Aplysia

''Aplysia'' () is a genus of medium-sized to extremely large sea slugs, specifically sea hares, which are one clade of large sea slugs, marine gastropod mollusks.

These benthic herbivorous creatures can become rather large compared with most other mollusks. They graze in tidal and subtidal zones of tropical waters, mostly in the Indo-Pacific Ocean (23 species); but they can also be found in the Atlantic Ocean (12 species), with a few species occurring in the Mediterranean.

''Aplysia'' species, when threatened, frequently release clouds of ink, it is believed in order to blind the attacker (though they are in fact considered edible by relatively few species). Following the lead of Eric R. Kandel, the genus has been studied as a model organism by neurobiologists, because its gill and siphon withdrawal reflex, as studied in ''Aplysia californica'', is mediated by electrical synapses, which allow several neurons to fire synchronously. This quick neural response is necessary for a speedy reaction to danger by the animal. Aplysia has only about 20,000 neurons, making it a favorite subject for investigation by neuroscientists. Also, the 'tongue' on the underside is controlled by only two neurons, which allowed complete mapping of the innervation network to be carried out.

Long-term memory

In neurons that mediate several forms of long-term memory in ''Aplysia'', the DNA repair enzyme poly ADP ribose polymerase 1 (PARP-1) is activated. In virtually all eukaryotic cells tested, the addition of polyADP-ribosyl groups to proteins (poly ADP-ribosylation) occurs as a response to DNA damage. Thus the finding of activation of PARP-1 during learning and its requirement for long-term memory was surprising. Cohen-Aromon et al. suggested that fast and transient decondensation of chromatin structure by polyADP-ribosylation enables the transcription needed to form long-term memory without strand-breaks in DNA. Subsequent to these findings in ''Aplysia'', further research was done with mice and it was found that polyADP-ribosylation is also required for long-term memory formation in mammals.

In 2018, scientists from the University of California, Los Angeles, have shown that the behavioral modifications characteristic of a form of nonassociative long-term memory in ''Aplysia'' can be transferred by RNA.

Operant conditioning

Operant conditioning is considered a form of associative learning. Because operant conditioning involves intricate interaction between an action and a stimulus (in this case food) it is closely associated with the acquisition of compulsive behavior. The ''Aplysia'' species serve as an ideal model system for the physical studying of food-reward learning, due to "the neuronal components of parts of its ganglionic nervous system that are responsible for the generation of feeding movements." As a result, ''Aplysia'' has been used in associative learning studies to derive certain aspects of feeding and operant conditioning in the context of compulsive behavior.

In ''Aplysia'', the primary reflex studied by scientists while studying operant conditioning is the gill and siphon withdrawal reflex. The gill and siphon withdrawal reflex allows the ''Aplysia'' to pull back its siphon and gill for protection. The links between the synapses during the gill and siphon withdrawal reflex are directly correlated with many behavioral traits in the ''Aplysia'' such as its habits, reflexes, and conditioning. Scientists have studied the conditioning of the ''Aplysia'' to identify correlations with conditioning in mammals, mainly regarding behavioral responses such as addiction. Through experiments on the conditioning of the ''Aplysia'', links have been discovered with the synaptic plasticity for reward functions involved in the trait of addiction within mammals. Synaptic plasticity is the idea that the synapses will become stronger or weaker depending on how much those specific synapses are used. Conditioning of these synapses can lead them to become stronger or weaker by causing the neurons to fire or not fire when influenced by a stimulus. The conditioning of behavioral traits is based on the idea of a reward function. A reward function is when a stimulus is conditioned to fire according to a certain stimulus. The neurons will adapt to that stimulus, and fire those neurons more easily, even if the stimulus has a negative effect on the subject (in this case the Aplysia). In mammals, the reward function is mainly controlled by ventral tegmental area (VTA) dopamine neurons. During conditioning (in mammals), the VTA dopamine neurons have an increased effect on the stimuli being conditioned, and a decreased effect on the stimuli not being conditioned. This induces the synapses to form an expectation for reward for the stimuli being conditioned. The properties of the synapses displayed in the tests on conditioning involving the ''Aplysia'' (which has dopamine neurons but not a ventral tegmental area) are proposed to be directly comparable to behavioral responses such as addiction in mammals.

