The erythropini mysid, Pleurerythrops secundus Murano, 1970, is recorded in shallow waters of the northeastern coast of Izu-Ohshima Island, Pacific coast of central Japan. Underwater surveys at a depth of 15–30 m by a scuba diver revealed that P. secundus lived on the benthic hydroids Aglaophenia whiteleggei Bale, 1888, Dentitheca hertwigi (Stechow, 1909), Gymnangium hians (Busk, 1852), Plumularia habereri Stechow, 1909, and several unidentified hydroid species. This finding represents the first evidence of P. secundus associated with benthic organisms. Furthermore, to the best of our knowledge, this is the first report of a mysid species in association with hydrozoans.
We examined relative growth of the pereiopods in megalopae and first to fifth crab stages of Portunus trituberculatus (Miers, 1876) reared in the laboratory. Relative growth of the body parts in relation to a reference dimension (carapace length) was analyzed by the log-transformed allometric growth equation lny＝lna＋blnx. Body proportions differed between the megalopae and juvenile crabs. In juveniles, the chela size showed isometric growth (b＝1); the second to fourth pereiopods (walking legs) showed mainly negative growth (b＜1) in length, and isometric growth (b＝1) in width; and the width and length of the fifth pereiopod showed positive allometric growth (b＞1). Portunus trituberculatus cling to drifting seaweeds using their chelae and pereiopods before undertaking a benthic life after the fourth or fifth crab stages; the chelipeds and fifth pereiopods are utilized mainly in the burying behavior of juveniles after settlement. Accordingly, the negative allometric growth in length of the walking legs likely represents an adaptation for a lifestyle shift from drifting seaweeds to benthos, whereas the isometric or positive allometric growth of the chelae and fifth pereiopods would be advantageous for the burying behavior of the crabs post-settlement.
DNA sequences from a portion of the mitochondrial 16S rRNA gene were used to examine genetic differentiation among the local coastal populations of the Japanese wood-boring isopod Sphaeroma wadai Nunomura, 1994. Of the 15 haplotypes identified, only 3 were shared among the sampled localities. The most dominant haplotype was shared by all populations from the Japanese mainland. All haplotypes identified from Okinawa Island and Iriomote Island were endemic to each island. For the Japanese mainland group, the haplotype network showed a star-like shape, with rare haplotypes radiating from the central most common haplotype by only one or two mutation steps. Haplotypes identified from Iriomote Island were separated by many steps from those identified from all other sampled localities, and haplotypes identified from Okinawa Island were separated by several steps from those identified from the Japanese mainland. Phylogenetic analyses revealed the existence of two lineages: one comprising specimens from Iriomote Island and the other comprising specimens from the Japanese mainland and Okinawa Island. These two lineages diverged at an uncorrected p-distance of 9.1%–10.3%, probably representing a different species. There were no clear morphological differences between the two lineages except for the propodus length of the seventh pereopod of male individuals.
Salinity is an important ecological factor affecting larval survival and development of coastal and estuarine decapod crustaceans. We investigated the low salinity tolerance limits of larvae in the six terrestrial hermit crab species, the coconut crab Birgus latro, and the land hermit crabs Coenobita brevimanus, C. cavipes, C. purpureus, C. rugosus, and C. violascens to infer their early life history strategies. Zoeae and megalopae were exposed to six different salinity levels ranging from 5–30 ppt with intervals of 5 ppt for 24 h, and the median lethal salinity (MLS) was estimated as the salinity at which 50% of test larvae died. The MLS estimates were lowest in the first zoeae, increased during the zoeal stage, and declined in the megalopal stage in all species. Early zoeae and megalopae were euryhaline and later zoeae stenohaline, suggesting that coenobitids exhibit a larval export strategy towards the offshore (oceanic) marine waters. Interspecific variation was evident in the salinity tolerance of the first zoeae, probably reflecting the salinity conditions at the species-specific larval hatching place. In contrast, the low salinity tolerance ability of megalopae did not differ among species, suggesting that coenobitid megalopae might require similar habitats for the settlement and initiation of benthic life.
