Sequence comparison of the mitochondrial genomes of Plesionika species (Caridea: Pandalidae), gene rearrangement and phylogenetic relationships of Caridea.

Background: Despite the Caridean shrimps' vast species richness and ecological diversity, controversies persist in their molecular classification. Within Caridea, the Pandalidae family exemplifies significant taxonomic diversity. As of June 25, 2023, GenBank hosts only nine complete mitochondrial genomes (mitogenomes) for this family. The Plesionika genus within Pandalidae is recognized as polyphyletic. To improve our understanding of the mitogenome evolution and phylogenetic relationships of Caridea, this study introduces three novel mitogenome sequences from the Plesionika genus: P.  ortmanni, P. izumiae and P. lophotes. Methods: The complete mitochondrial genomes of three Plesionika species were sequenced utilizing Illumina's next-generation sequencing (NGS) technology. After assembling and annotating the mitogenomes, we conducted structural analyses to examine circular maps, sequence structure characteristics, base composition, amino acid content, and synonymous codon usage frequency. Additionally, phylogenetic analysis was performed by integrating existing mitogenome sequences of true shrimp available in GenBank. Results: The complete mitogenomes of the three Plesionika species encompass 37 canonical genes, comprising 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs), and one control region (CR). The lengths of these mitogenomes are as follows: 15,908 bp for P. ortmanni, 16,074 bp for P. izumiae and 15,933 bp for P. lophotes. Our analyses extended to their genomic features and structural functions, detailing base composition, gene arrangement, and codon usage. Additionally, we performed selection pressure analysis on the PCGs of all Pandalidae species available in Genbank, indicating evolutionary purification selection acted on the PCGs across Pandalidae species. Compared with the ancestral Caridea, translocation of two tRNA genes, i.e., trnP or trnT, were found in the two newly sequenced Plesionika species-P. izumiae and P. lophotes. We constructed a phylogenetic tree of Caridea using the sequences of 13 PCGs in mitogenomes. The results revealed that family Pandalidae exhibited robust monophyly, while genus Plesionika appeared to be a polyphyletic group. Conclusions: Gene rearrangements within the Pandalidae family were observed for the first time. Furthermore, a significant correlation was discovered between phylogenetics of the Caridea clade and arrangement of mitochondrial genes. Our findings offer a detailed exploration of Plesionika mitogenomes, laying a crucial groundwork for subsequent investigations into genetic diversity, phylogenetic evolution, and selective breeding within this genus.

A new species of the mud shrimp genus Naushonia Kingsley, 1897 (Decapoda: Gebiidea: Laomediidae) from the Ryukyu Islands, southwestern Japan, inhabiting burrows of an axiidean shrimp.

A new species of the laomediid mud shrimp genus Naushonia Kingsley, 1897 is described and illustrated based on seven specimens collected from Okinawa Island, Ryukyu Islands, southwestern Japan. All specimens of Naushonia karashimai n. sp. were collected from burrows of a large axiidean shrimp, Neaxius acanthus (A. Milne-Edwards, 1879), which inhabits seagrass beds in inner reef lagoons. The new species is easily distinguished from all 16 known congeners by its tridentate rostrum and relatively narrow pereopod 1 palm with a proximally located pollex. Sequences of the mitochondrial 16S rRNA and COI genes were newly generated for five species and two species of Naushonia, including the new species, respectively. Preliminary phylogenetic analysis using sequences of the 16S rRNA gene was performed.

Second finding, first complete specimen and range extension of the rare alpheid shrimp Bermudacaris britayevi Anker, Poddoubtchenko amp; Marin, 2006 (Caridea: Alpheidae).

