acorn worm
noun
1- a burrowing worm-like marine animal of shallow waters. Its body consists of a proboscis, a collar, and a long trunk with gill slits, and contains a structure resembling a notochord.柱头虫, 栎实虫。
1.1
- Class Enteropneusta, phylum Hemichordata.肠腮纲, 半索动物门。