Australiformis

The morphological traits of a simple, double-walled proboscis receptacle, eight cement glands each with a giant nucleus, a brain at the posterior end of proboscis receptacle, and dorsal and ventral lacunar canals place this genus confidently in the order Moniliformida. No genetic testing has been conducted on this species to confirm this classification. 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 host of marsupials is also unique to this genus.[1]

The genus Australiformis is named after Australia, the locality of the species. The genus is monotypic, the only species Australiformis semoni (von Linstow, 1898)[lower-alpha 1][lower-alpha 2], being necessarily the type species.[7] Linstow named the species semoni after the German zoologist who discovered it, Richard Semon.[2]

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 or 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 between 40 and 56 μm long, the second is between 50 and 60 μm long, the third is between 42 and 50 μm long, the fourth is between 42 and 54 μm long and the remaining spines are between 30 and 60 μm long. At the base of the proboscis is a double-walled proboscis receptacle with the outer wall smooth lacking spirally arranged muscle fibers with a large space between the walls. The brain is located near the posterior end of the proboscis receptacle with retinacula piercing the proboscis receptacle wall laterally. Proboscis retractor muscles pierce the posterior end of the proboscis receptacle.[1]

The trunk is long and is very thin at the anterior end becoming thickest at the posterior end. No pseudosegmentation is present. The main longitudinal lacunar canals are dorsal and ventral, with 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 body wall), and contain 10 to 15 giant nuclei each. They extend between one quarter to one third the length of the body.[1]

The females are around twice as long as the males. The eggs are oval with three apparent membranes. The outer membrane is thick with the exception of the anterior end where it is thin and often indented and the posterior end which 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 also have eight oval cement glands, each with single giant nucleus, and possess a Saefftigen's pouch just behind the testes.[1] 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.[1]

The distribution of A. semoni is determined by that of its hosts. A. semoni has been found in several provinces 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, Australia.[1]

A. semoni parasitizes Australian and New Guinean 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), brush-tailed phascogale (Phascogale tapoatafa) by infesting their small and large intestines.[1] Infestation may cause debilitating ulcerative granulomatous gastritis.[10] Juvenile worms were found in the accidental host (an organism that generally does not allow transmission to the definitive host) brown antechinus (Antechinus stuartii).[1]

• Hosts for Australiformis semoni
• 
  The Southern brown bandicoot is the type host of A. semoni
• 
  Northern brown bandicoot
• 
  Long-nosed bandicoot
• 
  Striped bandicoot
• 
  Brush-tailed phascogale