The very uncommon alpheid shrimp Bermudacaris britayevi Anker, Poddoubtchenko Marin, 2006, previously known only from the incomplete holotype from Nha Trang Bay, Vietnam, is recorded from Guam, Mariana Islands, extending its previously known distribution range into the oceanic islands of the western Pacific. The single specimen from Guam, an ovigerous female, was collected adjacent to a near-shore coral reef, on fine sand under a large piece of coral rubble, at a depth of about 10 m. This habitat is different from the collection data of the holotype, which was extracted from a burrow of unknown host on an intertidal sand-mud flat close to mangroves. Despite these ecological differences, the specimen from Guam corresponds to the holotype of B. britayevi in all diagnostic morphological characters and can be distinguished from the closely related B. australiensis Anker Komai, 2004 and B. harti Anker Iliffe, 2000. Since the holotype of B. britayevi was lacking one of the chelipeds, the complete specimen from Guam enables to complement the original description of the species. The stouter (= major) cheliped of the Guam specimen is illustrated to show a marked difference in the armature of the cheliped fingers, between the left and right cheliped. The colour pattern of B. britayevi, which was superficially described in the original description, is herein illustrated by photographs of the living individual. The relatively low number and large size of eggs in the Guam specimen of B. britayevi suggests an abbreviated larval development in this species.

DNA barcoding of deep-sea shrimp Sicyonia parajaponica Crosnier, 2003 (Crustacea: Decapoda: Sicyoniidae) from southwest coast of India.

The present work reports detailed taxonomic information on deep-sea shrimp Sicyonia parajaponica from southwest Indian waters. The samples were caught in bottom trawls conducted between the depths of 200 and 230 m from Sakthikulangara fishing harbour off Kollam, Kerala along the Arabian Sea during November 2019. DNA barcoding and a phylogenetic analysis was used to explore the relationship of the genus Sicyonia based on mitochondrial cytochrome c oxidase subunit 1 (COI: MN816389, MN816390) with the present specimen and sequences retrieved from NCBI GenBank. There is no difference in the intraspecies genetic distance (0%) while interspecies genetic distance (19.028.1%) revealed divergence between the species (COI) of the genus Sicyonia.

Cycloachelous levigatus sp. nov., a new swimming crab (Crustacea: Decapoda: Portunidae) from the South China Sea.

A new species of portunid crab from the genus Cycloachelous Ward, 1942 is described from Vietnamese waters. Cycloachelous levigatus sp. nov. is morphologically most similar to C. orbitosinus (Rathbun, 1911), which was originally described from the syntype series collected from Western Pacific area (Cargados Carajos Islands, Amirante Islands, Seychelles) and C. octodentatus (Gordon, 1938) described from one single male from Singapore. There are differences in the sternal segments, third maxilliped, chela, abdomen and male gonopode shapes. The specific status of C. levigatus sp. nov. is also clearly supported by molecular data. Aside from a comparison of this new species with other known congeners, new photographs of syntypes of C. orbitosinus and the holotype of C. octodentatus are also provided.

Comparative mitochondrial genomics of sponge-dwelling snapping shrimps in the genus Synalpheus: Exploring differences between eusocial and non-eusocial species and insights into phylogenetic relationships in caridean shrimps.

The genus Synalpheus is a cosmopolitan clade of marine shrimps found in most tropical regions. Species in this genus exhibit a range of social organizations, including pair-forming, communal breeding, and eusociality, the latter only known to have evolved within this genus in the marine realm. This study examines the complete mitochondrial genomes of seven species of Synalpheus and explores differences between eusocial and non-eusocial species considering that eusociality has been shown before to affect the strength of purifying selection in mitochondrial protein coding genes. The AT-rich mitochondrial genomes of Synalpheus range from 15,421 bp to 15,782 bp in length and comprise, invariably, 13 protein-coding genes (PCGs), two ribosomal RNA genes, and 22 transfer RNA genes. A 648 bp to 994 bp long intergenic space is assumed to be the D-loop. Mitochondrial gene synteny is identical among the studied shrimps. No major differences occur between eusocial and non-eusocial species in nucleotide composition and codon usage profiles of PCGs and in the secondary structure of tRNA genes. Maximum likelihood phylogenetic analysis of the complete concatenated PCG complement of 90 species supports the monophyly of the genus Synalpheus and its family Alpheidae. Moreover, the monophyletic status of the caridean families Alvinocaridae, Atyidae, Thoridae, Lysmatidae, Palaemonidae, and Pandalidae within caridean shrimps are fully or highly supported by the analysis. We therefore conclude that mitochondrial genomes contain sufficient phylogenetic information to resolve relationships at high taxonomic levels within the Caridea. Our analysis of mitochondrial genomes in the genus Synalpheus contributes to the understanding of the coevolution between genomic architecture and sociality in caridean shrimps and other marine organisms.

