Chondrichthyes Research Articles

Ontogenetic scaling of disc width with total length in west African batoids

AbstractMorphological scaling describes changes in the size or shape of one morphological character (e.g. mass, length, width, area etc.) as another increases in size. Understanding how morphological characters scale with body size can shed light on how natural selection influences morphology, and the nature of ecomorphological relationships through ontogeny. Batoids (Elasmobranchii: Batoidea) are a highly specialised lineage of cartilaginous fishes displaying extreme dorsoventral flattening. Despite this, little is known about morphological scaling in batoids compared to sharks. In this study we test the relationship between disc width and total length in five batoid species (Torpedo torpedo, Mobula tarapacana, Fontitrygon margarita, Raja parva, Rhinobatos irvinei) representing four orders that differ in both ecology and morphology, measured from artisanal fisheries in Western and Central Ghana. Whilst a lack of existing ecological data presents some limitations, our results are broadly consistent with ecomorphological theory previously applied to sharks. Moreover, we find that for some lineages (including some myliobatiform taxa) total length may represent a valid proxy for estimating overall body size. This finding has applications for body size and shape estimation in partially processed batoids obtained from fishing camps, and extinct taxa known only from incomplete or fragmented remains.

Fishes Associated with a Vulnerable Marine Ecosystem Network in the Central Mediterranean Sea

In order to collect information on ichthyofauna of a deep-sea vulnerable marine ecosystem (VME) network along the Apulian margin (central Mediterranean Sea), two low-impact sampling tools were used in three VMEs characterized by cold-water corals (CWC), namely Bari Canyon (BC), off Monopoli (Mn), and off Santa Maria di Leuca (SML). Using an experimental longline, 53 deployments were carried out between a 314 and 650 m depth for a total of 217 fishing hours, whereas when using the baited lander MEMO (Marine Environment MOnitoring system), 31 deployments were carried out between 427 and 792 m, for a total of 223 h of video recordings. A total of 37 taxa were recorded, comprising 13 Chondrichthyes and 24 Osteichthyes. The similarities in species observed among the VMEs confirm the presence of a network of CWC-VMEs along the Apulian margin, whereas some differences detected are due to the different abundance of some species, such as Galeus melastomus, Helicolenus dactylopterus, and Phycis blennoides. The presence of commercial species, vulnerable/endangered cartilaginous fishes, and large and sexually mature individuals of G. melastomus, H. dactylopterus, and Pagellus bogaraveo in all the VMEs confirms that the network of CWC-VMEs along the Apulian margin can act as a network of refuge areas and an essential fish habitat (EFH) for species threatened by fishing activities.

The Palaeozoic assembly of the holocephalan body plan far preceded post-Cretaceous radiations into the ocean depths.

Among cartilaginous fishes, Holocephali represents the species-depauperate, morphologically conservative sister to sharks, rays and skates and the last survivor of a once far greater Palaeozoic and Mesozoic diversity. Currently, holocephalan diversity is concentrated in deep-sea species, suggesting that this lineage might contain relictual diversity that now persists in the ocean depths. However, the relationships of living holocephalans to their extinct relatives and the timescale of their diversification remain unclear. Here, we reconstruct the evolutionary history of holocephalans using comprehensive morphological and DNA sequence datasets. Our results suggest that crown holocephalans entered and diversified in deep (below 1000 m) ocean waters after the Cretaceous-Palaeogene mass extinction, contrasting with the hypothesis that this ecosystem has acted as a refugium of ancient cartilaginous fishes. These invasions were decoupled from the evolution of key features of the holocephalan body plan, including crushing dentition, a single frontal clasper, and holostylic jaw suspension, during the Palaeozoic Era. However, these invasions considerably postdated the appearance of extant holocephalan families 150 million years ago during a major period of biotic turnover in oceans termed the Mesozoic Marine Revolution. These results clarify the origins of living holocephalans as the recent diversification of a single surviving clade among numerous Palaeozoic lineages.

Unraveling the Complexity of the N e/N c Ratio for Conservation of Large and Widespread Pelagic Fish Species: Current Status and Challenges.

