helmet crab
A species of crab, Telmessus acutidens, known as the helmet crab. The name is usually written in katakana.
Helmet crabs can be found along the coast of Hokkaido.
Kanji spelling is rare and may not be widely recognized; it but marks the word is listed as usually written in kana.
The name トゲクリガニ literally means 'thorn chestnut crab', likely referring to its spiny carapace and resemblance to a chestnut. The exact derivation is uncertain.