Rediscovery of the rare Mediterranean marine cave stenopodid shrimp emOdontozona/em emaddaia/em Pretus, 1990, 30 years after its original description (Crustacea: Decapoda: Stenopodidea).

Thirty years after its first finding and description, the marine cave stenopodid shrimp Odontozona addaia is here reported for the second time. The new localities, particular marine caves of southern France, are more than 300 km apart from the type locality in the Balearic Islands. First live in situ photographs are provided, and the morphological intraspecific variability is detailed by comparing the new specimens to the types. DNA sequences were also obtained for comparison with other Odontozona species. Based on both morphology and molecular analysis, closest relatives of O. addaia appear to be the western Atlantic Odontozona meloi and the eastern Mediterranean Odontozona minoica, although their detailed relationships remain unresolved.

A new species of palaemonid prawn emMacrobrachium/em emramae/em sp.nov. (Malacostraca:Decapoda:Palaemonidae) from Rupnarayana River, West Bengal, India with its molecular profiles.

A new species Macrobrachium ramae is described from Rupnarayana river, West Bengal, India along with its molecular characterization and Scanning electron microscopy. The species shares certain characters with M.gurudeve, M.jayasreei, M.kunjuramani and M.saengphani but differs remarkably from these species in the structure and shape of rostrum, telson, appendix masculina and in the size of the proximal segment of the antennular peduncle. Molecular characterization and phylogenetic analysis of M.ramae with mitochondrial COI and 16S rRNA genes reinforce the morphological conclusion and supports the view that it is a new species.

Description of Paraxiopsis/ kensleyi/ n. sp., a new axiid lobster from the Gulf of Mexico (Crustacea: Decapoda: Axiidea).

A new species of axiid was discovered during sampling offshore deep banks on the middle continental shelf off Louisiana. Paraxiopsis kensleyi n. sp. appears to inhabit interstices and cavities of coralline algal rubble, rhodoliths, coral rubble, and other eroded calcareous substrates. Weakly separated from Eutrichocheles Wood-Mason, 1876 on the basis of morphology, present assignments of western Atlantic species to Paraxiopsis de Man, 1905 are regarded as provisional. The new species is described morphologically, and the coloration of freshly captured specimens is documented and compared to related species where possible. Coloration readily distinguishes mature specimens of the new species from Paraxiopsis spinipleura Kensley, 1996, with which it was initially confused. The diagnosis includes GenBank accession numbers for COI sequences to allow future molecular phylogenetic comparisons. Compared to regional species that share a similar dentation or spination on the submedian carina, the pleon of the new species is distinctive in the truncate ventral margin on pleura 2-4, as opposed to being broadly rounded or directed ventrally in an acutely triangular tip. The new species is the eighteenth species of Paraxiopsis worldwide and the ninth from western Atlantic waters, seven of which are now known to range into the Gulf of Mexico. An updated key to western Atlantic members of the genus is provided.

New data on Beurlenia araripensis Martins-Neto & Mezzalira, 1991, a lacustrine shrimp from Crato Formation, and its morphological variations based on the shape and the number of rostral spines.

