The open ocean is a vast, highly connected environment, and the organisms found there have been hypothesized to represent massive, well-mixed populations. Of these, the Portuguese man-o’-war ( Physalia ) is uniquely suited to dispersal, sailing the ocean surface with a muscular crest. We tested the hypothesis of a single, panmictic Physalia population by sequencing 133 genomes, and found five distinct lineages, with multiple lines of evidence showing strong reproductive isolation despite range overlap. We then scored thousands of citizen-science photos and identified four recognizable morphologies linked to these lineages. Within lineages, we detected regionally endemic subpopulations, connected by winds and currents, and identified individual long-distance dispersal events. We find that, even in these sailing species, genetic variation is highly partitioned geographically across the open ocean. Summary The open ocean is a vast and highly connected environment. The organisms that live there have a significant capacity for dispersal and few geographic boundaries to separate populations. Of these, the Portuguese man-o’-war or bluebottle (genus Physalia ) is uniquely suited to long-distance travel, using its gas-filled float and muscular crest to catch the wind and sail the sea surface. Physalia are distributed across the globe, and like many pelagic organisms, have been hypothesized to represent a massive, well-mixed population that extends across ocean basins. We tested this hypothesis by sequencing whole genomes of 133 samples collected from waters of over a dozen countries around the globe. Our results revealed five distinct lineages, with multiple lines of evidence indicating strong reproductive isolation, despite regions of range overlap. We combined these data with an independent dataset of thousands of images of Physalia uploaded to the citizen-science website inaturalist.org, which we scored for morphological characters including sail size, tentacle arrangement, and color. From these images, we identified four recognizable morphologies, described their geographical distribution, and linked them to four of the lineages identified with genomic data. We conclude there are at least four species, three of which correspond to species proposed by scientists in the 18th and 19th centuries: P. physalis , P utriculus , and P. megalista , along with one as yet unnamed species Physalia sp. from the Tasman Sea. Within each species, we observe significant population structure, with evidence of persistent subpopulations at a regional scale, as well as evidence for individual long-distance dispersal events. Our findings indicate that, instead of one well-mixed, cosmopolitan species, there are in fact multiple Physalia species with distinct but overlapping ranges, each made up of regionally endemic subpopulations that are connected by major ocean currents and wind patterns. ### Competing Interest Statement The authors have declared no competing interest.

Species of Placobdella have been the frequent subject of revisionary and alpha-taxonomy in the past 2 decades. Recent molecular analyses introduced uncertainty about the taxonomic status of several broadly distributed and morphologically variable Placobdella species, including Placobdella picta (Verrill 1872), compounded by incomplete original descriptions reliant upon characters that are no longer unique in comparison to modern congeners. We assessed specimens of P. picta to identify any distinct phylogenetic entities that align with our morphological observations of the type series and novel topotype specimens. Using mitochondrial COI and ND1 and nuclear 18S rDNA with Maximum Likelihood and Bayesian Inference, we evaluated species boundaries using species delimitation analyses (ABGD, mPTP, bPTP, and GMYC) and molecular phylogenetics. Our analyses revealed 2 species entities equivalent to 2 non-reciprocal monophyletic clades. Morphological examinations revealed the lectotype was determined to be Placobdella ornata (Verrill 1872), and paralectotypes are other leech species or were poorly preserved and unidentifiable. Due to the problems with the type series, P. picta is now considered a junior synonym of P. ornata. Based on our results, we describe 2 new species: Placobdella unimaculata n. sp. from Connecticut and Placobdella desseri n. sp. from Algonquin Provincial Park, Ontario, Canada.

Alboglossiphonia pallida (Verrill, 1872) comb. nov. is resurrected and redescribed based on morphological and molecular data from specimens of the type locality (New Haven County, Connecticut, USA) that demonstrate it is distinct from North American Alboglossiphonia heteroclita, European Alboglossiphonia heteroclita, and Alboglossiphonia papillosa. Alboglossiphonia pallida is characterized by having dark chroma-tophores on the dorsal surface arranged lateral to patrilaterally and medially as a thin line or interrupted thin line along with three pairs of eye spots (with the first pair closest together), six pairs of crop ceca, and a united gonopore. Additional sampling of specimens of the genus Alboglossiphonia is needed to understand its phylogeny especially as many species have not been collected since their description.

