During a survey of the Wando-gun rockpool area in Korea, two species belonging to the family Cyatholaimidae were discovered within a sponge, Hymeniacidon sinapium, and are hereby reported. Despite the monophyletic nature of the family Cyatholaimidae, it has been a topic of discussion among nematologists due to its lack of synapomorphic characteristics and overlapping generic diagnoses. Many genus-defining features consist of a combination of non-unique characters, which may not hold significant taxonomic importance. Consequently, most genera within the family are non-monophyletic according to phylogenetic findings. The absence of molecular data complicates the identification of taxonomically important characteristics that may have been previously overlooked. While the pore complex and the lateral pore-like structure have been suggested as potentially important traits, these insights are lacking in most recorded species, along with molecular data to confirm their significance in topology. Given the considerable amount of work required from the ground up, this study provides both morphological information (including taxonomic description, morphometric measurements, tabular key comparing key features to all valid congeners, illustration, and microscope photographs) and molecular data (partial sequences of three molecular regions, K2P distance comparison, and phylogenetic trees) for the two species discovered in Korea. The study also offers insights on potentially significant traits, such as the pore complex and other pore structures. The Korean specimen of Acanthonchus (Seuratiella) tridentatus resembles the original description regarding aspects such as the number and type of precloacal supplements, as well as the shape of the spicules and gubernaculum. However, variations are observed in the following characteristics: body ratio, nerve ring location, pharynx length, and the presence or absence of the oscelli. Our partial molecular sequences of the specimens also match identically with a single existing entry on NCBI identified as A. (S.) tridentatus. The new species, Paracanthonchus spongius sp. nov., is most similar to P. kamui in terms of the general shape of the body and gubernaculum but can be distinguished by differences in the number of precloacal supplements, amphid position, and gubernaculum ratio. The phylogenetic tree constructed based on the 28S rRNA region shows both species grouped within the monophyletic clade of Cyatholaimidae with high bootstrap support. However, achieving generic resolution of these species will require more molecular sequences of congeners to accumulate in the future. Full article

Three species of the genus Phyllopodopsyllus T. Scott, 1906 (Copepoda: Harpacticoida: Tetragonicipitidae) were reported from the intertidal sand of Jeju Island and Busan in Korea, Phyllopdopsyllus kitazimai Karanovic, 2017, Phyllopodopsyllus saywakimi sp. nov. and Phyllopodopsyllus similis sp. nov. The latter two were described here. Phyllopodopsyllus saywakimi sp. nov. collected from only Udo, Jeju is similar to a Pacific species from Costa Rica, Phyllopodopsyllus ancylus Mielke, 1992. However, P. saywakimi sp. nov. differs from the Costa Rica species in the body size, the number of armatures on the antenna, the length ratio of endo- and exopod of the mandible, and the chaetotaxy of the fifth female pereiopod and the sixth male pereiopod. The second new species, P. similis sp. nov., found in Busan and several localities of Jeju, significantly resembles the species complex related to Phyllopodopsyllus aegypticus Nicholls, 1944, which is widely distributed in the Indian, Pacific, and Atlantic oceans. P. similis sp. nov. can be distinguished from the P. aegypticus complex by the body size, the shape of the rostrum, the type of armatures, the length ratio of rami and armatures, and the chaetotaxy of the female P5. In addition to the species descriptions, partial fragments of small and large subunit ribosomal RNA genes, cytochrome b, and cytochrome c oxidase subunit I were provided. Using molecular markers, a phylogenetic analysis was also performed to estimate the relationships among the three Korean species of Phyllopodopsyllus for the first time. Full article

During a field survey of Korean marine and brackish water ciliate diversity, we collected a tiny benthic ciliate (13–18 µm long in vivo) from the opening of a brackish water lagoon (10‰). At low magnification, it resembles members of the genus Aspidisca because of the oval body shape and the benthic life style, but is not thigmotactic. Based on the observations of living cells, silver-impregnated specimens (i.e., using protargol, silver carbonate, and wet silver nitrate), SEM images, and the 18S rRNA gene sequences, we confirmed that it is a new member of the genus Cinetochilides. The new species, C. minimus sp. nov., can be easily distinguished from other congeners mainly by the fragmented somatic kinety 1. In spite of the small size, the new species has more than 200 basal bodies, including those in the oral apparatus. The arrangement of the ciliary pattern is rather confusing because of the polymerized kinetids, the sparse basal bodies, the non-ciliated area on the dorsal side, and the presence of parasomal sacs next to the kinetosomes. In the present study, we provide a detailed morphological description and infer the phylogenetic position of Cinetochilides minimus sp. nov. based on 18S rRNA gene sequences. Full article

