Photo of the Week: May 30, 2011

Hi Gang!

This week’s POTW is an image of a nudibranch known as the Spanish shawl, Flabellina iodinea. This image was created last summer at Santa Cruz Island, one of California’s eight Channel Islands. No doubt about it, with its bright display of eye-catching colors this rather common, yet quite spectacular little creature is a favorite of many west coast divers.

Nudibranchs have been described as both the most bizarre looking and the most beautiful of all marine animals. Essentially the colors of their bodies are reflections of the sponges, algae and cnidarians that they consume, and there is little question that the underwater world is a cornucopia of colors. Nudibranchs are mollusks that exhibit an evolutionary trend towards the reduction, internalization and complete loss of the external shells found in many members of their phylum, Mollusca

The word nudibranch is derived from the Greek meaning “naked gills.” This is a reference to their shell-less (thus naked) bodies and their uncovered (thus naked) gills that extend from the outside of their bodies. The structure of the gills takes the form of skin ruffles, or fringe-like projections on the back. The gills of the Spanish shawl are the numerous orange colored appendages attached to the animal's back.

The colors, shapes and behavior that characterize nudibranchs are evolutionary adaptations that enable them to survive. There are four suborders of nudibranchs. They are Aeolidacea, Doridacea, Dendronotacea and Arminacea. The general body shape of the members of each suborder is significantly different than that of the species described in the other suborders, and the same is true of their food preferences. The nudibranchs that are the most commonly encountered by divers are described in the suborders Aeolidacea (the aeolids) and Doridacea (the dorids).

The Spanish shawl is an aeolid nudibranch. Aeolid nudibranchs primarily feed upon cnidarians. All nudibranchs feed by using a rasping, tongue-like organ known as a radula that is armed with a ribbon of teeth. There is great variability in the size and shape of the radula as well as the number and shape of the teeth. The variations in design can be directly correlated to the favored prey of each species. The radulas of dorid nudibranchs are broad for scraping sponges from the hard substrate. In contrast, the hook-shaped teeth of aeolid nudibranchs are arranged in several rows.This arrangement helps them pluck the polyps and stinging cells of their cnidarian prey.

The range of the Spanish shawl extends from Vancouver Island, British Columbia to Baja, Mexico. This nudibranch typically occurs on rocks that are in or very close to kelp forests at depths ranging from the intertidal zone to 100 feet. The Spanish shawl feeds primarily on hydroids and other cnidarians, and like many of its close relatives, this nudibranch has the amazing ability to ingest the stinging nematocysts of its cnidarian prey without stimulating the stinging cells and causing them to fire. Once the nudibranch has ingested the nematocysts it is capable of transferring these stinging cells to the tips of its own cerata where the cells are used for the nudibranch’s own defense. Mother Nature truly has some astonishing tricks up her sleeve!

As adults, the Spanish shawl, like all nudibranchs, is a hermaphrodite, meaning that individual animals simultaneously possess functioning male and female reproductive organs. This means that when two animals get together it is truly a case of boy meets girl meets boy meets girl with each animal supplying sperm that fertilizes the eggs of the other. Copulation lasts anywhere from a few minutes to several hours. As many as several thousand eggs are laid in spiral shaped masses of mucus in a single event. The mucus causes the eggs to attach to each other en masse, and “glues” them to the substrate.

The Spanish shawl attains a length of approximately 1.5 inches. This size makes it an ideal subject for a macro lens. I created this week’s POTW with a Nikon 60 mm lens mounted on a Nikon D300 camera

I hope you enjoy this week’s POTW!

See you next week,

Marty