Two new species of ciliates parasitizing marine molluscs in the Yellow Sea were described using live observation, protargol and wet silver impregnation: Sphenophrya solinis sp. nov. from the gills of Solen grandis and Planeticovorticella paradoxa sp. nov. from the gills as well as the mantle cavity of Meretrix meretrix. Sphenophrya solinis is elongate boat-shaped, and characterized by having the right system of 5–6 kineties more or less distinctly longer than the left system of 3–5 kineties and the bud formed on the dorsal left of body during budding. Planeticovorticella paradoxa is a second member of the genus Planeticovorticella, and characterized by the free-swimming, cylindroidal trophonts usually with no stalk or with a very short and non-contractile stalk, the C-shaped macronucleus longitudinally oriented in mid-body, and the apically located contractile vacuole. The morphology, infraciliature and morphometry of the two new species were studied in detail and compared with those of their most similar congeners.

Sponge samples were taken by SCUBA diving from four sites around Stanley and nine sites at the Jason Islands in the Falkland Islands. Twelve new species are described: Iophon pictoni sp. nov., Lissodendoryx (Ectyodoryx) jasonensis sp. nov., Phorbas ferrugineus sp. nov., Phorbas shackletoni sp. nov., Myxilla (Styloptilon) acanthotornota sp. nov., Amphilectus fleecei sp. nov., Amphilectus dactylus sp. nov., Mycale (Aegogropila) nodulosa sp. nov., Scopalina erubescens sp. nov., Scopalina bunkeri sp. nov., Amphimedon calyx sp. nov. and Pachychalina erinacea sp. nov. Information is also provided on the distribution and external appearance of other sponge species: Iophon proximum Ridley, 1881, Clathria (Dendrocia) tuberculata Burton, 1934, Tedania (Tedania) mucosa Thiele, 1905, Tedania (Tedania) murdochi Topsent, 1915, Halichondria (Eumastia) attenuata Topsent, 1915, Siphonochalina fortis Ridley, 1881 and Haliclona (Soestella) chilensis Thiele, 1905. The biogeography of the Falklands' sponge fauna is discussed.

A collection of 32 specimens of the genus Plakortis (Demospongiae: Plakinidae) from Australia and the Indo-Pacific is here examined. Six species are described, four of which are new to science. Plakortis lita has microrhabds, an irregular tangential ectosomal reticulation, a confused choanosomal skeleton and irregular diods and triods. Plakortis quasiamphiaster has quasiamphiasters (spined diods and triods), spheres and a skeleton with a distinct subectosomal region. Plakortis communis sp. nov. has diods and a tangential ectosomal reticulation with circular meshes; triods and spheres may be present or absent. Plakortis bergquistae sp. nov. has diods in two size-classes, the larger one up to 330–356 µm long, and large triods (actines up to 75–121 µm long). Plakortis fromontae sp. nov. has large diods (up to 220 µm long), rare triods and a double ectosomal reticulation. Plakortis hooperi sp. nov. has diods, triods, microrhabds and spheres, with a confused ectosomal skeleton, a thinly encrusting shape and cream colour. Detailed descriptions of external morphology, skeletal arrangement of the ectosome and spicules in SEM are essential for the taxonomy of Plakortis. The number of valid species in the genus is raised from 15 to 19. A key to Indo-Australian species of Plakortis is given.

A new species of Craniella from the Aleutian Islands is described. Craniella sputnika sp. nov. differ from all other species of Craniella in its habitus, absence of microscleres and size of spicules. The name refers to its resemblance to Earth's first artificial satellite, due to its spherical body with long spines. The new species was observed growing on another demosponge, Myxilla sp. We propose transferring two species currently in Craniella to Tetilla (Craniella ellipsoidea Hoshino, 1982 and Craniella laminaris (George & Wilson, 1919)) and two subspecies (Craniella globosa anamonaena Tanita, 1968 and Craniella laminaris symmetrica (Wilson, 1931)) from Craniella to Tetilla. As Craniella globosa anamonaena Tanita, 1968, is actually a species of Tetilla we suggest raising the subspecies to species rank as Tetilla anamonaena. Conversely we think that two species, Tetilla ovata (Thiele, 1898) and Tetilla hamatum Koltun, 1966 should be transferred to Craniella.

