noun
protostome
Zoological term for animals in which the mouth develops from the first embryonic opening (blastopore). Contrasts with 新口動物 (deuterostome).
See also: 新口動物
節足動物や軟体動物は旧口動物に分類される。
Arthropods and mollusks are classified as protostomes.
新口動物 (deuterostome) is the contrasting group where the anus forms first from the blastopore; includes chordates and echinoderms.
Compound of 旧 (former, old) + 口 (mouth) + 動物 (animal), calque of the taxonomic term 'protostome' (from Greek 'proto-' first + 'stoma' mouth).