A new species of the family Pheronematidae is described in this study. Specimens were collected at Yap seamount and Caroline seamount in the Northwest Pacific Ocean. Poliopogon distortus sp. nov. contains oval macramphidiscs, three categories of amphidiscs, clavate monaxons and sceptres, making it distinguished from the eight known congeners easily. This is the fourth record of genus Poliopogon from the Northwest Pacific Ocean. We also used a partial sequence of 16S rDNA gene to confirm the family assignment of the new specimen.

The rare ophiuroid species, Ophioleila elegans, was collected by the submersible Jiaolong from 1 660 m depth on the Caiwei Guyot located in the Magellan Seamount Chain in the Northwest Pacific Ocean. This is the first published record of this species since the types were described from similar habitat off Hawaii. We provide more detailed morphologic characteristics of arm skeleton and a phylogenetic analysis based on CO1 sequences. Both morphology and phylogeny results suggest that the genus Ophioleila is more closely related to Ophiactids than Hemieuryalids.

Porcellanasteridae is a group of starfish that live in the deep ocean around the world. The type species of this family, Porcellanaster ceruleus Wyville Thomson, 1878, is cosmopolitan as well as polymorphic. The first record of its occurrence in the South China Sea is reported in this paper. One specimen was caught in the South China Sea on June 6, 2015 by trawl and identified to be a P. ceruleus. The morphological characteristics of this specimen are described and detailed pictures are provided. The discovery of this specimen further expands the distribution of P. ceruleus in the Pacific Ocean. The world distribution records of P. ceruleus and its synonymic species are reviewed in this paper.

The littoral paranthurid isopod crustacean Paranthura nigropunctata (Lucas, 1846) is recorded for the first time from the littoral of El Jadida located on the Atlantic northwest coast of Morocco. Specimens were obtained from the invasive brown seaweed Sargassum muticum and the natives Bifurcaria bifurcata and Cystoseira tamariscifolia in January 2015. This new record further confirms a significant southward distribution of P. nigropunctata and contributes to the knowledge of the biogeography of this isopod. Heretofore, the species was only known from the western and eastern Mediterranean and some Atlantic coasts. The present finding is the first of the species from Moroccan Atlantic shores, and suggests that the species may also be present in other coastal localities from Morocco and Africa. Some data on morphology, ecology and spatial distribution of the species are provided.

A new species Willenstenhelia mirabilipes sp. nov. (Copepoda: Harpacticoida: Miraciiidae) is described based on specimens collected from the South China Sea. This is also the first report of the genus Willenstenhelia from the China seas. The new species differs from congeners by the combined characters: all somites without spinules on surface except anal somite; third segment of female P4 exopod with two inner setae; female P5 baseoendopodal lobe with four elements and P5 exopod with sharp apical spine; caudal ramus about six times as long as broad.

The male of Candacia varicans Giesbrecht, 1892 from the South China Sea was recorded and described. In general, the male of C. varicans is morphologically similar to those of C. armata and C. curta. However, it is distinguished with them by below several morphological characters: (1) posterolateral corners of the fifth thoracic segment prominently sharp and symmetrical; (2) right side of posterior edge of genital segment with a small backward protuberance; and (3) the dorsal surface of the third segment of the fifth pereiopod with a squama-shaped protuberance.

Two chiton specimens were collected from sedimentary habitat by China’s manned Jiaolong submersible diving to a depth of 6 754 m in the north of the Yap Trench. This is a new locality record for chiton. Both morphological and molecular data support that the two specimens are the same species belonging to the genus Leptochiton. Morphologically, this species strongly resembles L. vanbellei and L. deforgesi. Phylogenetically, it has a close evolutionary relationship with L. vanbellei, L. deforgesi and L. boucheti. This is the third deepest record for deep-sea chitons so far.

A neritid species Vittina pennata (von Born, 1778) is reported for the first time from the South China Sea. This is also the first report of this genus from Chinese waters. The specimen was collected from the Sanya Harbor, Hainan Province, China and deposited in Marine Biological Museum, Chinese Academy of Sciences. Detailed descriptions of its shell feature are presented. Differences between this species, Vittina coromandeliana and Neritina pulligera are compared and discussed.

Four species of caridean shrimps collected from the East China Sea and South China Sea represent new records for the Chinese waters: Lysmata kempi Chace, 1997; Lysmata lipkei Okuno and Fiedler, 2010; Chlorocurtis jactans (Nobili, 1904) and Rhynchocinetes conspiciocellus Okuno and Takeda, 1992. The diagnostic characters and illustrations of these four species are presented, with remarks on their taxonomy. The identification keys of these species from Chinese waters are provided.

In order to investigate the tintinnid diversity, vertical distribution and latitudinal variation in the tropical West Pacific Ocean, water samples of different depths from surface to 200 m were collected along four transects. Totally 124 tintinnid species in 39 genera were detected. Most species preferred to live in the surface and subsurface waters. High tintinnid species richness, abundance and diversity index mainly occurred at depths slight shallower than the layer of deep chlorophyll maximum. Species richness, abundance and Shannon’s diversity index were significant positive correlation with temperature and chlorophyll a in vivo fluorescence, but significant negative correlation with salinity and depth. The correlations between most dominant species and environmental factors were not significant. Tintinnid diversity was extremely high in this area, species richness ranged from 25 to 52 at each station, Shannon’s diversity indexes were higher than 3 at most sampling positions from surface to 75 m. Proportions of redundant species were high, accounted for 87.90% of species pool and 60.38% of total abundance, indicating high capacity to response to changes in resource composition and predation pressures of tintinnid communities in the tropical West Pacific Ocean.