Tropical shallow-water crinoids offer shelter to a diversity of marine life, including various symbiotic palaemonid shrimp species. In this study, the reproductive features of the shrimps Cristimenes commensalis and Pontoniopsis comanthi inhabiting comatulid crinoids are studied and compared. Ovigerous females were collected from the crinoids Anneissia bennetti and Comaster nobilis from Iriomote-jima, Japan. All specimens were examined for the following traits: carapace length, fecundity, embryo volume, brood mass volume and dry weight of the females and the eggs. Cristimenes commensalis produced 15–117 eggs with a volume of 0.04 mm3±0.00, whereas the smaller-sized species P. comanthi produced 12–57 eggs with a volume of 0.02 mm3±0.01. The reproductive output (RO) of C. commensalis was 0.16±0.03, considerably lower than that of P. comanthi at 0.31±0.05. Data is beginning to emerge on the fecundity and reproductive output of symbiotic palaemonid shrimps, although comparisons remain hampered by the general lack of knowledge on their biology in general. Pontoniopsis comanthi has the highest recorded reproductive output so far, despite being the smallest species studied. Our results confirm that inhabiting a sheltered habitat allows symbiotic shrimps to allocate more energy to embryo production than free-living species. Different reproductive strategies are, however, apparent for these species inhabiting the same host species, implying the existence of differential selective forces.
The corallanid isopod Tachaea chinensis Thielemann, 1910 is a parasite attached on the carapace of freshwater shrimps and prawns. The isopod is reported from Palaemon paucidens De Haan, 1884 (Palaemonidae) at two localities in Kagawa Prefecture (Shikoku) and two localities in Shimane Prefecture (western Honshu), and from Neocaridina sp. (Atyidae) at one locality in Shimane Prefecture, Japan. This represents the first record of T. chinensis from Shikoku. The species is briefly described and illustrated based on non-ovigerous females. Prevalence of T. chinensis in populations of P. paucidens and Neocaridina sp. ranged from 10.7–57.1%, and the intensity of infestation was almost constantly one, which indicates its intra-specific competition on the host carapace. Palaemon paucidens is considered as a preferred host of T. chinensis in Honshu and Shikoku, Japan. Based on the literature published between 1910 and 2018 including this paper, T. chinensis has been reported from 14 nominal and some unidentified species of shrimps and prawns belonging to three atyid genera (Caridina, Neocaridina, and Paratya), two palaemonid genera (Macrobrachium and Palaemon), and one penaeid genus (Penaeus), ranging from temperate (Honshu, Shikoku, and Kyushu in Japan, and central-eastern China) through subtropical (Okinawa in Japan, and Hong Kong in southeastern China) to tropical (Hainan in southeastern China, Vietnam, Thailand, and Malaysia) regions in East Asia.
A new genus and new species of potamid freshwater crab is described from Genting Highlands in the Central Highlands of Peninsular Malaysia. Beccazia licin n. gen., n. sp. is atypical among potamids in possessing a bilobed terminal segment of the mandibular palp, and is only the second known member of the family with such a character; the other genus being the recently described Gempala bilobata Ng & Ahmad, 2016, also from Peninsular Malaysia. All other congeners have a single terminal lobe on the mandibular palp. The carapace and third maxilliped morphology of Beccazia superficially resembles montane species of the Malaysian potamid Stoliczia Bott, 1966, but can easily be distinguished by its much smoother carapace, unarmed carpus of the cheliped and relatively wider male pleon.
The symbiotic association between hermit crabs and sea anemones is a classic example of mutualism in the sea. Some species of hermit crabs have the ability to transfer the symbiotic anemones onto their new shells when they change shells. The hermit crab Dardanus deformis (H. Milne Edwards, 1836) (Decapoda: Diogenidae) carries some anemones on the dorsal surface of the shell (e.g, Calliactis) it inhabits and frequently has the sea anemone Verrillactis sp. (most probably conspecific with “Verrillactis paguri” in Uchida and Soyama, 2001) placed at the shell aperture. In this study, we observed that D. deformis transferred Verrillactis sp. from the aperture of its old shell to that of its new shell. This suggests that the peculiar position of Verrillactis sp. is determined by the hermit crab, which recognizes its proper position. Dardanus deformis engaged in a specific behavior of tapping before transferring Verrillactis sp. to the new shell. This is similar to the behavior shown previously by D. deformis to remove the sea anemones of Calliactis (Hormathiidae) from the dorsal surface of the shell. This suggests that this hermit crab species evolved a very similar tactile process for communication between the different Sagartiidae and Hormathiidae lineages of sea anemones.