The blind fossil amphipod, Caecorchestia bousfieldi, Hegna and Lazo-Wasem, new genus and species, is described from the lower Miocene Campo La Granja amber mines in Chiapas, Mexico, based on more than 130 specimens in diverse states of preservation. It is the second amphipod species to be described from Chiapas amber. C. bousfieldi belongs to the Talitridae, a family of amphipods that have successfully colonized terrestrial habitats. Exactly how fully terrestrial Caecorchestia bousfieldi was is unclear, and its blindness likely indicates that it occupied a cryptic habitat. A review of the amphipod fossil record is given which demonstrates that the amphipods first appeared as fossils in the Eocene.

The phylogenetic structure of 23 populations of Crangonyx hobbsi, a stygobitic amphipod species endemic to the Floridan aquifer, is detailed. Molecular genetic analyses (based on three genes the nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA) point to the presence of at least two phylogenetic clades within the aquifer. These clades align into two major zoogeographic regions, the Northern Suwannee River Basin and the Coastal and Central Lowlands in the Florida peninsula. Three species delimitation models indicate that the Northern Suwannee River Basin Clade represents a species level differentiation from C. hobbsi sensu stricto. Morphological analyses support the molecular analyses, revealing the presence of several taxonomically significant differences between the two species, including presence/absence of calceoli on the second antennae of males and differences in telson shape in both sexes. Additionally, the molecular diversity of C. hobbsi sensu stricto was shown to be surprisingly variable, suggesting the potential presence of additional diversity within the taxon.

The aorid amphipod Grandidierella japonica Stephensen, 1938, originally described from northern Japan, is reported for the first time from the Gulf of Maine and Long Island Sound in the Northwest Atlantic Ocean. It was discovered among grab samples of eelgrass (Zostera marina Linnaeus, 1753) beds taken in Casco Bay, Maine in summer 2018 and has been found intertidally in Long Island Sound since 2013 along Connecticut shores. It occurs in habitats like its native range but also in rocky areas and tidepools in bedrock. The presence of adults of both sexes, ovigcrous females, and immature stages in all collections indicates the species is established. Among males, some morphological characteristics of gnathopod 1 vary with increasing total body length: the number of accessory carpal teeth increases, the carpus shape (length/width ratio) changes, and numbers of stridulating ridges increase. Maine and Connecticut specimens are distinguished from each other by the shape of male gnathopod 1 basis. Morphological variation, temporal differences in discovery, and separation by the biogeographic barrier Cape Cod suggests Maine and Connecticut populations originate from separate introductions.

Placodella michiganensis (Sawyer, 1972) was originally described from free-living individuals collected from Mill Creek, St. Joseph County, Michigan, USA. The acquisition of contemporary specimens from its type locality has facilitated redescription of P michiganensis. Placobdella michiganensis does not have a confusing taxonomic history like many other members of the genus Placobdella as it has only been collected two other times since its description. Placodella michiganensis is distinguished from its congeners by its five rows of whitish single-tipped papillae, genital and pre-anal patches, five pre-anal papillae, and absence of a dark dorsal-medial line. Placobdella michiganensis is a morphologically distinct species with a 16.0% to 22.0% difference in cytochrome c oxidase subunit I sequence data among congeners.

Abstract Placobdella parasitica (Say, 1824) is one of the most commonly encountered turtle leeches in North America. Molecular analysis of individuals of P. parasitica representing various populations throughout its range in North America using the cytochrome c oxidase subunit I gene, revealed the presence of nine distinct groups: (1) P. parasitica sensu stricto containing members, including the neotype specimen, occurring broadly throughout the central United States westward from the Mississippi River to the Rocky Mountains and throughout southern Ontario, Canada, and the upper midwestern United States as far east as New York State; (2) West Virginia; (3) Mississippi/Alabama; (4) Northeast, including New York, Massachusetts, and Vermont; (5) New England, including Rhode Island, Massachusetts, and Connecticut; (6) North Carolina/West Virginia; (7) South Carolina; (8) Tennessee; and (9) Florida. Both neighbor-joining and maximum likelihood analyses recovered an east-west split along the Appalachian Mountains with groups 1–3 clustering together and groups 4–9 clustering separately, with the exception of group 8 (Tennessee) that placed with the eastern groups. Group 1 includes specimens from a broad geographic distribution, yet with relatively low genetic variation, a pattern observed in other glossiphoniid species in North America. The groups with members east of the Appalachian Mountains are more tightly clustered by locality. This leech species is known to parasitize several turtle species, including Chrysemys picta, the painted turtle that originated in the central Gulf Coast region and dispersed northward representing a recolonization after Pleistocene glaciation. The neighbor-joining tree and pairwise distance data could suggest that P. parasitica has a similar phylogeographic pattern and dispersal history with its turtle hosts. In view of the morphological uniformity among the various groups, P. parasitica is provisionally considered to be a widely distributed, molecularly variable species.