Reproduction

''Aplysia'' are simultaneous hermaphrodites, meaning each adult individual sea hare possesses both male and female reproductive structures that may be mature at the same time.

''Aplysia'' have the ability to store and digest allosperm (sperm from a partner) and often mate with multiple partners. A potent sex pheromone, the water-borne protein attractin, is employed in promoting and maintaining mating in ''Aplysia''. Attractin interacts with three other Aplysia protein pheromones (enticin, temptin or seductin) in a binary fashion to stimulate mate attraction.

Studies of multiple matings in the California sea hare, ''Aplysia californica,'' have provided insights on how conflicts between the sexes are resolved.

Self-defense

''Aplysia'' species was once thought to use ink to escape from predators, much like the octopus. Instead, recent research has made it clear that these sea slugs are able to produce and secrete multiple compounds within their ink, including the chemodeterrant Aplysioviolin and toxic substances such as ammonia for self-defense. The ability of the ''Aplysia'' species to hold toxins within their bodies without poisoning itself is a result of the unique way that the toxin is stored within the slug. Different molecules essential to the creation of the toxin are accumulated in separate parts of the body of the slug, rendering them benign, as only the mixing of all the molecules can result in a toxic chemical cloud. When the sea hare feels threatened it immediately begins the process of defending itself by mixing the distinct molecules in an additional part of the body used specifically for that purpose. At which point, enzymes within the sea slug begin the process of making the substance toxic, and the mixture is ejected out at the predator in self-defense.

Species

Species within the genus ''Aplysia'' are as follows.
This list follows the studies of Medina et al. who established a phylogenetic hypothesis for the genus ''Aplysia'' through study of the partial mitochondrial DNA (mtDNA) sequence data of ribosomal genes (rDNA).

