#aplysia

Favorite Sea Slug

Man, thats a hard one. My favorites actually arent nudibranchs, but actually my favorites are the Sea Hares (family Aplysiidae).

California Sea Hare (Aplysia californica), releasing ink as a defense, family Aplysiidae, found along the coast of California and Mexico

photograph by Genny Anderson

Atlantic Black Sea Hares swimming near shore (youtube.com)

Sea hare swimming (youtube.com)

LET’S PLAY!

Get to know more about this invertebrate by reading this blog! It contains the classification, biology, relationship to humans, and interesting facts about this marvelous organism, specifically one of its subgroup  — Aplysia.

CLASSIFICATION

Kingdom: Animalia  

             Subkingdom: Bilateria          

                Infrakingdom: Protostomia            

                   Superphylum: Lophozoa              

                      Phylum: Mollusca  

                         Class: Gastropoda  

                            Subclass: Opisthobranchia

                               Order: Anaspidea            

                                  Family: Aplysiidae        

                                     Genus: Aplysia

                                        Species: Aplysia californica

(ITIS, n.d.)

Aplysia, commonly known as spotted sea hares, belongs to the group of gastropod molluscs. There are 37 known species in this genus. The word Aplysia came from the word L’Aplysia which means “that which one cannot wash”. They are one of the oldest mentioned animals from historical texts with the first authentic description provided by Pliny in his Historia Naturalis (published on 60 A.D) (Moroz, 2011) .

BIOLOGY

Ocean Globetrotters

These invertebrates are benthic dwellers that occupies the middle and lower intertidal zones, grazing on sea beds or corals. They are distributed in subtropical and tropical tide zones with one species (A. punctata) even reaching the Arctic Circle. Seven species of Aplysia can navigate long distances  for example A. brasiliana  which can travel up to 1 km in one swim episode (Moroz, 2011).

Spotted sea hares move in two ways, either by swimming or crawling on the sea bed. They swim by doing synchronized waves of muscular contraction pass from anterior to posterior to make a funnel that pulls in water, squeezing the anterior parts of the parapodia together forces the water out behind the creature and pushes it forward. While, they can crawl by raising the leading edge of the foot and extending it forward in an arching pattern so the rest of its body follows the arching pattern until it reaches the tail (Dice, 2014).

The Naked Alien

The body of spotted sea hares consists of a head, foot, and visceral mass. It is partially distorted, not coiled, and superficially bilaterally symmetrical (Fox, 2006).

The head has an anterior pair oral tentacles. The median union of the two tentacles forms a transverse oral veil over the mouth.  A pair of rhinophores project dorsally from the surface of the neck. The oral tentacles and rhinophores serve as sensory organ. Specifically, their eyes are located at the base of each rhinophore (Fox, 2006).

(Brooks & Hiller, 2001)

The foot lies along the midline of the ventral surface. Its posterior part serves as a sucker that is used to attach the posterior end of the animal while anterior end is elevated above the substratum. The foot extends posterior to the body as a short tail. Dorsolaterally, it is divided into two wing-like parapodia that is used for locomotion (Fox, 2006).

(Brooks & Hiller, 2001)

Their mantle and mantle cavity are found in the middle. The mantle is the dorsal body wall of the visceral mass. Inside it, the shell can be found. Below the shell is the reduced and small mantle cavity that opens broadly to the right containing the gill, anus, and gonopore. At the posterior right corner of the shell is a folded mantle resulting to a short, tubular, exhalant siphon that encloses the anus (Fox, 2006).

A Salad Lifestyle

Spotted sea hares feed on algae. A. californica (California sea hares) feeds on several kinds of red algae such as Laurencia pacifica, Plocamium pacificum and Ceramium spp. as well as sea lettuce and eelgrass. These organisms utilize their toothed radula to grasp the algae and store it briefly in the esophagus. Then, the food moves into the stomach fixed with pyramidal teeth to further crush the substances The food is blended in with different stomach-related digestive fluids to further breakdown the matter while the wastes are discharged out through the anus (Dice, 2014).

Dating on Another Level

Sea hares gather to mate. With the absence of dating apps, they find each other through tactile and chemical cues. They have photoreceptors that recognize fluctuations in the intensity of white light. Sadly, they find it hard to detect red wavelengths. To compensate, they respond more to chemical changes in seawater using the osphradium which detects dissolved chemicals in the water (Dice, 2014).

Loyalty, whomstve?

From a spiral cleavage to blastula, gastrula, trochophore and finally, the first larval stages — the development of their embryo happens inside the egg capsules. Newly hatch veligers swim upwards using their cilia and may take months drifting in the ocean while feeding on microscopic algae and bacteria until they detect cues that prompts them to settle to the alga which they will feed on. After this, they undergo rapid metamorphosis wherein they lose larval characteristics. They become juveniles that resemble miniature adults in all major features except reproductive organs (Moroz, 2011). California sea hares reach sexual maturity after about 120 days (Dice, 2014). 

Sea hares are hermaphrodites, but they never self-fertilize by nature. Their copulation generally involves dozens. Every creature might be either getting or conveying sperm (or both) in respect of their present sex and position inside the chain (Dice, 2014). 

Short Fruitful Years

Their life expectancy is normally short, most commonly survive for just a year. Many of them loose their life after reproduction. Amazingly, cool temperatures help delay reproduction; hence, cooler waters can fairly protract their life expectancy (Emore, 2002).

Hey, Leave Me Alone!

Distressed spotted sea hares secrete a purple ink which contains chemicals that disrupts the sensory function of opportunistic predators (Moroz, 2011). This chemical defense coupled with the distasteful algal toxins accumulated from their diet significantly creates a habitat where they can roam freely and has few natural predators (Emore, 2002).

