The morphology of the two marine hypotrichous ciliates Apokeronopsis bergeri and A. ovalis, isolated from the Yellow Sea, Korea, are described based on live and protargol-impregnated specimens. It is the first time that these species have been recorded in Korea. In addition, the small subunit ribosomal RNA gene was sequenced for comparison with the public database. The genus Apokeronopsis has recently been established in the family Pseudokeronopsidae, and the two congeners of the Korean population share the following characteristics: one row of one or more buccal cirri; usually two frontoterminal cirri; midventral complex composed of two distinctly separated rows; one left and one right marginal row; number of transverse cirri, more than eight; absence of caudal cirri; two types of cortical granules. Apokeronopsis bergeri differs from A. ovalis primarily in body shape (fusiform vs. oval form), size (usually $260{\times}80{\mu}m$ vs. $160{\times}55{\mu}m$), type II cortical granules (oval vs. round shape; yellow-green vs. mostly colourless and only a few yellow-green in colour), and morphometric data (75-106 vs. 53-70 in adoral membranelles; 37-47 vs. 24-36 in frontal cirri; 9-15 vs. 1-2 in buccal cirri), as well as molecular data (2.87% of pairwise distance).

The primitive beachflea, Paciforchestia pyatakovi (Derzhavin, 1937) living in gravel beaches was previously reported only from Japan and Russia. This species can be easily distinguished from another species in the same genus, P. klawei (Bousfield, 1961), by the degradation of all plepods and both rami that each consist of single article bearing 2-4 distal plumose setae. Descriptions of the diagnostic characteristics of the species are presented.

For the purpose of taxonomical description of marine oligotrich ciliates, water samples were collected from the southern coast of Korea (Masan Bay and Jangmok Bay). Ciliate cells were identified based on protargol impregnated specimens. As a result, four oligotrich ciliates were identified and redescribed: Rimostrombidium conicum (Kahl, 1932), Omegastrombidium kahli Song et al., 2009 and Spirotontonia turbinata (Song and Bradbury, 1998), and Spirotontonia grandis (Suzuki and Han, 2000). Of them, R. conicum, O. kahli, and S. turbinata are newly recorded and S. grandis is recorded for the second time in Korea, while the last one is redescribed to compare its variations according to locality. In addition, their abundances were analyzed and discussed the changes in accordance with water temperature and salinity.

Five species in the genus Thalia of the family Salpidae are described: Thalia cicar van Soest, 1973, Thalia democratica (Forskal, 1775), Thalia orientalis Tokioka, 1937, Thalia rhomboides (Quoy and Gaimard, 1824), and Thalia sibogae van Soest, 1973. All of these species are new to the Korean fauna. A key to the Korean Thalia species is provided.

Fish community structure in the Pyeongchanggang River was investigated from April to November 2009. About 900 individuals representing 24 species from eight families at six sites in the Pyeongchanggang River were collected. It was similar to the 2001's survey and it was less than 2006's survey. The Korean endemic species, Zacco koreanus was the most abundant, whereas subdominant species were native species, such as Pungtungia herzi, Zacco platypus, Rhynchocypris kumgangensis and Rhynchocypris oxycephalus. Three endangered species were collected at the sampling area, Acheilognathus signifier (relative abundance [RA] 0.9%), Pseudopungtungia tenuicorpa (RA 1.4%), and Cottus koreanus (RA 3.6%). One natural monument species, Hemibarbus mylodon, was included. According to the analysis of ecological indicator characteristics, the relative proportion of tolerant species was 6.3% (57 individuals), whereas the proportion of sensitive species was 65.9% (593 individuals). Species evenness, richness and diversity indices decreased gradually through the month from April to November during the study. Community indices in Pyeongchanggang River showed a high evenness index (J'>0.6), a low level of species richness (R<3.5) and a medium level of diversity (1.5

DNA barcoding of Bryozoa or "moss animals" has hardly advanced and lacks reference sequences for correct species identification. To date only a small number of cytochrome c oxidase subunit I (COI) sequences from 82 bryozoan species have been deposited in the National Center for Biotechnology Information (NCBI) GenBank and Barcode of Life Data Systems (BOLD). We here report COI data from 53 individual samples of 29 bryozoan species collected from Korean seawater. To our knowledge this is the single largest gathering of COI barcode data of bryozoans to date. The average genetic divergence was estimated as 23.3% among species of the same genus, 25% among genera of the same family, and 1.7% at intraspecific level with a few rare exceptions having a large difference, indicating a possibility of presence of cryptic species. Our data show that COI is a very appropriate marker for species identification of bryozoans, but does not provide enough phylogenetic information at higher taxonomic ranks. Greater effort involving larger taxon sampling for the barcode analyses is needed for bryozoan taxonomy.

We report a larentiine species, Collix stellata Warren, for the first time from Korea. Two males and one female were collected from Jeju-do Island, South Korea. Collix stellata is similar to Collix ghosa Walker in external appearances, but can be distinguished by the relatively larger discal dot on forewing and the relatively slender valva with distally projected margin of male genitalia. Diagnosis and description of the species are given with the figures of the genitalia.

The genus Pseudodryinus Olmi, 1989 belonging to the subfamily Dryininae has been reported for the first time in Korea, base on the discovery Pseudodryinus shihoae Mita, 2009. We have provided a redescription and photographs of the diagnostic characteristics of the species.

We report on the discovery of Hellwigia obscura Gravenhorst, 1823, a species new to Korea. A description based on both sexes with photographs and a key to the world Hellwigia species are provided.

A pagurid hermit crab, Pagurixus patiae collected from Hyung-ge Island, Busan, southern Korea is newly recorded into the Korean fauna. Pagurixus patiae is the only species of the genus recorded in Korea. Morphological descriptions of P. patiae are provided.

Sea stars were collected with fishing nets between depths of 40-150 m from the Gangwon-do coastal region, East Sea. Specimens were identified as Evasterias echinosoma Fisher, 1926 belonging to the family Asteriidae, which is new to the Korean fauna. This species was characterized by strong external spines and a general size of more than 200 mm, thus the largest sea star identified in Korea to date. Its morphological characteristics are described here with photos. Thirty two asteroid species including E. echinosoma have been reported from the East Sea of Korea.

Three xanthid crabs, Liomera margaritata, Neoxanthops lineatus and Pilodius miersi, are described and illustrated for the first time in Korea. Liomera margaritata and N. lineatus are the first species of their genera to be found in Korea. The three species represent extensions of their previously known ranges and bring the number of known species of the xanthid crabs to 25 from Korean waters.

Two pilumnid species, Echinoecus nipponicus and Zehntneriana amakusae, are described and illustrated from Jejudo Island, southern Korea. These species are recorded for the first time in Korea, and Z. amakusae is the sole representative of the subfamily Rhizopinae of the family Pilumnidae.

Tunicates were collected from three harbors (Gampo, Bangeojin, Daebyeon) in Gyeongsangnam-do and one harbor (Seogwipo) in Jejudo Island during the period from August 2008 to January 2011 and were identified on the basis of their morphological characteristics. Among them, colonial tunicate Clavelina lepadiformis (Muller, 1776) belonging to the family Clavelinidae was found to be an invasive alien species introduced from the North Atlantic, and this is the first record of its occurrence in Korea.

A melitid species, Melita bingoensis Yamato, 1987 collected from the Yellow Sea, is reported for the first time in Korea. This species has a slit-like pocket in coxa 6 of female, which is not found in other Korean melitid amphipods. In this paper, we compared this species with three other previously known Korean species in the same genus.