MicroCT illuminates the unique morphology of Shiinoidae (Copepoda: Cyclopoida), an unusual group of fish parasites.

The copepod family Shiinoidae Cressey, 1975 currently comprises nine species of teleost parasites with unusual morphology and a unique attachment mechanism. Female shiinoids possess greatly enlarged antennae that oppose a rostrum, an elongate outgrowth of cuticle that originates between the antennules. The antennae form a moveable clasp against the rostrum which they use to attach to their host. In this study, we use micro-computed tomography (microCT) to examine specimens of Shiinoa inauris Cressey, 1975 in situ attached to host tissue in order to characterize the functional morphology and specific muscles involved in this novel mode of attachment and to resolve uncertainty regarding the segmental composition of the regions of the body. We review the host and locality data for all reports of shiinoids, revise the generic diagnoses for both constituent genera Shiinoa Kabata, 1968 and Parashiinoa West, 1986, transfer Shiinoa rostrata Balaraman, Prabha & Pillai, 1984 to Parashiinoa as Parashiinoa rostrata (Balaraman, Prabha & Pillai, 1984) n. comb., and present keys to the females and males of both genera.

First record of Caligusdussumieri Rangnekar, 1957 (Copepoda, Siphonostomatoida, Caligidae) from Malaysia, with notes on caligids found from Malaysia and on host-specificity of caligids on lutjanid fishes.

Background: In total, 14 species of Caligus have been reported from Malaysia. Amongst them, four species are reported from lutjanid fishes. New information: Caligusdussumieri Rangnekar, 1957 is reported from Malabar snapper, Lutjanusmalabaricus, purchased from a local wet market in Terengganu, Peninsular Malaysia. This is the first record of this species in Malaysia and it is only the second species assigned to the bonito-group of the genus Caligus to be reported from Malaysia. A key to species of the bonito-group is presented herein. The list of caligids infecting lutjanid fishes and the geographical distributions plus the known hosts of members of the bonito-group of Caligus are discussed.

Major Revisions in Pancrustacean Phylogeny and Evidence of Sensitivity to Taxon Sampling.

The clade Pancrustacea, comprising crustaceans and hexapods, is the most diverse group of animals on earth, containing over 80% of animal species and half of animal biomass. It has been the subject of several recent phylogenomic analyses, yet relationships within Pancrustacea show a notable lack of stability. Here, the phylogeny is estimated with expanded taxon sampling, particularly of malacostracans. We show small changes in taxon sampling have large impacts on phylogenetic estimation. By analyzing identical orthologs between two slightly different taxon sets, we show that the differences in the resulting topologies are due primarily to the effects of taxon sampling on the phylogenetic reconstruction method. We compare trees resulting from our phylogenomic analyses with those from the literature to explore the large tree space of pancrustacean phylogenetic hypotheses and find that statistical topology tests reject the previously published trees in favor of the maximum likelihood trees produced here. Our results reject several clades including Caridoida, Eucarida, Multicrustacea, Vericrustacea, and Syncarida. Notably, we find Copepoda nested within Allotriocarida with high support and recover a novel relationship between decapods, euphausiids, and syncarids that we refer to as the Syneucarida. With denser taxon sampling, we find Stomatopoda sister to this latter clade, which we collectively name Stomatocarida, dividing Malacostraca into three clades: Leptostraca, Peracarida, and Stomatocarida. A new Bayesian divergence time estimation is conducted using 13 vetted fossils. We review our results in the context of other pancrustacean phylogenetic hypotheses and highlight 15 key taxa to sample in future studies.

Resolving taxonomic and nomenclatural problems in the genus Caligus O.F. Mller, 1785 (Copepoda: Caligidae).