Two new Uromunna species, Uromunna mundongensis sp. n. and Uromunna jejuensis sp. n., are described from the Korean Peninsula, representing the first record of the genus in Korean waters. Genetic analyses using two mitochondrial (COI, Cytb) and one ribosomal (18S rRNA) gene allowed us to confirm high pair-wise interspecific differences with the establishment of reliable barcoding gaps of COI (19.9%) and 18S (0.4%) between the new species. Finally, the phylogenetic relationship between the Uromunna species as well as the position of the genus within the munnoid groups are reconstructed using 18S. Full article

An undescribed species belonging to the family Eunicidae was detected in a sublittoral habitat of the southern coast of Korea. This Korean eunicid species was initially thought to belong to the genus Lysidice based on its general appearance, including the absence of prostomial lateral palps and peristomial cirri. However, a more detailed characterization of the morphological features of the maxillae and mandible coupled with mtCOI and 18S rRNA gene sequence analyses confirmed that this species is a member of the genus Paucibranchia. The absence of lateral palps found in the intact adult specimens with 153 segments is a unique feature not previously reported in species belonging to Paucibranchia. Thus, the new species, Paucibranchia triantennata sp. nov., can be easily distinguished from other known congeneric species. Except for the absence of lateral palps, P. triantennata sp. nov. resembled P. conferta, P. gathofi, and P. patriciae in the shape of the prostomium, brief location and shape of branchiae, and absence of compound spinigers. However, P. triantennata could be clearly distinguished from these species by the shorter prostomial antennae, a large number of subacicular hooks, and the morphological features of the maxillae and compound falcigers. Full article

A new species, Robertgurneya jejuensis sp. nov., was described from sandy sediment samples collected at a depth of 25 m on Mun Island, Jeju, in June 2018. The new species is morphologically similar to Robertgurneya similis similis (Scott A., 1896) and Robertgurneya donghaensis Bang, 2021; this is the second record of the genus Robertgurneya in South Korea. The morphological characteristics of the similis group within the genus Robertgurneya, to which the new species is ascribed, are summarized here. Furthermore, an identification key is provided based on the summary. Molecular identification of the collected specimens, based on the nuclear 18S ribosomal RNA (18S rRNA) and the mitochondrial cytochrome oxidase subunit I fragment, was obtained. Finally, a phylogenetic tree was constructed to present the position of Robertgurneya within the Miraciidae family based on 18S rRNA sequences which is relatively conserved. As a result, the relationship with sister genera morphologically similar to Robertgurneya was also molecularly confirmed. Full article

Two new species of the genus Scottolana Huys, 2009, were collected from Korean waters. S. daecheonensis sp. nov. is morphologically similar to S. jasani Song, Kangtia, Khim, and Chullasorn, 2018, from the Yellow Sea, Korea, and S. gomezi Nazari, Mirshamsi, Sari, Aliabadian, and Martinez Arbizu, 2018, from Bandar Abbas, Iran. However, it can clearly be distinguished from its congeners by rostrum with two tiny lateral sensilla, 4-segemented antennule in female, and 5-segmented antennule in male, 3-segmented mandibular exopod, P3 basis with an inner spinous process on the posterior surface, P3 endopod-3 without a modified tube-pore along the inner margin in male, P4 endopod-2 crumpled inner margin with strong spinules in male, P5 second outermost seta naked, caudal rami with an unguiform extension on the inner margins, and caudal seta V with a normal base in female. S. wonchoeli sp. nov. is similar to S. geei Mu and Huys, 2004 from the Bohai Sea, and S. longipes (Thompson I.C. and Scott A., 1903) sensu Wells and Rao (1987) from the Andaman Islands, but it can clearly be distinguished from its congeners by a combination of the following features: rostrum with a broadly rounded apex, 3-segemented antennule in female and 5-segmented in male, antennary exopod 8-segmented, female genital field relatively small, extending about one-third of genital double-somite, genital somite with paired lateral spinous processes in male, P6 with a long proximal element in male, and maxillular endopod with 11 setae in total. In a molecular analysis using the mitochondrial cytochrome c oxidase subunit I (COI) and 18S ribosomal RNA (18S rRNA) genes, the interspecific distance was 20.031% for COI and 3.214% for 18S rRNA between the two new species. A key for the identification of the species of Scottolana is included. Full article

