The waters around Izu are seasonal. That is to say...the ambient conditions underwater change all year long, driven by the Kuroshio current, deep-water upwellings, topside conditions and a whole host of other factors.
Part of the ebb and flow of the aquatic seasons is a turnover of fauna. That is to say...different animals show up at different times of the year, so you can dive the same spot over and over again and see different stuff.
One of the popular animals "in season" now is this shrimp known locally as the balsu-ibaramo-ebi (バルスイバラモエビ), or just "balsu" for short. The proper binomial name is Lebbeus balssi.
The shrimp seems to be named after a Heinrich Balss, a German zoologist who specialised in decapods (...and I bet you thought you led an exciting life!).
Anyway, this shrimp normally lives quite deep, down to 120 metres or so. During the first few months of the year, some of these deep-water crustaceans come up to scuba depths and take up residence on pretty anemones...sparking a flurry of flashes from local underwater photographers.
Other than this, it doesn't seem like much is known about these shrimp; a quick Google search didn't turn up a lot.