The pennellid copepod Lernaeenicus ramosus Kirtisinghe, 1956 is a marine fish parasite in the Indo-West Pacific region. Serranid fishes (Perciformes) are the major hosts of L. ramosus, and as its non-serranid host, a single blenniid fish (Blenniiformes) is known from Australia. A metamorphosed ovigerous female of L. ramosus was collected from a grub fish, Parapercis sexfasciata (Temminck & Schlegel, 1843) (Perciformes: Pinguipedidae), in coastal waters of Suruga Bay, an inlet of the western North Pacific Ocean, Shizuoka Prefecture, central Japan. This represents a new and the second non-serranid host records for L. ramosus and it is also the first record from a pinguipedid fish. The female is briefly described. A pennellid copepod previously reported as “Pennella sp.” from the same host species from the Iyo-Nada Sea, part of the Seto Inland Sea, western Japan, is considered to be L. ramosus.

To characterize the reproductive behavior of the land crab Cardisoma carnifex, their nighttime activities on the ground surface around their burrows were monitored using infrared-triggered cameras on the Iriomote-jima Island, Japan. Matings of three pairs were recorded near the entrance of the female’s burrow. The results showed that the species shares a common mating pattern of gecarcinids: hard-female mating and short courtship. The males did not exhibit courtship behavior, except for drumming on the surface sediment. The duration of copulation was longer (29, 30, and 49 min) than that in the reference data (1–10 min). After mating, males guarded their mate’s burrow and plugged the opening from the outside. By contrast, the resident crabs sometimes plug their burrows from the inside. Burrow plugging by C. carnifex males is similar to post-copulatory guarding by males of brachyurans, to prevent multiple matings by females. The non-invasive cameras revealed novel features of mating behavior of C. carnifex such as longer copulation, drumming behavior, and burrow plugging by males.

Temperature is one of the most important environmental factors affecting the geographic distribution of ectotherms. We evaluated the low- and high-temperature tolerance limits of juveniles of two mud crab species, Scylla paramamosain and Scylla serrata, which are distributed in temperate and subtropical/tropical areas in Japan, respectively. Experiments were performed twice for S. paramamosain and four times for S. serrata using laboratory-raised juveniles. The juveniles were stocked in small containers, and the temperature was reduced or raised by 1°C every 24 h. The critical low or high temperatures (CLT or CHT) were estimated as the temperatures at which 50% of test juveniles ceased walking behaviour or died. The estimated CLT values for walking and survival were summarised as 8.4±0.7°C (mean±standard deviation) and 6.4±0.9°C in S. paramamosain and 9.6±0.6°C and 7.4±0.4°C in S. serrata, respectively. The CHT for walking could not be estimated, as almost all surviving juveniles exhibited walking behaviour, whereas the estimated CHT values for survival were summarised as 39.0±0.4°C in S. paramamosain and 39.1±0.6°C in S. serrata. Thus, interspecific variation in low-temperature adaptation was evident, and S. paramamosain are adapted to the lower-temperature environment.

We developed short tandem repeat markers for Palaemon septemtrionalis and tested their utility for analysing population genetics. Six markers were selected for their genotyping ability and suitability for population genetic analyses, and the genetic differences between two populations from different rivers were evaluated using these markers. The pairwise fixation index value between the two populations was 0.01756 (P=0.036), weak but statistically significant, suggesting a low level of genetic differentiation between the two populations. Although the results were not fully conclusive, we are confident these markers can be utilised for investigating the genetic population structure of P. septemtrionalis.

An un-named Eosamon Yeo & Ng, 2007 (Brachyura: Potamidae) specimen was discovered in the reference collection of the Natural History Museum, London. Further investigation of this freshwater crab proved it to be of interest because it is the first record of the genus from Cambodia and the male to be a hitherto undescribed Eosamon species. The new species, E. cambodiense n. sp., is here described, illustrated and compared with other congeners: E. brousmichei (Rathbun, 1904), E. paludosum (Rathbun, 1904), E. hafniensis (Bott, 1966), E. yotdomense (Naiyanetr, 1984), E. boonyaratae (Naiyanetr, 1987), E. phuphanense Naiyanetr, 1992, and E. nominathuis Yeo, 2010.