Fossil freshwater carideans are very rare worldwide. Here, we present new taxonomic remarks about Beurlenia araripensis from the Early Cretaceous laminated limestones of the Crato Formation, Araripe Basin, northeastern Brazil. We analyzed five fossil samples, testing the morphological variations such as, rostrum with 5 to 14 supra-rostral spines and 2 to 3 sub-rostral spines, which appears as serrate for Caridea. This variation demonstrates a morphologic plasticity also seen in extant species of the group, such as those of the genera Macrobrachium and Palaemon.

First worldwide molecular phylogeny of the morphologically and ecologically hyperdiversified snapping shrimp genus Alpheus (Malacostraca: Decapoda).

Hyperdiverse animal groups raise intriguing questions regarding the factors that generate and maintain their diversity. The snapping shrimp genus Alpheus (with >300 described species) is a spectacularly diversified group of decapod crustaceans that serves as an exemplary system for addressing evolutionary questions regarding morphological adaptations, symbiosis, cryptic diversity and molecular divergence. A lack of information regarding evolutionary relationships among species has limited investigations into the mechanisms that drive the diversification of Alpheus. Previous phylogenetic studies of Alpheus have been restricted in scope, while molecular datasets used for phylogenetic reconstructions have been based solely on mitochondrial and a handful of nuclear markers. Here we use an anchored hybrid enrichment (AHE) approach to resolve phylogenetic relationships among species of Alpheus. The AHE method generated sequence data for 240 loci (>72,000 bp) for 65 terminal species that span the geographic, ecological and taxonomic diversity of Alpheus. Our resulting, well-supported phylogeny demonstrates a lack of monophyly for five out of seven morphologically defined species groups that have traditionally been used as a framework in Alpheus taxonomy. Our results also suggest that symbiotic associations with a variety of other animals have evolved independently in at least seven lineages in this genus. Our AHE phylogeny represents the most comprehensive phylogenetic treatment of Alpheus to date and will provide a useful evolutionary framework to further investigate questions, such as various modifications of the snapping claw and the role of habitat specialization and symbiosis in promoting speciation. Running head: PHYLOGENY OF THE SNAPPING SHRIMP GENUS ALPHEUS.

Multiple transcriptome mining coupled with tissue specific molecular cloning and mass spectrometry provide insights into agatoxin-like peptide conservation in decapod crustaceans.

Over the past decade, in silico genome and transcriptome mining has led to the identification of many new crustacean peptide families, including the agatoxin-like peptides (ALPs), a group named for their structural similarity to agatoxin, a spider venom component. Here, analysis of publicly accessible transcriptomes was used to expand our understanding of crustacean ALPs. Specifically, transcriptome mining was used to investigate the phylogenetic/structural conservation, tissue localization, and putative functions of ALPs in decapod species. Transcripts encoding putative ALP precursors were identified from one or more members of the Penaeoidea (penaeid shrimp), Sergestoidea (sergestid shrimps), Caridea (caridean shrimp), Astacidea (clawed lobsters and freshwater crayfish), Achelata (spiny/slipper lobsters), and Brachyura (true crabs), suggesting a broad, and perhaps ubiquitous, conservation of ALPs in decapods. Comparison of the predicted mature structures of decapod ALPs revealed high levels of amino acid conservation, including eight identically conserved cysteine residues that presumably allow for the formation of four identically positioned disulfide bridges. All decapod ALPs are predicted to have amidated carboxyl-terminals. Two isoforms of ALP appear to be present in most decapod species, one 44 amino acids long and the other 42 amino acids in length, both likely generated by alternative splicing of a single gene. In carideans, a gene or terminal exon duplication appears to have occurred, with alternative splicing producing four ALPs, two 44 and two 42 amino acid isoforms. The identification of ALP precursor-encoding transcripts in nervous system-specific transcriptomes (e.g., Homarus americanus brain, eyestalk ganglia, and cardiac ganglion assemblies, finding confirmed using RT-PCR) suggests that members of this peptide family may serve as locally-released and/or hormonally-delivered neuromodulators in decapods. Their detection in testis- and hepatopancreas-specific transcriptomes suggests that members of the ALP family may also play roles in male reproduction and innate immunity/detoxification.

