This paper reviews the alien polychaete species in the world's oceans and their impacts on the marine ecosystems and humans. A total of 292 polychaete species belonging to 164 genera and 39 families have been transported around the world's oceans with human-mediated assistance. Almost 15% of total number of known polychaete genera and 3.4% of total number of species are included in this phenomenon. A total of 180 species have become established in the world's oceans and 31 species (casual species) have a potential to establish viable populations in a new location. The most speciose genera are Hydroides (16 species) and Polydora (16 species), both accounting for 10% of the total number of alien species. The families Spionidae (53 species) and Serpulidae (46 species) have the highest number of alien species. The Mediterranean Sea (134 species), and the coasts of the Hawaii Islands (47 species) and the USA Pacific (34 species) have been intensively invaded by alien polychaetes. The origins of alien species vary among regions. Alien polychaete species in the Mediterranean Sea mostly originated from the Red Sea and Indo-Pacific areas. Benthic habitats of the areas between 40°N and 40°S were colonized by polychaetes mostly originating from other tropical and subtropical regions. The Suez Canal and shipping are the major vectors for species introductions. Some species imported and exported as fishing baits have become established at non-native localities. The invasive polychaete species have greatly altered habitat structures in some areas, restructured the food webs, and created important economic problems.

Several poorly known species of the family Syllidae (Annelida) have been revised and re-described. New diagnosis and taxonomic remarks are provided for Erinaceusyllis erinaceus, Opisthosyllis neglecta comb. nov., Parapionosyllis parapionosylliformis comb. nov., Prosphaerosyllis semiverrucosa comb. nov. and Amblyosyllis granosa.

This investigation aimed to study the relative growth, morphological sexual maturity and fecundity of the swimming crab Achelous spinicarpus in a tropical region, on the south-eastern continental shelf of Brazil (25°S). Biometry of all specimens was conducted, including measurements of the cephalothorax, cheliped, abdomen and gonopods. Relative growth was described based on the equation for allometry (y = axb), and size at sexual maturity was determined from inflections in relations involving the cheliped, gonopods (males), and abdomen (females), as dependent variables, related to the cephalothorax width (independent variable). Fecundity was estimated by the gravimetric method. The relations of the length of the chelar propodus and carpal spine to the carapace width without the lateral spines (CW) showed positive allometry in both sexes, with a significant variation in the constant ‘b’ for males between the developmental stages (juvenile and adult) and the size at maturity estimated at 37 mm CW. In females, the abdomen was most appropriate for the estimate of morphological maturity, which occurred at a smaller size (32 mm CW), with a change in the growth pattern between the stages, passing from isometric (juveniles) to positive allometric (adults). The gonopods also showed different growth rates between developmental stages, in synchrony with the variables of the cheliped. Mean fecundity for the species was 53,984 eggs, with a positive correlation between the number of eggs exteriorized and the size of the female; the equations allowed interconversion between these variables, due to the adjustment of the power function (r2 ≥ 86%).

A new marine tardigrade of the genus Tanarctus is described from Japan. Tanarctus diplocerus sp. nov. was collected from Shimabara Bay, Kumamoto and Tanabe Bay, Wakayama. It is characterized by simple leg IV appendages, the lack of the internal–external relation in the dorsal and ventral cirri and the lack of the club-shaped secondary clavae. The secondary sexual dimorphism of the primary clavae and probable two-digit juveniles of the new species are reported. The problematic terminology of the so-called ‘internal’ and ‘external’ cirri is also discussed. A taxonomic key for the species of Tanarctus is provided.

Acrothoracican barnacles of the genus Trypetesa are obligate symbionts of hermit crabs that burrow into the gastropod shells occupied by their hosts. In the present study, hermit crabs were examined for the presence of trypetesids, based on collections from the United States, Jamaica, and the Philippines made between 1997 and 2008. Shells from Jamaica and New York contained Trypetesa lateralis, a trypetesid previously documented from central California. Trypetesa lateralis is redescribed based on light and scanning electron microscopy, showing the presence of an external mantle flap and asymmetrical opercular bars diagnostic for this species. The mean prevalence of trypetesids in Jamaica was 8.3% and most barnacles were associated with Calcinus tibicen; in New York the barnacles were found in 1.6% of shells occupied by Pagurus longicarpus. Specimens from the Philippines were identified as Trypetesa spinulosa (formerly known only from Madagascar) based on the presence of their diagnostic orificial palps. The mean prevalence of T. spinulosa in the Philippines was 3.7% and most barnacles were associated with Calcinus spp. Hermit crab eggs were observed in the guts of T. lateralis from Jamaica and T. spinulosa from the Philippines. In both of these regions the trypetesids were found significantly more often in shells occupied by female hermit crab hosts (80–87% with females). These findings suggest the barnacles be classified as transient parasites. The biology of trypetesids is reviewed and a key to the family is provided. Further studies are needed to determine if egg predation occurs in all trypetesids and the impacts on hosts.