The red swamp crayfish Procambarus clarkii is an invasive alien species worldwide but it was commercially exploited. Laboratory studies have been conducted to examine the reproductive aspects of this species, pairing males and females for 1–5 days, as a basis for developing the control measures for invasive populations and improving aquaculture technologies. However, the effect of pairing periods on the mating and spawning success is largely unknown, and the present study therefore aimed to elucidate the effect of different periods (one, five and 10 days) in this species. The pairs were videorecorded for each entire pairing period, and the length of pairing did not significantly affect copulation or spawning. Copulation was prolific on the first day and its intensity was similar among the test groups, indicating that a one-day pairing period is sufficient for successful mating in P. clarkii under laboratory conditions.

Two copepod parasites, Salmincola edwardsii (Olsson, 1869) and S. markewitschi Shedko & Shedko, 2002, were collected from salmonids in eastern Hokkaido, Japan: these copepods were taken from whitespotted char, Salvelinus leucomaenis (Pallas, 1814), and brook trout, S. fontinalis (Mitchill, 1814) in the Nishibetsu River, and Salmincola edwardsii from southern Asian Dolly Varden, Salvelinus malma krascheninnikova Taranetz, 1933, in the Ichani River. Both whitespotted char and brook trout are new Japanese hosts for Salmincola edwardsii, and the two rivers represent new locality records for S. edwardsii and S. markewitschi. The Nishibetsu River is regarded as a new southernmost distribution limit of S. edwardsii in Asia and is also recorded as the first locality of S. markewitschi infecting wild salmonids in Hokkaido. The morphology of S. edwardsii and S. markewitschi is reported based on adult female specimens collected from the salmonids.

Three ANDEEP expeditions yielded five Petalophthalmidae species of the genus Hansenomysis in 1030–3683 m depth on the floor of the Southern Ocean. Hansenomysis pseudophthalma sp. nov. is distinguished by features of the carapace, antenna, and telson. A fully adult specimen is first described for H. chini. A world key to the species of Hansenomysis is given. Unlike certain previous interpretations, the dactylus of thoracic endopods 3–5 has a single claw opposing a pair of modified paradactylary setae. Propodus and dactylus 6–8 are separate, not fused, and bear a smooth nail in all Hansenomysis species examined. Juveniles were available in three species and start with two bulb-shaped eye rudiments inside a common cuticular sheath forming a transverse bar. The bulbs then flatten, although a bulb-like formation persists until the adult stage; no eyeplate is formed. The carapace bears hepatic bulges resembling eyes in adult H. pseudophthalma and H. chini. The distal hyaline coat of bulges possibly represents lenses in H. pseudophthalma and H. sorbei. The modification of bulges is indicative of photophores, described for the first time here in the family Petalophthalmidae. The exclusive occurrence of mature photophores in adults points to possible role in reproductive behavior.

Here, the aegathoid stage of Nerocila japonica Schioedte & Meinert, 1881 is described based on a specimen collected from the Seto Inland Sea, Japan, and its identity is confirmed by both morphology and molecular barcoding. Cytochrome c oxidase subunit I and 16S rRNA sequences of the collected individual shared ≥99% similarity with the previous DNA records of N. japonica. In terms of morphology, the aegathoid stage of the specimen examined in the present study differed from that of N. phaiopleura Bleeker, 1857 by intermediate size of the eyes and setation on pereopods. This is the first record of N. japonica infesting the red seabream Pagrus major (Temminck & Schlegel, 1843).