Distribution patterns, carbon sources and niche partitioning in cave shrimps (Atyidae: Typhlatya).

Cave shrimps of the Typhlatya genus are common and widespread in fresh, brackish and marine groundwater throughout the Yucatan Peninsula (Mexico). These species are ideal models to test niche partitioning within sympatric species in oligotrophic systems. Nevertheless, their food sources remain unidentified, and despite their frequency and functional importance, distribution and abundance patterns of these species within caves have not been fully recognized. Here, we describe the abundance of three Typhlatya species in different temporal and spatial scales, investigate changes in water conditions, and potential sources of carbon as an indication of food origin. Species composition and abundance varied markedly in space and time revealing patterns that differed from one system to another and in relation to environmental parameters. Isotope analysis showed that each species reflects a particular δ13C and Δ14C fingerprint, suggesting they feed in different proportions from the available carbon sources. Overall, our findings suggest a niche partitioning of habitat and feeding sources amongst the three Typhlatya species investigated, where environmental characteristics and physiological differences could play an important role governing their distribution patterns.

Crustacean neuroparsins-a mini-review.

Crustacean neuroparsins are poly-cysteine rich neuropeptides that share some similarities with the ovary ecdysteroidogenesis hormone (OEH) of mosquitoes, the N-terminal end of the growth factor binding protein region of the vertebrate and mollusk insulin-like growth factor binding protein and single insulin binding domain protein. Neuroparsins can promote reproduction and neurite outgrowth in various insects. Though many studies have been made in insects, the amount of work reported in crustaceans is still limited. This review emphasizes the neuroparsins found in decapod crustaceans with references to the neuroparsin first discovered in insects. To be more complete in identifying all the neuroparsin members and to understand the structure/function relationship within a single species, we have collected all neuroparsins from the GenBank and our transcriptome datasets. Then, we employed a comparative approach to study the sequence homology, tissue expression patterns, making predictions of their function and the evolutionary relationship particularly in decapod crustaceans. Results from alignment and phylogenetic studies indicated that crustacean neuroparsins consist of unique feature that can be used as criteria for their classification. These features include the presence of 12 cysteine residues in the mature peptide, the strict spacing between these cysteine residues and the size of the mature peptide. Because of the limited data on the expression information, the functions of most neuroparsin are unknown. The review will focus on the site of synthesis, expression, functions, the sequence homology and the evolutionary relationship of this group of neurohormones.

Characterization and comparison of the mitochondrial genomes from two Alpheidae species and insights into the phylogeny of Caridea.

The mitochondrial genome (mitogenome) has been widely used in phylogenetics and molecular evolution as a parameter, due to its simple genetic structure, high evolutionary rate, and compositional heterogeneity properties. Alpheidae is a large and highly diverse family of the Caridea infraorder, currently containing about 600 species dispersed all over the world. However, only a few shrimps in Alpheidae have their complete mitogenome annotated in GenBank. In our study, the entire mitogenomes of two shrimps from Alpheidae were determined, Alpheus randalli and Alpheus bellulus. The mitogenomes of both shrimps share the complete set of 37 mitochondrial genes found in other Alpheidae species. In A. randalli the AT-skew is slightly positive and GC-skew is negative, whereas in A. bellulus the AT-skew is negative and GC-skew is slightly positive. Furthermore, the secondary structures of trnS1 in the two shrimps are partially missing, and another three tRNAs formed the typical cloverleaf shaped secondary structures. Also, the trnS1 of A. randalli has an unusual anticodon stem with some unpaired nucleotides. Comparative genomic analysis suggests that the mitochondrial gene order of Alpheus genus exhibits a different gene rearrangement compared with that of Caridea. Most species in Alpheus share the same gene order, except for A. lobidens, which has an additional pseudogenomic trnQ (trnQ*). Compared with the mitochondrial gene order of Caridea the Alpheus trnE underwent both translocation and inversion, which were caused by a recombination event. Bayesian inferences (BI) and Maximum Likelihood (ML) phylogenetic analyses of 105 species amino acid datasets resulted in a well-supported topology, whereas four families in Caridea are monophyletic and can be divided into two major clades. Moreover, we demonstrated the phylogenetic relationships of six infraorders in Decapoda (Dendrobranchiata, (Caridea, (Stenopodidea, (Achelata, (Polychelida, Astacidea))))). This study used the large taxon sampling available to date for phylomitogenomic analysis. The results provide a theoretical basis for further research on the evolution of the Decapoda order, specifically Caridea infraorder.