Two species of Farranula, including a new species, are described from off Jeju Island, Korea (East China Sea). Farranula orbisa sp. nov. can be distinguished from its congeners F. curta (Farran, 1911) and F. rostrata (Claus, 1863) by a combination of morphological characteristics as follows: in females, (1) eyes located on the frontal part of prosome adhered to each other, (2) second urosomal somite distinctly rounded from the anterior to mid-region in lateral and dorsal view, (3) second urosomal somite ornamented with fine spinules on anteroventral margin; in males, (4) sharply contracted portion of second somite located at two-thirds distance from anterior margin, (5) caudal rami relatively longer compared to width at its base. The new species F. orbisa was erroneously identified as F. rostrata (Claus, 1863) from the East China Sea and as F. curta (Farran, 1911) from the Indian Ocean. The poorly described F. carinata (Giesbrecht, 1891) from the East China Sea is redescribed here based on both sexes of specimens and compared to its morphological variability with specimens from other regions.

Several divergent sympatry mtDNA lineages have been described in redlip mullet Liza haematocheilus, and this high inter-lineage divergence raises questions about the taxonomic status of L. haematocheilus lineages in the north-western Pacific. In this study, the amplified fragment length polymorphism technique was employed to examine genetic structure of L. haematocheilus and estimate the level of independence of the different mtDNA lineages in the north-western Pacific. A total of 186 bands were amplified from 91 individuals among 8 populations by 4 primer combinations and the percentage of polymorphic bands was 91.74%. The Unweighted Pair Group Method with Arithmetic Mean tree based on Nei genetic distance revealed two clusters (North Clade and South Clade). Molecular variance analysis and pairwise FST supported the separation of north and south populations of L. haematocheilus in the north-western Pacific. The incongruence between nuclear groups and mitochondrial lineages suggests the three distinct lineages do not represent cryptic species and the presence of divergent mitochondrial lineages in the same sample is a result of secondary contact after an extended period of isolation. The Pleistocene isolation and biological characteristics of species may be responsible for the genetic differentiation of L. haematocheilus.

Reproductive characteristics of poorly studied hyperiid amphipods, especially Phronimella elongata, are described. Among nine species of hand-collected phronimids, females of Phronimella elongata, Phronima dunbari and Phronima sedentaria cohabited with their young in a ‘barrel' derived from gelatinous zooplankton. Five growth stages of young were identified in Phronimella elongata: young of stages I–IV were found with the mother in the barrel, but stage-V young clinged to the mother retaining no barrel. The cohabiting young in Phronimella elongata and Phronima sedentaria always consisted of single growth stage. In a single female of Phronima dunbari, however, two different stages of young coexisted in a barrel. In Phronimella elongata, the mother size significantly correlated with the number of brooded eggs or cohabiting young regardless of growth stages of young. Considerable variation in the number of eggs or young per female among phronimid species may attribute to the differences in the volumes of the brood pouches.

The genus Achirus is made up of demersal fish that have a close relationship with the substrate and exhibit peculiar aspects during their larval stage. The aim of the present study was to determine whether the abundance of Achirus larvae differed among a set of habitats in the estuary of the Formoso River in the State of Pernambuco (north-eastern Brazil). Sampling was performed monthly between April 2009 and March 2010, and comprised horizontal hauls with plankton net during the day and night in mangrove, beach and reef habitats. Fish larvae were sorted, identified, measured and larval stage recorded. Density and body length values were used in a non-parametric analysis of variance for the determination of variations between seasons, habitats and diel periods. A total of 204 larvae were collected, with an average density of 2.1 larvae.100 m−3. Density was greater in the nocturnal samplings, with no differences found between habitats. The larvae occurred in the yolk-sac to post-flexion stage, with pre-flexion the most abundant stage (78%). Size segregation was observed. Larger larvae were captured at night and in the mangrove. The smallest larvae were caught on the reef, with length increasing toward the mangrove. The results indicate that Achirus larvae come from deeper regions near reefs, where spawning probably occurs, and perform ontogenetic migration towards the shallow waters of mangrove, where they settle.

