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.

This study reviews all genera and species belonging to the family Bougainvilliidae from the South China Sea. The Nubiella atentaculata Xu and Huang, 2004 formerly included in the genus Nubiella, now is transferred to a new genus Paranubiella and included in the Bougainvilliidae as Paranubiella atentaculata (Xu and Huang, 2004) n. comb.. Two new species, Paranubiella nanhaiensis Xu, Huang and Guo, sp. nov. and Nubiella apapillaris Xu, Huang and Guo, sp. nov. from the South China Sea are described and illustrated in the present paper. In addition, the key to known genera of family Bougainvilliidae and species of genus Nubiella are described. Other data are briefly summarized to the list of species presented on the family Bougainvilliidae in the South China Sea. The type species were deposited at the Third Institute of Oceanography, State Oceanic Administration.

A taxonomic study of Hyalinoecia species based on the materials deposited in the Marine Biological Museum of the Chinese Academy of Sciences (MBMCAS) yielded two species: Hyalinoecia tubicola (Müller, 1776) and H. papillata Imajima, 1999. Both species were collected from the sandy bottoms in the northern South China Sea. Hyalinoecia tubicola is widely distributed from the coast of Guangdong Province southwards to the Xisha Islands. Hyalinoecia papillata is reported for the first time in the South China Sea. It differs from H. tubicola in having a prolonged, tongue-like prechaetal lobe with papillae along the lateral margins in the first parapodium (vs. auricular prechaetal lobe with smooth margins). The morphological description and illustration of both species are given.

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 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.

Planktonic ostracods are small crustaceans abundant in marine ecosystem worldwide as appreciable part of marine zooplankton. Family Halocyprididae is a large group of halocyprid ostracods, and the tribe Conchoeciini has contained 21 genera previously. We described a further genus with a species Polyconchoecia commixtus gen. et sp. nov. from the middle of South China Sea in this study. The new species can be distinguished from related genera and species in having a unique combination of these characteristics: a lateral gland placed over right asymmetric gland and open near posterior margin; dense edge glands placed along ventral margin of carapace in line; shape of frontal organ; e-seta of first antenna is bare; endopod of second antenna has one small oval hump with central concave on mid-ventral margin, instead of processus mamillaris, exopod 1 has a small disto-dorsal spine, exopod 1 and 2 are fused, exopod 3 and 4 are bare; endopod 1 of mandible has one long ventral seta, endopod 2 has one ventral seta; maxillary endopod 1 has two basal setae; endopod 1 of fifth limb has only one ventral seta; endopod 1 of sixth limb and endopod 2 have no ventral seta. The definite distinctions in locations of major glands are the key characteristics of the new genus.

Based on specimens collected in Yinggehai, Hainan, China from 2013 to 2016, a stable epiphytic taxon is found on the surface of the individual of marine green alga Cladophora aokii Yamada. According to the morphological characteristics, the taxonomy of Cl. aokii and its epiphytes is carried out. There are some epiphytes attached on Cl. aokii Yamada including Cl. fascicularis (Mertens ex C. Agardh) Kützing, Chaetomorpha pachynema (Montagne) Kützing, Ceramium camouii Dawson, Licmophora abbreviata Agardh, Lyngbya sp. and Chattonella sp.. The formation of the individual of Cl. aokii is dissected and explained, which can help to analyze the adaption in details among this species, its epiphytes and native marine environment. The results reveal the marine macro-epiphytic taxonomy in Hainan, China, and preliminarily explain the adaptive relationship between macroalgae and environment.

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.

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.

A new record of the ampharetid genus Auchenoplax, A. worsfoldi Jirkov and Leontovich, 2013, is reported and described from the East China Sea. The specimens agree well with the original description of Auchenoplax worsfoldi with two pairs of branchiae, two thoracic uncinigers with enlarged neuropodia and 12 abdominal uncinigerous segments. The present specimens have long and filiform branchiae extending to thoracic chaetiger 9, which was not included in the original description. This is the first record of this species in Chinese waters.