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The Haikouichthys is a primitive fishlike animal from the Lower Cambrian Maotianshan shales of China. Cladistic analysis indicates that the animal is probably a primitive agnathid fish most closely related to the Lampreys. It is about 2.5cm long and is narrower than the Myllokunmingia, which comes from the same beds. The holotype was found in the Yuansshan member of the Qiongzhusi Formation in the 'Eoredlichia' Zone near Haikou at Ercaicun, Kunming City, Yunnan, China. The animal has a distinct head and trunk. The head has at least six and perhaps nine probable gills. There are a number of segments (myomeres) with rear directed Vs in the trunk. There is probably a notochord although only a short segment is preserved in the single known specimen. The tail end of the animal is apparently missing. There is a prominent dorsal fin with fin radials. The fin radials seem to angle "forward" toward the end thought on the basis of internal structures to be the head. This happens with a few modern fish but is an uncommon arrangement. There is a ventral fin fold. There are 13 circular structures along the bottom that may be gonads, slime organs, or something else entirely. There is no sign of mineralization of the skeletal elements.

There is one species Haikouichthys ercaicunensis Luo, Hu & Shu

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