* '' Aplysia argus'' Rüppell & Leuckart, 1830
* '' Aplysia atromarginata'' Bergh, 1905
* '' Aplysia brasiliana'' Rang, 1828
*'' Aplysia californica'' (J.G. Cooper, 1863) California sea hare
**Distribution: Northeast Pacific
*'' Aplysia cedrocensis'' (Bartsch & Rehder, 1939)
**Distribution: Northeast Pacific
*''Aplysia cervina'' (Dall & Simpson, 1901)
**Distribution: West Atlantic
*'' Aplysia cornigera'' Sowerby, 1869
**Distribution: Indian Ocean, West Pacific
*'' Aplysia cronullae'' Eales, 1960: synonym of '' Aplysia extraordinaria'' (Allan, 1932) (uncertain synonym)
**Distribution: Southwest Pacific
*'' Aplysia dactylomela'' (Rang, 1828) spotted sea hare
**Distribution: Cosmopolitan; tropical and temperate seas.
**Color: from pale gray to green to dark brown.
**Description: large black rings on the mantle; good swimmer
*'' Aplysia denisoni'' Smith, 1884: synonym of '' Aplysia extraordinaria'' (Allan, 1932) (possible senior synonym)
**Distribution: Indian Ocean, West Pacific
*'' Aplysia depilans'' ( Gmelin, 1791)
**Distribution: Northeast Atlantic, Mediterranean.
**Description: thin, yellow inner shell
*'' Aplysia dura'' Eales, 1960
**Distribution: Southeast Atlantic, Southwest Pacific
* '' Aplysia elongata'' (Pease, 1860)
*'' Aplysia euchlora'' Adams in M.E.Gray, 1850: represented as ''Aplysia'' (''Phycophila'') ''euchlora'' (Gray, 1850) (alternate representation)
**Distribution: Northwest Pacific
*'' Aplysia extraordinaria'' (Allan, 1932) (possibly = ''Aplysia gigantea'')
**Distribution: Western Australia, New Zealand.
**Length: more than 40 cm
*'' Aplysia fasciata'' (Poiret, 1798) ( ''Aplysia brasiliana'' Rang, 1828 is a junior synonym).
**Distribution: East Atlantic, Mediterranean, West Africa, Red Sea
**Length: 40 cm
**Color: dark brown to black.
**Description: sometimes has a red border to the parapodia and oral tentacles
* '' Aplysia ghanimii'' Golestani, Crocetta, Padula, Camacho, Langeneck, Poursanidis, Pola, Yokeş, Cervera, Jung, Gosliner, Araya, Hooker, Schrödl & Valdés, 2019
*'' Aplysia gigantea'' Sowerby, 1869
**Distribution: Indian Ocean, West Pacific
* '' Aplysia hooveri'' Golestani, Crocetta, Padula, Camacho, Langeneck, Poursanidis, Pola, Yokeş, Cervera, Jung, Gosliner, Araya, Hooker, Schrödl & Valdés, 2019
*'' Aplysia inca'' d'Orbigny, 1837
**Distribution: Southeast Pacific
* '' Aplysia japonica'' G. B. Sowerby II, 1869
* '' Aplysia juanina'' (Bergh, 1898)
*'' Aplysia juliana'' ( Quoy & Gaimard, 1832) Walking sea hare
**Distribution: cosmopolitan, circumtropical in all warm seas
**Color: various, from uniform to pale brown
**Description: no purple gland, therefore no ink secretions; posterior end of the foot can act as a sucker
*'' Aplysia keraudreni'' Rang, 1828