Geographical and temporal origins of Neocaridina species (Decapoda: Caridea: Atyidae) in Taiwan.

BACKGROUND: The freshwater species on Taiwan Island have been documented to have originated from mainland China and the Japanese islands from multiple events and by multiple colonization routes. Moreover, the sequences from the mitochondrial DNA cytochrome c oxidase subunit I (COI) have been used for DNA barcoding to identify the species. This study used the COI sequences to identify Neocaridina species in Taiwan and to examine their geographical and temporal origins. RESULTS: In total, 479 specimens were collected from 35 localities, which covered almost all rivers in Taiwan. In addition, some sequences were downloaded from GenBank. The maximum likelihood (ML) tree displayed that all sequences were sorted into 13 taxa (clades), and all sequences in Taiwan were sorted into four clades. The Bayesian skyline plots revealed that these four Neocaridina species have declined recently in Taiwan. CONCLUSIONS: All results support that (1) there are four Neocaridina species in Taiwan, which are N. davidi, N. saccam, N. ketagalan and an undescribed Neocaridina species (N. sp.); (2) these four species colonized Taiwan Island in four colonization events; (3) N. sp. colonized Taiwan first; (4) after the island reached its shape, N. ketagalan and N. saccam colonized Taiwan from the Japanese islands and mainland China, respectively; (5) N. davidi colonized northern Taiwan last; and (6) the cyclic glacial and landform changes in East Asia shaped the colonization events and population structures of the Neocaridina species.

Comparative mitogenomics of the Decapoda reveals evolutionary heterogeneity in architecture and composition.

The emergence of cost-effective and rapid sequencing approaches has resulted in an exponential rise in the number of mitogenomes on public databases in recent years, providing greater opportunity for undertaking large-scale comparative genomic and systematic research. Nonetheless, current datasets predominately come from small and disconnected studies on a limited number of related species, introducing sampling biases and impeding research of broad taxonomic relevance. This study contributes 21 crustacean mitogenomes from several under-represented decapod infraorders including Polychelida and Stenopodidea, which are used in combination with 225 mitogenomes available on NCBI to investigate decapod mitogenome diversity and phylogeny. An overview of mitochondrial gene orders (MGOs) reveals a high level of genomic variability within the Decapoda, with a large number of MGOs deviating from the ancestral arthropod ground pattern and unevenly distributed among infraorders. Despite the substantial morphological and ecological variation among decapods, there was limited evidence for correlations between gene rearrangement events and species ecology or lineage specific nucleotide substitution rates. Within a phylogenetic context, predicted scenarios of rearrangements show some MGOs to be informative synapomorphies for some taxonomic groups providing strong independent support for phylogenetic relationships. Additional comparisons for a range of mitogenomic features including nucleotide composition, strand asymmetry, unassigned regions and codon usage indicate several clade-specific trends that are of evolutionary and ecological interest.

Simultaneous authentication of species identity and geographical origin of shrimps: Untargeted metabolomics to recurrent biomarker ions.