Freshwater crabs of the genus Geothelphusa Stimpson, 1858 were collected from a river on Oshima Peninsula, Hokkaido, northern Japan. They were identified as Geothelphusa dehaani (White, 1847) based mainly on structures of the carapace and the male first gonopods. In the study river, G. dehaani occurred in the upper reach of the main stream and in several tributaries but was not found in the middle reach. The presence of brooding females and many immature individuals suggests that the G. dehaani population is established in the river.

An ovigerous female of Argulus matuii Sikama, 1938 was collected from the body surface of a yellowfin seabream Acanthopagrus latus (Houttuyn, 1782) in a cove facing the Bungo Channel off Ehime Prefecture, western Japan. This represents a new host record for A. matuii, and the female collected is herein described. This female, which was fixed and preserved in 70% ethanol, showed a prominent body coloration, i.e., six streaks of yellow fringed with dark brown pigments, on the dorsal surface of the carapace even on 279th day (ca. nine months) after fixation, but the yellow streaks disappeared and the dark brown fringes were fading on 1675th day (ca. four years and seven months) after fixation. Thus, this paper reports on the usefulness of those yellow streaks in identification of A. matuii for a certain period after fixation but also emphasizes the importance of a detailed examination of morphological features in identification of long-term ethanol-preserved argulid specimens. The species is distinguished from the five marine congeners from Japan by its possession of numerous supporting rods in the marginal membranes of the first maxillae.

This is the first record of the burrows of the Japanese mitten crab Eriocheir japonica. Morphologies of the burrows found in the clay sediment used by this crab were recorded by excavating them in a small freshwater river in Japan. Only E. japonica was found inside 2 of the 10 burrows examined (15 crabs and one crab, respectively), and the other 8 were empty. Crabs of various sizes (6.1–47.0 mm in carapace width) were collected from inside the occupied burrows. Burrow morphology ranged from single tunnels to complex burrows with multiple openings and tunnels. Openings (2–10 cm in diameter) were mostly located underwater. The single tunnels were 14–65 cm long. Considering the different digging habits of other burrowing animals found in this area, it can be concluded that E. japonica constructed these burrows. Burrows resembled those of the Chinese mitten crab E. sinensis, but were different in their location (freshwater vs. tidal), sediment type (clay vs. sand and silt), opening placement (mainly underwater vs. intertidal) and occupation rate (low vs. high). The low occupation rate suggests that E. japonica do not always rest in their burrows and rather prefer to hide beneath the riverbed’s large rocks. These results reflect the adaptation of E. japonica to the unstable environment of Japanese rivers.

The pennellid copepod Lernaeenicus ramosus Kirtisinghe, 1956 is a parasite of perciform and blenniiform fishes in the Indo-West Pacific region. A metamorphosed female of the species was collected from a perchlet, Chelidoperca hirundinacea (Valenciennes, 1831), caught on the neritic continental shelf of Suruga Bay, central Japan. The copepod is almost exclusively a parasite of groupers (Epinephelus spp.) in the serranid subfamily Epinephelinae, but C. hirundinacea belongs to a different serranid subfamily Serraninae. The present collection of L. ramosus represents its first record from a serranine fish in the Indo-West Pacific region.

This study investigated size at sexual maturity of the male sergestid shrimp Lucensosergia lucens (“Sakura-ebi” in Japanese). The shrimps were captured in the inner part of Suruga Bay, Japan in August 2013 using experimental trawls. Carapace length (CL), body length (BL), development of petasma, and presence of spermatophores in the terminal ampoule were documented. Probabilities of maturity as a function of CL were modeled using general linear models with a binomial and logit link function and predicted the CL at which 50% of individuals were mature (CL₅₀). Morphologically mature males had a petasma connected with the pars astringens, and the basal part of the pars media was developed. In physiologically mature males, chambers in terminal ampoules were filled with spermatophores, including spermatozoa and appendages. CL₅₀ (mm) was estimated to be 8.87 (=27.86 mm BL) and 7.84 (=24.65 mm BL) based on the morphological and physiological criteria, respectively. It is believed that most of the age-0 males attain sexual maturity within the first year and mature males are exploited in the autumn fishing season (October–December).