Estimating and understanding the ratio between effective population size (N e) and census population size (N c) are pivotal in the conservation of large marine pelagic fish species, including bony fish such as tunas and cartilaginous fish such as sharks, given the challenges associated with obtaining accurate estimates of their abundance. The difficulties inherent in capturing and monitoring these species in vast and dynamic marine environments often make direct estimation of their population size challenging. By focusing on N e, it is conceivable in certain cases to approximate census size once the N e/N c ratio is known, although this ratio can vary and does not always increase linearly, as it is influenced by various ecological and evolutionary factors. Thus, this ratio presents challenges and complexities in the context of pelagic species conservation. To delve deeper into these challenges, firstly, we recall the diverse types of effective population sizes, including contemporary and historical sizes, and their implications in conservation biology. Secondly, we outline current knowledge about the influence of life history traits on the N e/N c ratio in the light of examples drawn from large and abundant pelagic fish species. Despite efforts to document an increasing number of marine species using recent technologies and statistical methods, establishing general rules to predict N e/N c remains elusive, necessitating further research and investment. Finally, we recall statistical challenges in relating N e and N c emphasizing the necessity of aligning temporal and spatial scales. This last part discusses the roles of generation and reproductive cycle effective population sizes to predict genetic erosion and guiding management strategies. Collectively, these sections underscore the multifaceted nature of effective population size estimation, crucial for preserving genetic diversity and ensuring the long-term viability of populations. By navigating statistical and theoretical complexities, and addressing methodological challenges, scientists should be able to advance our understanding of the N e/N c ratio.

The evolution of tenascins

BackgroundThe evolution of extracellular matrix is tightly linked to the evolution of organogenesis in metazoans. Tenascins are extracellular matrix glycoproteins of chordates that participate in integrin-signaling and morphogenetic events. Single tenascins are encoded by invertebrate chordates, and multiple tenascin paralogs are found in vertebrates (designated tenascin-C, tenascin-R, tenascin-W and tenascin-X) yet, overall, the evolution of this family has remained unclear.ResultsThis study examines the genomes of hemichordates, cephalochordates, tunicates, agnathans, cartilaginous fishes, lobe-finned fishes, ray-finned fishes and representative tetrapods to identify predicted tenascin proteins. We comprehensively assess their evolutionary relationships by sequence conservation, molecular phylogeny and examination of conservation of synteny of the encoding genes. The resulting new evolutionary model posits the origin of tenascin in an ancestral chordate, with tenascin-C-like and tenascin-R-like paralogs emerging after a whole genome duplication event in an ancestral vertebrate. Tenascin-X appeared following a second round of whole genome duplication in an ancestral gnathostome, most likely from duplication of the gene encoding the tenascin-R homolog. The fourth gene, encoding tenascin-W (also known as tenascin-N), apparently arose from a local duplication of tenascin-R.ConclusionsThe diversity of tenascin paralogs observed in agnathans and gnathostomes has evolved through selective retention of novel genes that arose from a combination of whole genome and local duplication events. The evolutionary appearance of specific tenascin paralogs coincides with the appearance of vertebrate-specific cell and tissue types where the paralogs are abundantly expressed, such as the endocranium and facial skeleton (tenascin-C), an expanded central nervous system (tenascin-R), and bone (tenascin-W).

Invariant VD and DJ Motifs Define a Novel Class of Human Antibodies and TCRs Prototyped by antigen receptors of Dual-Expresser Lymphocytes

ABSTRACT Introduction Dual-expressing lymphocytes (DEs) are unique immune cells that express both B cell receptors (BCRs, surface antibody) and T cell receptors (TCRs). In type 1 diabetes, DE antibodies are predominated by one antibody (x-mAb), an IgM monoclonal antibody with a germline-encoded CDR3 that recognizes self-reactive TCRs. We explored if x-mAb and its interacting TCRs have distinct structural features. Methods Using bioinformatics, we compared x-mAb and its most common interacting TCRαβ to billions of antigen receptor sequences to determine if they were unique or randomly generated. Results X-mAb represents a unique class of human antibodies with a conserved CDR3 sequence (CARx1-4DTAMVYYFYDW), consisting of a fixed DJH motif (DTAMVYYFDYW) paired with various VH genes. A public TCRβ clonotype (CASSPGTEAFF) associated with x-mAb on DEs features two invariant segments, VβD (CASSPGT) and DJβ (PGTEAFF), key to two large families of public TCRβ clonotypes—CASSPGT-Jβx and CASSPGT-Jβx—formed by recombining the VβD motif with Jβ genes and the DJβ motif with Vβ genes. B cells also use CASSPGT as a VHD motif for public IGH clonotypes (CASSPGT—Jβx). Discussion DEs, unlike conventional T and B cells, use invariant motifs to create public antibodies and TCRs, a trait previously seen only in cartilaginous fish.

