A seashell galore!? -- Unveiling the secrets of the Kumasaka clam
Date posted: 2026.04.10
Update date: 2026.04.10
深海というと、みなさんはどんな生きものを思い浮かべるでしょうか？
少し前のことですが、葛西臨海水族園では今年（2026年）の2月に、深海イベント「Deep of Wonder──不思議な深海の生き物たち」を開催しました。
期間中、情報資料室のカウンターでは、深海に生息する生きものの標本を展示し、みなさんに観察していただきました。そのなかでも、「おもしろい」「不思議」など、多くの方に興味をもっていただいた貝についてご紹介します。
一見すると貝殻が落ちているようにしか見えませんが、こちらは「クマサカガイ」という巻貝のなかまです。
The name "Kumasaka" is said to have been derived from Kumasaka Chōhan, a notorious thief from the Heian period who was said to have worn seven tools, due to his appearance, which was adorned with many seashells and other materials.
The mussel clam uses secretions from its soft body to attach other shells or pebbles to its own shell.
There are several theories as to why the shells are attached in this way: some suggest it's to reinforce the thin shell of the clam, others that it's to conceal itself, and still others that since bivalves attach their shells with the inside facing upwards, it might make them appear dead, thus making them less likely to be targeted by predators. However, the actual reason remains unknown. Upon closer inspection of the specimens, one can see that the way the shells are attached is quite artistic.
Looking at it from the underside, you can clearly see where the shell of the scallop ends and the rest begins. Also, since it is a type of gastropod, it has an aperture (a hole through which the soft body enters and exits).
There are specimens in Information Desk at Tokyo Sea Life Park, so please feel free to ask a staff member if you would like to see them.
In the "Deep Sea Creatures 1" tank, live specimens are also on display.
Take a close look at the sand in the aquarium. You should be able to see seashells clinging to it. Be sure to look for the mussel clams in your aquarium!
[Sophie Kato, Education and Outreach Tokyo Sea Life Park]