Functional differences between the extraordinary eyes of deep-sea hyperiid amphipods.

The ocean's midwater is a uniquely challenging yet predictable and simple visual environment. The need to see without being seen in this dim, open habitat has led to extraordinary visual adaptations. To understand these adaptations, we compared the morphological and functional differences between the eyes of three hyperiid amphipods-Hyperia galba, Streetsia challengeri and Phronima sedentaria. Combining micro-CT data with computational modelling, we mapped visual field topography and predicted detection distances for visual targets viewed in different directions through mesopelagic depths. Hyperia's eyes provide a wide visual field optimized for spatial vision over short distances, while Phronima's and Streetsia's eyes have the potential to achieve greater sensitivity and longer detection distances using spatial summation. These improvements come at the cost of smaller visual fields, but this loss is compensated for by a second pair of eyes in Phronima and by behaviour in Streetsia. The need to improve sensitivity while minimizing visible eye size to maintain crypsis has likely driven the evolution of hyperiid eye diversity. Our results provide an integrative look at how these elusive animals have adapted to the unique visual challenges of the mesopelagic.

Sexual dimorphism in subterranean amphipod crustaceans covaries with subterranean habitat type.

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species.

Another new species of Glossocephalus (Crustacea: Amphipoda: Hyperiidea: Oxycephalidae) from the Monterey Bay region, California, USA.

A new species of Glossocephalus, G. aurantium sp. nov., is described based on two female specimens collected from the Monterey Canyon, California, eastern Pacific Ocean. It was found associated with an undescribed lobate ctenophore. Glossocephalus aurantium is readily distinguished from its congeners by the large crescent-shaped bulbous eye fields relative to the size of the head capsule. The pereopod morphology is most similar to G. rebecae, recently described from the same general region by Zeidler and Browne (2015), but that species is readily distinguished by it's relatively narrow crescent-shaped eye fields. Apart from it's prominent bulbous eye structures, G. aurantium is distinguished from G. milneedwardsi by the morphology of the gnathopods (not spoon-shaped). In addition, pereopods 5 and 6 are slender (not paddle-like) and the head capsule is relatively larger with a sharp rostrum (not rounded).

South America stygobiont crustaceans: a new species of Hyalellidae (Amphipoda) and new reports of Stygocarididae (Anaspidacea) and Protojaniridae (Isopoda) from Calingasta Valley, Pre-Andean region, San Juan, Argentina.

We describe one new eyeless Hyalella species, H. cuyana n. sp., from the hyporheic zone of Calingasta River, San Juan Province, Argentina. Hyalella cuyana n. sp. differs morphologically from its stygobiont congeners by characters of antennae (both antennae subequal in size; aesthetascs elongated); coxal plate 4 (posteriorly without excavation); epimeral plates 1-3 (rounded posterodistally); male gnathopod 2 propodus (almond-shaped, ovate, palm slope strongly oblique); and pleopods (inner ramus reduced to 2-3 articles). We provide a detailed morphological comparison between stygobiont and stygophile Hyalella species. We comment on the sympatry and new report of stygobiont Malacostraca species Parastygocaris andina and Cuyojanira sp. Severe environmental changes and significant decline of habitat quality recorded along the Calingasta River increase the risk of extinction for this vulnerable and endemic fauna. We recommend that the new Hyalella species should be listed as Critically Endangered (CR) in the IUCN categorization according to criteria B1a as it is only known from the type locality; and criteria B1b iii (continuing decline, observed, inferred in the quality of habitat).

Ontogenetic Expressions of Sexually Dimorphic Traits in the Skeleton Shrimp Caprella scaura (Crustacea: Amphipoda).

In sexual dimorphism, males often exhibit exaggerated characters as weapons or ornaments. Among the numerous amphipod species (Amphipoda, Crustacea) showing sexual dimorphism, caprellids (Caprellidae) are characterized by considerably larger males that possess weapons, although the developmental processes underlying these sex-related differences are largely unknown. Therefore, to clarify the process of sexual differentiation during postembryonic development in caprellids, morphometric analyses of Caprella scaura were conducted. Principal component analysis using 31 morphometric traits showed drastic allometric changes occurring at two ontogenetic body length (BL) points (i.e., 3.8 and 8.8 mm). In individuals larger than 3 mm, head spines appeared in both sexes, and penises did only in males, allowing the discrimination of juveniles from larvae. Moreover, in larger males (BL > 8.8 mm), traits used in reproductive behavior, i.e., the first antenna, second gnathopod, and first to fifth pereonites, were extremely exaggerated. Observations of pre-copulatory behavior along with morphological assays revealed that sexually mature males could be identified by the size ratio between the triangular projection and palmar spine on the propodus of the second gnathopod. In contrast, female maturation could be determined by the marginal setae of oostegites forming a brood pouch. The body size distribution of sexually mature females was concentrated within a narrow range of BLs (6-9 mm), whereas that of sexually mature males showed a broader range (BL 9-18 mm), suggesting that, in C. scaura, males continue to molt and grow even after sexual maturation via indeterminate growth, to increase their lifetime reproductive success.

Description of a novel genus with three new species of Phoxocephalidae G. O. Sars, 1891 (Crustacea: Amphipoda) from off northeastern Brazil.