Genomic analysis and behavioral ecology records of the vulnerable Kong skate (Okamejei kenojei).

Wild populations of cartilaginous fish (sharks, skates, rays, and chimaeras) are encountering challenges. Here, we are unveiling genomic data and behavioral ecological records of Okamejei kenojei, a species listed in the IUCN Red List of Threatened Species, aiming to offer insights into the conservation and environmental adaptability of cartilaginous fish.

Functional Divergence in the Affinity and Stability of Non-Canonical Cysteines and Non-Canonical Disulfide Bonds: Insights from a VHH and VNAR Study.

Single-domain antibodies, including variable domains of the heavy chains of heavy chain-only antibodies (VHHs) from camelids and variable domains of immunoglobulin new antigen receptors (VNARs) from cartilaginous fish, show the therapeutic potential of targeting antigens in a cytosol reducing environment. A large proportion of single-domain antibodies contain non-canonical cysteines and corresponding non-canonical disulfide bonds situated on the protein surface, rendering them vulnerable to environmental factors. Research on non-canonical disulfide bonds has been limited, with a focus solely on VHHs and utilizing only cysteine mutations rather than the reducing agent treatment. In this study, we examined an anti-lysozyme VNAR and an anti-BC2-tag VHH, including their non-canonical disulfide bond reduced counterparts and non-canonical cysteine mutants. Both the affinity and stability of the VNARs and VHHs decreased in the non-canonical cysteine mutants, whereas the reduced-state samples exhibited decreased thermal stability, with their affinity remaining almost unchanged regardless of the presence of reducing agents. Molecular dynamics simulations suggested that the decrease in affinity of the mutants resulted from increased flexibility of the CDRs, the disappearance of non-canonical cysteine-antigen interactions, and the perturbation of other antigen-interacting residues caused by mutations. These findings highlight the significance of non-canonical cysteines for the affinity of single-domain antibodies and demonstrate that the mutation of non-canonical cysteines is not equivalent to the disruption of non-canonical disulfide bonds with a reducing agent when assessing the function of non-canonical disulfide bonds.

Single-cell RNA sequencing illuminates the ontogeny, conservation and diversification of cartilaginous and bony fish lymphocytes

Elucidating cellular architecture and cell-type evolution across species is central to understanding immune system function and susceptibility to disease. Adaptive immunity is a shared trait of the common ancestor of cartilaginous and bony fishes. However, evolutionary features of lymphocytes in these two jawed vertebrates remain unclear. Here, we present a single-cell RNA sequencing atlas of immune cells from cartilaginous (white-spotted bamboo shark) and bony (zebrafish and Chinese tongue sole) fishes. Cross-species comparisons show that the same cell types across different species exhibit similar transcriptional profiles. In the bamboo shark, we identify a phagocytic B cell population expressing several pattern recognition receptors, as well as a T cell sub-cluster co-expressing both T and B cell markers. In contrast to a division by function in the bony fishes, we show close linkage and poor functional specialization among lymphocytes in the cartilaginous fish. Our cross-species single-cell comparison presents a resource for uncovering the origin and evolution of the gnathostome immune system.

The Janus (dual) model of immunoglobulin isotype evolution: Conservation and plasticity are the defining paradigms.

The study of antibodies in jawed vertebrates (gnathostomes) provides every immunologist with a bird's eye view of how human immunoglobulins (Igs) came into existence and subsequently evolved into their present forms. It is a fascinating Darwinian history of conservation on the one hand and flexibility on the other, exemplified by the Ig heavy chain (H) isotypes IgM and IgD/W, respectively. The cartilaginous fish (e.g., sharks) Igs provide a glimpse of "how everything got off the ground," while the amphibians (e.g., the model Xenopus) reveal how the adaptive immune system made an about face with the emergence of Ig isotype switching and IgG-like structure/function. The evolution of mucosal Igs is a captivating account of malleability, convergence, and conservation, and a call to arms for future study! In between there are spellbinding chronicles of antibody evolution in each class of vertebrates and rather incredible stories of how antibodies can adapt to occupy niches, for example, single-domain variable regions, cold-adapted Igs, convergent mechanisms to dampen antibody function, provision of mucosal defense, and many more. The purpose here is not to provide an encyclopedic examination of antibody evolution, but rather to hit the high points and entice readers to appreciate how things "came to be."