Nuclear 18S rRNA gene sequences of oyster shell borers, Polydora websteri, P. calcarea and P. haswelli (Polychaeta: Spionidae), were determined for the first time. A wide range of morphological variation, particularly with regard to pigmentation, is observed among these three species. This variation was characterized at the species level. Black pigmentation pattern on the palps is suggested to be a key characteristic for species determination. Polydora websteri and P. haswelli were sister species. This is the first record of P. calcarea from Japan and Australia and P. haswelli from Japan.

The composition of fatty acids and sterols of Crangon crangon abdomen muscle was determined during two periods in the year 2010/2011. For determination of lipids classes, especially of fatty acids and sterols, high performance liquid chromatography with a laser light-scattering detector and gas chromatography–mass spectrometry were applied. Diversity and variety of saturated and unsaturated fatty acids was the highest during the spring period. Twenty-seven free fatty acids with from nine to 24 carbon atoms were determined in the spring periods. Among this fraction, 14 saturated and 13 unsaturated fatty acids (eight mono- and five polyunsaturated) were present. Only seven saturated and four unsaturated free fatty acids (14:2, 17:1, 16:1 and 18:1) were identified in December 2010. Arachidonic acid (20:4) and eicosapentaenoic acid (20:5) were detected in these two periods, and during the spring season an additional essential fatty acid—docosahexaenoic acid (22:6)—was present, which was not detected in the winter period. The number of identified sterols was correlated with phytoplankton, which was abundant during April 2011. Also, the sterol fraction in winter periods was very poor—only cholesterol was detected.

The aim of this paper is to describe the population structure and some reproductive aspects of Hippolyte zostericola during an annual cycle. Samples were taken bimonthly, from June 2009 to April 2010, with a Colman–Seagrove sledge net on seagrass meadows located in the internal margin of Isla del Carmen, Campeche, Mexico. The population structure of H. zostericola was similar throughout the cycle analysed. The males, significantly smaller than females (0.57–1.8 and 0.55–3.52 mm carapace length (CL), respectively), were more frequent between 0.8 and 1.54 mm CL, whereas in larger size-classes (1.8–3.52 mm CL) only females were registered, ovigerous principally. The sex-ratio was always in favour of males, mean of 1.3 males per female. Size at maturity (CL50) was 2.28 ± 0.1 mm CL. Based on the presence of ovigerous females throughout the year it is considered that the reproduction of H. zostericola is continuous. The main breeding season and recruitment occurs during the first third of the year. The mean fecundity of the species was 144 ± 69 eggs and varies with female size. The higher egg loss occurred in larger females (37.3%) and the relationship between fecundity and female size was estimated as negative allometric, which suggests that age influences the fecundity of the species.

The species range of Calanus sinicus along the Chinese coast extends from the Bohai Sea and the Yellow Sea in the north to the northern part of the South China Sea in the south. The subtropical seas along the southern coast of China mark the southern edge of the range of C. sinicus. In coastal seas off eastern Hong Kong, C. sinicus appears first in December, but densities comparable to those in the Yellow Sea and the East China Sea are reached only in January and February when temperature is <15°C. Density decreases in March as temperature increases. No individuals remain after May when temperature is >25°C. The average prosome length of females collected in February is comparable to that of females from the Yellow Sea, but females collected after mid-March are smaller than the smallest females from the Yellow Sea. Reproduction occurred mainly between January and March. Rapid decline of the population in April and the absence of a summer population suggest that the local population is derived from individuals advected from the north by ocean currents. Eggs produced locally probably did not hatch or develop into adults.

Nuchalosyllis Rullier & Amoureux, 1979 is an extremely rare syllid genus, only known from the holotype of its type species, N. lamellicornis Rullier & Amoureux, 1979. The genus is characterized by the dorso-ventrally flattened body and the unique comb-like nuchal epaulettes. We herein describe the second specimen of this genus ever found, which is also a new species, Nuchalosyllis maiteae sp. nov.; it differs from N. lamellicornis in having different morphology of nuchal epaulettes, spinose papillae on cirrophores of dorsal cirri throughout and sub-bidentate posterior body falcigers.

