Ronan and Needham cite another context in Wang's biography that says his boat had shuanglong 雙龍 "two dragons" on the side, which they construe as a "literary emendation" for shuanglun 雙輪 "two wheels" describing an early paddleboat.
[1] Dilong or dilongzi 地龍子 "earth dragon child" is an elegant name for the "earthworm; worm", which is usually called qiuyin 蚯蚓.
Dilong first means "earthworm" in the Qixiu Leigao 七修類稿 written by the Ming dynasty scholar Lang Ying 郎瑛 (1487–1566 CE).
The 1578 Bencao Gangmu pharmacological entry for qiuyin 蚯蚓 "earthworm" lists alternate names of dilong and tulong 土龍 (see above).
Li Shizhen notes these names derive from the myth that earthworms (like dragons) can create yinqing 陰晴 "cloudy and clear; unsettled weather".