The California Sea Hare

There's dozens of species of sea hares, sluglike marine animals found around the world. The California Sea Hare is a brown or reddish spotted species found all along the coast of California down into Baja.

• Names: California Sea Hare, California Sea Slug, Aplysia californica
  
  
• Size: Varies. A foot (30 cm) is typical for full-sized adults when stretched out. Those pictured here were closer to 5 to 8 inches.
  
  
• Weight: According to this Aplysia Californica size chart, foot-long California Sea Hares are typically around 100 grams; the ones I saw were closer to 20 grams.
  
  
• Diet: Unlike some sea hare species, Califonia Sea Hares are vegetarians! They eat Coralline Algae (brown or red algae), soft frilly stuff found in rocky tidepools during low tides. In other words, they fill the same role as aquarium fish used to clean up algae and keep tanks scum-free.
  
  
• Color: Dark brown to reddish-brown, sometimes with a yellowish or pink cast, depending on the color of their food. Adults are mottled and well-camouflaged. Young juveniles are pinkish-orange and don't show mottling.
  
  
• Anatomy: They're gastropods, from the Greek for "stomach-foot," which describes most of their body. They have a small bit of leathery shell inside, protecting some of their organs. They have a sucker-like mouth and a pair of small black eyes on the top of their head. But they do most of their tasting/smelling/sensing using their "rabbit ears," the pair of short tentacles behind their eyes that gives sea hares their common name. These tentacles are called "rhinophores." Sea hares use them not only to detect food but also enemies, their surroundings, and other sea hares. (They also have two more tentacle-like "toes" at the leading edge of their foot, on either side of the mouth, which can look like rabbit ears from above).
  
  
• Lifespan: Usually a year. Here's a diagram with videos showing you the life cycle of sea hares at different ages.
  
  
• Reproduction: California Sea Hares are hermaphrodites, meaning they have both male and female parts -- in fact they alternate being male or female on different days! Eggs hatch after 8 or 9 days into microscopic larva, which gradually grow into full-sized slugs, dining on other kinds of red algae as juveniles.
  
  
• Habitat: Shallow tidepools with red algae in the "Low Tide Zone," only exposed during the lowest tides each month. In Orange County, I've noticed bright purple sea urchins during these especially low tides, so if you can see them, start hunting for sea hares in shallow pools with pinkish red algae. You'll also see blue mussels, hermit crabs, and sea anemones in the area (although these also live higher up, so they are not reliable indicators of sea slug habitat).
  
  
• Fun Facts: This kind of animal has been called "sea hare" since antiquity, since some European species are markedly rabbit-shaped. The purple ink of one species was used by ancient scholars in Jerusalem to write sacred texts-- maybe even the Old Testament!