species ( Elasmobranchii ) from the southern Gulf of Mexico

Article References: Zea-de la Cruz, H., Meiners-Mandujano, C., Tovar-Ávila, J., Jiménez-Badillo, L., & Oviedo-Pérez, J. L. (2025). Length–weight relationships of eleven demersal ray and shark species (Elasmobranchii) from the southern Gulf of Mexico. Acta Ichthyologica et Piscatoria, 55, 191-195. https://doi.org/10.3897/aiep.55.156837

Image Credits: AI Generated

DOI: 10.3897/aiep.55.156837

Keywords: elasmobranchs, sharks, rays, Gulf of Mexico, length-weight relationships, fisheries science, shrimp trawl fishery, bycatch, allometric growth, stock assessment, conservation, Mexican fisheries

The revision, led by researchers examining dozens of newly recovered teeth from Upper Jurassic marine deposits near the village of Mahlstetten in southwestern Germany, demonstrates that this animal was not a synechodontiform at all. Instead, the evidence points to it being a galeomorph, the superorder that contains most familiar modern sharks, including hammerheads, tiger sharks and catsharks. The finding reshapes how palaeontologists view the diversity of Jurassic shark faunas and highlights just how much evolutionary experimentation was underway in the seas of that era.

Elasmobranchs, the group that includes sharks, rays and skates, are among the most successful lineages of cartilaginous fishes. They first appeared at the end of the Palaeozoic and underwent a major diversification during the Jurassic, when nearly all of their major clades show up in the fossil record. Yet reconstructing that history is notoriously difficult. Because shark skeletons are made of cartilage, they rarely fossilise intact. The overwhelming majority of what palaeontologists know about ancient sharks comes from isolated teeth and dermal denticles, the tiny tooth-like scales that covered their skin.

Teeth are abundant because sharks are polyphyodont, meaning they continuously shed and replace their teeth throughout their lives. This constant turnover produces enormous quantities of dental remains, which are highly valuable for taxonomy. But it also creates problems. Shark dentitions are heterodont, meaning that teeth vary considerably in shape depending on their position along the jaw, with differences running from the front of the mouth to the back and sometimes between upper and lower jaws. Distinguishing between features that are genuinely diagnostic of a species and those that simply reflect where a tooth sat in the mouth requires careful analysis, and many fossil species described in past centuries were based on material far too incomplete to capture this variation.

The genus Synechodus itself illustrates the problem. Its type species, Synechodus dubrisiensis, was described from an associated tooth set found in Late Cretaceous deposits in England. Over twenty additional species were subsequently assigned to the genus, spanning an extraordinary range from the Permian to the Palaeocene. But researchers have increasingly noticed that many of these species differ from the type in significant ways, including crown ornamentation and the pattern of vascularisation inside the roots. The Permian species Synechodus antiquus and several Triassic forms already show clear differences, and it is likely that many of them belong to genera that have yet to be identified. Synechodus, in other words, may be functioning as a waste-basket taxon, a convenient label for anything that looks vaguely similar but resists precise classification.

Curvorudentis prorogatus was caught in exactly this trap. Kriwet described it in 2003 from Callovian deposits at Kłęby in northwestern Poland, assigning it to Synechodus primarily on the basis of root characters such as short root grooves and several margino-lingual foramina. When four additional teeth were later discovered at Ogrodzieniec Quarry in southern Poland, from Middle Callovian and lower Oxfordian layers, questions began to mount. Those teeth showed significant differences from Synechodus dubrisiensis, particularly in root structure and crown ornamentation, casting doubt on the original assignment.

The new material from Mahlstetten changes the picture entirely. The fossiliferous layers there are greyish marls of the Mutabilis zone, dating to the early Kimmeridgian stage of the Late Jurassic, deposited under outer-shelf and open-water conditions. This contrasts with the restricted environments of the contemporaneous Solnhofen Archipelago and Nusplingen Lagerstätten. A private collector, E. Unger of Ravensburg, spent many years recovering palaeontological material from the site, and the specimens used in the study were subsequently donated to the State Museum of Natural History Stuttgart. Researchers photographed the teeth using scanning electron microscopy after sputter-coating them at the Museum of Natural History in Berlin, allowing extremely detailed examination of their surface features.

What those images revealed is a dental architecture unlike anything else in the Jurassic. The teeth are wide, with up to three pairs of lateral cusplets flanking a triangular main cusp. The basal labial margin, the front edge of the tooth near its base, is distinctly sinuous and curves into a pronounced concave arch beneath the main cusp. The labial crown face carries folds that run parallel to the cutting edges, with additional short vertical ridges on the cusps and cusplets, and a prominent labial crown extension that covers the root. Inside the root, the vascularisation follows a hemiaulacorhize pattern, with foramina and parallel nutritive grooves opening onto the lingual protuberance. None of these features match Synechodus, whose teeth lack the basal labial curvature and the parallel labial folds, and whose roots show a pseudopolyaulacorhize vascularisation pattern with a basally flat root and a typical labial depression.