In January 2019, epilithic diatoms were collected from two streams on Mount Gumdan and Mount Yongma near Lake Paldang in central South Korea. A total of 16 diatoms were isolated and classified by molecular and morphological analysis. Morphology was studied by LM and SEM, while the molecular study focused on small subunit (SSU) rRNA and ribulose bisphosphate carboxylase (rbcL) genes. Molecular analysis showed that the three species had clear differences in phylogenetic distance. Based on these findings, we studied the ultrastructure of three species. Among the morphological characteristics, Hannaea librata is longer but narrower and always has conical spines, while the similar species H. pamirensis has bifurcated spines in the central region and conical spines near the pole. Gomphonema seminulum is wider in the axial–central area than G. pumilium. Nitzschia inclinata has a bended valve apex, while N. oligotraphenta has a straight apex. Full article

Taxonomical research on siphonophores is lacking despite their high biodiversity. We collected siphonophores in Jeju and the southern coasts of Korea and conducted morphological redescriptions using multi-focus stacked digital images. As a result, we revealed eight unrecorded siphonophores (Abyla haeckeli, Ceratocymba leuckartii, Bassia bassensis, Dimophyes arctica, Lensia subtilis, Lensia subtiloides, Muggiaea atlantica, and Nanomia bijuga). Six genera, excluding Muggiaea, were reported for the first time in Korean waters, and subfamily Abylinae, to which Abyla haeckeli and Ceratocymba leuckartii belong, was also first recorded in Korea. The distributions and habitats of these species were summarized, with most of the species having cosmopolitan distributions but variations in individual size depending on environmental conditions. Phylogenetic analysis based on mtCOI was conducted for each family. Finally, we updated the species list of siphonophores in Korean waters to include 3 suborders, 5 families, 3 subfamilies, 14 genera, and 21 species. Our findings constitute baseline data for further research on Korean siphonophores. Full article

As a part of ongoing efforts for monitoring benthic ecosystem in the Gulf of Mexico, Harpacticoid copepods were collected from the southwestern Gulf of Mexico. Among them we report three new species of Zosime, and a new species of Peresime for the study area. Zosime is the most specious-rich genus in the family. Three species of Zosime were morphologically similar to Z. paratypica Becker and Schriever, 1979, Z. atlantica Bodin, 1968, and Z. destituta Kim J.G., Jung and Yoon, 2016, respectively. However, all three species have unique characteristics that distinguish them from similar species such as setal formulae and shape of female P5 and caudal rami. The new species of Peresime has similar morphological characters with P. reducta (Becker and Schriever, 1979). These two species can be distinguished by differences in mouth parts and the length of the setae on P2. This is the first report on the genera Zosime and Peresime from the Gulf of Mexico. We also discuss the global diversity and distribution of Zosimeidae and provide a key to the genera of the family and species of each genus, including the four new species from the Gulf of Mexico. Full article

The morphology and molecular phylogeny of a new haptorid ciliate, Fuscheriides baugilensis sp. nov., discovered in a temporary pond in South Korea, were investigated. The new species is characterized by its small body size (30–55 × 15–20 μm in vivo), oblong to rod-shaped extrusomes in the oral bulge and cytoplasm, 14–16 somatic kineties, two dorsal brush rows, and single subapical ciliary condensation. The phylogenetic analyses based on the 18S rRNA gene sequences show that the family Fuscheriidae is paraphyletic and the species belong to the genera Fuscheriides and Pseudofuscheria cluster together in the same subclade, while Fuscheria is in a different subclade, suggesting that the subapical ciliary condensation characterizing the two former genera has a higher taxonomic value than the shape of extrusomes for genera separation. Full article