A new species, T. strongylata sp. nov. is described on the basis of material collected from the Pacific Ocean. The new species is characterized by the presence of sinuous strongyles. Moreover the incomplete description of T. simplex (Sarà, 1959) is implemented on the basis of new abundant material allowing, for the first time, the complete description of the skeleton of a Triptolemma species and the detecting of the presence of monaxonic spicules in the spicular complement of the genus. The skeleton is composed of a thick crust of disorderly arranged mesotriaenes and scattered microscleres, supported by diverging spicule tracts formed by oxeas towards the surface. Both species were recorded associated to boring sponges (Spiroxya and Cliona) in excavations of the calcareous scleraxis of precious corals or in organogenic concretions. In the cavities where the tissue of Triptolemma was recorded the wall of the excavation partially lost its typical pattern characterized by ovoid scars and became irregularly eroded. Our hypothesis is that Triptolemma insinuates inside the erosions produced by other sponges and it is able to enlarge them by an etching mechanism based on chemical dissolution only.

Boring sponge diversity in the area of the Conero Promontory, the most important rocky emergence on the west coast of the Adriatic Sea (Italy), was assessed. Four species were recorded; one of them, Cliona adriatica, is new and is described here. The new species differs from all the other excavating sponge species, characterized by yellow papillae and lacking or scarcity of microscleres, in the large size of the boring chambers and the presence of numerous styles. Cliona adriatica is present on about 12% of the surface of rocky bottoms in the Conero Promontory area. The impact of this highly destructive species on the carbonatic micritic rock of the promontory was evaluated calculating a relationship between the volume of the boring chambers and the surface of the epilithic portions. Consequently, it was estimated that 1 cm2 of epilithic tissue corresponds to 8.5 g of excavated rock. The recorded correlation between the excavated volume and the area of the papillar zone (roughly the area of the substratum affected by the erosion) allows an estimation of the substratum removed by a boring sponge, using only visually oriented, non-destructive, sampling methods.

In 1996 a sponge was found in a well studied area in the Ria of Etel, Brittany, France, that had never been recorded there before. This sponge was later described as a new species and genus, Celtodoryx girardae by Perez et al. (2006), who concluded that it is probably an invasive species. Over several years C. girardae was found to occur successively in the Gulf of Morbihan, France, and Oosterschelde estuary, Netherlands. This sponge is characterized by an extensive spatial broading and therewith it rates today among the dominant benthic megafauna in the shallow waters of the Gulf of Morbihan and Dutch inshore waters. During our recent survey of the Chinese Yellow Sea sponge fauna, we found an abundant species with close morphological similarities to C. girardae. Further taxonomic studies have revealed that both the Chinese and European sponges are in fact conspecific with Cornulum ciocalyptoides described by Burton (1935) from Posiet Bay, Sea of Japan and later recorded from other localities of the North West Pacific (e.g. Koltun, 1971; Sim & Byeon, 1989). In this paper we transfer the species of Burton from Cornulum to Celtodoryx and consequently it becomes the senior synonym of C. girardae. Furthermore, we conclude that Celtodoryx ciocalyptoides was introduced to the North East Atlantic from the North West Pacific with aquaculture of the Pacific oyster Crassostrea gigas as the probable vector. This is probably the first case recorded so far of a sponge species being transferred from one ocean to another by human activity.

A new record of Crambionella stuhlmanni is reported from the east coast of South Africa. The material is described using quantitative morphological data, and mitochondrial (CO1) and nuclear (ITS-1) sequence data. The species can be diagnosed by a combination of morphological features including the presence of conical projections on velar lappets, the absence of orbicular appendages among mouthlets and the short length of the terminal club on the oral arm. Mitochondrial sequence data unambiguously delineate C. stuhlmanni as a separate species from C. orsini, and phylogenetic analyses support its placement within the monophyletic genus, Crambionella.

Two new species belonging to the precious coral genus Corallium were collected during a series of exploratory cruises to the New England and Corner Rise Seamounts in 2003–2005. One red species, Corallium bathyrubrum sp. nov., and one white species, C. bayeri sp. nov., are described. Corallium bathyrubrum is the first red Corallium to be reported from the western Atlantic. An additional species, C. niobe Bayer, 1964 originally described from the Straits of Florida, was also collected and its description augmented.