**Distribution: South Pacific
**Length: 25 cm
**Color: dark brown
*'' Aplysia kurodai'' (Baba, 1937)
**Distribution: NW Pacific
**Length: 30 cm
**Color: dark brown to purplish black, dotted with white spots
* '' Aplysia lineolata'' A. Adams & Reeve, 1850: synonym of '' Aplysia oculifera'' A. Adams & Reeve, 1850
*'' Aplysia maculata'' Rang, 1828
**Distribution : Western Indian Ocean
*'' Aplysia morio'' ( A. E. Verrill, 1901) Atlantic black sea hare, sooty sea hare
**Distribution: Northwest Atlantic
**Length: 40 cm
**Color: black to deep brown; no spots
*'' Aplysia nigra'' d'Orbigny, 1837
**Distribution: Southwest Atlantic, South Pacific
*'' Aplysia nigra brunnea'' Hutton, 1875
**Distribution: New Zealand
**Length: 10 cm
**Color: dark brown
* '' Aplysia nigrocincta'' von Martens, 1880
*'' Aplysia oculifera'' (Adams & Reeve, 1850) spotted sea hare
**Distribution: Indian Ocean; West Pacific; common along the north, east and south coast of South Africa
**Length: 15 cm
**Description: greenish brown, with small brown to black spots with white centres
**Habitat: shallow bays and estuaries
**Behaviour: hides by day; emerges at night to feed on seaweed
* '' Aplysia parva'' Pruvot-Fol, 1953
*'' Aplysia parvula'' (Guilding in Moerch, 1863) pygmy sea hare, dwarf sea hare
**Distribution: worldwide in warm to temperate seas
**Length: 6 cm
**Color: brown to green spots
* '' Aplysia peasei'' (Tryon, 1895) ('' taxon inquirendum'')
* '' Aplysia perviridis'' (Pilsbry, 1895)
* '' Aplysia pilsbryi'' (Letson, 1898)
* '' Aplysia pulmonica'' Gould, 1852
*'' Aplysia punctata'' ( Cuvier, 1803)
**Distribution: NE Atlantic
**Length: 20 cm
**Color: very variable
*'' Aplysia rehderi'' Eales, 1960
**Distribution: Northeast Pacific
*'' Aplysia reticulata'' Eales, 1960
**Distribution: Southwest Pacific
*'' Aplysia reticulopoda'' (Beeman, 1960) net-foot sea hare
**Distribution: Northeast Pacific
*'' Aplysia robertsi'' Pilsbry, 1895
**Distribution: Northeast Pacific
*'' Aplysia rudmani'' Bebbington, 1974
**Distribution: Indian Ocean
*'' Aplysia sagamiana'' (Baba, 1949)
**Distribution: East Australia, Japan; Northwest Pacific
* Aplysia sowerbyi Pilsbry, 1895
**Distribution: Southwest Pacific
*'' Aplysia sydneyensis'' (Sowerby, 1869)
**Distribution: Australia
**Length: 15 cm
**Description: not clearly defined
*'' Aplysia tanzanensis'' Bebbington, 1974
**Distribution: Indian Ocean
*'' Aplysia vaccaria'' (Winkler, 1955) California black sea hare (possibly ?= ''Aplysia cedrocensis'')
**Distribution: Pacific Coast of California
**Length: very big – up to 75 cm
**Color: black
**Description: no purple ink; huge internal shell
* ''Aplysia venosa'' Hutton, 1875 ('' taxon inquirendum'')
* '' Aplysia vistosa'' Pruvot-Fol, 1953