Supplementary descriptions are provided for six poorly known species of Caligus, based on a study of type and other material carried out by the late Roger F. Cressey but never published. As part of that study new illustrations were produced by Hillary Boyle Cressey who has kindly made these previously unpublished drawings available to this paper. The present account also contains critical re-assessments of the validity of several other species of Caligus Mller, 1785. It is proposed to recognise that: C. glacialis Gadd, 1910 and C. raniceps Heegaard, 1943 are junior subjective synonyms of the type species C. curtus Mller, 1785 and we consider the published geographical locality given for C. raniceps by Heegaard (1943) to be erroneous; C. guerini Guiart, 1913 is a junior subjective synonym of C. elongatus von Nordmann, 1832; C. mordax Leigh-Sharpe, 1934 is a junior subjective synonym of C. coryphaenae Steenstrup & Ltken, 1861; C. lessonius Risso, 1826 is not a caligid and is probably a junior synonym of the pandarid Demoleus heptapus (Otto, 1821); C. clavatus Kirtisinghe, 1964 is a junior subjective synonym of C. sphyraeni Pillai, 1963; C. rotundigenitalis Y, 1933 is a junior subjective synonym of C. torpedinis Heller, 1865; C. hyalinae Heegaard, 1966 is a junior subjective synonym of C. chelifer Wilson, 1905; C. biseriodentatus, Shen, 1957 is a junior subjective synonym of C. pauliani Nues-Ruivo & Fourmanoir, 1956; and C. cornutus Heegaard, 1962 can be formally treated as a junior subjective synonym of C. lobodes (Wilson, 1911) because the name C. cornutus belongs with the male holotype; the female allotype collected by Heegaard (1962) remains unidentified. We also conclude that C. mebachii Marukawa, 1927 was based on a young male of Euryphorus brachypterus (Gerstaecker, 1853) and a male of Caligus coryphaenae Steenstrup & Ltken, 1861 which was mistakenly identified as the female. A lectotype is designated for C. mebachii and this species is treated as a synonym of Euryphorus brachypterus. It is noted that C. hamatus Heegaard, 1955 is conspecific with, and has priority over, C. undulatus Shen & Li, 1959. However, given that C. undulatus is a high profile and well known species, frequently recorded from across the Pacific, Indian and Atlantic oceans, a case has been submitted to the ICZN to grant precedence of C. undulatus over C. hamatus. We reject the transfer of Chalimus tenuis Leidy, 1889 to Caligus by Fowler (1912) on the basis of lack of evidence supporting the transfer, and return it to Chalimus, where it can be treated as a species inquirendum within a genus that is no longer considered as valid. We consider that C. alalongae Kryer, 1863 and C. gracilis Dana, 1852 are species inquirenda. Caligus truttae is a nomen nudum because Giard (1890) provided no morphological information or illustration associated with the new name.

Chromosome-level genome assembly, annotation, and phylogenomics of the gooseneck barnacle Pollicipes pollicipes.

BACKGROUND: The barnacles are a group of >2,000 species that have fascinated biologists, including Darwin, for centuries. Their lifestyles are extremely diverse, from free-swimming larvae to sessile adults, and even root-like endoparasites. Barnacles also cause hundreds of millions of dollars of losses annually due to biofouling. However, genomic resources for crustaceans, and barnacles in particular, are lacking. RESULTS: Using 62× Pacific Biosciences coverage, 189× Illumina whole-genome sequencing coverage, 203× HiC coverage, and 69× CHi-C coverage, we produced a chromosome-level genome assembly of the gooseneck barnacle Pollicipes pollicipes. The P. pollicipes genome is 770 Mb long and its assembly is one of the most contiguous and complete crustacean genomes available, with a scaffold N50 of 47 Mb and 90.5% of the BUSCO Arthropoda gene set. Using the genome annotation produced here along with transcriptomes of 13 other barnacle species, we completed phylogenomic analyses on a nearly 2 million amino acid alignment. Contrary to previous studies, our phylogenies suggest that the Pollicipedomorpha is monophyletic and sister to the Balanomorpha, which alters our understanding of barnacle larval evolution and suggests homoplasy in a number of naupliar characters. We also compared transcriptomes of P. pollicipes nauplius larvae and adults and found that nearly one-half of the genes in the genome are differentially expressed, highlighting the vastly different transcriptomes of larvae and adult gooseneck barnacles. Annotation of the genes with KEGG and GO terms reveals that these stages exhibit many differences including cuticle binding, chitin binding, microtubule motor activity, and membrane adhesion. CONCLUSION: This study provides high-quality genomic resources for a key group of crustaceans. This is especially valuable given the roles P. pollicipes plays in European fisheries, as a sentinel species for coastal ecosystems, and as a model for studying barnacle adhesion as well as its key position in the barnacle tree of life. A combination of genomic, phylogenetic, and transcriptomic analyses here provides valuable insights into the evolution and development of barnacles.

