For Blue’s current cover (Jan–April 2016 issue), macro-photography in Anilao, Philippines is highlighted. One of the most fascinating attractions there, is the vivid color seen on so many sea slugs (shell-less marine mollusks), especially nudibranchs.
Nudibranch (pronounced “noodie-brank”) comes from Greek, meaning “naked gills,” which literally describes their distinct physical appearance. From their flattened bodies and protruding from their backs, are two conspicuous sets of structures—rhinophores and anal gills.
Since “nudis” as they are informally called, have extremely poor eyesight, they rely mainly on senses of smell and taste. At the front, is a pair of rhinophores; chemosensory antennae that often have numerous folds and lamellae (or ridges) that serve to increase the sensitive surface area. This is how they smell each other or their prey. Toward the rear end, are the feathery anal gills, which encircle the anus. Their function is in respiration or gaseous exchange, hence the need for a large surface area, with the dense, flowerlike appearance.
Nembrotha kubaryana or variable neon slug, is a typically colorful dorid nudibranch that is widespread in the Indo-Pacific. It is a relatively large nudibranch (about 120 mm). It has a conspicuous black body with neon-green spots or lines, and bright-orange rhinophores, as well as an orange margin along the foot. While many other nudibranchs feed on sponges, Nembrotha kubaryana feeds only on certain tunicates, also called sea squirts, such as Clavellina moluccensis and Sigillina signifera (seen on the right, in the photo).