Mandatory disclosure of the species identity, production method, and geographical origin are embedded in the regulations and traceability systems, governing international seafood trade. A high-resolution mass spectrometry-based metabolomics approach could simultaneously authenticate the species identity and geographical origin of commercially important shrimps. The highly innovative approach spared the need for multiple testing methods which are in routine use currently. A robust chemometric model, developed using the metabolite fingerprint dataset, could accurately predict the species identity of the shrimp samples. Subsequently, species-specific biomarkers were discovered and a tandem mass spectrometry method for authentication of the species was developed. Two other chemometric models from the metabolomics experiment accurately predicted the geographical origin of king prawns and tiger prawns. The study has shown for the first time that food-metabolomics along with chemometrics can simultaneously check for multiple seafood fraud issues in the global seafood supply-chain.

Cloning and characterisation of Na+/K+-ATPase and carbonic anhydrase from oriental river prawn Macrobrachium nipponense.

Na+/K+-ATPase (NKA) and carbonic anhydrase (CA) are ion transporters that play important roles in osmotic pressure balance in crustaceans. Oriental river prawn (Macrobrachium nipponense) is one of the most economically important shrimps in China. This species can live in freshwater and low-salt water, but the molecular mechanism of salinity regulation is unclear. In this study, full-length cDNAs of M. nipponense α-NKA and CA were obtained by rapid amplification of cDNA ends (RACE)-PCR (GenBank accession numbers MH378774 and MH827971, respectively), and characterised. Full-length cDNAs of Mnα-NKA (3778bp) and MnCA (1407bp) contain open reading frames of 3030bp and 930bp, respectively, encoding polypeptides of 1009 and 930 amino acids. Bioinformatic analysis showed that Mnα-NKA and MnCA harbour the representative features of NKAs and CAs, and share high homology with orthologs in other crustaceans. Quantitative real-time PCR revealed that Mnα-NKA and MnCA were expressed in various tissues, with highest expression in posterior gills and hepatopancreas. Both Mnα-NKA and MnCA were up-regulated in response to salinity acclimation, but expression patterns differed. Our results provide a theoretical basis for the mechanism regulating salinity acclimation in M. nipponense.

Systematic analysis of the caridean shrimp superfamily Pandaloidea (Crustacea: Decapoda) based on molecular and morphological evidence.

One of the systematically controversial superfamilies in Caridea is the predominately deep-sea or cold water Pandaloidea, largely because this species-rich group of nearly 200 species in 25 genera exhibits a very high diversity of body forms and ecology. Although the relationships amongst the taxa within Pandaloidea have been repeatedly discussed based on morphology, no comprehensive molecular phylogeny exists. In this study, we present the first molecular phylogeny of the group, based on a combined dataset of two mitochondrial (12S and 16S rRNA) and six nuclear (ATP synthase ß-subunit, enolase, glyceraldehyde-3-phosphate dehydrogenase, histone 3, phosphoenolpyruvate carboxykinase and sodium-potassium ATPase α-subunit) markers, based on 62 species (about 1/3 of known biodiversity) in 22 genera (88% of genera) of two pandaloid families (Pandalidae, Thalassocarididae) and outgroups from seven other caridean families. With generally high support, the relationships within the clade are fully resolved. Pandalidae is shown to be paraphyletic with Thalassocarididae deeply nested within as a monophyletic group, and the latter is herein considered to be a synonym of Pandalidae. Five major clades are recovered, with the shallow water genera Anachlorocurtis, Chlorocurtis, Chlorotocella and Miropandalus forming a sister clade to the remaining genera. At the genus level, the phylogeny indicates Plesionika, Heterocarpus and Pandalus to be not monophyletic. The validity of Pandalopsis, Stylopandalus and Calipandalus is challenged and these genera are considered herein to be junior synonyms of Pandalus (Pandalopsis) and Plesionika (Stylopandalus and Calipandalus). Although not fully resolved, some evidence potentially considers Nothocaris to be a valid genus. Ancestral State Reconstruction successfully recovered 15 synapomorphies for the major clades, with 11 of them reported to be of systematic significance for the first time.