All Pseudocorynosoma species inhabit freshwater environments of the American continent, but little is known about their life cycles. We report Pseudocorynosoma enrietti (Molfi & Freitas Fernandes, 1953) from natural and experimental specimens in Patagonia and identify the intermediate and definitive hosts of its life cycle for the first time in South America. Adult worms were recovered from Anas platyrhynchos (Linnaeus) and from a new definitive host, Coscoroba coscoroba Molina. Naturally infected amphipods, Hyalella patagonica Ortmann, were collected to obtain cystacanths that were fed to Gallus gallus domesticus (Linnaeus) and Anas platyrhynchos. Specimens of P. enrietti are described in detail using light and scanning electron microscopy. A key to species of the genus Pseudocorynosoma is included. Worms are characterized in both sexes by fore-trunk spines, and genital spines in an isolated field. The proboscis has 19–20 hook rows; males have 9–11 (10) hooks per row and females 7–9 (8). Males with four cement glands similar in size. Eggs elongated, with filaments. Experimental male and female worms were recovered from A. platyrhynchos at seven and 14 days, post-infection.

Two new genera and six new species of benthic amphipods from the soft sediments of the Perdido Fold Belt region, western Gulf of Mexico, are described. Morphological comparisons of the new species with description of their congeners resulted in the determination of one new genus and one new species of the family Melitidae as Dentimelita lecroyae gen. nov., sp. nov., one new genus and four new species of the family Pardaliscidae as Pardaliscella perdido sp. nov., Paraeperopeus longirostris gen. nov., sp. nov., Pardaliscoides ecosur sp. nov. and Tosilus cigomensis sp. nov., and one new species of the family Unciolidae as Neohela winfieldi sp. nov. The occurrence of the newly described amphipods in the Perdido Fold Belt region represented new geographic range extensions for the genera, including new records of Neohela in the Gulf of Mexico, Pardaliscella and Pardaliscoides in the western Atlantic and Tosilus in the Atlantic.

The amphipod Ericthonius didymus Krapp-Schickel, 2013 is reported for the first time outside its type locality in European waters, from the French Atlantic coast and from the Azores, Portugal. In particular, a large population was recorded in Arcachon, France. Molecular analyses were made to confirm the validity of three closely related Ericthonius species: E. didymus, E. convexus and E. pugnax. An identification key is provided, distinguishing Ericthonius species into three groups, based on the presence or absence of stridulating ridges on coxa 2 and posterodistal lobe on basis of male pereopod 5.

The nocturnal displacement to the water column of species hiding in the substrate during the day (so-called demersal migration) is a widespread phenomenon in coastal habitats. However, despite the relevance of these migrations to coastal ecosystem functioning, most of their ecological aspects are poorly understood. We aim to characterize spatial distribution patterns of demersal amphipods by comparing samples collected by light traps deployed both at rocky and nearby sandy areas. Dispersal abilities of such species were explored by considering two spatial scales of separation between rocky and sandy substrates: (1) <100 m and (2) >1 km. A total of >45,000 amphipod specimens were collected in the water column during the whole study, belonging to 50 species. The numerically dominant species were Guernea coalita, Bathyporeia cf. elegans, Perioculodes longimanus and Nototropis swammerdamei. The present study highlights the relevance of substrate type and study location on coastal demersal amphipod migrations. Amphipod assemblages were significantly different in the water column above rocky and sandy bottoms, even at a small spatial scale. Species emerging from rocky bottoms tend to remain in the proximity of this habitat; they showed lower abundances in sandy areas located nearby and almost none of them reached distant sandy areas. In contrast, migrant species commonly found on sediment during the day were collected at higher abundances in light traps deployed above rocky bottoms. Although several factors (e.g. food availability, predation pressure) are proposed to explain these patterns, the purpose of this horizontal migration remains unknown.

Multidimensionality in parasite-induced phenotypic alterations (PIPA) has been observed in a large number of host–parasite associations, particularly in parasites with complex life cycles. However, it is still unclear whether such a syndrome is due to the successive activation of independent PIPAs, or results from the synchronous disruption of a single mechanism. The aim of the present study was to investigate the onset and progression of two PIPAs (a behavioural alteration: reversion of geotaxis, and castration) occurring in the crustacean amphipod Gammarus pulex infected with the acanthocephalan Polymorphus minutus, at different parasite developmental stages. Modifications of geotaxis in hosts differed according to the parasite developmental stage. Whereas the cystacanth stage induced a negative geotaxis (exposing the gammarid to predation by birds, the definitive hosts), the acanthella stage, not yet infective for the definitive host, induced a stronger positive geotaxis (presumably protecting gammarids from bird predation). In contrast, castration was almost total at the acanthella stage, with no significant variation in the intensity according to parasite maturation. Finally, no significant correlation was found between the intensity of behavioural changes and the intensity of castration. We discuss our results in relation with current views on the evolution of multidimensionality in PIPA.

