The

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

Anaspidea, commonly known as sea hares ('' Aplysia'' species and related genera), are medium-sized to very large

opisthobranch Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopi ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

s with a soft internal shell made of protein. These are

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...

s in the superfamilies Aplysioidea and Akeroidea. The

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

"sea hare" is a direct translation from la, lepus marinus, as the animal's existence was known in Roman times. The name derives from their rounded shape and from the two long rhinophores that project upward from their heads and that somewhat resemble the ears of a

hare Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The g ...

Taxonomy

Many older textbooks and websites refer to this suborder as "Anaspidea". The original author

Paul Henri Fischer Paul Henri Fischer (also spelled Paul-Henri Fischer), (7 July 1835 Paris – 29 November 1893) was a French physician, zoologist and paleontologist. He is generally known as Paul Fischer. Biography He studied science and medicine, securing do ...

described the taxon Anaspidea at unspecified rank above family. In 1925

Johannes Thiele Johannes Thiele may refer to: *Johannes Thiele (zoologist) *Johannes Thiele (chemist) Friedrich Karl Johannes Thiele (May 13, 1865 – April 17, 1918) was a German chemist and a prominent professor at several universities, including those in ...

established the taxon Anaspidea as a suborder.

2005 taxonomy

Since the taxon Anaspidea was not based on an existing genus, this name is no longer available according to the rules of the

ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...

. Anaspidea has been replaced in the new

Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) The taxonomy of the Gastropoda as it was revised in 2005 by Philippe Bouchet and Jean-Pierre Rocroi is a system for the scientific classification of gastropod mollusks. (Gastropods are a taxonomic class of animals which consists of snails and s ...

by the

Aplysiomorpha. The scientific name for the order in which they used to be classified, the Anaspidea, is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

for "without a shield" and refers to the lack of the characteristic head shield found in the cephalaspidean opisthobranchs. Many anaspideans have only a thin, internal and much-reduced shell with a small

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

cavity; some have no shell at all. All species have a

radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food ...

and gizzard plates.

2010 taxonomy

Jörger et al. (2010) have moved this taxon (named as Anaspidea) to Euopisthobranchia.

2017 taxonomy

The name "Aplysiomorpha" was preferred by Bouchet and Rocroi (2005) over "Anaspidea Fischer", 1883, but the authors now agree that there is a consistent usage for Anaspidea in the recent literature and that the older name must be preferred.

Description

Sea hares are mostly rather large, bulky creatures when adults. Juveniles are mainly unobserved on the shoreline. The biggest species, ''

Aplysia vaccaria ''Aplysia vaccaria'', also known as the black sea hare and California black sea hare, is a species of extremely large sea slug, a marine, opisthobranch, gastropod mollusk in the family Aplysiidae.Bouchet, P. (2011). Aplysia vaccaria Winkler, 195 ...

'', can reach a length of and a weight of and is arguably the largest gastropod species. Sea hares have soft bodies with an internal shell, and like all opisthobranch molluscs, they are

hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...

. Unlike many other gastropods, they are more or less bilaterally symmetrical in their external appearance. The foot has lateral projections, or "

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

Life habits

Sea hares are herbivorous, and are typically found on

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and '' Chlorophyta'' (green) macroalgae. Seaweed species such as ...

in shallow water. Some young sea hares seemingly are capable of burrowing in soft sediment, leaving only their rhinophores and mantle opening showing. Sea hares have an extremely good sense of smell. They can follow even the faintest scent using their rhinophores, which are extremely sensitive chemoreceptors. Their color corresponds with the color of the seaweed they eat: red sea hares have been feeding on red seaweed. This

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

s them from predators. When disturbed, a sea hare can release ink from its ink glands, providing a fluid, smoke-like toxic screen, adversely affecting its predators' olfactory senses while acting as a powerful deterrent. The toxic ink may be white, purple, or red, depending on the pigments in their seaweed food source and lightens in color as it spreads, diluted by seawater. Their skin contains a similar toxin that renders sea hares largely inedible to many predators. In addition to the colored ink, sea hares can secrete a clear slime akin to that released defensively by

hagfish Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, ...

which physically plugs the olfactory receptors of predators like lobsters. Some sea hares can employ

jet propulsion Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet. Reaction engines operatin ...

as a locomotion and others move like stingrays but with greater fluttering fluidity in their jelly-like "wings". In the moving marine environment and without the sophisticated cognitive machinery of the

cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s, their motion appears to be somewhat erratic, but they do reach their goals, such as the seabed, according to the wave-action, currents, or calmness of their area.

Human use

Sea hares are consumed in several parts of the world. An example may be "酱爆海兔" ('' jiàng bào hǎi tù''), lit. "sauce-fried sea hare", a Chinese dish featuring sea hare and occasionally squid quickly fried in a sauce. In

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

, sea hares, or ''kualakai'', are typically cooked in an imu wrapped in ti leaves. ''

Aplysia californica The California sea hare (''Aplysia californica'') is a species of sea slug in the sea hare family, Aplysiidae.Rosenberg, G.; Bouchet, P. (2011). Aplysia californica J. G. Cooper, 1863. Accessed through: World Register of Marine Species at http:/ ...

'' is a species of sea hare noteworthy for its use in studies of the

neurobiology Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developme ...

learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of lea ...

and

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remember ...

, due to its unusually large

axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...

s. It is especially associated with the work of

Nobel Laureate The Nobel Prizes ( sv, Nobelpriset, no, Nobelprisen) are awarded annually by the Royal Swedish Academy of Sciences, the Swedish Academy, the Karolinska Institutet, and the Norwegian Nobel Committee to individuals and organizations who make o ...

Eric Kandel Eric Richard Kandel (; born Erich Richard Kandel, November 7, 1929) is an Austrian-born American medical doctor who specialized in psychiatry, a neuroscientist and a professor of biochemistry and biophysics at the College of Physicians and Surge ...

. Research surrounding the aplysia gill and siphon withdrawal reflex may be of particular interest with respect to this.

Reef aquaria

Sea hares are often used as a method of eradicating nuisance algae and cyanobacteria (" red slime algae") in reef aquaria. The hares usually do an excellent job, but when they have eaten all of the algae and cyanobacteria, they often shrink from starvation and eventually starve to death. Many reef-keeping clubs have started programs where groups of hobbyists "share" a single sea hare among a large group.

Gallery

File:Sea hare, Aplysia dactylomela, 12 04 2009 2-00pm.jpg, Sea hare ''

Aplysia dactylomela ''Aplysia dactylomela'', the spotted sea hare, is a species of large sea slug, a marine opisthobranch gastropod in the family Aplysiidae, the sea hares. Distribution and taxonomy As traditionally defined, this species of sea hare was cosmopolit ...

'' File:Sea hare, Aplysia dactylomela, 12 04 2009 2-02pm.jpg, ''

'' showing mouth

References

External links

California Brown Sea Hare
—

Cabrillo Marine Aquarium Cabrillo Marine Aquarium is an aquarium in Los Angeles at San Pedro, California. The aquarium interprets both the physical processes of oceanography and marine biology of Southern California by use of displays and educational programs for the pu ...

Aplysiidae (sea slugs) of Hawaii
{{Authority control Taxa named by Paul Henri Fischer Euopisthobranchia