The marine cartilaginous fishes and sturgeons of the Sea of Marmara: an updated and annotated checklist

A revised checklist of sharks, batoids, and sturgeons in the Sea of Marmara, Turkey encompasses 41 species across 18 families. It provides a concise historical context and addresses issues related to problematic reports. Furthermore, the paper delves into the analysis of taxonomic changes in other literature reports, aiming to provide a framework for upcoming ichthyological surveys and ecological studies, while also presenting relevant data on the economic significance of select species.

Refining Sampling Efforts for Fish Diversity Assessment in Subtropical Urban Estuarine and Oceanic Waters Using Environmental DNA With Multiple Primers

ABSTRACTThe environmental DNA (eDNA) approach is an emerging tool for monitoring marine biodiversity. However, the sampling effort needs optimization according to the site characteristics and target taxonomic groups. In this study, we optimized the eDNA sampling effort in terms of sample volume and number of replicates to monitor the diversity of marine vertebrates (mainly fish) in Hong Kong's subtropical waters that show a gradient of estuarine to oceanic waters. To maximize detection, we used three pairs of metabarcoding primers (12S‐v5, MiFish‐U, and MiFish‐E). We compared vertebrate diversity in 78 water samples, ranging from 1 to 10 L, collected from oceanic and estuarine sites. Metabarcoding yielded a total of 140 vertebrate species, of which 18 were unique to the estuarine site, 66 unique to the oceanic site, and 56 shared between both sites. The detected species were predominantly ray‐finned fish (136 species), and the three primer pairs exhibited differential sensitivity toward different taxa, especially cartilaginous fish and cetaceans. Increasing sampling volume per replicate generally increased the total detected species, average species per replicate, and species coverage, and sampling 3 or 4 × 4 L represented the most efficient sampling effort for the estuarine and oceanic sites, respectively. The diversity analysis revealed that sampling >2 L per replicate reduced variability and improved diversity analysis. The results also showed that a larger sampling volume per replicate increased the probability of detecting endangered, indicator, invasive, and elusive species, with 4 L representing the most efficient volume. This study recommended sampling 4 L per replicate and 3 replicates for estuarine and 4 for oceanic sites, respectively for effectively monitoring marine fish in subtropical waters using the eDNA approach.

Revealing chemistry-structure-function relationships in shark vertebrae across length scales

Shark cartilage presents a complex material composed of collagen, proteoglycans, and bioapatite. In the present study, we explored the link between microstructure, chemical composition, and biomechanical function of shark vertebral cartilage using Polarized Light Microscopy (PLM), Atomic Force Microscopy (AFM), Confocal Raman Microspectroscopy, and Nanoindentation. Our investigation focused on vertebrae from Blacktip and Shortfin Mako sharks. As typical representatives of the orders Carcharhiniformes and Lamniformes, these species differ in preferred habitat, ecological role, and swimming style. We observed structural variations in mineral organization and collagen fiber arrangement using PLM and AFM. In both sharks, the highly calcified corpus calcarea shows a ridged morphology, while a chain-like network is present in the less mineralized intermedialia. Raman spectromicroscopy demonstrates a relative increase of glucosaminocycans (GAGs) with respect to collagen and a decrease in mineral-rich zones, underlining the role of GAGs in modulating bioapatite mineralization. Region-specific testing confirmed that intravertebral variations in mineral content and arrangement result in distinct nanomechanical properties. Local Young's moduli from mineralized regions exceeded bulk values by a factor of 10. Overall, this work provides profound insights into a flexible yet strong biocomposite, which is crucial for the extraordinary speed of cartilaginous fish in the worlds’ oceans. Statement of significanceShark cartilage is a morphologically complex material composed of collagen, sulfated proteoglycans, and calcium phosphate minerals. This study explores the link between microstructure, chemical composition, and biological mechanical function of shark vertebral cartilage at the micro- and nanometer scale in typical Carcharhiniform and Lamniform shark species, which represent different vertebral mineralization morphologies, swimming styles and speeds. By studying the intricacies of shark vertebrae, we hope to lay the foundation for biomimetic composite materials that harness lamellar reinforcement and tailored stiffness gradients, capable of dynamic and localized adjustments during movement.

1H, 13C and 15N resonance assignments of a shark variable new antigen receptor against hyaluronan synthase.