The comparison with other Jurassic sharks was equally revealing. Teeth of Paraorthacodus, another synechodontiform genus, have a straight labial margin ornamented with sub-vertical ridges and delicate, well-separated cusplets, quite unlike the curved, fold-bearing teeth of Curvorudentis. The monotypic genus Bavariscyllium, from the Tithonian of the Solnhofen Archipelago, has shorter anterior teeth with lower, more acute cusplets and asymmetric root lobes. Palaeocarcharias, traditionally considered an early lamniform, has mesiodistally compressed teeth with no ornamentation and no lateral cusplets at all. Palaeoscyllium, another Solnhofen genus, shows strongly marked apico-basally directed ridges and a compressed lingual protuberance. Curvorudentis stands apart from all of them, and the researchers concluded that it required not just a new species assignment but a new genus, named from the Latin words for curvatures and tooth, in reference to the distinctive curved basal labial margin.

The reassignment to galeomorphs rests on several characters of high taxonomic value: the centrally developed concavity of the basal labial crown face, the well-developed crown shoulders, the presence of numerous open foramina in the lingual face of the root, and the hemiaulacorhize vascularisation pattern with divergent and basally oriented root branches. These traits are widely observed in both modern galeomorphs, such as the catshark Halaelurus bürgeri and the proscylliid Proscyllium habereri, and in fossil galeomorphs like Palaeoscyllium and Bavariscyllium. Interestingly, the teeth also show what appears to be a minor dignathic heterodonty, the kind of difference between upper and lower jaw teeth seen in living galeomorph sharks, where upper jaw teeth have cusps inclined toward the commissure while lower jaw teeth stand upright. More material will be needed to confirm this, but the pattern is suggestive.

Where exactly Curvorudentis sits within the galeomorphs remains unresolved. The researchers note that it shares some features with modern carcharhiniform taxa but differs in others, including the lateral extension of the enameloid, the labial crown folds parallel to the cutting edges, and the almost squared, mesiodistally elongated root with oblique and divergent branches. The systematic positions of Palaeoscyllium and Bavariscyllium within galeomorphs have also recently been challenged and remain uncertain, and Curvorudentis appears to be in a similar position, a galeomorph whose precise affinities cannot yet be pinned down.

The Mahlstetten discovery also extends the geographic and temporal range of the species considerably. Previously known only from Middle Jurassic deposits in Poland, Curvorudentis prorogatus is now documented from the early Kimmeridgian of Germany, its stratigraphically youngest occurrence to date. Its environmental distribution spans from nearshore settings in Poland to the offshore conditions of Mahlstetten, suggesting that this was a small, unspecialised mesopredator, comfortable in a range of marine habitats. As palaeontologists continue to re-examine old collections with modern imaging techniques and larger comparative datasets, it seems likely that more waste-basket taxa will be unpacked, and more unexpected branches of the shark family tree will come into focus.

Subject of Research: Taxonomic revision of a Jurassic shark species based on fossil teeth

Article Title: Revision of the extinct shark Synechodus prorogatus Kriwet, 2003 ( Chondrichthyes , Elasmobranchii ) and its galeomorph affiliation

Article References: Begat, A., Villalobos-Segura, E., Amadori, M., Klug, S., & Kriwet, J. (2026). Revision of the extinct shark Synechodus prorogatus Kriwet, 2003 (Chondrichthyes, Elasmobranchii) and its galeomorph affiliation. Swiss Journal of Palaeontology, 145, 303-311. https://doi.org/10.3897/sjp.145.187852

Image Credits: AI Generated

DOI: 10.3897/sjp.145.187852

Keywords: Jurassic, sharks, paleontology, elasmobranchs, teeth, taxonomy, galeomorphs, Synechodus, Germany, Poland, fossil, heterodonty

The vertebrate somatosensory system is a natural laboratory for studying circuit evolution. In mammals, touch, pain, and body-position sensing are carried by more than a dozen genetically distinct subtypes of dorsal root ganglion (DRG) neurons, the sensory cell bodies clustered beside the spinal cord. Three principal classes—mechanoreceptors for touch, nociceptors for pain, and proprioceptors for muscle feedback—transmit modality-specific information to spatially organized layers of the spinal cord. During mammalian development, each class preferentially expresses one of three neurotrophin receptors: ntrk1 in nociceptors, ntrk2 in mechanoreceptors, and ntrk3 in proprioceptors. Signals through these receptors, triggered by target-derived growth factors from the skin and muscle, sculpt neuronal identity, connectivity, and survival. Whether this target-dependent strategy for circuit assembly was present in the common ancestor of all jawed vertebrates, or is a mammalian innovation, was unknown.

