Epibiotic Communities of Common Crab Species in the Coastal Barents Sea: Biodiversity and Infestation Patterns

Crabs are important ecosystem engineers in marine habitats worldwide. Based on long-term data, we analyzed the species composition and infestation indices of epibionts and symbionts colonizing the great spider crab, Hyas araneus, and two lithodid crabs—the northern stone crab, Lithodes maja, and the red king crab, Paralithodes camtschaticus—in the coastal zone of the Barents Sea. The epibiotic communities found on great spider crabs were closer to northern stone crabs (33%) compared to red king crabs (25%). The prevalence of mobile symbionts (amphipods, Ischyrocerus, and polychaetes, Harmothoe) and common epibionts, such as barnacles and hydrozoans, was low on great spider crabs and high on the body and in the gills of lithodid crabs. Epiphytes were abundant on great spider crabs but not present on both species of lithodid crabs. Egg symbionts found on H. araneus and P. camtschaticus do not affect their local populations. Differences in the fouling communities found on the three crab species are associated with host size range, surface properties of their carapaces, and behavior patterns.

A new spider crab (Brachyura, Epialtidae) from the Castle Hayne Limestone Formation (Eocene), North Carolina, USA

A new spider crab, Eoinachoides bretoni n. sp. (Epialtidae MacLeay, 1838) from the Comfort Member of the Castle Hayne Formation (Eocene) of Onslow County, North Carolina (USA), is herein described, representing the second spider crab recovered from this member. Although the new species does not enlarge the stratigraphical range for the genus which is currently restricted from the Eocene to Miocene, it is the first report in North America, extending the palaeogeographic distribution of Eoinachoides, limited currently in the fossil record of South America. In addition, an updated list of the species of the Castle Hayne Formation is herein provided.

Ontogenetic niche specialisation of the spider crab Libinia ferreirae associated with the medusa Lychnorhiza lucerna

Symbiotic relationships in marine environments are not fixed and can change throughout the animal’s life. This study investigated the ontogeny of symbiosis of the spider crab Libinia ferreirae with the host medusa Lychnorhiza lucerna. We described the type of relationship, the temporal correlation among species and food habits. More than 50% of the sampled crabs were symbionts, most in early life stages. The highest number of crabs found in a single medusa was 11. Symbiosis was observed throughout most of the year but was more evident in warm periods. The crab has many benefits in this relationship with a medusa. One is the use of food resources captured by the medusa, primarily copepods. Since the crab steals the medusa's food, it is a kleptoparasitic relationship. There is a niche partition between symbiont and the free-living crabs as they occupy different habitats and use nonoverlapping food resources. Previous research reported that symbiosis first developed during the crab’s last larval phase (megalopa) when crab and medusa are in the same habitat. Observation of the crab's behaviour shows that symbiosis occurs when the crab can grab to the medusa when the host touches the sea bottom. The crab also took advantage of water currents, releasing itself from the substrate and then drifting towards the medusa. The symbiotic relationship that crabs have with the medusa provides then with a nursery, food resources, shelter, dispersion, and decreased competition with free-living adult crabs, all essential for the crab's survival.

NEW RECORD OF THE SPIDER CRAB Mithrax tortugae RATHBUN, 1920 IN THE NORTHEAST OF BRAZIL, FIRST RECORD ON THE COAST OF RIO GRANDE DO NORTE

The Northeast region of Brazil has gaps in the distribution of several species of crustaceans. In the last decade, the increase in the sampling effort and the elaboration of species lists have minimized this problem. In some cases, studies suggest that these “gaps” in the distribution of some organisms may be a natural part of a discontinuity in their geographical limits. During the lobster fishing expeditions on coral reefs in the north coast of Rio Grande do Norte (RN), for the first time, the spider crab Mithrax tortugae was captured in RN. After capture, some specimens were sent to the UFRN aquatic fauna laboratory for identification and biometrics. After confirmation of identification, they were deposited in the UFRN invertebrate collection. Thus, the present work aims to update the distribution area of the species, and to fill an existing gap for the Northeast region, bringing the first record of Mithrax tortugae on the coast of Rio Grande do Norte.

Chromatin characteristics of spermatogenesis in the spider crab Lissa chiragra (Fabricius, 1775) (Majoidea, Epialtidae)

This article uses the male spider crab Lissa chiragra, collected from Ras el Tin beach on the Mediterranean Sea at Alexandria, Egypt between January and December 2017, as a model to isolate the histone variants, H2A, H2B, H3 and H4 from spermatozoal nuclei to detect the presence of their genes and the chromatin-associated proteins. The spermatozoal chromatin in Brachyura is electron dense. During spermiogenesis somatic histones and sperm nuclear basic proteins (SNBP’s) are replaced partially or totally by protamines or keratin proteins, which are rich in arginine and oxidized cysteine. Histones, which are part of the nucleosome, are classified according to their functional and structural criteria into H2A, H2B, H3 and H4. Amino acids of the purified chromatin associated proteins are analysed with high resolution liquid chromatography. The low condensation of the nucleus of the spermatozoa is due to a low proportion and modification of the chromatin-associated histones. The DNA is organized into nucleosomes but not in higher order structures due to acetylation of histone H4, but rather via regions of histone-free DNA.

Fine structure of spermatogenesis in the spider crab Lissa chiragra (Fabricius, 1775) (Eubrachyura, Epialtidae)

This article uses the male spider crab Lissa chiragra, collected from Ras el Tin beach on the Mediterranean Sea at Alexandria, Egypt, between January and December 2017, as a model for a descriptive study of the functional morphology of the different structures of spermatogenesis with the aid of the transmission electron microscope. This study divides the seminiferous tubule into three zones, i.e., the germinal, transformation, and evacuation zone. The transformation or maturation zone occupies the central area. The evacuation zone lies at a pole opposite to the germinal zone. The anterior vas deferens is a tube where the formation of the spermatophore occurs by means of secretions from the epithelium. The ejaculatory duct is located between the muscles of the coxae of the fifth walking legs. This study concluded that the complex acrosome vesicle is formed during spermiogenesis and the cytoplasm includes the membrane system, constituted by the endoplasmic reticulum, Golgi apparatus, and vesicles associated with microtubules, and a few mitochondria. The Golgi apparatus is developed and is organized progressively to produce various vesicles. The cytoplasm forms a ring at the base of the nuclear extensions. The merger of the plasma and nuclear membranes, results in a pentalaminar membranous structure in some regions of the cell surface.