The red swamp crayfish Procambarus clarkii exhibits different sexual morphotypes (reproductive type, form I; non-reproductive type, form II) in both sexes after reaching sexual maturity. This crayfish species shows intra- and inter-sexual dimorphisms of chela size: the chelae are largest in the form I males, followed by the form I females and form II males, and are the smallest in the form II females. Chelipeds of this species are asymmetrical, with one chela being larger than the other. However, little is known about the degree of chela asymmetry in P. clarkii. We examined the chela asymmetry and further elucidated the chela dimorphism. Larger chelae occurred randomly on either the right or left sides. The size differences between larger and smaller chelae were primarily small, and some individuals had smaller regenerating chelipeds. Allometric growth analyses revealed the intra- and inter-sexual dimorphisms of chela size and shape, with males and females of form I morphotypes exhibiting slender and wide chelae, respectively. Male P. clarkii’s slender chela may function as useful weapons, whereas female P. clarkii’s large and wide chelae may also function as tools for constructing and maintaining deeper burrows for breeding.

Examination of Japanese eels Anguilla japonica Temminck & Schlegel, 1846 from Kadota Reservoir, Fukuoka Prefecture, western Japan, revealed the infection by Argulus mongolianus Tokioka, 1939 in the eel buccal cavity. This is the second record of A. mongolianus in Japan and extends its distributional range from Miyagi Prefecture, northern Honshu, southwestward to Fukuoka Prefecture, northern Kyushu. Anguilla japonica represents a new host record. The specimens of both sexes of A. mongolianus are briefly described. This paper suggests that the parasite has been co-introduced with non-native fish hosts into Kadota Reservoir and other inland waters in northern Kyushu.

During 2019, two specimens belonging to a new species of the alpheid shrimp genus Automate De Man, 1888 were collected from two islands in the northern part of the Persian Gulf. The new species is a member of the A. hayashii group which hitherto only comprised two species. However, the new species A. arturi can be separated from them by several morphological features: a shorter rostrum with rounded tip, a shorter stylocerite barely extending beyond the first antennular article, the scaphocerite not reaching to the end of the second antennular article, the third maxilliped coxa with a subtriangular-shaped lateral plate, the ischia of the first pereiopods (chelipeds) dorsally armed with spiniform setae and ventrally with a small tubercle, and the ischia of the walking pereiopods armed with a single ventrolateral spiniform seta.

We conducted two laboratory experiments to evaluate the dietary effects of phytoplankton and zooplankton on the larval survival, duration and growth of the amphidromous atyid shrimp Atyopsis spinipes. In the first experiment, commercially preserved or cultured phytoplankton Tetraselmis sp. and cultured zooplankton rotifers were used to rear larvae. In the second experiment, cultured Tetraselmis and rotifers were used to feed larvae for 17 days after hatching, after which the effect of supplementing their diet with Artemia nauplii was tested. The effects of different culture vessel volumes (8 mL and 40 mL) on larval performance were also assessed. In the first experiment, larvae fed only with preserved Tetraselmis did not survive to the juvenile stage, whereas larvae fed with rotifers showed better survival and development. In the second experiment, most larvae receiving Artemia supplementation survived to the juvenile stage. Larvae cultured in larger containers (40 mL) had significantly higher survival rates than those cultured in smaller containers (8 mL). The present study demonstrates larval culture methodologies for A. spinipes that can promote the development of larvae into the juvenile stage with high survival rates.

A morphological description of the postlarval specimen of the polychelid lobster Stereomastis panglao Ahyong & Chan, 2008, collected from Suruga Bay, on the Pacific coast of Japan, and at depths of 1,305–1,565 m, was given for the first time. Larval characteristics of the previously known polychelid postlarvae and the distribution range of S. panglao were also noted.

Markevitchielinus anchoratus Titar, 1975 is reported based on an adult female from the floor of the buccal cavity of a sea raven Hemitripterus villosus (Pallas, 1814) caught in Onagawa Bay, an inlet of the Northwestern Pacific Ocean, Miyagi Prefecture, northern Japan. The female specimen is briefly described. The female inserted its head with a pair of large, lateral processes and the anterior part of an elongate neck into the tissues of the buccal cavity floor. The present collection of M. anchoratus represents the third occurrence record of the species and extends its distributional range from Kunashiri and Shikotan islands, east of Hokkaido, to Onagawa Bay off Honshu, the largest main island of Japan. The species is specific to the sea raven and may be a subarctic species.

