This paper described female guarding avoidance behaviors against precopulatory guarding attempts by males and examines the effect of the number of days until female prenuptial molting on rejection behaviors in the hermit crab Pagurus nigrofascia. We used three types of females in an experiment; (1) ovigerous females (OV–female), (2) females which had not been guarded in the field (NG–female), and (3) females which had been guarded by other males in the field (G–female). We placed a male that had been solitary and a female of either type in a small container, observed the interaction, and compared the female behaviors among the three types of female. The frequencies of retreat and escape from approaching male were highest in OV–females, and lowest in G–females. During male assessment behaviors of females, frequencies of struggle and escape in OV– and G–females were higher than NG–females. 33 of 51 G–females were guarded by males although OV– and NG–females were rarely guarded by males. Many G–females showed rejection behavior during male guarding. However, no significant effect was found in the number of days until the female prenuptial molt on the frequencies of rejection behavior.

This report covers two malformations among coconut crabs Birgus latro observed on islands of Okinawa, Japan: an extra pleopod recorded in Iriomote Island, and an abnormal ambulatory leg found in Hatoma Island. A total of 328 crabs was investigated in Iriomote Island, two individuals that have an abnormal pleopod were found. Normally, female coconut crabs have three pleopods on the left side of the second to the fourth abdominal somites. However, the abnormal individuals had an additional pleopod on the right side of the third abdominal somite. This malformation is the first report within the species. We also found one coconut crab with an abnormal ambulatory leg, having a trifid tip on the dactylus of the left second thoracic appendage, among 156 crabs observed in Hatoma Island. This abnormality is probably caused by the battles within the species or against natural predators.

A total of 42 specimens of aegathoid stage, immature of cymothoid isopod (Crustacea), were investigated on the basis of sample collected by a shore seine from the coast of Katase (Fujisawa, Kanagawa Pref.), inner part of Sagami Bay, Pacific coast of central Japan, on 24 October 2015. There were identified as Nerocila phaiopleura Bleeker, 1857. The morphological characters of them were similar to descriptions and illustrations of that of previous records. The relationship of body length and maximum body width of all specimens of aegathoid stage of N. phaiopleura collected through in our previous studies on Japanese cymothoid isopods including present study are regressed to linear equation with high correlation coefficient. These isopod specimens could be separated to three other groups by distribution frequency of their body lengths: 1st group, 8 specimens, 8.1–11.9 mm BL; 2nd group, 43 specimens, 13.5–18.0 mm BL; 3rd group, 1 specimen, 20.4 mm BL.

A semiterrestrial sesarmid crab Clistocoeloma villosum (A. Milne-Edwards, 1869), known to be widely distributed in the tropical Indo-West Pacific, is newly recorded from the Boso and Izu Peninsula, Honshu Island of Japan. Our specimens extend the geographical range of the species northwards to the temperate Pacific coast of the Japanese main islands. The presence of intraspecific variation in the strength of the notch behind the external orbital tooth on the carapace is recognized. The habitat of the newly collected specimens is also described.

Three stygobiotic atyid shrimps, Halocaridinides trigonophthalma (Fujino & Shokita, 1975), Caridina rubella Fujino & Shokita, 1975 and Caridina sp., are recorded firstly on the basis of specimens collected from an anchialine cave in Yoron-jima Island, central Ryukyus, Japan.

In October 2018, the occurrence of ghost crabs (genus Ocypode) was surveyed at 10 beaches from 5 prefectures located along the Pacific coast of Tohoku and North Kanto. As a result, one temperate species, Ocypode stimpsoni and two tropical/subtropical species, Ocypode ceratophthalmus and Ocypode sinensis were collected in Miyagi, Fukushima and Ibaraki. The two tropical/subtropical species made up 61% of crabs collected. They were all juvenile in size. In the study area, it is estimated that larvae from the tropical/subtropical species are carried by current to the study area from seas to the south.