Magnaphoxus ajaja gen. et sp. nov., Ma. simplex gen. et sp. nov. and Ma. longicarpus gen. et sp. nov. are described. The material examined was collected off the states of Cear, Rio Grande do Norte and Bahia during the projects Avaliao da Biota Bentnica e Planctnica na poro offshore das Bacias Potiguar e Cear (BPOT) and Programa de Avaliao do Potencial Sustentvel de Recursos Vivos na Zona Econmica Exclusiva (REVIZEE). Additionally, material from other surveys off Brazilian northeastern coast is included. The samples were collected by rectangular dredges, box corer and Van Veen grabs, ranging from shallow waters to 168 meters in depth. The new genus is morphologically similar to the genera Grandifoxus Barnard, 1979, Metharpinia Schellenberg, 1931, Microphoxus Barnard, 1960 and Rhepoxynius Barnard, 1979. However, it can be recognized by the exclusive constricted and very broad rostrum and bilobated coxa 6, plus the combination of characters such as: lower lip outer plate with apical cusps; right mandible without lacinia mobilis; pereopods 34 carpus posterior margin with one distal robust long seta; propodus strongly armed with robust setae; uropods 12 peduncle dorsolateral margin combed distally; telson with two apical robust setae on each side. All three new species, are fully described, illustrated, and discussed.

A newHyalella species (Crustacea: Amphipoda: Hyalellidae) from South American Highlands (Argentina) with comments on its cuticular ultrastructure.

Hyalella Smith, 1874 includes approximately 92 species present only in the Neotropical and Nearctic regions. Hyalella is a dominant taxon in Central Andean Highland wetlands of Northwestern Argentina. We describe a new Hyalella species from Chorrillos, a cold-hyperfresh Puna peatbog in Salta province. Two other species occur in the Puna biogeographic province, namely H. kochi Gonzlez Watling, 2001 and H. puna Peralta Isa Miranda, 2019. The new species differs from H. puna mainly in having a smooth body surface; propodus of male gnathopod 1 hatchet-shaped, with nine serrate setae on inner margin; uropod 3 peduncle with two strong distal setae; and number and distribution of telson setae; from H. kochi by having the male uropod 1 without modified curved seta on inner ramus; six sternal gills on pereionites II-VII; globose peduncle of uropod 3 with two strong distal setae; long palp of maxilla 1. We also compared its external morphology with that of H. fossamancinii Cavalieri, 1959, another species recorded in the High Andes. We contribute new details on ultrastructural morphology of cuticular extensions (setae; microtrichs; denticles and pores). With this new species, the number of known Hyalella species in Argentina and Falkland Islands (Islas Malvinas) rises to 13.

A new deep-sea species of Vemana J.L. Barnard, 1964 (Amphipoda, Amphilochidea, Vemanidae) from off southern Gulf of Mexico.

Vemanidae Lowry & Myers, 2017, is an amphipod family restricted to the world's deep waters, with four benthic species inhabiting both bathyal and abyssal zones from the Caribbean Sea, South California, and the Mozambique Channel. During an oceanographic campaign carried out in the southern Gulf of Mexico, a single male specimen of a new species of Vemana J.L. Barnard, 1964 was collected from the deep-sea soft bottom, which is described in detail herein. The new species mainly differs from those four Vemana species by coxa 4 posteroventral corner prolonged forming an acute tooth, basis posterior margin of pereopod 7 with 6 evident teeth, antenna 1 flagellar article 1 lower margin with callynophore, and first urosome segment convex with a diminutive hump. The new species is morphologically closest to Vemana lizata Barnard, 1964, which was collected from the Caribbean Sea at 4077 m depth. Besides, a dichotomous key for the identification of the 5 known Vemana species worldwide is provided.

Physiological and behavioral responses of Orchestia gammarellus (Amphipoda, Talitridae) towards trace elements contamination soil.

Effects of trace elements on the hepatopancreas ultrastructure and on the locomotor activity rhythm were investigated in the amphipod talitrid Orchestia gammarellus collected from Bizerte lagoon banks situated in the north of Tunisia. Animals were exposed to a series of contaminated soil with different concentrations of cadmium and zinc. The locomotor activity rhythm was studied under constant darkness. Histopathological analysis showed that the trace elements, especially the Cd, induced significant changes in the morphology and in the ultrastructural organization of hepatopancreatic cells. The significant alterations obtained were dose dependent. Concerning the behavioral response, results revealed the presence of two components whatever the experimental conditions. In addition, a great inter-individual variability of the locomotor rhythm was observed. Patterns were in majority bimodal for the control individuals and became unimodal and multimodal when exposed under Cd and Zn, respectively. Furthermore, ultradian and circadian periods were determined. The circadian period lengthened after Zn exposure. In addition, the locomotor activity rhythm was more stable for control individuals. However, those exposed to Cd were less active.

A subterranean adaptive radiation of amphipods in Europe.

Adaptive radiations are bursts of evolutionary species diversification that have contributed to much of the species diversity on Earth. An exception is modern Europe, where descendants of ancient adaptive radiations went extinct, and extant adaptive radiations are small, recent and narrowly confined. However, not all legacy of old radiations has been lost. Subterranean environments, which are dark and food-deprived, yet buffered from climate change, have preserved ancient lineages. Here we provide evidence of an entirely subterranean adaptive radiation of the amphipod genus Niphargus, counting hundreds of species. Our modelling of lineage diversification and evolution of morphological and ecological traits using a time-calibrated multilocus phylogeny suggests a major adaptive radiation, comprised of multiple subordinate adaptive radiations. Their spatio-temporal origin coincides with the uplift of carbonate massifs in South-Eastern Europe 15 million years ago. Emerging subterranean environments likely provided unoccupied, predator-free space, constituting ecological opportunity, a key trigger of adaptive radiation. This discovery sheds new light on the biodiversity of Europe.