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Aplysiida

life science Maturity 11-13 Next article →

Sea hares are large, soft-bodied marine animals belonging to the order Aplysiida. They are opisthobranch gastropod molluscs, which means they are a type of sea snail. Most sea hares are medium-sized, but some can become very large. The name "sea hare" comes from their rounded bodies and two long rhinophores. These rhinophores project upward from their heads and look like the ears of a hare.

Sea hare DSC01663
Sea hare DSC01663

Because they lack the hard head shield found in other similar animals, their name comes from Greek words meaning "without a shield."

Inside their soft bodies, most sea hares have a reduced internal shell. This shell is made of protein rather than hard calcium. Some species have a very thin shell, while others have no shell at all. Every species in this group possesses a radula, which is a scraping tongue, and gizzard plates for processing food. They are also hermaphroditic, meaning they possess both male and female reproductive organs.

Sea hare DSC01663
Sea hare DSC01663

Sea hares have developed several complex biological mechanisms to survive in the ocean. They are herbivores that live on seaweed in shallow waters. To stay hidden, they use camouflage by matching the color of the seaweed they eat. If a red sea hare eats red seaweed, its body becomes red. To defend themselves, they use ink glands to release a thick, smoke-like fluid. This ink can be white, purple, or red depending on the pigments in their food. This toxic ink acts as a deterrent by interfering with a predator's sense of smell.

Sea hare DSC01663
Sea hare DSC01663

They can also secrete a clear slime that physically plugs the olfactory receptors of predators like lobsters.

Movement for a sea hare can look quite unusual. Some species use turbo jet propulsion to move through the water. Others use lateral projections on their feet called parapodia. These parapodia act like jelly-like wings that flutter, allowing them to move similarly to a stingray. While their motion might appear erratic due to a lack of complex brain machinery, they successfully reach destinations like the seabed. They rely on ocean currents, waves, and the calmness of the water to navigate.

Sea hare DSC01663
Sea hare DSC01663

The classification of these animals has changed as scientific understanding grew. Paul Henri Fischer first described the taxon Aplysiida at an unspecified rank. In 1925, Johannes Thiele established Aplysiida as a suborder. In 2005, Bouchet and Rocroi introduced the name Aplysiomorpha in the Taxonomy of the Gastropoda. However, recent literature shows that the older name, Aplysiida, is still frequently used. In 2010, Jörger and other researchers moved the taxon to the group Euopisthobranchia.

Sea hare DSC01663
Sea hare DSC01663

Humans have interacted with sea hares for a very long time. People in Roman times were already aware of their existence. In Hawaii, sea hares are known as kualakai and are cooked in an imu wrapped in ti leaves. In the Philippines, people harvest long egg strands from the wedge sea hare, known as Dolabella auricularia. These strands, called lokot or lukot, are often called "mock noodles" because they look like pancit. They can be eaten raw with vinegar or added to soups like fish tinola. Egg masses from these creatures are also eaten in Samoa, Kiribati, and Fiji.

Sea hare DSC01663
Sea hare DSC01663

Beyond food, sea hares play a massive role in modern science. The species Aplysia californica is famous in the field of neurobiology. This animal has unusually large axons, which are the long fibers that carry nerve signals. Because these axons are so large, scientists can study them easily. Nobel Laureate Eric Kandel used these animals to study the biology of learning and memory. He specifically researched the gill and siphon withdrawal reflex to understand how memory works.

Sea hare DSC01663
Sea hare DSC01663
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