RELATIONSHIP TO HUMANS

Sea hares are known to be highly valuable laboratory animals especially in the field of neurobiology, more specifically in studying memory and learning behaviors. The California Sea Hare (Aplysia californica) is an important neurobiological model and is used extensively in studies of behavior and psychology. They have the largest neurons in the animal kingdom making it feasible to identify the specific nerve cells responsible for certain mechanisms.

As for their ecosystem role, this herbivorous organism serves as keystone species in the intertidal ecosystem by affecting the density and abundance of its algal prey.

5 Interesting FYIs about SEA HARES

1. DUAL PURPOSE WINGS

Sea hares have two large wing-like flaps that fold back on the body to protect their gills and internal shell plate. This wing-like extension is also used by some species of sea hares for short bursts of awkward swimming when threatened. 

2. IT’S THE CIRCLE OF LIFE

As they say the more, the merrier. A circle of sea hares dubbed as a “Roman Circle” is formed during mating and copulation where each animal inseminates the one in front- a group sex indeed. As hermaphroditic organisms, sea hares serve as males at their front and females at their back. 

3. GO AND MULTIPLY TO THE POWER OF 10

(Eleas, 2020)

Who cares about a twin, a quadruplet or a quintuplet? A single of this creature can lay up to 500 million eggs during one breeding season- that is more than a country’s population. Sea hares’ eggs are colored pink and often appear threaded.

4. WHAT YOU SEE, IS WHAT WE EAT

(Gfycat, 2019)

The color of sea hares are affected by the color of algae they consume. For example, young sea hares that tend to eat red algae are red in color, mature sea hares are colored green and brown because they consume algae that is also green and brown in color.

5. SEA HARES ARE CERTIFIED BTS STANS 💜 💜 💜

Sea hares have the right to use the infamous purple hearts on social media, and that’s a fact! This sea organism produces purple ink as a defense mechanism. Native Americans used this purple ink to dye clothing. Sea hares can also produce white or red ink depending on the color of the pigments in the seaweed they have consumed.

References

Angello, M. (n.d.). Full Frame Shot Of Sea Water [Photograph]. Getty Images. https://www.gettyimages.com/detail/photo/full-frame-shot-of-sea-water-royalty-free-image/730260985

Anonymous. (2017). Sea Hare Eggs [Photograph]. Ocean Safari Scuba. https://oceansafariscuba.com/photos/view_album/trip-11417-tidepool

Anonymous. (n.d.). Dinner Time with Sea Hares [GIF]. Gfycat. https://gfycat.com/unsteadydirectfreshwatereel-sea-hare

Brooks, R. & Hiller, J. (2001). The Role of Chemical Mechanisms in Neural Computation and Learning. [Photograph] .Research Gate. https://www.researchgate.net/publication/2524430_The_Role_of_Chemical_Mechanisms_in_Neural_Computation_and_Learning

Brown, C. (2010). Untitled [Photograph]. Flickr. https://inhabitat.com/wp-content/blogs.dir/1/files/2015/06/Sea-Hare-2-889x667.jpg

Dice, S. (2014). Aplysia californica. Animal Diversity  Web. https://animaldiversity.org/accounts/Aplysia_californica/

Eleas. (2020). Naruto Clone GIF. Tenor. https://tenor.com/view/naruto-naruto-clone-funny-dancing-dance-gif-17857501

Emore, M. (2002). Aplysia dactylomela. Animal Diversity Web. https://animaldiversity.org/accounts/Aplysia_dactylomela/

Fox, R. (2006). Sea Hare. Lander University. http://lanwebs.lander.edu/faculty/rsfox/invertebrates/aplysia.html 

ITIS. (n.d.). Aplysia californica  J. G. Cooper, 1863. ITIS.gov. https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78032#null 

A great question!

1. Appendicularia larvae

They look like litte Aliens and can be up to 7cm big (usually they are smaller though <1cm). They are filter feeders and use a mucus net around their bodies to filter very small particles out of the surrounding water. They can create a current with their tail so the water get's pulled inside their mucus house.

So now, they can 'drive' around in it like a spaceship. Should a predator try to eat them, they will only get the mucus mesh because they have an Emergency exit built into their spaceship that allows them to flee the structure in seconds. The Larvae itself is mostly small enough so the predator won't find it on it's own. They also discard it when it's clogged or they need to make a bigger one. The whole structure can be rebuilt in about 24h, pretty impressive don't you think?

2. Kleptocnides

Some gastropodes of the Nudibranchia are able to accumulate stinging cells from the sponges they prey on for their own defence.

The Flabellina affinis feeds almost exclusively on Eudendrium species (Hydrozoa) and is able to transport their Stinging cells through it's digestive system without them being triggered. They are then distributed under the skin of the tentacles on the back of Flabbellina so that they will harm predators should they try and feed on the snail. Why make them yourself if you can steal them?

3. Kleptoplasts

You think they can only steal stinging cells? Well you are mistaken! The species of the group Elysia are able to accumulate Chloroplasts from the algae they feed on.

Elysia translucens feeds on green Algae of the group Codium and can perserve their Chloroplasts for up to two months inside their digestive system. All products generated by them benefit the snail.

Aplysia: Morphology, Classification, Habitat, and Neurobiological Importance of the Sea Hare Aplysia is a genus of large sea slugs commonly known as sea hares, belonging to the family Aplysiidae. These marine gastropod mollusks are notable for their soft, often leathery bodies and reduced internal shells. Sea hares have distinctive parapodia—wing-like flaps—that aid in swimming, and their two…