A new species of Trischizostoma collected at depths of 1392–1420 m from western Mexico is described. It represents the first record of the genus in the NE Pacific. The new species is morphologically similar to T. circulare, T. tohokuense and T. richeri. These species all share a large rostrum, expanded eyes and an entire telson. Distinctive characters of the new species include a dorsally unnotched urosomite 1, a subconical coxa 2, a subtriangular propodus of gnathopod 1, a single seta and one protuberance on the palm of gnathopod 2, the presence of 10 spine-teeth in the outer plate of maxilla 1 and of a large, 1-articulate maxilla 1 palp, and the telson with 2 minute simple setae and 2 minute projections distally.

Existing population studies of deep-sea amphipods have focused on species that inhabit deep-sea vent or trench environments but few cosmopolitan species have been studied. Here we provide new insight into the life history and population ecology of the pan-oceanic scavenging amphipod Paralicella caperesca and discuss the influence of nutrient-rich submarine canyon environments on the growth and reproduction of this species. Data were collected through the dissection and measurement of 2997 P. caperesca from 14 samples taken from abyssal plains, continental slopes and submarine canyons in the North-East Atlantic. Sexual dimorphism was less pronounced than observed for other scavenging amphipod species but females were significantly larger and had shorter antennae than males. The size of oostegites in female P. caperesca varied considerably within size classes, ovaries contained a relatively large number of oocytes, and no empty ovaries were observed. These factors, in combination with absence of mature females, suggest that P. caperesca practices semelparity, a reproductive strategy that complements the feeding strategy of this obligate necrophage. Five male and seven female size-grouped cohorts were identified for P. caperesca. Cohorts from deep-sea submarine canyon populations showed consistently larger mean total body lengths than non-canyon cohorts. Individuals from canyon samples also expressed sexual characteristics at smaller sizes than non-canyon individuals. We hypothesize that these trends are indicative of nutrient-mediated growth, maturation, and reproduction in P. caperesca. The species is able to grow and reproduce relatively quickly in response to increased nutrient input in canyon environments and therefore dominates scavenging amphipod assemblages.

Three specimens of Platyscelus armatus (Crustacea: Amphipoda: Hyperiidea: Platyscelidae) are reported from coastal waters of the Canary Islands, Spain; these are the first records from these waters. The specimens were collected south-west of Tenerife and El Hierro Islands during the ‘CETOBAPH 2012' (April 2012) oceanographic cruise. Morphological and morphometric measurements of the specimens, geographical and bathymetric distribution of this species and a key to species of the genus reported in the Canary Islands are provided.

A new species of Curidia is described based on material collected from Sisal Coral Reef System, south-east Gulf of Mexico, Mexico. It is the eighth species of this genus described worldwide. Curidia nunoi sp. nov. is morphologically similar to C. wakabarae and C. andreae. Curidia nunoi sp. nov., however, differs from these two species by a combination of several characters, including: the posteroventral spine of peduncle articles 1 and 2 of antenna 1, the distoventral spine of peduncle article 4 of antenna 2, the distal margin of coxa of gnathopod 1, the dactylus of gnathopod 2, the inner and outer plates of maxilla 1, and the distal margin of telson. The global geographical distribution of the genus Curidia is mostly from tropical to subtropical seas; five species are documented in the southern hemisphere and three in the northern hemisphere. Only C. debrogania, C. monicae, and C. nunoi sp. nov. are restricted to the Gulf of Mexico and the Caribbean Sea.