Elasmobranchs—skates, sharks, and rays—are the earliest vertebrate lineage in which primary somatosensory neurons are encapsulated in DRG, making them an ideal entry point for reconstructing the ancestral state. Anatomical work over decades suggested their somatosensory system is comparatively simple: DRG soma of uniform size, bimodal distributions of axon diameter, and, strikingly, an apparent absence of unmyelinated C-fibers, the pain-carrying neurons that constitute the majority of DRG cells in mammals. Prior studies of aquatic sensory systems had focused on specialized modalities such as the lateral line, electroreception, or embryonic Rohon-Beard neurons, leaving the evolutionary history of canonical touch and pain circuits unexplored. The little skate, whose embryos develop in transparent egg cases and whose adults walk on the seafloor with fin-based locomotion, offered a tractable system for closing that gap.

The team combined bulk and single-nucleus RNA sequencing with 10x Genomics Xenium spatial transcriptomics on skate embryos at stages 31 and 32, when fins are becoming mobile. Using PIPseq, a microfluidics-free nuclear capture method, they profiled 22,724 nuclei from pooled spinal cords and individually isolated DRG. A custom 300-gene Xenium probe set, designed from the sequencing data and enriched for fate determinants, channels, and receptors, resolved expression patterns in intact tissue across pectoral and pelvic segments. Roughly 90 percent of targeted genes yielded spatially informative signals, and bulk RNA-seq differential expression analysis between spinal cord and DRG showed largely concordant spatial localization, validating the approach.

The spinal cord results were strikingly conservative. Re-clustering of spinal nuclei identified 29 clusters, many with molecular profiles matching mammalian subtypes: motor neurons marked by chat, mnx1, and slit3; dorsal excitatory dI1 interneurons marked by lhx2 and lhx9. Spatial transcriptomics assigned major classes—ventral and dorsal interneurons, progenitors, floor plate cells, glia—to stereotyped positions. Most importantly, the dorsal spinal cord showed a laminar organization deeply reminiscent of mammals. Superficial layers expressed lmx1a, lmx1b, and tlx3b, markers of the dI5 neurons that receive nociceptive input in mammals. More ventral populations expressed lhx2, lhx9, and barhl2, markers of mechanosensory-receiving dI1 neurons. Deeper layers expressed satb2, otpa, and palvb. Because skate DRG neurons express vglut1 (slc17a7) while spinal neurons largely do not, the researchers could use a VGLUT1 antibody to trace sensory afferent terminals. By stage 32, VGLUT1-positive projections enriched the dorsal spinal cord and extended toward the LHX2-positive dI1-like population—evidence that modality-specific targeting of sensory axons to spinal layers is an ancestral vertebrate feature.

The DRG results, by contrast, were anything but conservative. Skate sensory neurons segregated into broad mechanosensory-like and nociceptor-like classes, but the neurotrophin receptor code defining them had been radically reconfigured. Medially positioned runx3-positive neurons co-expressed ntrk3, as mammalian proprioceptors do—but they also co-expressed ntrk1, the mammalian nociceptor receptor, along with nociceptive markers including trp channels (trpv1, trpc4, trpa1) and tac1. Meanwhile, ntrk2a-positive neurons expressed the mechanoreceptor channel piezo2, consistent with conservation of the ntrk2 mechanosensory association. In mammals, this combination is incompatible: ectopic expression of ntrk3 in ntrk1-positive neurons disrupts nociceptor identity and drives proprioceptive features. In skate, the two programs coexist within single neurons. A fourth population expressed ntrk2a alone. Transcription factor profiling added further layers: broadly expressed factors such as tlx3b and pou4f3; ntrk1/3-restricted factors including runx3, skor2, ebf3a, and casz1; ntrk2a-restricted factors including tbx2b, onecut2, and etv4; and overlapping factors such as shox2 and runx1. Nine TFs were expressed in both DRG neurons and specific dorsal spinal populations, raising the possibility that shared transcriptional programs contribute to wiring specificity between connected classes.

