‘Photography’ as a useful method for estimating the density, sex-ratio and body size of the surface-active Austruca perplexa (H. Milne Edwards, 1852) (Brachyura, Ocypodidae)

Estimations of crab density, sex-ratio, and body sizes are difficult. Though the ‘burrow excavation’ method is widely used to estimate these parameters in surface-active crabs, it is destructive to crab populations. Therefore, an alternative, non-destructive method is desirable. This study compared the non-destructive ‘photography’ method with the ‘burrow excavation’ method in a fiddler crab (Austruca perplexa (H. Milne Edwards, 1852)) population. Twenty 0.25 m2 quadrats were set out and 4 photos were taken of the surface-active crabs in each quadrat. All crab burrows were then excavated, and the crabs were collected to estimate their numbers, sexes, and body and claw sizes. Afterward, the photographs were analysed to estimate the same parameters by using the GIMP program. These parameters were then compared between the two methods. The results showed that these parameters were not different between the methods compared. This study thus reveals that the ‘photography’ method could safely be used instead of the ‘burrow excavation’ method, and yield the same results.

Infestation by Octolasmis species (Lepadiformes, Poecilasmatidae) of the marine crab Lupocycloporus gracilimanus (Decapoda, Portunidae) from India

The portunid crab Lupocycloporus gracilimanus from Digha, Bay of Bengal, India was investigated for an infestation by the lepadomorph cirriped Octolasmis spp. About 93% of the epibionts examined were found attached to the surface of the carapace, abdomen and legs, and these were identified as Octolasmis warwicki (EOW). Only 7% of the epibionts were attached to the branchial lamellae, and these were identified as Octolasmis angulata (EOA). Twenty-seven O. warwicki were also found to have conspecific dwarf males (CDM) attached to the scutum: probably an adaptive strategy to maximize the total insemination. Both the epibionts and the CDM showed spatial preference for the posterior mesobranchial region of the carapace. Most of the CDM (27%) were seen as a single attachment on the epibiont. The distance between the epibiont and its nearest neighbour (DNN) was found to be strongly and negatively correlated (, ) with the number of epibionts, indicating its preference to stay in an intermediate-sized group rather than remain solitary, which probably would have facilitated the evolution of dwarf males (CDMs). A higher percentage of epibionts were observed to have attached CDMs when the DNN increased, and above the 25 mm DNN, all epibionts were having CDM attachments, which is believed to be a strategy to maximize the fertilization success of CDMs by reducing sperm competition. A strong, positive correlation (, ) was observed between the carapace width of the host crab and the numbers of the infesting epibionts, proving that the larger crabs are more susceptible to the infestation compared to the smaller ones. The sex ratio of the host crab was 1 : 5.5 (Male : Female), nevertheless, only the females were infested by the epibionts. The percentage of the prevalence, relative abundance and mean intensity of EOW infestation were recorded as 46.15%, 182.05% and 394.44%, respectively. None of the crabs had serious external or internal infestations that seemed to hinder the activities of the animal. This is the first report of the infestation of these Octolasmis species on the portunid crab Lupocycloporus gracilimanus from India.

Allometry of the box crab Calappa convexa De Saussure, 1853 (Brachyura, Calappidae) in the southeastern Gulf of California

The relative growth of Calappa convexa can be used to identify dimorphism or morphological change related to sexual maturation. The carapace width (CW) against width and length of the propodus of the right and left cheliped were tested to obtain a coefficient of allometry. CW against total wet weight WT values were analysed for length-weight relationships (LWR). Relative growth was analysed by a multi-model approach. Five models were tested and the best was selected due to the greater weight of the Akaike criterion (). Significant differences between sexes were found in CW (, ) and WT (, ). The negative or positive allometry varied according to the morphometric relationship and sex. No real winner model () was observed in the LWR analysis under a multi-model approach. The average model estimated a breakpoint at 118 mm CW in males and 132 mm CW in females.

