''Bipalium kewense'', also known as the shovel-headed garden worm, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of large

predatory Predation is a biological interaction in which 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 ...

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, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

. 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 sem ...

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 Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

, but currently is found worldwide. It has been reported on every continent aside from Antarctica. 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 south-west Greater London, London, England, forms part of Outer London and is the only London boroughs, London borough on both sides of the River Thames. It was created in 1965 when three smaller ...

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

, hence the name ''kewense''.

Feeding habits

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

earthworm An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass, depending on the author) Oligochaeta. In classical systems, they we ...

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

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

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

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

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

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

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 (biology), order that includes Tetraodontidae, pufferfish, porcupinefish, ocean sunfish, and triggerfish; several of these species carry the toxin. Alt ...

, a

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

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

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 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 is encoded by the ''MT-CO1'' gene in eukaryotes. The gene is also called ''COX1'', ''CO1'', or ''COI''. Cytochrome c oxidase ...

(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 and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

, 15,666-bp in length, was obtained in 2019 form a specimen collected in France; . In 2025, a complete mitogenome was obtained for another specimen, this time coming from Madagascar; only four differences were found between both sequences.

References

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