''Australiformis'' is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus of

acanthocephala Acanthocephala ( Greek , ' 'thorn' + , ' 'head') is a group of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses t ...

ns (thorny-headed or spiny-headed

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

worms) containing a single species, ''Australiformis semoni'', that infests

marsupials Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

. Its body consists of a

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

armed with hooks which it uses to pierce and hold the gut wall of its host, and a long trunk. This genus resembles species in the genus '' Moniliformis'' but is characterized by a lack of spiral muscles in the outer wall of the proboscis receptacle. The proboscis is armed with 12 rows of 13 to 15 hooks which are used to attach themselves to the small or large intestines of the host. The female worms range from long, virtually all of which is the trunk, and wide. There is pronounced

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

in this species as females are around twice the size of the males whose trunks range from long and wide. Infestation by ''A. semoni'' may cause debilitating inflammation of the stomach (

gastritis Gastritis is the inflammation of the lining of the stomach. It may occur as a short episode or may be of a long duration. There may be no symptoms but, when symptoms are present, the most common is upper abdominal pain (see dyspepsia). Othe ...

) with

granulomatous A granuloma is an aggregation of macrophages (along with other cells) that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such subst ...

ulcers.

Taxonomy

The taxonomic history of ''A. semoni'' is complex. It was originally named ''Echinorhynchus semoni'' by Linstow in 1898, and then moved to ''Gigantorhynchus'' by Porta in 1908 and Johnston in 1909, later moved to ''Prosthenorchis'' by Travassos in 1917, then renamed ''Moniliformis semoni'' by Johnston and Edmonds in 1952 before taking the present name and genus by Schmidt and Edmonds in 1989. The genus is

, the only species, ''Australiformis semoni'' (Linstow, 1898), being necessarily the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

. Linstow named the species ''semoni'' after the German zoologist who discovered it,

Richard Semon Richard Wolfgang Semon (22 August 1859, in Berlin – 27 December 1918, in Munich) was a German zoologist, explorer, evolutionary biologist and memory researcher who believed in the inheritance of acquired characteristics and applied this to soci ...

. The morphological traits of a simple, double-walled

receptacle, eight cement glands (which are used to temporarily close the posterior end of the female after copulation) each with a giant nucleus, the brain at the posterior end of proboscis receptacle, and dorsal and ventral lacunar canals place this genus confidently in the order Moniliformida. The genus ''Australiformis'' Schmidt and Edmonds, 1989 was created for ''Moniliformis semoni'' as this species differed from other species in '' Moniliformis'' and the other genera of the family Moniliformidae, '' Promoniliformis'', because it lacked spiral muscles in the outer wall of the proboscis receptacle. The parasitizing of marsupials is also a unique trait of this genus among Acanthocephala. The

National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is lo ...

does not indicate that any

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis has been published on ''Australiformis'' that would confirm its position as a unique genus in the family Moniliformidae.

Description

''A. semoni'' consists of a proboscis covered in hooks, a proboscis receptacle, and a long trunk. There is pronounced

in this species; the females are around twice as long as the males (up to approximately in females and in males). The proboscis is long and swollen at the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

end and tapers rapidly to a narrow base. The proboscis is armed with 12 rows of 13 to 15 hooks. The first three to four hooks in each row are large, aligned in straight rows, and have bifid roots whereas the other 10 to 12 posterior hooks are small rootless spines arranged in spirals down the proboscis. The first hook of each row is long, the second is long, the third is long, the fourth is long and the remaining spines are long. At the base of the proboscis is a double-walled proboscis receptacle with a smooth outer wall, lacking spirally arranged muscle fibers, and a large space between the walls. The brain is located near the posterior end of the proboscis receptacle with retinacula (a band of thickened

deep fascia Deep fascia (or investing fascia) is a fascia, a layer of dense connective tissue that can surround individual muscles and groups of muscles to separate into fascial compartments. This fibrous connective tissue interpenetrates and surrounds the m ...

around

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

s that holds them in place) piercing the proboscis receptacle wall laterally. Proboscis retractor muscles pierce the posterior end of the proboscis receptacle. The trunk is not pseudosegmented, is very thin at the anterior end and thickest at the posterior end averaging only a few millimeters in width. The main longitudinal lacunar canals are

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

and

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

, with the dorsal canal being conspicuous and the ventral canal being very narrow. The

transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...

commissural canals are evenly spaced and connect to the main longitudinal canals. The lemnisci (bundles of sensory nerve fibers) are long, slender, twisted, and coiled in the body cavity (not attached distally to the body wall), and contain 10 to 15 giant nuclei each. They extend between one quarter to one third the length of the body. The eggs are oval with three apparent membranes. The outer membrane is thick with the exception of the anterior end where it is thin. The outer membrane is often indented and the posterior end is usually covered in small dots on the outer surface with a knob on the inner surface. The second membrane is very thin and the third membrane is thick. The males have a sensory pore on each side of the neck. Males have eight oval cement glands, each with a single giant nucleus, and possess a Saefftigen's pouch just behind the

testes A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The ...