Epifaunal invertebrates are sensitive to changes in the identity of the dominant host plant, so assessing differences in the structure of epifaunal assemblages is particularly pertinent in areas where seagrasses have been replaced by alternative vegetation (e.g. green seaweeds). In this study, we aimed to compare the diversity, abundance and structure of epifaunal assemblages, particularly amphipods, between meadows dominated by the seagrass Cymodocea nodosa and the green rhizophytic algae Caulerpa prolifera on shallow soft bottoms of Gran Canaria Island, determining whether patterns were temporally consistent between two times. The epifaunal assemblage structure (abundance and composition) consistently differed between both plants, those assemblages associated with C. prolifera-dominated beds being more diverse and abundant relative to C. nodosa meadows. Amphipods constituted ~70% of total crustaceans for the overall study, including 37 species belonging to 16 families. The amphipod abundance was ~3 times larger in C. prolifera-dominated beds than in C. nodosa meadows. We detected species-specific affinities; for example, Microdeutopus stationis, Dexamine spinosa, Aora spinicornis, Ischyrocerus inexpectatus and Apherusa bispinosa were more abundant in C. prolifera-dominated beds; while the caprellid Mantacaprella macaronensis dominated in C. nodosa meadows. However, some species, such as Pseudoprotella phasma and Ampithoe ramondi, were found in both habitats with varying abundances between times.

Examination of sampled material and review of the relevant literature revealed the presence of 299 benthic and 46 pelagic amphipod species from the Aegean Sea. Two of the species identified, Caprella hirsuta Mayer, 1890 and Apohyale crassipes (Heller, 1866), are recorded for the first time in the Aegean Sea and the Levantine Basin respectively. A checklist of the Mediterranean amphipods is given, as well as their distribution in the Mediterranean territorial areas and the Black Sea. The faunal comparison of the Mediterranean areas showed that the number of species decreases from west to east. In terms of zoogeographical categories the Atlanto-Mediterranean species dominate in all Mediterranean areas followed by the endemic species concerning the benthic amphipods while in pelagic amphipods cosmopolitan species dominate and are then followed by Atlanto-Mediterranean. Three species, Bemlos leptocheirus (Walker, 1909) and Linguimarea caesaris Krapp-Schickel, 2003, Photis lamellifera Schellenberg, 1928, are lessepsian migrants and are reported in the Levantine and Central Mediterranean Seas.

Seven taxa including three new species of Mallacoota are reported from the South Pacific locations of Papua New Guinea, New Caledonia and the Kermadec Islands. Mallacoota mizegwaden sp. nov. was collected from Papua New Guinea, and M. lifou sp. nov. and M. xepenehe sp. nov. from New Caledonia including the Loyalty Islands. Additional material of M. nananui Myers, 1985 is identified from New Caledonia, supporting previous records by Ledoyer, 1984. Three species, Mallacoota capricornia Lowry & Hughes, 2009; M. chiltoni Kilgallen & Ahyong, 2011 and M. sirius Hughes, 2011 are reported from the Kermadec Islands. There are now 33 known species of Mallacoota, with 19 species occurring in tropical to subtropical waters.

Medicorophium runcicorne is described from the Canary Islands. This is the first record of the genus from outside the Mediterranean and Black Seas. A key is provided to the species of Medicorophium.

A new species of deep water Epimeria is described based on material collected in 1526–1586 m depth during the TALUD X expedition in the central Gulf of California, Mexico. It is the sixth species of this genus reported for the East Pacific. Epimeria morronei sp. nov. is morphologically similar to E. norfanzi Lörz, 2011 (New Zealand, 1268 m depth) and E. cora J.L. Barnard, 1971 (off Oregon, USA, 2086 m depth). Epimeria morronei sp. nov., however, differs from these two species by a combination of several characters, including: vestigial eyes; multidentate mandibular lacinia mobilis; a distinct setae arrangement in palm and dactylus of gnathopods 1–2; the shape and relative size of coxae 1–5; and the shape of the telson.

A new bathyal leucothoid amphipod, Leucothoe cathalaa sp. nov., is described and illustrated based on specimens collected at the Le Danois Bank (‘El Cachucho’ Marine Protected Area), southern Bay of Biscay. This species can be distinguished from the other species of the genus Leucothoe by the hardly visible eyes (translucent ocelli, in preserved specimens); antenna 1 with minute accessory flagellum; coxae 1–3 with 2 serrations on posterodistal margin; epimeron 3 posterodistal corner produced, bifid, with one seta between blunt lobes and telson apex pointed without accessory teeth. In live specimens, the eyes are easily visible, each represented as a rounded whitish-pigmented spot. The new species has been found living on fine sandy soft-bottoms between 486 and 574 m depth at the top of the bank. An identification key to the deep Atlantic European species of Leucothoe is provided, as well as ecological and biological comments.