To test whether skate sensory neurons depend on peripheral targets the way mammalian ones do, the team performed unilateral fin-bud ablations at stages 27 to 28 and let embryos develop for 14 to 28 days. About 90 percent survived normally, minus the ablated fins. The effects were selective and temporal. Fin-innervating motor neurons, marked by FOXP1, degenerated rapidly: 65 to 70 percent of pectoral and 30 to 40 percent of pelvic motor neurons were lost by stage 31, while axial-muscle motor subtypes were spared. DRG neurons were initially resilient but by stage 32 showed losses exceeding 70 percent in rostral pectoral segments. Crucially, the researchers identified SMAD phosphorylation as an early readout of target-derived signaling. In chick embryos, pSMAD labeled roughly 30 percent of brachial DRG sensory neurons; in skate, pSMAD appeared by stage 30, enriched in RUNX3-negative, ntrk2a-like mechanosensory subtypes. After limb ablation in chick, pSMAD dropped by about 70 percent on the ablated side; after fin ablation in skate, by about 53 percent. SMAD phosphorylation thus marks a conserved early response of sensory neurons to limb- and fin-derived cues in both species.

Fin ablation also revealed a biphasic model of sensory specification. The initial segregation of ntrk2a-positive and ntrk1/3-positive neurons into medial-lateral populations occurred normally without fins, indicating that broad sensory class identity is established target-independently—likely reflecting the birth order of neurogenin2 versus neurogenin1 lineages described in mammals. But downstream maturation failed. Expression of etv4 and ret, genes regulated by limb-derived signals in mice, was markedly depleted. Runx3, instead of restricting to ntrk1/3-positive populations, expanded throughout the DRG, with the RUNX3-positive fraction of ISL1/2-positive neurons rising from 53 to 82 percent on the ablated side. Central connectivity collapsed in parallel: VGLUT1-positive sensory terminals were confined to the most superficial spinal layers, with significant reductions across all dorsal laminar bins and the greatest losses in deeper regions. Target-derived cues, the data show, couple molecular specification with the fidelity of dorsal afferent targeting—an ancestral mechanism now demonstrated in a cartilaginous fish.

The findings carry implications beyond developmental biology. The long-standing debate over whether cartilaginous fish experience pain has often cited the absence of C-fibers as evidence for limited nociceptive capacity. This study shows skate DRG neurons express canonical mammalian nociceptive markers—trp channels, tac1, calca—and that recipient spinal neurons marked by npy1r are enriched in superficial layers, features consistent with nociceptive processing resembling mammalian thinly myelinated Aδ-fibers that mediate rapid first pain. Equally provocative is the apparent absence of dedicated muscle proprioceptors. Skate runx3-positive neurons express nociceptor markers but lack piezo2 and etv1, determinants essential for mammalian proprioceptor development. The authors hypothesize that muscle-based proprioception may be a later evolutionary innovation, emerging with terrestrial locomotion, and that ancestral fish relied on alternative mechanosensory feedback—such as the intraspinal piezo2-positive neurons recently described in adult zebrafish, or cutaneous afferents modulating motor output through deep dorsal spinal circuits.

What emerges is a principle with broad reach: conserved circuit architecture is compatible with malleability in receptor usage and fate-determinant deployment. The layered spinal cord, the modality-specific targeting of sensory axons, and the reliance on retrograde target-derived signaling are all deeply conserved. The molecular programs implementing sensory identity—the neurotrophin receptor code, the deployment of runx3, the combinatorial TF logic—have been extensively reconfigured across vertebrate evolution. This decoupling of architecture from specification provides a general mechanism by which sensorimotor systems accommodate innovation while preserving function. Whether the mixed molecular identities of skate sensory neurons represent retention of an ancestral program or a lineage-specific innovation remains open, as does the full diversity of mature sensory types, which embryonic profiling likely underrepresents. Definitive linkage of molecularly defined types to modality-specific physiology and behavior will require functional assays—electrophysiology, activity imaging, behavioral analyses—building on the molecular and spatial foundation this study establishes. But the conceptual shift is already clear: the stability of somatosensory organization across vertebrates rests not on a frozen genetic blueprint, but on a flexible one.

Subject of Research: Evolutionary neuroscience of somatosensory circuits in an early-diverging vertebrate

Article Title: Ancient somatosensory circuit architectures employ flexible molecular strategies

Article References: Lee, H., Frazel, P. W., Singer-Freeman, E., Cavanagh, A. E., Shin, H. D., Rice, K., Selvaraj, S., Alu, M., Kim, H., Loomis, C., Liddelow, S. A., Baek, M., & Dasen, J. S. (2026). Ancient somatosensory circuit architectures employ flexible molecular strategies. iScience, 29(11), Article 117919. https://doi.org/10.1016/j.isci.2026.117919

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117919

Keywords: neuroscience, evolutionary biology, somatosensory system, dorsal root ganglion, spatial transcriptomics, elasmobranchs, developmental neurobiology, iScience, Ancient, somatosensory, circuit, architectures

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