A synthesis tree of the Copepoda: integrating phylogenetic and taxonomic data reveals multiple origins of parasitism.

The Copepoda is a clade of pancrustaceans containing 14,485 species that are extremely varied in their morphology and lifestyle. Not only do copepods dominate marine plankton and sediment communities and make up a sizeable component of the freshwater plankton, but over 6,000 species are symbiotically associated with every major phylum of marine metazoans, mostly as parasites. Unfortunately, our understanding of copepod evolutionary relationships is relatively limited in part because of their extremely divergent morphology, sparse taxon sampling in molecular phylogenetic analyses, a reliance on only a handful of molecular markers, and little taxonomic overlap between phylogenetic studies. Here, a synthesis tree method is used to integrate published phylogenies into a more comprehensive tree of copepods by leveraging phylogenetic and taxonomic data. A literature review in this study finds fewer than 500 species of copepods have been sampled in molecular phylogenetic studies. Using the Open Tree of Life platform, those taxa that have been sampled in previous phylogenetic studies are grafted together and combined with the underlying copepod taxonomic hierarchy from the Open Tree of Life Taxonomy to make a synthesis phylogeny of all copepod species. Taxon sampling with respect to molecular phylogenetic analyses is reviewed for all orders of copepods and shows only 3% of copepod species have been sampled in phylogenetic studies. The resulting synthesis phylogeny reveals copepods have transitioned to a parasitic lifestyle on at least 14 occasions. We examine the underlying phylogenetic, taxonomic, and natural history data supporting these transitions to parasitism; review the species diversity of each parasitic clade; and identify key areas for further phylogenetic investigation.

Genomics of Black American colon cancer disparities: An RNA sequencing (RNA-Seq) study from an academic, tertiary referral center.

BACKGROUND: Black Americans have a higher incidence and mortality rate from colorectal cancer compared to their non-Hispanic White American counterparts. Even when controlling for sociodemographic differences between these 2 populations, Black Americans remain disproportionately affected by colorectal cancer. The purpose of our study was to determine if differences in gene expression between Black American and non-Hispanic White American colon cancer specimens could help explain differences in the incidence and mortality rate between these 2 populations. METHODS: Black Americans and non-Hispanic White Americans undergoing colon resection for stages I, II, or III colon cancer at a single institution were identified. Black American and non-Hispanic White American patients were matched for age, sex, and colon cancer stage to minimize the risk of confounding variables. Tissue samples were obtained at the time of colon resection and were analyzed using RNA sequencing to determine if there were differences in the expression of genes and biologic processes between the 2 groups. RESULTS: A total of 17 colon cancer specimens were analyzed; 8 (47.1%) patients were Black Americans. A total of 456 genes were identified as being expressed differently (ie, up or downregulated) in Black American compared to non-Hispanic White American colon cancer specimens. Moreover, 500 different genetic pathways were noted to be significantly over-represented with differentially expressed genes in our comparison of Black American and non-Hispanic White American colon cancer specimens, the majority of which plays a role in inflammation and immune cell function. CONCLUSION: Significant differences in gene expression and genetic pathways exist between Black Americans and non-Hispanic White Americans. Additional and multi-institutional and registry-based studies are needed to validate our findings and to further elucidate the contribution that these differences have to the overall incidence and mortality rate from colon cancer in these 2 patient populations.

Transcriptomic analysis of hookworm Ancylostoma ceylanicum life cycle stages reveals changes in G-protein coupled receptor diversity associated with the onset of parasitism.