Lithodoid and paguroid crabs are morphologically assigned to the superfamilies Lithodoidea and Paguroidea, respectively. Molecular analyses, however, have revealed closer genetic proximity of the lithodoid crabs to the family Paguridae than to other families of Paguroidea, provoking a long debate. We investigated the length and nucleotide sequence variation of the nuclear ribosomal DNA internal transcribed spacer 1 (ITS1) in lithodoid and paguroid species. Uniquely short ITS1s (215–253 bp) were observed in seven lithodoid species. In contrast, ITS1 length varied considerably in 13 paguroid species belonging to the families Coenobitidae, Diogenidae, and Paguridae. Short-to-long ITS1s (238–1090 bp) were observed in five species of the family Paguridae, and medium to long ITS1s (573–1166 bp) were observed in eight species of the families Coenobitidae and Diogenidae. Considerably different size ITS1s coexisted in individual paguroid species. Nucleotide sequence analysis indicated that the short ITS1s observed in the family Paguridae were descendants of longer ITS1s and were homologous to the short ITS1 of lithodoid species. ITS1 sequences of the families Coenobitidae and Diogenidae shared no nucleotide elements with lithodoid and pagurid species. These molecular signals indicate that the short ITS1 in pagurid lineage was passed on to lithodoid lineage, strongly supporting the “hermit-to-king” crab hypothesis.

We studied the artificial incubation method of red swamp crayfish Procambarus clarkii embryos using cell culture plates. In the first experiment, cleavage stage embryos or egg-nauplius stage embryos were individually cultured at 20°C in the well of cell culture plates with different water volumes per well [12 well (4 ml), 24 well (2 ml), 48 well (1 ml) and 96 well (0.25 ml)]. In the second experiment, egg-nauplius stage embryos were cultured using 12-well plates at 15, 20 and 25°C. Almost all cleavage stage embryos died without hatching. Egg-nauplius stage embryos survived to hatch. In the 96-well plates, the embryo hatched, but all first instar juveniles died soon. In other plates, the mortality of the first instar juveniles tended to increase with decreasing culture water volume; particularly, high mortality was recorded in the 48-well plates. Hatching and moulting rates were high at 15°C and 20°C, but approximately half of the first instar juveniles died at 25°C. We concluded that a 12-well cell culture plate (4 ml per well) is suitable for incubating P. clarkii embryos to hatch and the first instar juveniles to moult to the second instar at 15–20°C.

The male of the rare deep-water porter crab, Dicranodromia danielae Ng & McLay, 2005 (Homolodromiidae) is reported for the first time from Mindanao in the southern Philippines. The species was previously only known from the holotype female from Panglao in central Philippines. The diagnostic male characters are described and variation in various characters documented.

We examined the survival and moulting of starved early-stage-zoeae of atyid shrimps—amphidromous Paratya compressa and landlocked Paratya improvisa—under different salinity and temperature conditions to attain a better understanding of larval adaptation to freshwater environments in landlocked shrimp. The first stage zoeae were cultured without foods under 25 combinations of different salinity (0, 8.5, 17, 25.5, and 34 ppt) and temperature (20, 23, 26, 29, and 32°C) levels. The larvae of P. compressa did not moult, whereas larvae of P. improvisa are lecithotrophy and moulted to the third stage zoeae at 0–25 ppt (and rarely to the fourth stage zoeae at 8.5–25 ppt). However, all larvae lost the ability to moult in open seawater conditions of 34 ppt salinity. The larval survival time was not largely different between these two species, even though the first stage zoeae of P. improvisa were much larger than those of P. compressa. The larvae of P. improvisa advanced the development shorter rather than surviving longer under starvation conditions. These findings suggest that the starvation tolerance, that is, lecithotrophic faster developmental rate of early stage zoeae of landlocked P. improvisa, adapted better to stay in or near parental habitats as well as to limited food conditions in freshwater environments.