T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Flatworm (Hammerhead) Bipalium kewense

Kingdom: Animalia
Phylum: Platyhelminthes
Class: Rhabditophora
Order: Tricladida
Suborder: Continenticola
Family: Geoplanidae
Subfamily: Bipaliinae
Genus: Bipalium
Species: B. kewense
Binomial name: Bipalium kewense
Synonyms: Sphyrocephalus kewensis, Placocephalus kewensis, Placocephalus isabellinus, Bipalium costaricense.
Common name: Hammerhead flatworm, Hammerhead worm

Bipalium kewense is a species of large predatory land planarian with a cosmopolitan distribution. It is the world's largest flatworm and is believed to be native to Southeast Asia, but currently is found worldwide. It was probably introduced to New Zealand by international plant trade, as it is frequently found associated with plant pots.

Bipalium kewense is a very long land planarian that can be up to 60 cm in length. 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 colour 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. The head usually has a darker colour than the background colour of the dorsum. The ventral side is white and externally lined by two diffuse grey longitudinal lines.

Bipalium kewense is a known predator of earthworms. It immobilizes the prey using muscular movements and possibly toxins and then everts its pharynx, connecting it to the earthworm's body and beginning digestion. The digestion seems to be at least partially extracorporeal by means of a collagenolytic enzyme.

Bipalium kewense is known to produce tetrodotoxin, a neurotoxin that results in paralysis. It is possible that the toxin aids the planarian in subduing its prey as well as in protecting it from predators.

Some overseas specimens like the one below have reached 60cm in length.

The half-moon shaped head.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0