Schmidt and Edmonds, 1989
Australiformis is a
The taxonomic history of A. semoni is complex. It was originally named Echinorhynchus semoni by
|Phylogenetic reconstruction for select species in the class Archiacanthocephala based on a 28S rRNA gene comparison from Gomes et. al (2019) and a 18S rDNA gene comparison from Amin et al. (2020). Unlike the other species shown, no genetic testing has been conducted on Australiformis semoni to confirm this classification which is inferred based on morphological traits.|
|Measurements||Female (mm)||Male (mm)|
|Length of proboscis||0.640–0.800||0.600–0.840|
|Width of proboscis||0.280–0.320||0.200–0.288|
|Length of proboscis receptacle||1.2–1.58||1.0–1.7|
|Width of proboscis receptacle||0.3–0.48||0.32–0.36|
|Length of neck||0.225–0.240||0.150–0.240|
|Width of neck at base||0.200–0.270||0.200–0.270|
|Length of trunk||95–197||46–80|
|Width of trunk||1.75–3.5||2|
|Length of lemnisci||25–27||20–25|
|Size of anterior testis||2.7–3.2 x 0.75–1.0|
|Size of posterior testis||2.5–3.2 x 0.75–1.0|
|Size of cement glands||0.64–1.2 x 0.44–0.72|
|Size of Saefftigen's pouch||1.28 x 0.48–0.64|
|Size of eggs||0.080–0.086 x 0.035–0.044|
|Distance from the uterine bell to genital pore||1.95–2.2|
A. semoni consists of a proboscis covered in hooks, a proboscis receptacle, and a long trunk. There is pronounced sexual dimorphism in this species; the females are around twice as long as the males (up to approximately 20 centimetres (7.9 in) in females and 8 centimetres (3.1 in) in males). The proboscis is long and swollen at the anterior 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 40 to 56 micrometres (0.0016 to 0.0022 in) long, the second is 50 to 60 micrometres (0.0020 to 0.0024 in) long, the third is 42 to 50 micrometres (0.0017 to 0.0020 in) long, the fourth is 42 to 54 micrometres (0.0017 to 0.0021 in) long and the remaining spines are 30 to 60 micrometres (0.0012 to 0.0024 in) 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 around tendons 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 and ventral, with the dorsal canal being conspicuous and the ventral canal being very narrow. The transverse 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
The distribution of A. semoni is determined by that of its hosts. A. semoni has been found in several states of Australia, including Queensland, New South Wales, and Tasmania. This parasite has also been found in Boroko, Papua New Guinea. The type locality is the Upper Burnett River region in south-eastern Queensland.
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
A. semoni parasitizes Australian and
Thetype hostof A. semoni.
- A binomial authority in parentheses indicates that the species was originally described in a genus other than Australiformis.
- von Linstow, O.F.B. (1898). "Nemathelminthen von Herrn Richard Semon in Australien gesammelt". Denkschriften der Medizinisch-Naturwissenschaftlichen Gesellschaft zu Jena (in German). 8: 471–472. Retrieved 23 March 2020.
- Porta, A. (1908). "Gli acantocefali dei mammiferi. Noto preventiva". Archives de parasitologie. 12 (2): 268–282.
- Johnston, T.H.; Edmonds, S.J. (1952). "Australian Acanthocephala No. 9". Transactions of the Royal Society of South Australia. 75: 16–21. Archived from the original on 21 March 2023. Retrieved 21 March 2023.
- "Moniliformida Schmidt, 1972". Integrated Taxonomic Information System (ITIS). 23 November 2019. Archived from the original on 3 May 2023. Retrieved 30 January 2020.
- Schmidt, G.D. (1985). "Development and life cycles". In Crompton, D.W.T.; Nickol, B.B. (eds.). Biology of the Acanthocephala (PDF). Cambridge: Cambridge Univ. Press. pp. 273–305. Archived (PDF) from the original on 22 July 2023. Retrieved 16 July 2023.