Free-living nematodes respond to variable and unpredictable environmental stimuli whereas parasitic nematodes exist in a more stable host environment. A positive correlation between the presence of environmental stages in the nematode life cycle and an increasing number of G-protein coupled receptors (GPCRs) reflects this difference in free-living and parasitic lifestyles. As hookworm larvae move from the external environment into a host, they detect uncharacterized host components, initiating a signalling cascade that results in the resumption of development and eventual maturation. Previous studies suggest this process is mediated by GPCRs in amphidial neurons. Here we set out to uncover candidate GPCRs required by a hookworm to recognise its host. First, we identified all potential Ancylostoma ceylanicum GPCRs encoded in the genome. We then used life cycle stage-specific RNA-seq data to identify differentially expressed GPCRs between the free-living infective L3 (iL3) and subsequent parasitic stages to identify receptors involved in the transition to parasitism. We reasoned that GPCRs involved in host recognition and developmental activation would be expressed at higher levels in the environmental iL3 stage than in subsequent stages. Our results support the model that a decrease in GPCR diversity occurs as the larvae develop from the free-living iL3 stage to the parasitic L3 (pL3) in the host over 24-72 h. We find that overall GPCR expression and diversity is highest in the iL3 compared with subsequent parasitic stages. By 72 h, there was an approximately 50% decrease in GPCR richness associated with the moult from the pL3 to the L4. Taken together, our data uncover a negative correlation between GPCR diversity and parasitic development in hookworm. Finally, we demonstrate proof of principal that Caenorhabditis elegans can be used as a heterologous system to examine the expression pattern of candidate host signal chemoreceptors (CRs) from hookworm. We observe expression of candidate host signal CRs in C. elegans, demonstrating that C. elegans can be effectively used as a surrogate to identify expressed hookworm genes. We present several preliminary examples of this strategy and confirm a candidate CR as neuronally expressed.

Parasitic copepods of the family Lernanthropidae Kabata, 1979 (Copepoda: Siphonostomatoida) from Australian fishes, with descriptions of seven new species.

The total number of species of Lernanthropidae previously recorded from Australian waters is 15 (i.e., one species each of Aethon Krøyer, 1837, Lernanthropodes Bere, 1936, and Lernanthropsis Do, in Ho Do, 1985; 10 species of Lernanthropus de Blainville, 1822; and two species of Sagum Wilson, 1913), and all of these records are reviewed. We report here the presence of three species of Aethon. One species, A. garricki Hewitt, 1968, is reported from Australian waters for the first time and a new species, A. bicamera sp. nov., is described from the latrid, Latris lineatus (Forster, 1801) caught off South Australia. The genus Lernanthropodes is represented by a single species, L. trachinoti Pillai, 1962. We recognize Chauvanium Kazachenko, Kovaleva, Nguyen Ngo, 2017 as a subjective synonym of Lernanthropodes and transfer its type and only species C. chauvani Kazachenko, Kovaleva, Nguyen Ngo, 2017 which becomes Lernanthropodes chauvani (Kazachenko, Kovaleva, Nguyen Ngo, 2017) n. comb. Lernanthropsis mugilii (Shishido, 1898) is reported here from Mugil cephalus Linnaeus, 1758 sampled in Queensland and in New South Wales. The genus Lernanthropus is the most species rich and we report the presence of 20 nominal species on Australian marine fishes. This total includes six new species: L. alepicolus sp. nov. from Alepes apercna Grant, 1987, L. elegans sp. nov. from Atractoscion aequidens (Cuvier, 1830), L. gnathanodontus sp. nov. from Gnathanodon speciosus (Forsskål, 1775), L. paracruciatus sp. nov. from Protonibea diacanthus (Lacepède, 1802), L. pemphericola sp. nov. from Pempheris compressa (White, 1790), and L. selenotoca sp. nov. from Selenotoca multifasciata (Richardson, 1846). In addition, we report the presence of another four species in Australian waters for the first time: L. abitocephalus Tripathi, 1962, L. cadenati Delamare Deboutteville Nuñes-Ruivo, 1954, L. microlamini Hewitt, 1968, and L. pomadasysis Rangnekar Murti, 1961. After reexamination of the types of L. paenulatus Wilson, 1922 held in the USNM, we relegate this species to subjective synonymy with L. seriolii Shishido, 1898. Previous records of L. paenulatus from Australian Seriola species should be reassigned to L. seriolii. Lernanthropus ecclesi Kensley Grindley, 1973 is recognized as a junior subjective synonym of L. micropterygis Richiardi, 1884, and L. delamarei Marques, 1960, which is based on the male only, is tentatively considered to be a junior subjective synonym of L. micropterygis. Males are described for the first time for three species; L. breviculus Kabata, 1979, L. microlamini and L. mollis Kabata, 1979. A member of the genus Mitrapus Song Chen, 1976, M. oblongus (Pillai, 1964), is reported from Australia for the first time, on Herklotsichthys castelnaui (Ogilby, 1897) caught off Queensland and New South Wales. Finally, two species of Sagum were previously known from Australia and here we add three more. Two of the newly reported species were originally described as species of Lernanthropus but we formally transfer them here to Sagum as S. lativentris (Heller, 1865) n. comb. and S. sanguineus (Song, in Song Chen, 1976) n. comb. The males of S. lativentris and S. vespertilio Kabata, 1979 are described for the first time. A key to the females of the 31 species of lernanthropids found in Australian waters is provided.

