Although it looks like a nudibranch, it is actually a headshield slug
We are looking at a marine sea slug called a California aglaja. Its scientific name is Navanax inermis. I took this photograph in about fifty feet of water in the Channel Islands National Park. This particular sea slug is only found from Tomales Bay, California south to Jalisco, Mexico. Although the California aglaja looks like a nudibranch, it is actually a headshield slug. Unlike nudibranchs, the California aglaja has an internal shell. It moves along the bottom using a muscular foot, and leaves behind a slime trail.
California aglaja do have eyes, but they also rely on chemoreceptors. Navanax prey upon snails, slugs, and nudibranchs using these chemoreceptors. They do this by following their prey’s slime trail. When the California aglaja senses it is in danger, it releases a yellow chemical into its slime trail. This yellow slime is used to deter predators from following.
These creatures max out at around ten inches long. However, the Navanax in this photo is only about four inches long. It is orange with white spots and lines. There are iridescent blue dots and an orange trim that run the length of its body. There are other color variations of the Navanax that include purple, black, and tan.
These are slow moving creatures, making them good subjects for photography. The challenge with photographing these creatures is proper lighting. In this case, the California aglaja was in a kelp forest, on the bottom crawling through algae. There was very little natural light and strobe photography was a requirement. Fortunately, I had two strobes that illuminated this ornate creature. This was the only California aglaja I saw during my week of diving in the Channel Islands National Park.
The Navanax in this photo is only about four inches long
Did you know?
- The headshield body design works perfectly for digging beneath the sand.
- Catalina Island Conservancy is the largest private land trust in Southern California.
- You can find over 1,000 species of plants and animals within the Channel Islands kelp forests!
- Human remains dating back to 13,000 B.C. were found on Santa Rose Island back in 1959.
- Caves on Santa Cruz Island were the inspiration for some sets on Pirates of the Caribbean.
- There are only four native land mammals found on the Channel Islands. These are the island fox, the harvest mouse, the island deer mouse, and the spotted skunk.
- Gray whales migrate through the Channel Islands every year between December and March.
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