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Dirona albolineata (photographed by http://www.naturediver.com)

It has been far too long since Ferrebeekeeper featured any miraculous molluscs! Therefore, today we are going to return to a timeless favorite topic and feature a predatory nudibranch sea slug that looks like a rogue lace jabot. This is Dirona albolineata (a.k.a the alabaster nudibranch) a predatory slug which lives in the cold rich waters of the Eastern Pacific Ocean from Alaska down to San Diego. The translucent slug grows to a length of 18 centimeters (7 inches) and hunts tiny invertebrates of the coastal zone such as bryozoans, little arthropods, hydroids, ascidians, and, um, lesser mollusks.

The beautiful little milky slug is generally whitish but specimens have been found which were pale pink, peach, or lavender. As a simultaneous hermaphrodite, the slug has an unusual mating ritual where he/she/it meets another alabaster mollusk and both parties copulate both as male and female (they each fire a reproductive dart into the other’s body and both parties leave the union fertilized). The leaf like appendages upon the slug’s body are known as ceratae. These scales are protective and serve as armor or as a diversion (under extreme duress, the snail can jettison the twitching scales in hopes of diverting a predator), however they also greatly increase the snail’s body area and help respiration/gas exchange. Or to be more plain, the ceratae are like a cross between gills and plate mail for this translucent hermaphroditic mollusc.

leaf-sheep-sea-slug-costasiella-kuroshimae-3.jpg

Behold! This is Costasiella kuroshimae, AKA the ‘leaf sheep.”  It isn’t a sheep at all, of course, it’s really a sea slug from the Sarcoglossan clade.  These marine gastropods can be found in the Indo-Pacific off the shores of Indonesia, Japan, and the Philippines. Costasiella kuroshimae scrapes up marine algae and digests it, but the animal then sequesters the living chloroplasts from inside the algae cells into its own tissues.  Chloroplasts, like many other cell plastids, seem to have been independent life forms in the ancient single-cellular dawn of life, but they have since been co-opted and assimilated into the living cells of plants and blue-green algae.  The leaf sheep pulls the same trick–a process known to biologists as kleptoplasty (which is common in protists, but unknown in multicellular creatures except for these slugs).  This is why the leaf sheep glows a glorious living green color.  The slug can keep the chloroplasts alive within its own tissues for extended periods and metabolize the photosynthetic products for its own uses.

Costasiella_cf_kuroshimae.png

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