''Phylliroe'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of average sized (up to ), highly transparent

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to mat ...

s, marine gastropod molluscs in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Opisthobranchia 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. Euopisth ...

, that consists of two known species. It is notable for being an open-ocean hunter that resembles a fish in body plan and locomotion, an example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

Distribution and habitat

* ''P. atlantica'' occurs in the (sub) tropical waters of the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe an ...

and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

oceans. * ''P. bucephalum'' is known from the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on th ...

Ecology

Juveniles of ''P. bucephalum'' are found exclusively feeding on the bell of the hydromedusa ''

Zanclea costata ''Zanclea'' is a genus of hydrozoans belonging to the family Zancleidae. The genus has cosmopolitan distribution. Species Species: *'' Zanclea alba'' *''Zanclea apicata'' *''Zanclea apophysis'' *'' Zanclea baudini'' *''Zanclea bomala'' * ...

'' (this junior synonym was given precedence over ''Mnestra parasites''). At first the nudibranch is attached to the inside of the bell of the meduse with its very small foot. It sucks tissue from the ring, radial canals and

manubrium The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sh ...

of the meduse and grows from 1.6 mm to 11 mm in just ten days, while the meduse shrinks. When the slug is as big as the meduse, it starts to swim, eating the remaining parts, including the tentacles. In adulthood its diet is no longer restricted to ''Zanclea'', although observations of feeding behaviour are sparse. ''Phylliroe'' uses its rhinophores (long horns) to prey on jellies, and the nearly vestigial remnant of its

foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg mad ...

to adhere to the jelly prey. ''Phylliroe'' has been seen approaching a swarm of the

larvacea Larvaceans, class Appendicularia, are solitary, free-swimming tunicates found throughout the world's oceans. Like most tunicates, larvaceans are filter feeders. Unlike most other tunicates, they live in the pelagic zone, specifically in the photi ...

n '' Oikopleura albicans'' from below, grabbing a specimen with its paired denticulate jaws and swallowing it in half a minute. Adults have also been observed to prey on the meduse ''Aequoria''. Branches of the digestive tract may contain symbiontic

zooxanthellae Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus '' ...

, but this relationship has not yet been studied. It is unclear if all specimens of ''P. bucephalum'' harbor these symbionts. It is possible they are obtained from their prey. ''P. bucephalum'' sometimes suffers from

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

trematodes Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive ...

, both attached to its skin and inside its body.

References

External links

film showing internal organs, and animal swimming

Distribution and habitat

Ecology

References

External links

Further reading