Microanatomy of the antennal glands and their Na+/K+-ATPase activity in three true crab species (Brachyura), Portunus pelagicus (Linnaeus, 1758) (Portunidae), Macrophthalmus dentipes Lucas in Guérin, 1836 (Macrophthalmidae) and Eriocheir hepuensis Dai, 1991 (Varunidae)

There are differences between various crab species in the function and structure of organs involved in ionic and osmotic regulation processes. The antennal glands together constitute one of the most important organs involved in the osmoregulation in crabs. The present investigation aimed to study the tissue structure of the antennal glands and their Na+/K+-ATPase (NKA) pump activity in three true crab species from three different habitats, including the marine (Portunus pelagicus (Linnaeus, 1758)), the estuarine (Macrophthalmus dentipes Lucas in Guérin, 1836) and the freshwater habitat (Eriocheir hepuensis Dai, 1991). In this regard, the tissue structure of the antennal glands and the activity of the Na+/K+-ATPase (NKA) pump were assessed in these three selected species. The results showed that the antennal glands in all studied species consisted of two anterior parts and a posterior part. The anterior parts are composed of the proximal tubular region (PT) and the distal tubular region (DT). The PT and DT parts comprised the coelomosac and labyrinths in the anterior portion, and the bladder located in the posterior portion. However, despite the similarity in the general tissue structure of the antennal gland in marine, estuarine and freshwater crab species, some structural differences were observed between those species. Labyrinth cells, coelomosac podocytes, and bladder cells in the estuarine crab M. dentipes contained large vacuoles especially on the top (i.e., near the lumen) of the cells. The highest amount of NKA pump activity was measured in the antennal glands of M. dentipes (). The NKA pump plays a more important role in the estuary and seawater adaptation of crabs, but freshwater species are not highly dependent on the NKA enzyme for osmoregulation.

Reconstruction of intrageneric relationships within the Indo-West Pacific littoral crab genus Metopograpsus (Decapoda, Brachyura, Grapsidae): an alternative speciation order according to a 28S rDNA molecular phylogeny

The genus Metopograpsus H. Milne Edwards, 1853 is widespread throughout the Indo-West Pacific and currently consists of seven species that can only be separated by minor morphological differences. Therefore, it represents a good example for the usefulness of genetic analyses for identification and classification. In order to obtain phylogenetic information at both lower and higher evolutionary levels, it is best to use a combination of mitochondrial and nuclear molecular markers. Here we present for the first time a molecular phylogeny based on a relative long fragment of the 28S rRNA nuclear gene for the genus Metopograpsus, after application of newly developed primers. Our data suggest an alternative intrageneric speciation order, with M. thukuhar and M. cannicci holding a basal position and a monophyletic grouping of M. frontalis, M. oceanicus and M. quadridentatus, which differs from prior phylogenetic reconstructions. Previously recognized intraspecific phylogeographic patterns in M. latifrons and M. quadridentatus could not be confirmed, due to limited variability of this conserved nuclear gene and due to an incomplete geographic coverage of the corresponding species. In contrast, the previously indicated phylogenetic subdivision within the formerly widespread species M. thukuhar, which led to the recent description of M. cannicci, is here supported.

A new species of Eusirus (Amphipoda, Amphilochidea, Eusiridae) described from a hydrothermal vent in the Okinawa Trough, North-West Pacific

A new species of Eusiridae, Eusirus liui sp. nov. is described from a hydrothermal vent on Okinawa Trough, North-West Pacific. The new species differs from the other 30 congeneric species mainly by the following combination of characters: the acute rostrum reaching to 1/3 the length of peduncular article 1 of antenna 1; the absence of eyes; pleonite 3 without acute protrusion on dorsal margin, and the posterior margin of epimeron 3 with 18 serrations. A key to all known Eusirus species is provided herein. This is the fourth species within the Eusiridae that has been found from vent fields.

Presence of Conchoderma auritum and C. virgatum (Maxillopoda, Lepadidae) and Gloiopotes huttoni (Copepoda, Caligidae) on the black marlin, from the Gulf of Tehuantepec, Mexico

This is the first report of coexistence of pedunculate barnacles, Conchoderma auritum and C. virgatum in the mouth, and with the copepod Gloiopotes huttoni in the precaudal zone, on the black marlin, Istiompax indica, a as host. This is also the first note of a new non-mammalian host for C. auritum. The host specimen was caught in sport fishing in the Gulf of Tehuantepec, eastern Pacific. A review of registered occurrences of the genus Conchoderma in species of the fish family Istiophoridae is provided.