Bipalium

''Bipalium'' is a genus of large predatory land planarians. They are often loosely called "hammerhead worms" or "broadhead planarians" because of the distinctive shape of their head region. Land planarians are unique in that they possess a "creeping sole", a highly ciliated region on the ventral epidermis that helps them to creep over the substrate. Several species are considered invasive to the United States, Canada, and to Europe. Some studies have begun the investigation of the evolutionary ecology of these invasive planarians.

Etymology

The name ''Bipalium'' comes from Latin ''bi-'', "two" + ''pala'', "shovel" or "spade", because species in this genus resemble a pickaxe.

Description

The genus ''Bipalium'' was initially defined by Stimpson to include land planarians with the head broadened, forming a head plate. Later, in 1899, Ludwig von Graff divided it into three genera according to the shape of the head:
#''Bipalium'': with a well-developed head plate, much broader than long, and with elongated lateral auricles
#''Perocephalus'': rudimentary head plate, not much broader than the body
#''Placocephalus'': flat head plate with a circular outline

Josef Müller, in 1902, considered that no sufficient anatomical basis existed for this distinction, and reunited them under ''Bipalium''. Later, von Graff accepted Müller's conclusions.

Towards the end of the 20th century, Robert E. Ogren and Masaharu Kawakatsu started a series of publications called "The Land Planarian Index series" in which they reviewed and organized all taxonomic information regarding land planarians. At first, they retained all broad-headed planarians in the genus ''Bipalium'', but later split them into four genera based on the anatomy of the reproductive organs: ''Bipalium'', '' Novibipalium'', '' Humbertium'', and '' Diversibipalium''.

Under this scenario, the genus ''Bipalium'' is defined as containing broad-headed land planarians with simple copulatory organs, without accessory ducts or copulatory bursa, and with a fold of tissue separating the male and female exit ducts.

Feeding habits

''Bipalium'' species are predatory. Some species prey on earthworms, while others may also feed on mollusks. These flatworms can track their prey. When captured, earthworms begin to react to the attack, but the flatworm uses the muscles in its body, as well as sticky secretions, to attach itself to the earthworm to prevent escape. The planarians cover, or cap, the prostomium, peristomium, and anterior end to stop the violent reaction by the earthworm.

To feed on their prey, species of ''Bipalium'' often evert their pharynges from their mouths, located on the midventral portion of their bodies, and secrete enzymes that begin the digestion of the prey. The liquefied tissues are sucked into the branching gut of the flatworms by ciliary action.

Reproduction

Reproduction in ''Bipalium'' may be asexual or sexual and all species are hermaphroditic.

''B. adventitium'' reproduces sexually and creates egg capsules, which hatch around 3 weeks post-deposition. The egg capsules have a tough exterior and generally contain multiple juveniles.

''B. kewense'' have rarely been observed using egg capsules as a primary method of reproduction. Asexual fragmentation is its main reproductive strategy in temperate regions and most individuals never develop sexual organs. Juveniles of this species, unlike ''B. adventitium'', do not appear the same coloration as parents in their early days.

Toxicity

In 2014, the presence of tetrodotoxin, a very dangerous neurotoxin, was recorded in ''B. adventitium'' and ''B. kewense''. It is the first record of tetrodotoxin in terrestrial invertebrates.

Invasive species

Little is known about the ecology of terrestrial planarians, but research has been done on different genera and species, including several native and invasive species in Brazil, '' Arthurdendyus triangulatus'', '' Rhynchodemus'' and ''Bipalium''.

Currently, four invasive species of ''Bipalium'' are known in the United States: ''B. adventitium'', ''B. kewense'', ''B. pennsylvanicum'', and ''B. vagum''. These planarians are thought to have come to the US on horticultural plants.

''Bipalium kewense'' has been found commonly in American greenhouses since 1901. This species is a voracious predator of earthworms, and has been identified as a nuisance in the southern USA in earthworm-rearing beds. Control of the species is difficult due to the lack of predators. As noted by the University of Florida IFAS department,

Other animals rarely devour land planarians, since surface secretions appear distasteful, if not toxic. Protozoans, including flagellates, ciliates, sporozoans, and nematodes have been detected in land planarians. Because of their cannibalistic habit, land planarians may be their own worst enemy.

