''Octopus sinensis'' (commonly the East Asian common octopus) is a mollusk belonging to the class

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 ...

a. ''Octopus sinensis'' is a well-known shallow-water

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...

species found in the coastal, temperature waters of South Korea, China, and Japan, with the species name, ''sinensis'' being Latin for Chinese. ''Octopus sinensis'' is closely related to the Atlantic and Mediterranean common octopus, '' Octopus vulgaris.'' Because of the morphological similarities, ''O. sinensis'' was considered synonymous with ''Octopus vulgaris'' until 2017. ''Octopus sinensis'' are carnivores that prey upon on many shallow-water animals such as crustaceans and mollusks.

Characteristics

Size and description

The East Asian common octopus is adapted to a benthic life at the bottom of the sea. ''Octopus sinensis'' has long arms with many suckers used for catching prey,
mantle
without a rigid skeleton, which allows them to inhabit and hunt in small spaces and crevices in the seabed, horizontal pupils, and versatile skin with ability to change colors and camouflage themselves with the sea floor. Compared to ''O. vulgaris'', ''O. sinensis'' have a broader mantle and relatively shorter arms with about 80 fewer suckers. Mature ''O. sinensis'' males lack a standard sex organ, rather one of their arms (their third right arm) is specially adapted for reproduction. This arm includes erectile tissue on its tip and has a channel for sperm packets. During copulation, ''O. sinensis'' males insert their third right arm into the female's mantle. The third right arm on mature ''O. sinensis'' males has far fewer suckers than that on ''O. vulgaris'' (120-140 vs. 150–190).

Physiology

The East Asian common octopus goes through a several-week

planktonic Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

phase, in which they are floating in the open sea. This occurs early in their development prior to their permanent benthic habitation, similar to many benthic octopus species. During their planktonic phase, the morphology of the East Asian common octopus is similar in morphology to the juvenile and adult life forms and is termed the

paralarva Paralarvae (singular: ''paralarva'') are young cephalopods in the planktonic stages between hatchling and subadult. This stage differs from the larval stage of animals that undergo true metamorphosis. Paralarvae have been observed only in membe ...

l stage after the octopus hatches. The paralarvae have certain characteristics that differ from the adult stage, which allow them to thrive in the planktonic phase, such as transparent musculature, circular pupils rather than horizontal ones, a proportionately larger mantle (2.1 mm in length) and shorter arms with fewer suckers (three to four on each arm), and a finely toothed beak. However, not much is known about the early life stages of the East Asian common octopus in their natural habitat due to their cryptic and allusive behavior. Recent studies suggest that transition from the planktonic stage to the benthic settlement is quite complex in ''O. sinensis'' and takes them a significant amount of time.

Cultural importance

Not until 2017 was ''O. sinensis'' named a separate species from ''O. vulgaris'' on the basis of

molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...

and morphological features. Both species are commercially important food sources in China and both are vulnerable to over fishing. Therefore, it is important to delineate the two species for sustainable and fisheries management. In fact, some researchers claim that the misidentification of ''O. sinensis'' as ''O. vulgaris'' may be masking the decline of octopuses worldwide. catches of octopus have been steadily declining across the globe. Due to its rapid rate of growth and its high commercial value, ''O. sinensis'' is of particular interest in aquacultural cultivation. There have been several studies since the 1960s that have attempted to rear ''O. sinensis'' and ''O. vulgaris'' aquaculturally with little success. Current studies are focused on developing more accurate gene expression profiles to better understand the metabolic process and nutritional requirements of ''O. sinensis'' during its paralarval stage for aquacultural production of ''O. sinensis.''

References

{{Taxonbar, from=Q61684087 Octopodidae Molluscs described in 1841