Crangonyx hobbsi Shoemaker, 1941, a variable stygobitic amphipod endemic to the Floridan aquifer, is redescribed from topotype material and populations adjacent to the type locality. In addition to the morphological redescription, genetic sequence data for sections of the nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA are provided from populations located near the type locality.

There is a wealth of published information on the epibiont communities of sea turtles, yet many of these studies have exclusively sampled epibionts found only on the carapace. Considering that epibionts may be found on almost all body-surfaces and that it is highly plausible to expect different regions of the body to host distinct epibiont taxa, there is a need for quantitative information on the spatial variation of epibiont communities on turtles. To achieve this, we measured how total epibiont abundance and biomass on olive ridley turtles Lepidochelys olivacea varies among four body-areas of the hosts (n = 30). We showed that epibiont loads on olive ridleys are higher, both in terms of number and biomass, on the skin than they are on the carapace or plastron. This contrasts with previous findings for other hard-shelled sea turtles, where epibionts are usually more abundant on the carapace or plastron. Moreover, the arguably most ubiquitous epibiont taxon for other hard-shelled sea turtles, the barnacle Chelonibia spp., only occurred in relatively low numbers on olive ridleys and the barnacles Stomatolepas elegans and Platylepas hexastylos are far more abundant. We postulate that these differences between the epibiont communities of different sea turtle taxa could indicate that the carapaces of olive ridley turtles provide a more challenging substratum for epibionts than do the hard shells of other sea turtles. In addition, we conclude that it is important to conduct full body surveys when attempting to produce a holistic qualitative or quantitative characterization of the epibiont communities of sea turtles.

The diatom genus Proschkinia is a common element of biofilms covering diverse substrata in saline inland or shallow coastal environments. It can be distinguished from other naviculoid taxa by its lanceolate valves with a fistula located within the central area and numerous open girdle bands with a U-shaped cross-section and a single row of perforations on the internal side of the fold. Despite this distinct morphology, frustules of Proschkinia are typically weakly silicified and often overlooked when cleaned diatom material is analysed. The current paper describes six new species of Proschkinia: P. browderiana sp. nov., P. lacrimula sp. nov., P. maluszekiana sp. nov., P. sulcata sp. nov., P. torquata sp. nov. and P. vergostriata sp. nov., found in numerous samples of marine organisms, such as sea turtles (including sea turtle museum specimens), sea turtle-associated barnacles and seagrass from across the three oceans. Some of the newly described taxa were found on multiple individuals belonging to different sea turtle species, whereas others were in samples collected from different continents. Molecular phylogenetic analysis indicated that examined Proschkinia strains formed a monophyletic clade, sister to Fistulifera.

Placobdella pediculataHemingway, 1908 was originally described from individuals that were attached to Aplodinotus grunniens (freshwater drum) in Lake Pepin, Minnesota, USA. Apparently, no type material was deposited. The acquisition of contemporary specimens from its type host in the type locality facilitated redescription of P. pediculata. Placobdella pediculata is different from its congeners in that its caudal sucker is extended from the body by a pedicel (peduncle), bears digitate processes near the rim of the caudal sucker, a smooth body surface, and its anal placement (few annuli anteriad of the caudal sucker). Molecular comparison of cytochrome c oxidase subunit I sequence data from P. pediculata revealed differences of 13.8% to 17.4% among congeners. Placobdella pediculata is a distinct species.

Crangonyx manubrium, a new stygobitic species, is described from hypogean localities in Jackson County, Florida. This analysis is based on detailed morphometric and genetic comparisons of Jackson County Cave populations with epigean populations of Crangonyx floridanus, including paratypes from Highlands Hammock State Park, the type locality of C. floridanus. The original description of C. floridanus was partially based on a population from Gerard's Cave, in Jackson County, which is now assigned to C. manubrium n. sp. Crangonyx floridanus is morphologically redescribed based on paratype material from Highlands Hammock State Park, Highlands County, Florida and a population from Hogtown Creek in Gainesville, Alachua County, Florida. Molecular and morphological analyses show surprising variation across the range of C. floridanus, indicating it may represent a species complex.