Benthic harpacticoids were collected from Korean waters. Two species were identified as members of the genus Longipedia Claus, 1863, because they have an extremely elongated distal segment of the P2 endopod. Longipedia koreana sp. nov. is morphologically most closely related to L. nichollsi Wells, 1980 and L. scotti Sars, 1903, but it can clearly be distinguished from both species based on the following morphological characteristics: P1 coxa with strong spinules near the outer margin and the distal element being much bigger than the proximal elements, P2 coxa with a small inner seta on the anterior surface, P4 exopod first segment without an inner element, and the P5 with a rectangular exopod (more than 3.5 times as long as wide). L. ulleungensis sp. nov. is similar to L. brevispinosa Gurney, 1927, L. spinulosa Itô, 1981, and L. weberi Scott A., 1909. However, L. ulleungensis sp. nov. is characterized by the P2 coxa with a reduced inner seta, the P4 exopod second segment without an inner seta, and the anal operculum with a long median projection, a single spine, and a group of outer spines on each side. In a molecular analysis using the mitochondrial cytochrome c oxidase subunit I (COI) and 18S ribosomal RNA (18S rRNA) genes, the inter-specific variation was 22.525–23.102% and 1.325–1.382% of COI and 18S rRNA between the two new species, respectively. A key to the family Longipediidae is provided herein. Full article

Jellyfish play a vital role in the ocean’s ecosystem, acting as a nursery for young fishes, crabs, and brittle stars, as well as a source of food for certain charismatic megafauna, such as sunfish and sea turtles. They also pose a threat to human activities, with jellyfish blooms negatively impacting fisheries, power generation, and tourism. However, very little information is available on the biodiversity of jellyfish within the waters of Borneo. Here, we present new records of jellyfish found along the coast of Sabah, Malaysia, located in northern Borneo, bordering the megadiverse region of the Coral Triangle. A total of six species belonging to two classes and six families hitherto not recorded to the state are reported, Chironex yamaguchii, Acromitus maculosus, Crambione mastigophora, Linuche aquila, Netrostoma sp., and Phyllorhiza punctata. Of these, two species (C. yamaguchii and L. aquila) are harmful to humans, with C. yamaguchii capable of causing human fatalities. Reports of harmful jellyfish are useful to the medical and tourism industry, as some of these species may inflict stings and adverse reactions to humans ranging from rashes and skin irritation to fatal envenomation. A checklist has also been provided for all collected jellyfish species from Sabah waters of Borneo, Malaysia. Full article

The recent accelerated ocean acidification and global warming caused by increased atmospheric carbon dioxide may have an impact on the physiology and ecology of marine animals. This study was conducted to determine the egg production rate (EPR) and hatching success (EHS) of Acartia ohtsukai in response to the combined effects of an increase in temperature and a lower pH. Acartiaohtsukai with fresh surface seawater were collected in the northwestern Yeoja Bay of Korea in September 2017. The temperature and pH conditions applied included two different pH levels (representing the present: 7.9 and the future: 7.6) and three temperature values (26 °C, 28 °C, and 30 °C). In the pH 7.9, EPR significantly increased with increased temperature, but in pH 7.6, it significantly decreased as the temperature increased. EHS was lower in pH 7.6 than in pH 7.9. These results suggest that changes in the marine environment due to global warming and ocean acidification may affect Acartia populations and cause overall fluctuations in copepods of the genus Acartia. Full article

Dasybranchusgeojedoensis sp. nov., obtained from the soft sublittoral bottom in southern Korea, is described as a new species. This new species of Dasybranchus is easily distinguishable from its congeners by the protruded parapodial lobes in the final few thoracic chaetigers. Dasybranchus geojedoensis sp. nov. closely resembles D. bipartitus (Schmarda, 1861) in number and position of abdominal branchiae but differs in position of genital pores and lateral organs, range of thoracic tessellated chaetigers, and denticulation of the abdominal hooks. The partial mtCOI gene sequences of the new Korean species were significantly distinct from those of undescribed species of Dasybranchus from Australia. In this study, a key for known species of Dasybranchus is also provided. Full article