Foraminiferal oozes were sampled from the tropical West Pacific seamount and seabed of deep sea, by a remotely operated vehicle (ROV) in December 2014 and March 2016. Using standard morphological method, four Miliolinella species, including Miliolinella obesa, M. circularis, M. suborbicularis and M. subrotunda were described. Among the four species, M. obesa is a new species. It is a large member (about 500 μm in length) of the genus. This species is characterized by having a very stout and transverse broadly circular outline, and its body width is greater than the body length. In addition, its chamber demarcations are obscure from the exterior appearance. Three chambers are unclearly visible on one side and two chambers are visible on the opposite. Finally, we provided very detailed taxonomic microphotographs and the ecological distribution information for each species.

The dinoflagellate genus Margalefidinium has been split from Cochlodinium as a new genus recently and Margalefidinium fulvescens is one of the five Margalefidinium species. Margalefidinium fulvescens is toxic and has been reported from the coastal waters of USA, Canada, Mexico, China, Japan, Indonesia, Korea, Pakistan and Spain. Here we provide the morphological and phylogenetic characterization for an isolate of it from the Jiaozhou Bay, Qingdao, China. Our results showed that the vegetative cells were subspherical to ellipsoidal, 34–60 μm in length, and 19–41 μm in width. Both single cell forms and colonies in chains of 2, 4, or 8 cells were observed in cultures, but chain forms with 2 or 4 cells were observed more often in the field samples. The cingulum was rather deep, encircling the cell approximately twice, but the sulcus was rather narrow, surrounding the cell about one turn. The nucleus was spherical and located at the central epicone. The chloroplasts were granular, brownish, and scattered peripherally. An orange pigmented body also appeared in the epicone. The apical groove appeared vase-like as previously described. Under epi-fluorescence microscopy, a pumpkin-like structure was clearly observed, in which cells were embedded. Cells were observed to exit from the structure, which led us to a hypothesis that the structure may provide cells a shelter to avoid predation or to respond to other stresses. The phylogenetic analyses based on partial LSU rDNA sequences indicated that M. fulvescens from the Jiaozhou Bay was grouped with M. fulvescens populations from other origins and closely related to the clade of M. polykrikoides. Our morphological observations and phylogenetic analyses together confirmed the presence of M. fulvescens in China and our monitoring has also observed the species dominant in the dinoflagellate community of the Jiaozhou Bay in the early autumn of 2015, which alerted us to continually monitor this bloom-forming species in the region.

A new marine benthic diatom, Pleurosira nanjiensis sp. nov., is described from the rocky intertidal zone of the Xiaochaiyu Island of the Nanji Islands in China. Its morphology was examined with light and scanning electron microscopy. Molecular phylogeny was reconstructed based on SSU rRNA and rbcL gene sequences. Pleurosira nanjiensis differs from congeners in possession of a combination of morphological features including the domed valve with broadly lanceolate, elliptical or circular valve outline, two elevated marginal ocelli, two (rarely three) rimportulae, and radiate striae.

One strain of unicellular flagellated yellow-green algae was successfully isolated from the coastal area near Tianjin in the Bohai Sea in May 2015. The strain ranged from round to elongated in shape. Most of the cells possessed active motility, and some cells formed non-motile aggregation. Based on evidences from morphology, ultrastructure and molecular analysis, we identified the strain as Pavlova pinguis which belonged to Pavlovophyceae, Haptophyta. For Pavlovophyceae, only Pavlova viridis (Diacronema viridis) was reported in China seas prior to this study and it played an important role in aquaculture. This is the first record of Pavlova pinguis in Chinese waters.

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.

This study reviews all species belonging to the families Laodiceidae, Lovenellidae, Malagazziidae, and Mitrocomidae in the South China Sea. Two new species, Eucheilota carinata sp. nov. and Halopsis nanhaiensis sp. nov., are described and illustrated. One genus, Staurostoma, and two species, Staurostoma sp. and Octophialucium aphrodite (Bigelow, 1928), are first recorded in China seas. The key to all medusa genera and species of Lovenellidae and Malagazziidae are presented. Other data are briefly summarized to the list and distribution of species presented on the family Laodiceidae, Lovenellidae, Malagazziidae and Mitrocomidae in the South China Sea. The type specimens are deposited in the Third Institute of Oceanography, State Oceanic Administration, China.

This study describes and illustrates four new species Laticanna nanhaiensis Xu, Huang and Wang, gen. nov. and sp. nov., Protiaropsis gemmifera Xu, Huang and Du, sp. nov., Merga nanhaiensis Xu, Huang and Guo, sp. nov. and Rhabdoon apiciloculus Xu, Huang and Du, sp. nov. based on specimens from the south-central South China Sea. Additionally, keys to known genera of family Bythotiaridae and species of genera Protiaropsis, Merga, and Rhabdoon are described. All type specimens are deposited in the South China Sea Fisheries Research Institute, Chinese Academy of Fishery Science.

Mediomastus is a common genus around the world, and Chinese specimens used to be identified as M. californiensis Hartman. In this study, 118 Mediomastus specimens collected from four localities along the southeast coast of China were examined. They belonged to an unknown species. We treat them as a new species, described herein. The new species is characterized as follows: (1) chaetigers 1–9 biannulate with chaetal fascicles at midsegment, thereafter multiannulate with chaetal fascicles posterior to midsegment; (2) parapodial ridges on posterior abdomen; (3) possession of bilimbate capillary chaetae on chaetigers 1–4; (4) thoracic hooks with long, straight shaft, hood length about 3–5 times width; (5) abdominal hooks shorter, with developed shoulder and distinct constriction, markedly different from those in thorax; (6) unique staining pattern with methyl green. The present study indicated that Mediomastus species inhabiting Chinese waters might be misidentified as M. californiensis, and that Mediomastus chinensis sp. nov. is widely distributed along the southeast coast of China.

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 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.