This is a vintage-style illustration of a vibrant blue sea slug. The slug is elongated and somewhat flattened, with a feathery plume extending from its back. Its body is a striking combination of deep blues, with longitudinal stripes of yellow and orange adding to its visual complexity. There's a small, dark protrusion on its head, possibly a sensory organ. To the left of the slug, there's a smaller, detached illustration of a similar structure, colored in dark blue. The background is a pale yellow, giving the image a delicate, aged appearance. Japanese text is written in black ink to the right and left of the sea slug, and there are some numbers and letters written in the bottom center of the image. The style of the illustration suggests it may be a scientific or natural history drawing from the early 20th century.