Single domain antibody (sdAb) is only composed of a variable domain of the heavy-chain-only antibody, which is devoid of light chain and naturally occurring in camelids and cartilaginous fishes. Variable New Antigen Receptor (VNAR), a type of single domain antibody present in cartilaginous fishes such as sharks, is the smallest functional antigen-binding fragment found in nature. The unique features, including flexible paratope, high solubility and outstanding stability make VNAR a promising prospect in antibody drug development and structural biology research. However, VNAR's research has lagged behind camelid-derived sdAb, especially in the field of structural research. Here we report the 1H,15N,13C resonance assignments of a VNAR derived from the immune library of Chiloscyllium plagiosum, termed B2-3, which recognizes the hyaluronan synthase. Analysis of the backbone chemical shifts demonstrates that the secondary structure of VNAR is predominately composed of β-sheets corresponding to around 40% of the B2-3 backbone. The Cβ chemical shift values of cysteine residues, combined with mass spectrometry data, clearly shows that B2-3 contains two pairs of disulfide bonds, which is import for protein stability. The assignments will be essential for determining the high resolution solution structure of B2-3 by NMR spectroscopy.

A pre-vertebrate endodermal origin of calcitonin-producing neuroendocrine cells.

Vertebrate calcitonin-producing cells (C-cells) are neuroendocrine cells that secrete the small peptide hormone calcitonin in response to elevated blood calcium levels. Whereas mouse C-cells reside within the thyroid gland and derive from pharyngeal endoderm, avian C-cells are located within ultimobranchial glands and have been reported to derive from the neural crest. We use a comparative cell lineage tracing approach in a range of vertebrate model systems to resolve the ancestral embryonic origin of vertebrate C-cells. We find, contrary to previous studies, that chick C-cells derive from pharyngeal endoderm, with neural crest-derived cells instead contributing to connective tissue intimately associated with C-cells in the ultimobranchial gland. This endodermal origin of C-cells is conserved in a ray-finned bony fish (zebrafish) and a cartilaginous fish (the little skate, Leucoraja erinacea). Furthermore, we discover putative C-cell homologs within the endodermally-derived pharyngeal epithelium of the ascidian Ciona intestinalis and the amphioxus Branchiostoma lanceolatum, two invertebrate chordates that lack neural crest cells. Our findings point to a conserved endodermal origin of C-cells across vertebrates and to a pre-vertebrate origin of this cell type along the chordate stem.

DNA metabarcoding unveils the hidden species composition in fish surimi: Implications for the management of unlabeled and mixed seafood products

Fish surimi products are traditional foods primarily made from fish meat and may contain a complex species composition. In Taiwan, the abundant fishery resources and diverse fish species lead to local catches being widely used as ingredients in fish surimi products. However, due to growing market demand and increasingly scarce resources, some surimi products contain sensitive species, such as sharks, posing potential threats to the ecological environment and biodiversity. In this study, by applying metabarcoding techniques, we analyzed 120 fish surimi product samples from different brands and types throughout the four seasons in Taiwan's market. The main fish species identified included milkfish (Chanos chanos), dolphinfish (Coryphaena hippurus), Pomfret (Taractes rubescens), swordfish (Istiophorus spp.) and cartilaginous. Moreover, at least 37 species of cartilaginous fish, including 26 endangered species, were found. Through comprehensive and accurate species identification of surimi product ingredients, we unveiled the usage of sensitive species in products on the market. This finding is important for the surimi industry's quality control and market supervision. Furthermore, it can promote the sustainable use of Taiwan's fishery resources and protect biodiversity.

Микроэлементный состав крови русского осетра

Establishing quantitative levels of chemical elements in the blood plays a leading role in studying the mi-croelement status of the body. The purpose of the work was to study the microelement composition of the blood and spleen of the Russian sturgeon Acipenser gueldenstaedtii (Brandt, 1833). The objects of the study were females and males of Russian sturgeon of different ages. The determination of metals was carried out using atomic absorption spectrometry. In each sample, iron, copper, manganese, zinc, nickel, cobalt, chromium, lead, and cadmium were determined. Specific features of the accumulation of chemical elements in the blood and spleen of Russian sturgeon have been revealed. The content of iron and zinc in the blood and spleen of fish is in the greatest quantities. At the same time, the concentration of zinc in the blood of fish, as well as the concentration of iron, depends on the systematic position of the fish, and falls within the limits of the concentrations of chemical elements according to A. P. Vinogradov: the content of iron and zinc in the blood of Teleostei is generally higher than in the blood of Elasmobranchii. Russian sturgeon belongs to the subclass Chondrostei and has characteristics of cartilaginous and bony fish, perhaps this can explain the amount of iron and zinc found in the blood. A positive correlation was revealed between iron and copper in the blood of female and male Russian sturgeon. At the same time, no gender differences were found in the content of chemical elements in the blood of female and male Russian sturgeon, with the exception of nickel, the concentration of which is higher in the blood of males. It has been shown that as fish age, the concentration of nickel, manganese, lead and copper in the blood increases.