A new species, Philosyrtis aegusae sp. nov., collected in the ‘Otoplanen-Zone’ of the sands of western Sicily, is described. The specimens show the typical morphological peculiarities of the subfamily Parotoplaninae (‘Turbellaria’: Otoplanidae), but differ clearly from the species already described. The body length of the sexually mature animals reaches 0.9–1.1 mm and they appear to belong to the genus Philosyrtis because of the general arrangement of testes and germo-vitellaria, and of the sclerotic apparatus. The vesicula granulorum is clearly distinct from the sclerotic apparatus unlike the other ten species belonging to the same genus. The male copulatory organ consists of a dorsal group of 7–8 spines similar in shape and length (33–40 mm), and a ventral group of at least 6 long thin spines with curved pointed tips. The new species differs from the already described species above all in its body dimensions, the shorter path of the vitellaries and especially the characteristics of the male sclerotic apparatus.

A new species, Endeolophus skeneae sp. nov., epibiotically associated with the gastropod Skenea profunda, is described from light microscope and scanning electron microscope observations. The new species is characterized by homogeneous ornamentation of the cuticle with annules with very fine and numerous longitudinal ridges, equally distributed around the body, subcuticular discontinuity in cuticle pattern along the lateral sectors of the body, relatively long body (1.1–1.6 mm) and relatively long tail (141–188 μm, c' = 7.5–11.4), short (19–22 μm) L-shaped spicules with ventrally bent blade and simple plate-like gubernaculum without apophysis. Symbiotic associations between aquatic nematodes and molluscs are discussed, with special emphasis on Dreissena polymorpha, zebra mussels. It is suggested that nematodes find food and shelter in the mantle cavity of the bivalve molluscs, and in the umbilicus and aperture of the gastropods, but to reveal the exact mechanisms of symbiotic associations of nematodes with aquatic molluscs requires further research.

Two new species of free-living marine nematodes Paramarylynnia filicaudata sp. nov. and Paramarylynnia stenocervica sp. nov. from the Yellow Sea, China are described. Paramarylynnia filicaudata sp. nov. is characterized by a homogeneous cuticle with transverse rows of even dots; spicules boat-shaped, swollen in the middle and gradually tapering towards both ends; tail conical with a long filiform terminal portion and without subventral setae on the conical part. Paramarylynnia stenocervica sp. nov. is characterized by the marked narrower anterior part of the neck region; heterogeneous cuticle with transverse rows of punctations and the punctations of anterior contracted portion larger and more widely spaced than the remaining portion; spicules curved and cephalate proximally; gubernaculum boat-shaped, swollen in the middle and gradually tapering towards both ends, five small tubular precloacal supplements.

The small, monogeneric family of polychaetes known as Trochochaetidae has been exclusively collected in the northern hemisphere, mainly in temperate–cold environments. Nine species have been described so far including Trochochaeta mexicana sp. nov. described herein, while one species remains unnamed. Only two species had previously been recorded in the eastern Pacific, so T. mexicana sp. nov. is the first record for the family in the tropical Mexican Biogeographic Province. The new species is characterized by having a pair of eyes, acicular neurochaetae on chaetigers 2 and 3, a small knob-like antenna and a nuchal crest projecting through chaetiger 1. Trochochaeta mexicana sp. nov., together with Trochochaeta kirkegaardi, Trochochaeta diverapoda and Trochochaeta cirrifera are the only trochochaetids that have been found exclusively in warm environments.

Cirratulus dollfusi Fauvel, 1928 is re-described from the material from the Sea of Marmara. The specimens collected from the Sea of Marmara were compared to the holotype of the species. The species is a multitentaculate and multibranchiate cirratulid; it differs from all other known cirratulid genera in its type of chaetae and the way the multiple branchial filaments arise from the notopodia. Chaetae are of two types: numerous long, fine capillaries in both rami throughout, also 2–4 shorter, wider, finely tapering spines in noto- and neuropodia. There are no slightly flattened sigmoid spines, typical of most Cirratulus species. Very short, slender grooved tentacles arise in a small circular group on either side of chaetiger 1. Branchial filaments are multiple; they arise as 1–2 filaments from each of 4–8 raised notopodial lobes on parapodia of anterior and middle segments, with lobes fading out and fewer (holotype) or no branchiae posteriorly (our material). No other cirratulid genera appear to have straight, tapering spines plus so many fine capillaries. We propose Fauvelicirratulus gen. nov. for this species. The species seems most closely related to Cirratulus hedgpethi Hartman, 1951, from the northern Gulf of Mexico, still only known from the incomplete original description. Features of some cirratulid genera are compared and the use of multiple branchiae as a generic character is discussed.

