The internet has come through - apparently they are ascidians - specifically Halocynthia roretzi. Ascidians are sea squirts — hermaphrodite marine invertebrates that live in shallow ocean waters, and which are thought to exhibit characteristics of the evolutionary ancestors of chordates and vertebrates. (Thanks goes to Karen Sanamyan at ascidiacea.com/

Camera:	Nikon F100
Date:	Thursday, October 31st, 2002
Film:	Fuji Velvia 50 (slide)
Lens:	28-70mm f/2.8 ED-IF AF-S Zoom-Nikkor
Photographer:	John Harvey
Scientific Name:	species related to Halocynthia roretzi (Maboya in Japanese)
Tag:	fish, market, Tokyo, Japan, seafood
Larger Image:	1333 x 2000
Raw Image:	2480 x 3720