Specimens of '' Bipalium adventitium'' are characterized by a single dark dorsal stripe. They were first discovered in the US in California and New York but have been found in Illinois as well as most northern states and in 2019 were discovered in Montreal, Canada ''B. kewense'' have five dark dorsal stripes and a partial dark collar. They have undergone several name changes since their discovery in North America. ''B. kewense'' is commonly found across the southern regions of the US. ''B. kewense'' is found worldwide in tropical and subtropical regions.'' Bipalium pennsylvanicum'' is characterized by its dark brown head and three dorsal stripes. Thus far, it has only been found in Pennsylvania and in coastal South Carolina in 2014. '' Bipalium vagum'' is characterized by two dark dorsal blotches on the head, a thick black band around the neck, and three dark dorsal stripes. This species has been found in several Gulf Coast states, and in 2022 specimens were located extending further north, into Arkansas. Recently it was found in Mumbai, India.

Image gallery

File:Bipalium kewense sighted in Austin, Texas 02.JPG, ''Bipalium kewense'' sighted in Austin, Texas
File:Bipalium kewense sighted in Austin, Texas 01.JPG, Close up of head of ''Bipalium kewense''
File:Bipalium from GA.jpg, Specimen of ''Bipalium'' found in Georgia, United States
File:Hammerhead worm 2.jpg, Hammerhead worm found in Kerala, India
File:Hammer Headed Worm.jpg, Hammerhead worm found in Chennai and Coimbatore, India
File:Bipalium kewense.ogv, Video of a ''Bipalium'' sp. from Mérida, Yucatán, Mexico
File:Hammerhead Worm.jpg, A hammerhead worm seen in Kolkata, India
File:Bipalium, Kayamkulam, Alappyzha, Kerala, India.jpg, Bipalium found in Kerala, India 03.08.2021
File:Bipalium, Kayamkulam, Kerala, India.jpg, alt=Bipalium, Hammer headed worm / snail found in Kerala, India

Species

The genus ''Bipalium'' currently includes the following species:

*'' Bipalium adensameri''
*'' Bipalium admarginatum''
*'' Bipalium adventitium''
*'' Bipalium albo-coeruleus''
*'' Bipalium alternans''
*'' Bipalium bengalensis''
*'' Bipalium bergendali''
*'' Bipalium bimaculatum''
*'' Bipalium chhatarpurensis''
*'' Bipalium choristosperma''
*'' Bipalium costaricensis''
*'' Bipalium crassatrium''
*'' Bipalium distinguendum''
*'' Bipalium dubium''
*'' Bipalium fuscatum''
*'' Bipalium fuscolineatum''
*'' Bipalium gestroi''
*'' Bipalium glandiantrum''
*'' Bipalium glandulosa''
*'' Bipalium glaucum''
*'' Bipalium gracilis''
*'' Bipalium graffi''
*'' Bipalium haberlandti''
*'' Bipalium hilgendorfi''
*'' Bipalium interruptum''
*'' Bipalium janseni''
*'' Bipalium javanum''
*'' Bipalium kaburakii''
*'' Bipalium katoi''
*''Bipalium kewense''
*'' Bipalium kisoense''
*'' Bipalium kraepelini''
*'' Bipalium manubriatum''
*'' Bipalium marginatum''
*'' Bipalium mjobergi''
*'' Bipalium mondimentum''
*'' Bipalium monolineatum''
*'' Bipalium moseleyi''
*'' Bipalium muninense''
*'' Bipalium myadenosium''
*'' Bipalium nigrum''
*'' Bipalium nobile''
*'' Bipalium ochroleucum''
*'' Bipalium pennsylvanicum''
*'' Bipalium penrissenicum''
*'' Bipalium penzigi''
*'' Bipalium persephone''
*'' Bipalium poiense''
*'' Bipalium rigaudi''
*'' Bipalium robiginosum''
*'' Bipalium semperi''
*'' Bipalium simrothi''
*'' Bipalium strubelli''
*'' Bipalium sudzukii''
*'' Bipalium sylvestre''
*'' Bipalium tetsuyai''
*'' Bipalium unistriatus''
*'' Bipalium univittatum''
*'' Bipalium vagum''
*'' Bipalium virile''
*'' Bipalium weismanni''
*'' Bipalium wiesneri''

References

External links

''Bipalium''
by University of Maine Turbellarian taxonomic database

Land planarians
by Texas A&M University Insects in the City

Photograph of ''B. nobile''

Photograph of ''B. simrothi''

{{Taxonbar, from=Q3761757

Geoplanidae
Rhabditophora genera
Taxa named by William Stimpson
Articles containing video clips