The gobies Eutaeniichthys gilli and Gymnogobius scrobiculatus were collected from burrows of the mud shrimp Upogebia yokoyai at low tide by digging and using a yabby pump from April 2007 to September 2008 at Susaki Bay, Kochi Prefecture, Japan. A total of 144 E. gilli and 103 G. scrobiculatus were collected. Densities of E. gilli and G. scrobiculatus collected by digging were 1.4 and 1.0 ind. per 0.25 m², respectively. Symbiotic prevalences of E. gilli and G. scrobiculatus in mud shrimp burrows (the percentage of burrows occupied by E. gilli and G. scrobiculatus) collected using the yabby pump were 2.7% and 2.6%, respectively. Juveniles of E. gilli were collected in June; juveniles of G. scrobiculatus were collected in April. Adults of both species were collected year round. The present study clearly shows that E. gilli and G. scrobiculatus both use Upogebia burrows at low tide. In order to conserve these threatened and near-threatened gobies, conservation of this habitat as well as the mud shrimp might be needed.

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The distribution of the fiddler crabs Uca arcuata and U. lactea was investigated. Observations were conducted from March 2008 to October 2009 at 781 sites along the coast and in a lake in Shizuoka Prefecture, Japan. Crabs that could be collected were counted, sexed, and measured. Those that could not be collected were counted and sexed visually. U. arcuata was recorded at three sites: Ohgamo River, Katsumata River and Hoh River. U. lactea were recorded at nine sites: Ohgamo River, Aono River, Katsumata River, Kiku River, Bezaiten River, Ohta River, Bohsoh River, Hoh River and Lake Hamana. The distribution of U. arcuata differed depending on substratum, area, and reed. The distribution of U. lactea differed depending on area, reed, and topographic feature.

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Unidentified free-living isopods (Crustacea, Sphaeromatidae) occurring in an important commercial seaweed bed of Caulerpa lentillifera at Miyako-jima island, southern Japan, are identified herein Paracerceis sculpta (Holmes, 1904) originating from the pacific coast from California to Mexico. This species has been reported as an alien species the world. The impact of P. sculpta on growth of C. lentillifera was observed for a week in laboratory aquaria, by comparison to control aquaria without isopods. No negative impact on the growth on the alga was observed except on already injured C. lentillifera exposing to mature P. sculpta. This shows usually that P. sculpta does not utilize C. lentillifera as its main food but usually feeds on other materials.

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In Lake Akan, Hokkaido, northern Japan, the local population of the native and endangered Japanese crayfish Cambaroides japonicus (De Haan, 1841) is extinct, whereas the signal crayfish Pacifastacus leniusculus (Dana, 1852), an invasive species from North America, has become established and rapidly increased. This study provides information about specimens of C. japonicus preserved by Dr. Saburo Hatta from the lake in 1872. The six specimens (two males and four non-ovigerous females) are valuable evidence of C. japonicus formerly inhabiting Lake Akan. The body sizes of the specimens were 24.4–29.5 mm in carapace length and 55.7–67.4 mm in total length, and the estimated age of the largest specimen was ten years, indicating that Lake Akan of that time provided a suitable habitat. Twenty-two ectosymbiotic crayfish worms (Annelida, Clitellata, Branchiobdellida) were found attached to the specimens. Three branchiobdellidan species were identified: Cirrodrilus cirratus Pierantoni, 1905, C. inukaii (Yamaguchi, 1934) and C. megalodentatus (Yamaguchi, 1934). This is the first record of the latter two species from Lake Akan.

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