About Monocentris japonica (Houttuyn, 1782)
This species is commonly called the pineconefish. Its body is yellow, with distinct large scutes outlined in black. Instead of true scales, pineconefish are entirely covered in scutes. Scutes serve the same basic function as regular fish scales, but have a different developmental origin: true fish scales form from the epidermis, while scutes form in the lower vascular dermal layer of the skin, with only the top surface coming from epidermal tissue. Developing within the living dermis, scutes produce a horny outer layer that looks superficially similar to the outer layer of true scales. The term scute comes from the Latin word for shield, and can refer to three main forms: an external shield-like bony plate; a modified, thickened scale that is often keeled or spiny; or a projecting, modified rough, strongly ridged scale. Scutes of these forms are usually associated with the lateral line, form caudal keels on the caudal peduncle, or run along the ventral body profile. Pineconefish have light-producing organs filled with luminescent bacteria on each side of the lower jaw. The exact purpose of these organs is not known, but researchers hypothesize they may help the fish see at night or attract prey. This species can grow to a maximum total length of 17 cm, though most individuals reach only 12 cm in length.