;Species brought into synonymy:
* ''Aplysia aequorea'' Heilprin, 1888: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia albopunctata'' ''Deshayes, 1853'': synonym of ''Aplysia punctata'' (Cuvier, 1803)
* ''Aplysia angasi'' G.B. Sowerby II, 1869: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia annulifera'' Thiele, 1930: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia ascifera'' Rang, 1828: synonym of '' Dolabrifera dolabrifera'' (Rang, 1828)
* ''Aplysia benedicti'' Eliot, 1899: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia bourailli'' Risbec, 1951: synonym of ''Aplysia dactylomela'' Rang, 1828
*''Aplysia brasiliana'' (Rang, 1828) mottled sea hare, sooty sea hare (junior synonym of ''Aplysia fasciata''; different geographical populations of the same species): synonym of '' Aplysia fasciata'' Poiret, 1789
* ''Aplysia cirrhifera'' Quoy & Gaimard, 1832: synonym of '' Barnardaclesia cirrhifera'' (Quoy & Gaimard, 1832)
* ''Aplysia concava'' Sowerby, 1869: synonym of ''Aplysia parvula'' Mørch, 1863
* ''Aplysia depressa'' Cantraine, 1835: synonym of '' Phyllaplysia depressa'' (Cantraine, 1835)
* ''Aplysia dolabrifera'' Rang, 1828: synonym of '' Dolabrifera dolabrifera'' (Rang, 1828)
*''Aplysia donca'' (Ev. Marcus & Er. Marcus, 1960): synonym of '' Aplysia morio'' (A. E. Verrill, 1901)
* ''Aplysia eusiphonata'' Bergh, 1908: synonym of ''Aplysia maculata'' Rang, 1828
* ''Aplysia fimbriata'' Adams & Reeve, 1850: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia gargantua'' Bergh, 1908: synonym of ''Aplysia maculata'' Rang, 1828
*''Aplysia geographica'' (Adams & Reeve, 1850): synonym of '' Syphonota geographica'' (A. Adams & Reeve, 1850)
* ''Aplysia gilchristi'' Bergh, 1908: synonym of ''Aplysia maculata'' Rang, 1828
* ''Aplysia gracilis'' Eales, 1960: synonym of ''Aplysia fasciata'' Poiret, 1789
* ''Aplysia griffithsiana'' Leach, 1852 synonym of ''Aplysia punctata'' (Cuvier, 1803)
* ''Aplysia guttata'' Sars M., 1840 synonym of Aplysia punctata (Cuvier, 1803)
* ''Aplysia hamiltoni'' Kirk, 1882: synonym of ''Aplysia juliana'' Quoy & Gaimard, 1832
* ''Aplysia hybrida'' Sowerby, 1806: synonym of ''Aplysia punctata'' (Cuvier, 1803)
* ''Aplysia longicauda'' Quoy & Gaimard, 1825: synonym of ''Stylocheilus longicauda'' (Quoy & Gaimard, 1825)
* ''Aplysia megaptera'' Verrill, 1900: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia nettiae'' Winkler, 1959: synonym of ''Aplysia californica'' J. G. Cooper, 1863
* ''Aplysia norfolkensis'' Sowerby, 1869: synonym of ''Aplysia parvula'' Mørch, 1863
* ''Aplysia oahouensis'' Souleyet, 1852: synonym of '' Dolabrifera dolabrifera'' (Rang, 1828)
* ''Aplysia ocellata'' d'Orbigny, 1839: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia odorata'' Risbec, 1928: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia operta'' Burne, 1906: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia petalifera'' Rang, 1828: synonym of '' Petalifera petalifera'' (Rang, 1828)
* ''Aplysia poikilia'' Bergh, 1908: synonym of ''Aplysia maculata'' Rang, 1828
* ''Aplysia protea'' Rang, 1828: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia pulmonica'' Gould, 1852: synonym of '' Aplysia argus'' Rüppell & Leuckart, 1830
* ''Aplysia radiata'' Ehrenberg, 1831: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia rosea'' Rathke, 1799: synonym of ''Aplysia punctata'' (Cuvier, 1803)
* ''Aplysia schrammi'' Deshayes, 1857: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia scutellata'' Ehrenberg, 1831: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia sibogae'' Bergh, 1905: synonym of ''Aplysia juliana'' Quoy & Gaimard, 1832
* ''Aplysia striata'' Quoy & Gaimard, 1832: synonym of ''Stylocheilus longicauda'' (Quoy & Gaimard, 1825)
* ''Aplysia tigrina'' Rang, 1828: synonym of ''Aplysia dactylomela'' Rang, 1828
* ''Aplysia tigrinella'' Gray, 1850: synonym of ''Aplysia maculata'' Rang, 1828
* ''Aplysia tigrinella'' Gray, 1850: synonym of '' Aplysia maculata'' Rang, 1828
* ''Aplysia velifer'' Bergh, 1905: synonym of ''Aplysia dactylomela'' Rang, 1828
*''Aplysia willcoxi'' (Hellprin, 1886): synonym of '' Aplysia fasciata'' Poiret, 1789
*''Aplysia winneba'' Eales, 1957: synonym of '' Aplysia fasciata'' Poiret, 1789

References

* Kandel Eric R., Schwartz, J.H., Jessell, T.M. 2000. ''Principles of Neural Science'', 4th ed., p. 180. McGraw-Hill, New York.
*

* Howson, C.M.; Picton, B.E. (Ed.) (1997). ''The species directory of the marine fauna and flora of the British Isles and surrounding seas''. Ulster Museum Publication, 276. The Ulster Museum: Belfast, UK. . vi, 508 (+ cd-rom) pp
* Gofas, S.; Le Renard, J.; Bouchet, P. (2001). Mollusca, in: Costello, M.J. et al. (Ed.) (2001). ''European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification''. Collection Patrimoines Naturels, 50: pp. 180–213

External links

*
* Photos of ''Aplysia''
MondoMarino.net

Cunha, C. M.; Rosenberg, G. (2019). Type specimens of Aplysiida (Gastropoda, Heterobranchia) in the Academy of Natural Sciences of Philadelphia, with taxonomic remarks. Zoosystematics and Evolution. 95(2): 361-372

{{Taxonbar , from=Q136564

Animal models
Animal models in neuroscience
Taxa named by Carl Linnaeus
Gastropod genera