Chirolophis japonicus is known from as far north as Peter the Great Bay and Hokkaido south to southern Korea and Tsintao, northern China, and grows over 50cm TL.In Mutsu Bay, they inhabit rocky shallow coastal waters.They show strong cryptic habits and are almost impossible to ob-serve by SCUBA diving observations.They mainly feed on the sea cucumber Sticopus japonicus and the gastropod Neptunea arthritica by snapping them off with the aid of the sharp continuous cutting edge of both jaws.The digestive tract is very long, being 0.7-1.5 times of its total length.The stomach is provided with 5-7 well-developed pyloric caeca.They attain sexual maturity at over ca.25cm TL in males and 30cm TL in females.In Mutsu Bay, the spawning period extends from late November to December, when the water temperature falls below 10°C.The ovary is of the two-lobed type and deeply separated basally.Secondary sexual characters are recognized in the elevation of the nape backward to the origin of dorsal fin, the elongation of the anterior four dorsal spines and the darkening of body coloration in males.
In spawning experiments in the aquarium, female parents guarded egg masses in all two cases.Eggs were attached to each other but did not adhere to other substrata.Spawnings took place in a tube-like hollow of a concrete block.Eggs were pressed on the wall of the hollow.Female parents guarded eggs in the hollow, but did not coil their body on the eggs.Egg membranes are spherical, light milky white, and measure 2.50±0.06mm (n=30) in diameter.They do not form any adhesive process, and are attached to each other at adhesive points or small faces.Yolk is light yellow, containing a large light yellow oil globule but without white cloudy material.Time for the hatching is estimated to be about two months under water temperatures of 3.5-10°C.Newly hatched prolarvae are 12.2-13.5mm TL, and are very slender and compressed.The distance from the tip of the snout to the anal opening is 35 % of TL.Myomere counts are 62 64 (15-16+46-47).
Rearing experiments of larvae show that yolk is consumed in two weeks after hatching.Larvae reached 16.5 19.3mm TL two weeks after hatching, and 20.4-24.2mm TL in 39 days, attaining the early juvenile stage.In Mutsu Bay, planktonic juveniles of 29.2 34.0mm TL were collected with fish lamps at Moura in March and April.Early benthonic juveniles, 29.2-34.0mm TL, were collected from baskets for scallop culture in April and May.
The present species is characterized by scaled cheeks, but in smaller specimens less than ca.20cm TL scales cannot be detected by naked eyes, because of their small size and the fact that they are imbedded in the skin.Examination of the development of dentition in cleared and stained.specimens shows that primary small teeth develop in the planktonic stage, arranged in two alternating rows.They are replaced by secondary developed incisors at ca.10cm TL.These incisors form a continuous cutting edge composed of two accurately alternating rows.
On the basis of the development of squamation on the cheeks and coloration of C.japonicus, Bryostemma otohime Jordan et Snyder, 1902, which was described from the 82mm TL holotype collected from Hakodate, southern Hokkaido, is considered to be the young form of C.japonicus.Azuma emmnion Jordan et Snyder, 1902 is considered to be a male of C.japonicus.