Transcriptional dysregulation in developing trigeminal sensory neurons in the LgDel mouse model of DiGeorge 22q11.2 deletion syndrome.

LgDel mice, which model the heterozygous deletion of genes at human chromosome 22q11.2 associated with DiGeorge/22q11.2 deletion syndrome (22q11DS), have cranial nerve and craniofacial dysfunction as well as disrupted suckling, feeding and swallowing, similar to key 22q11DS phenotypes. Divergent trigeminal nerve (CN V) differentiation and altered trigeminal ganglion (CNgV) cellular composition prefigure these disruptions in LgDel embryos. We therefore asked whether a distinct transcriptional state in a specific population of early differentiating LgDel cranial sensory neurons, those in CNgV, a major source of innervation for appropriate oropharyngeal function, underlies this departure from typical development. LgDel versus wild-type (WT) CNgV transcriptomes differ significantly at E10.5 just after the ganglion has coalesced. Some changes parallel altered proportions of cranial placode versus cranial neural crest-derived CNgV cells. Others are consistent with a shift in anterior-posterior patterning associated with divergent LgDel cranial nerve differentiation. The most robust quantitative distinction, however, is statistically verifiable increased variability of expression levels for most of the over 17 000 genes expressed in common in LgDel versus WT CNgV. Thus, quantitative expression changes of functionally relevant genes and increased stochastic variation across the entire CNgV transcriptome at the onset of CN V differentiation prefigure subsequent disruption of cranial nerve differentiation and oropharyngeal function in LgDel mice.

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

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

Two new species of parasitic copepods from the genera Nothobomolochus and Unicolax (Cyclopoida: Bomolochidae) from Australian waters.

A 2016 collaborative survey of commercial fish parasites in Moreton Bay, Queensland, Australia led to the discovery of two new species of parasitic copepods belonging to the family Bomolochidae. Females of Nothobomolochus johndaveorum n. sp. were found attached to the gill filaments of Gerres subfasciatus and Gerres oyena. The new species most closely resembles N. leiognathicola and N. quadriceros. All 3 species possess 3 modified setae on the first antennulary segment that are approximately the same length and have a robust seta on the second antennulary segment adjacent to the 3 modified setae giving a superficial appearance of 4 modified setae on the antennule. The new species can be distinguished from these two species in its possession of longer inner setae on the first two endopodal segments of leg 4: the seta on endopodal segment 1 extends past the midline of the distal segment in the new species vs to the proximal margin of the distal segment in the other two species, and the seta on segment 2 extends well beyond the distal margin of the endopod in the new species vs just to the margin in the other two species. Females and males of Unicolax longicrus n. sp. were found in the nasal sinuses of Sillago maculata and Sillago ciliata. The new species differs from 6 of its 7 congeners in having a leg 4 exopod formula of II, I, 4 rather than II, I, 3 or II, I, 5. The new species resembles U. anonymous in this feature, but differs in its possession of a leg 5 that is relatively longer and less wide, and, whereas U. anonymous possesses inner and outer distal spines on leg 5 that are approximately the same length, those of the new species are relatively longer and asymmetrical. Unicolax longicrus n. sp. is unique among its congeners in its possession of a leg 4 with highly elongated endopodal segments 2 and 3, from which its name is derived. In addition to describing the two new species, host and locality reports for all species of Nothobomolochus and Unicolax are reviewed.

Transcriptomic differentiation underlying marine-to-freshwater transitions in the South American silversides Odontesthes argentinensis and O. bonariensis (Atheriniformes).