An evolutionarily conserved AnkyrinG-dependent motif clusters axonal K2P K+ channels.

The evolution of ion channel clustering at nodes of Ranvier enabled the development of complex vertebrate nervous systems. At mammalian nodes, the K+ leak channels TRAAK and TREK-1 underlie membrane repolarization. Despite the molecular similarities between nodes and the axon initial segment (AIS), TRAAK and TREK-1 are reportedly node-specific, suggesting a unique clustering mechanism. However, we show that TRAAK and TREK-1 are enriched at both nodes and AIS through a common mechanism. We identified a motif near the C-terminus of TRAAK that is necessary and sufficient for its clustering. The motif first evolved among cartilaginous fish. Using AnkyrinG (AnkG) conditional knockout mice, CRISPR/Cas9-mediated disruption of AnkG, co-immunoprecipitation, and surface recruitment assays, we show that TRAAK forms a complex with AnkG and that AnkG is necessary for TRAAK's AIS and nodal clustering. In contrast, TREK-1's clustering requires TRAAK. Our results expand the repertoire of AIS and nodal ion channel clustering mechanisms and emphasize AnkG's central role in assembling excitable domains.

The olfactory system of sharks and rays in numbers.

Cartilaginous fishes have large and elaborate olfactory organs, but only a small repertoire of olfactory receptor genes. Here, we quantitatively analyze the olfactory system of 21 species of sharks and rays, assessing many features of the olfactory organ (OOR) (number of primary lamellae, branches of the secondary folds, sensory surface area, and density and number of sensory neurons) and the olfactory bulb (OB) (number of neurons and non-neuronal cells), and estimate the ratio between the number of neuronsin the two structures. We show that the number of lamellae in the OOR does not correlate with the sensory surface area, while the complexity of the lamellar shape does. The total number of olfactory receptor neurons ranges from 30.5 million to 4.3 billion and the total number of OB neurons from 1.5 to 90 million. The number of neuronsin the olfactory epithelium is 16 to 158 times higher (median ratio is 46) than the number of neuronsin the OB. These ratios considerably exceed those reported in mammals. High convergence from receptor neurons to neurons processing olfactory information, together with the remarkably small olfactory receptor repertoire, strongly suggests that the olfactory system of sharks and rays is well adapted to detect a limited number of odorants with high sensitivity.

Getting Nosy: Olfactory Rosette Morphology and Lamellar Microstructure of Two Chondrichthyan Species.

To smell, fish rely on passive water flow into their olfactory chambers and through their olfactory rosettes to detect chemical signals in their aquatic environment. The olfactory rosette is made up of secondarily folded tissues called olfactory lamellae. The olfactory morphology of cartilaginous fishes varies widely in both rosette gross morphology and lamellar microstructure. Previous research has shown differences in lamellar sensory morphology depending on the position along the rosette in hammerheads (family Sphyrnidae). Here, we investigate if this pattern continues in members of two other chondrichthyan families: Squalidae and Chimaeridae. Using contrast-enhanced microCT and scanning electron microscopy, we investigated patterns in lamellar morphology based on lamellar position along the olfactory rosette in Pacific spiny dogfish (Squalus suckleyi) and spotted ratfish (Hydrolagus colliei). We describe the gross olfactory rosette anatomy and lamellar microstructure of both species. We also put forth a new method, combining 3D morphological microCT data with 2D SEM microstructure data to better approximate lamellar sensory surface area. We found that in both species, lamellae in the center of the rosette were larger with more secondary folds. However, we found no significant differences in lamellar sensory surface area among lamellar positions. Previously, differences in lamellar sensory morphology have been tied to the internal fluid dynamics of the olfactory chamber. It is possible that the internal flow dynamics of these species are like other chondrichthyan models, where water flow patterns differ in the lateral vs the medial part of the organ, and the consistent distribution of sensory tissue does not correspond to this flow. Alternatively, the olfactory morphology of these species may result in uniform flow patterns throughout the olfactory chamber, correlating with the consistent distribution of sensory tissue throughout the organ. This study emphasizes that further investigations into chondrichthyan fluid dynamics is paramount to any future studies on the correlations between distribution of sensory tissues and water flow.