We present an updated taxonomic account of a few of the large branchiopod species present in the collections of the Yale Peabody Museum of Natural History. Our study shows that the Artemia species in the collections is not Artemia salina given the presence of spines at the base of the penis and its frontal knob morphology. This population cannot be assigned to any particular species due to lack of comparative material of other Artemia species and therefore, now reduces the authentic distribution record of Artemia salina to just one in the subcontinent. The morphology of eggs taken from the Streptocephalus longimanus allotype is distinct from what has been described later by having lower number of polygons on the egg surface. The gross morphology of the Triops cancriformis from Punjab, Pakistan resembles those of the Kashmir population from India except for its larger size. Based on the morphological comparison, we show that Eocyzicus deterrana is indeed synonymous to E. hutchinsoni. This work further changes the total species tally of large branchiopods from 44 of the Indian subcontinent to 45.

Several populations of a new Craspedostauros species were observed on museum specimens of juvenile green turtle and Kemp’s ridleys collected from Long Island Beach, New York, USA. The new taxon, Craspedostauros alatus Majewska & Ashworth sp. nov., exhibits a distinctive set of morphological features typical of the genus, including cribrate areolae, a stauros narrower than the fascia, multiple doubly perforated girdle bands, and two fore and aft chloroplasts, but clearly differs from all known Craspedostauros species in possessing partially fused proximal helictoglossae forming an internal thickening with a shallow central cavity, distinctive external wing-like silica flaps near the apices, and a combination of valve dimensions and stria density not observed in other taxa. The same taxon was identified in the NCMA culture collection (strain CCMP120), isolated in 1967 from a sample collected from the equatorial upwelling zone in the Pacific Ocean. Nine samples from three sea turtle species were collected from the same location (Long Island Beach). Statistical analyses suggested that the epizoic diatom flora composition was not affected by the collection season but differed among sea turtle species. The most significant difference was observed between the samples with and without C. alatus. Samples with C. alatus were always dominated by Achnanthes elongata and Berkeleya cf. rutilans, while those lacking the new taxon were characterized by remarkably higher contributions of epizoic Poulinea species. This observation suggests that the microhabitat provided by each sea turtle differs among specimens, which may be related to the different stages of biofilm development on the host sea turtle. Additionally, the value of zoological museum collections for epizoic diatom surveys is briefly discussed.

Crangonyx grandimanus Bousfield, 1963, a relatively large stygobitic amphipod endemic to the Floridan aquifer, is redescribed from its holotype specimen and topotype material. In addition to the morphological redescription, genetic sequence data for sections of the nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA are provided from the examined topotypes.

Crangonyx sulphurium n. sp., a new species of stygobitic amphipod, is described from three springs in central Florida, U.S.A. The description of the new species brings the number of described stygobitic species of Crangonyx found in the Floridan aquifer to three. The specimens were collected in the spring basins of Wekiwa and Volusia springs and De Leon Springs Cave. Specimens from De Leon Springs Cave were found swimming in and around white microbial mats characteristic of sulfur oxidizing bacteria. Next generation sequencing of microbial mat samples, collected from the spring ten years after the collection of the new species, indicates a heterotrophic and autotrophic community dominated by five phylotypes. The ecology of these three caves may be unique when compared to other caves within the Floridan aquifer.

Crangonyx sulphuriumn. sp., a new species of stygobitic amphipod, is described from three springs in central Florida, U.S.A. The description of the new species brings the number of described stygobitic species of Crangonyx found in the Floridan aquifer to three. The specimens were collected in the spring basins of Wekiwa and Volusia springs and De Leon Springs Cave. Specimens from De Leon Springs Cave were found swimming in and around white microbial mats characteristic of sulfur oxidizing bacteria. Next generation sequencing of microbial mat samples, collected from the spring ten years after the collection of the new species, indicates a heterotrophic and autotrophic community dominated by five phylotypes. The ecology of these three caves may be unique when compared to other caves within the Floridan aquifer.

A new species of freshwater crab, Potamonautes danielsi sp. n., is described from the southern region of the KwaZulu-Natal Province, South Africa. Potamonautes danielsi most closely resembles P. sidneyi which is re-described here, but can be distinguished by a suite of key morphological characters including carapace shape and width, slim pereopods, inflated propodi of the chelipeds, and the shape and terminal segment length:subterminal segment length ratio of the 1st gonopod. In a previous study (Gouws et al. 2015), a 9.2–11.8 % divergence was found in the mitochondrial COI and 16S genes of the P. sidneyi clade, allowing for the delineation of a new species. Despite the clear molecular distinction between the two species, it is difficult to separate them based on individual morphological characters, as there is a great deal of overlap even among key features. The new species is found in slow-moving mountain streams and pools at high altitudes between Umhlanga and Mtamvuna, in KwaZulu-Natal.