A new species of Chloeia (Annelida: Amphinomidae) is described from deep water (750–1045 m) off southern Brazil. Chloeia kudenovi sp. nov. differ from previously described species by the extremely elongated neuropodial cirri of the second chaetiger, number and position of noto- and neuroaciculae and lack of body pigmentation. This study provides additional data on the morphological diversity of the genus.

Rhodoliths or maërl are calcareous nodules of coralline red algae growing unattached to the substrata. They sustain a high biodiversity, being one of the most important marine benthic environments dominated by macrophytes. Sabellariidae are tube-dwelling filter feeding marine polychaetes that build their tubes by secreting cement from their thoracic glands. Some species are solitary, while others build tubes together, forming large aggregates. This study analyses Sabellariidae collected in rhodolith beds along the subtidal zone of the coast of João Pessoa and Cabedelo, Paraíba, north-eastern Brazil. A total of 100 individuals of six species were identified. Four are reported for the first time for the north-east coast of Brazil: Phragmatopoma caudata Mörch (1863), Sabellaria bella Grube (1870), Sabellaria nanella Chamberlin (1919), and Sabellaria wilsoni Lana & Gruet (1989). The first occurrence of Sabellaria pectinata Fauvel (1923) along the western Atlantic is provided as well as the description of a new species of the genus Sabellaria.

A new species of Sphaerodoridae (Annelida: Polychaeta), Sphaerodoropsis solis sp. nov., is described from the Challenger Plateau in the Tasman Sea, south-west Pacific. It is the third species of the genus with ventral macrotubercles and is further characterized by the lack of dorsal papillae and the specific arrangement pattern of ventral papillae. A character indicating sexual dimorphism, that has been observed in three morphologically similar species, S. arctowskyensis Hartmann-Schröder & Rosenfeldt, 1988, S. bisphaeroserialis (Hartmann-Schröder, 1974c), and S. garciaalvarezi Moreira, Cacabelos & Troncoso, 2004, is confirmed for S. solis sp. nov. Besides S. solis sp. nov., S. arctowskyensis and S. parva (Ehlers, 1913) are newly recorded from the Challenger Plateau and the East Campbell Plateau in the south-west Pacific. An updated key for the genus Sphaerodoropsis is provided.

On Tarifa Island (Strait of Gibraltar) several amphipod species were studied from intertidal algae: Ampithoe ferox, Apherusa mediterranea, Hyale spinidactyla, Hyale cf. youngi and Jassa cadetta. The allometric growth of gnathopod 2 in male is demonstrated for A. ferox. Jassa cadetta had been recorded previously only from the northern Adriatic Sea, while Hyale spinidactyla and Hyale cf. youngi had been only known from the Atlantic Ocean. Along the intertidal area, A. mediterranea and J. cadetta were dominant in the low levels located near the infralittoral area, while A. ferox, Hyale spinidactyla and Hyale cf. youngi were distributed in intermediate and upper levels, closer to the supralittoral zone. All the species showed the maximum peaks of abundance from April to October, coinciding with the maximum seawater temperatures.

The new species Batea aldebaranae from the coast of Belize is described and distinguished from the similar species Batea cuspidata (Shoemaker, 1926) and Batea carinata (Shoemaker, 1926). Characteristic for the new species are: additional set of dorsolateral teeth on pleonites 1–2; pereopod 1 second article small, scale-like; propodus of pereopod 7 elongate, dactylus shortened and telson shallowly cleft.

Epimeriidae is an amphipod family with a worldwide distribution. A new species was found from the Tasman Sea at a depth of 12 m depth and described in detail. Epimeria norfanzi sp. nov. can be distinguished from other Epimeria by a combination of the following characters: coxal plates 1–3 ventrally rounded; protrusion of coxa 5 reaching the distal end of epimeral plate 2; and urosomite 1 with dorsal keel, telson not cleft. This new species increases the number of Pacific Epimeria species to ten. A brief synopsis of the Pacific Epimeria species is given and a key provided.