Two new species of free-living marine nematodes of the genera Hopperia and Nemanema are described from the sublittoral sediment of the East China Sea. Hopperia macramphida sp. nov. is characterized by having large amphidial fovea with five turns; arcuate spicules with enlarged proximal end and central internal lamella extending one third of spicule length from proximal end; gubernaculum with bent apophyses, six papilliform precloacal supplements; and conico-cylindrical tail with swollen tip and terminal setae. Nemanema minutum sp. nov. is characterized by relatively smaller body size in the genus; large oval amphidial fovea; conical tail; slender spicules with alae and hooked proximal end; ring-like gubernaculum; and papilliform precloacal supplements with three short setae. An updated dichotomous key is provided for the 17 species of Hopperia.

A brief morphometric study of the recent planktonic foraminifera in the eastern Indian Ocean was provided with the taxonomic key to species, synonyms, SEM microphotographs of shells and chamber arrays. By recent classification, currently 20 species representing 13 genera and 6 families (Canderinidae, Heterohelicoidae, Hedbergellidae, Higerigerinoidae, Globigerinoidae, and Globorotaloidae) identified from the planktonic material of the eastern Indian Ocean up to a depth of 200 m. Their distribution in water (0–200 m) also reports on the new range of expansion in the eastern Indian Ocean, with Dentigloborotalia anfracta, Hastigerina pelagica, Streptochilus globigerus, Globigerinella calida, Globigerinella adamsi, Orcadia reidelii, Tenuitella parkerae, Tenuitella compressa, reported for the first time in this study area. In general, only around 50 planktonic species are valid worldwide, more specifically the species, e.g., H. pelagica, G. calida, G. adamsi, S. globigerus, O. riedeli, T. parkerae, T. compressa, which occur in the eastern Indian Ocean to fill the the paucity of the recent regional taxonomic literature and the problematic identification from the eastern Indian Ocean. This work aims to bridge this gap and help scientists, managers, educators and students to identify plankton foraminifers by using species notes and images.

Epipont peritrich ciliates are one of the most sessilie protists that attached to the substrate of zooplankton communities especially copepods and crustaceans. Peritrich ciliates can be solitary or colonial form found from the coastal zones and embayment around the world. Present research report is the first snapshot study of the peritrich ciliates and the horizontal distribution in open waters from surface to 200 m depth in the eastern Indian Ocean. Recently, five peritrich ciliates, e.g., Vorticella oceanica, Zoothamnium alternans, Z. alrasheidi, Z. pelagicum, and Z. marinum were collected from plankton net tow samples during the cruise from April 10 to May 13, 2014. The characteristics of the peritrich ciliate were determined according to the shape of the zooids, the ciliary structure and the stalks. The morphometric shape, sizes and characters also explained by examination under light/scanning electron microscopy. Vorticella oceanica and Z. pelagicum showed their association with host such as diatom (i.e, Chaetoceros coarctatus) and copepod (Oithona brevicornis) including some individuals around the dinoflagellate species (Ceraitum tripose). The distribution of these sessilid ciliates was dominated by the V. oceanica, Z. pelagicum and Z. marinum at the southeast zone while the large colonies of Z. alrasheidi observed at the Bay of Bengal. This distribution can be influenced by substrate availability like diatom (Ch. coarctatus) and copepods (O. brevicornis).

Two new free-living marine nematode species from the mangrove wetlands of Fujian Province, China are identified and illustrated. Sabatieria conicoseta sp. nov. is characterized by its short conical somatic setae. There are 12–15 tubular pre-cloacal supplements and 12–15 μm long straight gubernacular apophyses. Dorylaimopsis papilla sp. nov. is characterized by spicules which are 1.5–1.8 a. b. d. long with media cuticularized strip along entire spicules, and have a cephalated proximal end with small hooked. There are 16–18 small papillate pre-cloacal supplements and 37–40 μm long dorso-caudal gubernacular apophyses.

Sabaco sinicus sp. nov. is described based on material collected from Chinese coast. It has been misidentified as Asychis gangeticus Fauvel, 1932 since Uschakov and Wu (1962). Here, we recognized it as a new species based on combination of the following characters: dark-brown pigmentation spots on nuchal grooves and first three chaetigers; glandular pattern on chaetigers 4–6; preanal achaetigerous segments absent; anal plaque trumpet-shaped with a disc-shaped dorsal lobe; notochaetae consisting of geniculate capillaries and fine capillaries with or without spinose spiral bands; neurochaetae presented as a single row of rostrate uncini. Asychis gangeticus differ from the new species in having no pigmentations on body and a triangular dorsal lobe of anal plaque. Distribution region of this species have moved northward significantly from sea area south of Changjiang Estuary since the 1950s.

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.

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.

Based on polychaete specimens collected from coastal areas of China in 1959, a new species of the family Orbiniidae, Leodamas sinensis sp. nov. is described in the present paper. The new species can be distinguished from its cogeners by the combination of following characters: branchiae present from chaetiger 5; each thoracic neuropodial postchaetal lobe possessing broad tori, with a digital to triangular-shaped papilla at its midlength; 4 or 5 vertical rows of uncini and one posterior row of accompany capillaries in thoracic neuropodia; acicula present in both abdominal notopodia and neuropodia, slightly or distinctly projecting. A key to all known species of the genus is provided.

A small armed dinoflagellate bloomed in the aquaculture ponds off the coast of Liaodong Bay, Bohai Sea of China, resulting in heavy mortalities of the cultured prawns (Penaeus japonicus) and larvae of Chinese mitten handed crabs (Eriocheir sinensis). The bloom-forming species was successfully isolated, and cellular morphology of the specimen was consequently investigated through light, fluorescent and electron microscopy. The small ((14.4±1.6) μm in length) ellipsoid cells show typical Heterocapsa thecal plate arrangement (Po, cp, 5′, 3a, 7′′, 6c, 5s, 5′′′, 2′′′′). The episome is evidently bigger than the hyposome. One to three spherical pyrenoids are located above or beside the large elongated nucleus. The body scale is characterized by a triangle basal plate with one central upright and nine peripheral spines. Above all, Heterocapsa bohaiensis could be distinguished from other Heterocapsa species by the combination of the cell size, morphology, cellular structure and body scale. Sequence analyses of both ITS and LSU regions reveal the significant genetic divergence between H. bohaiensis and other established species in this genus, further supporting novelty of this species. Noticeably, different sample treatment methods resulted in morphological variation of the apical pore complex (APC) of H. bohaiensis, which needs to be taken into account in future study.

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.