This study investigated whether associated meiobenthic communities, especially harpacticoid copepods, differed amongst habitats. Five pre-defined habitats within and next to the Posidonia oceanica seagrass meadow were sampled: living seagrass canopy leaves (LL), small (SMF) and large (LMF) macrophytodetritus fragment accumulations and sand, bare (BS) and covered (CS). The highest meiofauna abundances were recorded in the BS for the core sampled habitats (BS, CS, SMF and LMF) and in the LMF for seagrass material habitats (SMF, LMF and LL). Harpacticoid copepods were the most abundant taxon in all habitats. The assemblage composition at copepod family level showed two distinct habitats clusters: a leaf (LMF and LL) and a sediment cluster (BS, CS and SMF). Subsequently, stable isotope analyses were conducted to analyse the relationship between copepods and their potential food sources in seagrass material habitats. Based on δ13C isotopic analyses and SIAR mixing model, harpacticoid copepods relied for 70% on epiphytes and for 30% on P. oceanica leaf material in the LMF and LL habitats.

The aim of this work was to study the dynamics of Alitta succinea population growth in a tropical estuary. The organisms were collected in the polyhaline area of Pina Basin, north-eastern Brazil, in lower and shallow subtidal consolidated substrates, from October 2009 to March 2011. Fifteen samples with a size of 0.01 m2 were collected every month. A total of 2064 A. succinea individuals were measured for growth analysis, and the measure used was the length from prostomium to the 25th setiger. Growth parameters were estimated by the frequency–length distribution data from three different functions (i.e. von Bertalanffy, Gompertz and Richards). The differences in the densities of A. succinea were significant between the months of the dry and the rainy season, with the rain pattern being the factor that most affects the A. succinea life cycle. According to Akaike information criteria, the von Bertalanffy and Gompertz models were the ones that presented the best fit with the growth curve of A. succinea for the studied period. Using the Bhattacharya method for the analysis of modal progression, we identified eight cohorts. The lowest recruitment values were found in July and August 2010, respectively, and the remaining months had numbers of recruits that were representative of the total population. The growth performance index (Ø′) found was 2.86. The maximum longevity indicates that specimens of A. succinea live between 586 and 953 d, and the instantaneous mortality rate (Z) is 1.53 yr−1.

A checklist of published records of coronuloid barnacles (Cirripedia: Thoracica: Coronuloidea) attached to marine vertebrates is presented, with 44 species (including 15 fossil species) belonging to 14 genera (including 3 fossil genera) and 3 families recorded. Also included is information on their geographical distribution and the hosts with which they occur.

Three species of Asterocheres, including two new species, are reported as associates of sponges in shallow Antarctic water. Asterocheres spinosus sp. nov. has a combination of diagnostic features: mandibular palp is one-segmented, caudal ramus is 1.88 times as long as wide, antennule is 20-segmented in the female and 18-segmented in the male, urosome is spinulose, and legs 1 and 2 display weak sexual dimorphsims. In A. rai sp. nov., the body is large, 1.66 mm long in the female, the lateral margin of genital double-somite is smooth without setules or spinules, the exopod of antenna bears only a single seta, with two mucilaginous substances transformed from setae, and the third endopodal segment of leg 1 bears a prolonged distal process. A supplementary description is given for A. hirsutus Bandera, Conradi and López-González, 2005, recorded previously from the Antarctic.

The small polychaete family Trochochaetidae is monogeneric and had been recorded almost exclusively in the northern hemisphere before this study. During a benthic investigation in the coastal shelf zone off Angola at 15°S several specimens were collected from 84 m depth differing from other members of the family and we described it as a new species herein. The only known African species so far was Trochochaeta kirkegaardi from the eastern Atlantic. Trochochaeta ankeae sp. nov. is characterized by having four minute eyes, a small conical antenna, a nuchal crest projecting through chaetiger 2, by lacking notochaetae on chaetiger 2, by having acicular spines on neuropodia 2 and 3 and a pair of conical papillae ventral on abdomen. A key to all 11 known species (including an unnamed one) is given.

A new species, Aciconula tridentata sp. nov., is described from the Brazilian coast. The type material were collected from Praia de Suape, Cabo de Santo Agostinho, Pernambuco, Brazil. This new species differs from all its congeners in having the propodus palm of male gnathopod 2 bearing a 3-dentate projection. Additionally, A. tridentata sp. nov. can be distinguished from A. australiensis and A. miranda in lacking a setose hump proximally in article 1 of the peduncle of antenna 1; the outer plate of maxilliped reaching the end of palp article 1, and the female pereopod 4 is 3-articulate. A key to species of the genus is provided.