Salinity gradients are critical habitat determinants for freshwater organisms. Silverside fishes in the genus Odontesthes have recently and repeatedly transitioned from marine to freshwater habitats, overcoming a strong ecological barrier. Genomic and transcriptomic changes involved in this kind of transition are only known for a few model species. We present new data and analyses of gene expression and microbiome composition in the gills of two closely related silverside species, marine O. argentinensis and freshwater O. bonariensis and find more than three thousand transcripts differentially expressed, with osmoregulatory/ion transport genes and immune genes showing very different expression patterns across species. Interspecific differences also involve more than one thousand transcripts with nonsynonymous SNPs in the coding sequences, most of which were not differentially expressed. In addition to characterizing gill transcriptomes from wild-caught marine and freshwater fishes, we test experimentally the response to salinity increases by O. bonariensis collected from freshwater habitats. Patterns of expression in gill transcriptomes of O. bonariensis exposed to high salinity do not resemble O. argentinensis mRNA expression, suggesting lack of plasticity for adaptation to marine conditions in this species. The diversity of functions associated with both the differentially expressed set of transcripts and those with sequence divergence plus marked microbiome differences suggest that multiple abiotic and biotic factors in marine and freshwater habitats are driving transcriptomic differences between these species.

A new species of Pseudopandarus Kirtisinghe, 1950 (Copepoda: Siphonostomatoida: Pandaridae) from sharks of the genus Squalus L. in New Caledonian waters.

Both sexes of a new species of pandarid copepod are described from sharks of the genus Squalus L. (Squaliformes: Squalidae). Specimens of Pseudopandarus cairae n. sp. were collected from Squalus bucephalus Last, Séret & Pogonoski and S. melanurus Fourmanoir & Rivaton in New Caledonian waters, the first parasitic copepod to be described from either host species. This is the eighth nominal species of Pseudopandarus Kirtisinghe, 1950 and the first to be described from a shark of the order Squaliformes. Pseudopandarus cairae n. sp. is easily distinguished from P. australis Cressey & Simpfendorfer, 1988, P. longus (Gnanamuthu, 1951) Cressey, 1967, and P. pelagicus Rangnekar, 1977 in having the female genital complex concealed beneath an elongate dorsal genital shield with a trilobed posterior margin. It can be distinguished from P. gracilis Kirtisinghe, 1950 and P. scyllii Yamaguti & Yamasu, 1959 by the armature of the leg 4 endopod and by the proportions of the dorsal genital shield. The new species is unique among known species of Pseudopandarus in its possession of only 1 setal element on the distal endopod segment of leg 4. In addition to describing the new species, the host associations of all species of Pseudopandarus are reviewed and observations are made regarding sexual dimorphism and mode of attachment. A key to the species considered valid is provided.

The dismantling of Calliobothrium (Cestoda: Tetraphyllidea) with erection of Symcallio n. gen. and description of two new species.

This paper aims to resolve the dual composition of the triakid shark-hosted tetraphyllidean genus Calliobothrium--an issue that has been recognized for over a decade. As it stands, this genus includes a number of large species with laciniate proglottids, most of which bear 3 suckers at the anterior margin of each bothridium, but it also includes a number of species that lack proglottid laciniations and bear only a single sucker per bothridium, most of which are relatively small. Discovery of 2 new species, 1 of each form, parasitizing the whitespot smoothhound shark, Mustelus palumbes, off South Africa, prompted the first molecular analysis of the genus. Bayesian inference and maximum likelihood analyses of 28S rDNA (D1-D3) sequence data generated for specimens of both new species as well as of 2 known species of the laciniate form (Calliobothrium australis and Calliobothrium cf. verticillatum) and 3 known species of the non-laciniate form (Calliobothrium violae, Calliobothrium riseri, and Calliobothrium barbarae) confirmed the reciprocal monophyly of the 2 clades, supporting establishment of a new genus. Because the type of Calliobothrium, C. verticillatum, is of the laciniate form, Symcallio n. gen., with Symcallio peteri n. gen., n. sp., from M. palumbes described as its type, is established to house members of the non-laciniate clade. The 11 described species consistent with this form are transferred to the new genus. A new species of the laciniate clade, Calliobothrium euzeti n. sp., is described from M. palumbes, and a revised diagnosis of Calliobothrium is presented.