Holophryxus fusiformis Shiino, 1937, a species of dajid isopod that attaches to the carapace of sakura shrimp, Lucensosergia lucens (Hansen, 1922), is reported from the sea of Taiwan for the first time. This species was first described as infesting Prehensilosergia prehensilis (Bate, 1881) from Kanbara, Shizuoka Prefecture, Japan. The current finding represents the second occurrence of H. fusiformis and identifies a new host. Approximately 1% of the sakura shrimps in Yilan, Taiwan are infected by H. fusiformis. Holophryxus fusiformis has been found offshore from both Yilan, Taiwan and Nagasaki and in Suruga Bay, Japan; thus, the distribution of the parasite possibly follows the Kuroshio Current. When large quantities of parasites occur in the sea of Taiwan, the parasites are likely to flow into the Japanese waters along with the Kuroshio Current, subsequently influencing the production of the Japanese sakura shrimps. The establishment of a monitoring program for infection of the dajid in sakura shrimps between Taiwan and Japan is recommended. This study provides additional information on this species, including a new host, distribution, redescription, infection rate, and morphological variation.
The social behaviors of crabs in the families Dotillidae and Macrophthalmidae inhabiting mangrove swamps in southern Thailand were observed in the field. The cheliped motion and duration of the waving display were determined for four dotillid crabs (Dotillopsis brevitarsis, Ilyoplax delsmani, Ilyoplax gangetica, and Ilyoplax orientalis) and two macrophthalmid crabs (Macrophthalmus erato and Macrophthalmus pacificus), and their motion patterns were compared with those of congeneric species. The sequential events of coupling by a male and a female were observed in D. brevitarsis, I. gangetica, and Ilyoplax obliqua. Fighting events were noted for D. brevitarsis, I. gangetica, I. obliqua, and M. erato. A threat display based on the vertical movement of the chelipeds was observed in the dotillid species Dotilla myctiroides. The chela-quivering display by male I. obliqua was described based on the cheliped motion and the context in which the display occurred.
Anilocra prionuri Williams & Bunkley-Williams, 1986, is reported based on a female specimen collected from the skin below the nostril of a scalpel sawtail, Prionurus scalprum Valenciennes, 1835, in the southern East China Sea off Kuchinoerabu-jima Island, one of the northern Ryukyu Islands, southern Japan. Anilocra prionuri was previously reported only from off the Pacific coast of central Honshu, Japan, but the present collection extends the geographical distribution range of the species from central Honshu southwest to the northern Ryukyu Islands and represents its first record from the East China Sea. The fish had a wound with heavily damaged epidermis at the attachment site of A. prionuri. It was a rare parasite of P. scalprum at the collection site.
A new species of Palaemon is described from Cần Giớ District, Vietnam. This species has previously been reported from Vietnam as a colour morph of Palaemon sewelli (Kemp, 1925), to which it is clearly morphologically very closely related. However, the new species can be separated from P. sewelli through the position of the branchiostegal tooth relative to the branchiostegal groove, the shape of the suborbital lobe, a hirsute carapace and abdomen and the colour pattern of living individuals. The description of this new species brings the number of species of Palaemon known from Vietnam to eleven species.
We studied the life history of Neocaridina davidi (Bouvier, 1904), native to mainland China and Korea, invading the Tomoe River, in the Boso Peninsula of eastern Japan. Sampling was carried out monthly from November 2012 to October 2013. Recruitment occurred from July to September, and the spawning season was from April to September. Large males with a carapace length more than 6.0 mm were rarely collected or absent from July to August, and, similarly, large females with a carapace length more than 7.0 mm were rarely collected or absent from September to October. Evidence from the current study suggests life span for this species is approximately 10–15 months. The life history of N. davidi is very similar to that of a congeneric species, N. denticulata, reported in previous studies.
Over more than one century since 1894, cymothoid isopods attached by the diclidophorid monogenean Choricotyle elongata (Goto, 1894) in the mouth cavity of Japanese sparids have not been exactly identified. This note reports that those isopods are identifiable as Ceratothoa verrucosa (Schioedte & Meinert, 1883) based on material of the species attached by Ch. elongata in the mouth cavity of a red seabream, Pagrus major (Temminck & Schlegel, 1843), from the Seto Inland Sea.
Macrophthalmus pistrosinus Barnes & Davie, 2008, which is endemic to Western Australia, was formerly treated as M. japonicus in East Asia because of their morphological similarity. Examination of the proportional features, such as carapace length relative to carapace width in each sex and propodus length relative to carapace width in mature males, revealed more similarities to M. japonicus compared with M. banzai, which is phylogenetically more closely allied to M. japonicus than to M. pistrosinus.