. The testes are oval in tandem and found near the posterior end of the trunk. The genital pore is located at the terminal end of the trunk in both sexes.

Distribution

The distribution of ''A. semoni'' is determined by that of its hosts. ''A. semoni'' has been found in several states of Australia, including

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, and

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

. This parasite has also been found in

Boroko Boroko is a suburb of Port Moresby, the capital city of Papua New Guinea. It includes a residential area and a sports and recreation precinct, and was once a significant commercial centre but the business area is now in decline. History The town ...

, Papua New Guinea. The type locality is the Upper

Burnett River The Burnett River is a river in the Wide Bay–Burnett and Central Queensland regions of Queensland, Australia. Course and features The Burnett River rises in the Burnett Range, part of the Great Dividing Range, close to Mount Gaeta and east ...

region in south-eastern Queensland.

Hosts

The life cycle of an acanthocephalan consists of three stages beginning when an infective acanthor (development of an egg) is released from the intestines of the

definitive host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

and then ingested by an arthropod, the

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

. Although the intermediate hosts of ''Australiformis'' are not known, without exception for the order Moniliformida, this intermediate host is an insect. When the acanthor

molt In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is a process by which an animal casts off parts of its body to serve some beneficial purpose, either at ...

s, the second stage called the acanthella begins. This stage involves penetrating the wall of the mesenteron or the intestine of the intermediate host and growing. The final stage is the infective cystacanth which is the

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l or juvenile state of an Acanthocephalan, differing from the adult only in size and stage of sexual development. The cystacanths within the intermediate hosts are consumed by the definitive host, usually attaching to the walls of the intestines, and as adults they reproduce sexually in the intestines. The acanthor are passed in the

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

of the definitive host and the cycle repeats. There are no known paratenic hosts (hosts where parasites infest but do not undergo larval development or sexual reproduction) for ''Australiformis''. ''A. semoni'' parasitizes Australian and

n marsupials including the type host, southern brown bandicoot (''Isoodon obesulus'') and related species such as the northern brown bandicoot (''Isoodon macrourus''), long-nosed bandicoot (''Perameles nasuta''), striped bandicoot (''Perameles gunnii''), common echymipera (''Echymipera kalubu''), and brush-tailed phascogale (''Phascogale tapoatafa''). ''A. semoni'' infests these hosts by using hooks on their proboscis to pierce and hold the wall of the small and large intestines. ''A. semoni'' has also been found with the anterior end embedded in the mucosa of the stomach in the striped bandicoot. This infestation, which all observed cases contained 5 or fewer individual worms, may cause debilitating ulcerative granulomatous gastritis, a form of

(inflammation of the stomach) characterised by

ulcer An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughin ...

s and

granuloma A granuloma is an aggregation of macrophages (along with other cells) that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such sub ...

(an aggregation of

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

s that forms in response to chronic

inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

). Juvenile worms were found in the accidental host (an organism that generally does not allow transmission to the definitive host) brown antechinus (''Antechinus stuartii''). There are no reported cases of ''A. semoni'' infesting humans in the English language medical literature. File:Southern Brown Bandicoot (Isoodon obesulus) 2, Vic, jjron, 09.01.2013.jpg, alt=Southern Brown Bandicoot on the ground in a forest, The Southern brown bandicoot is the type host of ''A. semoni.'' File:Northern Brown Bandicoot.jpg, alt=Northern brown Bandicoot on the ground, Northern brown bandicoot File:Long-nosed Bandicoot 0059.jpg, alt=Long-nosed bandicoot among grass, Long-nosed bandicoot File:Brush-tailed phascogale.jpg, Brush-tailed phascogale

Notes

References

{{Taxonbar, from1=Q21222891, from2=Q21255093 Archiacanthocephala Monotypic protostome genera Invertebrates of Australia Fauna of New Guinea Parasitic animals of mammals Taxa described in 1989