''Bipalium kewense'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of large

predatory Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

land planarian Geoplanidae is a family of flatworms known commonly as land planarians or land flatworms. These flatworms are mainly predators of other invertebrates, which they hunt, attack and capture using physical force and the adhesive and digestive proper ...

with a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

. It is sometimes referred to as a "hammerhead flatworm" due to its half-moon-shaped head, but this name is also used to refer to other species in the subfamily

Bipaliinae Bipaliinae is a subfamily of land planarians found mainly in Madagascar, the Indian subcontinent and Southeast Asia, although some species have been introduced worldwide. Description The subfamily Bipaliinae is characterized by having a semi ...

Description

''Bipalium kewense'' is a very long land planarian. Preserved specimens are up to 20 centimetres in length, and living specimens may be longer. The anterior end ("head") is expanded in a transversal semilunate shape and the body is the narrowest just behind the head, in a region called "neck". The dorsal color is light-brown with five black to grey longitudinal stripes that begin at the neck. The median and marginal stripes are narrow and black, very distinctly marked. The lateral stripes (between the median and marginal stripes) are usually grey, broad and with diffuse margins. The neck is usually marked by an incomplete black collar formed by the union of the marginal and lateral stripes, this being one of the main characteristics to distinguish it from similar species. The head usually has a darker color than the background color of the dorsum and lacks stripes. The ventral side has a light ochre color externally and whitish over the creeping sole, which is externally lined by two diffuse grey-violet longitudinal lines.

Distribution

''Bipalium kewense'' is believed to be native to Southeast Asia, but currently is found worldwide. It was probably introduced by international plant trade, as it is frequently found associated with plant pots.Winsor, L.; Johns, P. M.; Barker, G. M. (2004) "Terrestrial planarians (Platyhelminthes: Tricladida: Terricola) predaceous on terrestrial gastropods." In: Barber, G. M. (ed.) ''Natural enemies of terrestrial molluscs'', Wallingford, CABI, 227-278. The species was first found in 1878 in the area of the Kew Park in the

London Borough of Richmond upon Thames The London Borough of Richmond upon Thames () in southwest London forms part of Outer London and is the only London borough on both sides of the River Thames. It was created in 1965 when three smaller council areas amalgamated under the London ...

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

, hence the name ''kewense''. Figure 07 (PeerJ 4672) - Bipalium kewense predation

Feeding habits

''B. kewense'' is a known predator of

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. Th ...

s. It immobilizes the prey using muscular movements and possibly toxins and then everts its

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

, connecting it to the earthworm's body and beginning digestion. The

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

seems to be at least partially extracorporeal by means of a collagenolytic

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

Toxicity

''Bipalium kewense'' is one of the few terrestrial invertebrates known to produce

tetrodotoxin Tetrodotoxin (TTX) is a potent neurotoxin. Its name derives from Tetraodontiformes, an order that includes pufferfish, porcupinefish, ocean sunfish, and triggerfish; several of these species carry the toxin. Although tetrodotoxin was discovered ...

, a

neurotoxin Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ner ...

that results in paralysis. It is possible that the toxin aids the planarian in subduing its prey as well as in protecting it against predators.

Reproduction

Figure 09 (PeerJ 4672) - Bipalium kewense fragment

All species of ''Bipalium'' are hermaphroditic, but ''Bipalium kewense'' has rarely been observed using sexual reproduction as a primary means of reproduction. Asexual fragmentation is the primary means of reproduction in ''B. kewense'' in temperate regions. Long specimens usually release body fragments at the posterior end by transverse fission. The fragments are motile and regenerate the head plate and pharynx in a few weeks. Such a reproduction strategy is considered one of the reason for the successful colonization of this and other species of ''Bipalium''. Although there is little evidence of sexual reproduction in these planarians, there have been several reported cases of egg capsules being discovered. The egg capsules discovered had several of the same characteristics of those of ''B. adventitium'', including coloration and incubation period. The most recent egg capsule discovered hatched offspring that did not bear a complete resemblance to adults and were considerably larger in size to that of ''B. adventitum'' offspring.

Genetics

A 2018 study showed that sequences of

Cytochrome c oxidase subunit I Cytochrome c oxidase I (COX1) also known as mitochondrially encoded cytochrome c oxidase I (MT-CO1) is a protein that in humans is encoded by the ''MT-CO1'' gene. In other eukaryotes, the gene is called ''COX1'', ''CO1'', or ''COI''. Cytochrom ...

(a mitochondrial gene commonly used for barcoding) were identical for all specimens from various countries originating from several continents, suggesting that specimens were clonal. The complete

mitochondrial genome Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

, 15,666-bp in length, was obtained in 2019; the closest mitochondrial genome was that of ''

Obama Barack Hussein Obama II ( ; born August 4, 1961) is an American politician who served as the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, Obama was the first African-American president of the U ...

'' sp., a species also belonging to the family

Geoplanidae Geoplanidae is a family of flatworms known commonly as land planarians or land flatworms. These flatworms are mainly predators of other invertebrates, which they hunt, attack and capture using physical force and the adhesive and digestive proper ...

References

{{Taxonbar, from=Q3314783 Geoplanidae Animals described in 1878