Amphipods' assemblages living in the red algae communities were studied in Velikaya Salma Strait (Kandalaksha Bay, north-western White Sea) in the depth range of 3–11 m. Sampling sites were located along the depth and shore exposure gradients in the areas with a significant number of rhodophytes. In total 12 species of amphipods were found with Ampithoe rubricata and Crassicorophium bonellii being most common and abundant. Gammaropsis melanops and Pleusymtes glaber were revealed as subdominant species. As an algal grazer A. rubricata appeared to be the species most closely associated with various algal assemblages. Crassicorophium bonellii were found on substrates being a deposit feeder predominantly inhabiting mixed assemblages of red algae where deposition and accumulation of seston most likely took place. Gammaropsis melanops and P. glaber are known as grazers but they preferred the habitats with both red algae and sponges. None of the species can be considered as obligate inhabitants of red algae hosts. Ampithoe rubricata and C. bonellii occurred in red algae communities in the shallow area (about 4 m). The most diverse and quantitatively rich amphipod assemblages were found at depths of 8–9 m in the area protected from waves and surf by the islands. Three of the most common and abundant species A. rubricata, C. bonellii and P. glaber are considered as amphiboreal while most of the species associated with rhodophytes belong to the Arctic-boreal ones. Amphiboreal species are presumably adapted to a broader temperature-range, in particular to higher summer temperature, than the Arctic-boreal species; they most likely have an advantage when occupying biotopes at shallow subtidal depth with local conditions in the White Sea.

Within an amphipod collection from Bora Bora (Polynesia) several species of Elasmopus were found: E. alalo Myers, 1986, E. hawaiensis Schellenberg, 1938, E. hooheno Barnard, 1970 and E. polynesus sp. nov. Among them was also a second member of Carangoliopsidae, known until now only by one genus with one single species: here is presented another species in a new genus, Kairos segregans gen. nov., sp. nov.

The surroundings of the rocky island of Helgoland (German Bight, south-western North Sea) are one of the best-studied sites in European seas with species occurrence data available for nearly 150 years. As the area is strongly affected by global change (e.g. increase in mean sea surface temperature at Helgoland by 1.67°C since 1962), ecosystem structure and function are expected to change more than those of average marine systems. The paper presents a supplement to the local amphipod species inventory (5 nautical miles around the island). At least seven species of this ecologically important taxon seem to have newly established themselves at Helgoland since the late 1980s: Ampelisca typica, Amphilochus brunneus, Caprella mutica, Cheirocratus assimilis, Monocorophium acherusicum, Orchestia mediterranea and Orchomenella crenata. Most of them are not only new for the Helgoland area, but also for the German Bight; and two species (Amphilochus brunneus and Orchomenella crenata) are even new to the North Sea as a whole. Out of the seven new species, one (Caprella mutica) is a neozoon from the north-western Pacific. The other six species show clear warm water affinities (oceanic–Lusitanian species) which suggest a recent range expansion in the context of climate warming. The establishment of an increasing number of species formerly probably absent from the area does not seem to be compensated by losses of species, so that local species diversity is expected to increase.

The genus Princaxelia, Pardaliscidae, is a rarely recorded, infrequently collected and hitherto observed benthic amphipod, typically found at hadal depths (>6000 m) in the Pacific Ocean trenches. Little is known about the behaviour or physiology of this genus. Using a baited camera lander, observations of Princaxelia jamiesoni were made in the Japan Trench (7703 m) and Izu–Ogasawara Trench (9316 m) and of Princaxelia aff. abyssalis in the Kermadec Trench (7966 m) and Tonga Trench (8798 m). These amphipods rapidly intercepted the bait and preyed upon smaller lysianassoid amphipods. Mean absolute swimming speeds for P. jamiesoni and P. aff. abyssalis were 4.16 cm.s−1 ± 1.8 SD and 4.02 cm.s−1 ± 0.87 SD respectively. These amphipods have the capacity for long range swimming, high manoeuvrability in close range, and efficient predatory behaviour. Burst swimming speeds for P. aff. abyssalis were 9 and 10 cm.s−1 with accelerations up to 22–25 cm.s−2.

In this work, we report for the first time the presence of the amphipod Perioculodes aequimanus from the north-east Atlantic. Specimens were collected in Zostera meadows located in the O grove inlet (north-western Iberian Peninsula), where the species is well established and is one of the numerically dominant peracarid species. Some morphological differences were found in comparison to Mediterranean individuals but those are regarded as due to intraspecific variation. This species can be distinguished from other Atlantic species according to the features of the propodus of the first gnathopod, the first coxa, the pereiopod 7 basis and the antennal peduncle.