Polymorphus



''Polymorphus''

Polymorphus is a genus of obligate endoparasitic worms that belongs to the phylum Acanthocephala. There are currently 36 extant species within the genus Polymorphus characterized by their endoparasitic lifestyle, and red colouration .

Species

Polymorphus actuganensis Petrochenko, 1949Polymorphus acutis Van Cleave and Starrett, 1940Polymorphus arctocephali Smales, 1986Polymorphus ariusis Polymorphus biziurae Johnston and Edmonds, 1948Polymorphus boschadis Polymorphus brevis Polymorphus chongqingensis Liu, Zhang and Zhang, 1990Polymorphus cincli Belopolskaya, 1959Polymorphus contortus Polymorphus corynoides Skrjabin, 1913Polymorphus corynosoma Travassos, 1915Polymorphus crassus Van Cleave, 1924Polymorphus cucullatus Van Cleave and Starrett, 1940Polymorphus diploinflatus Lundström, 1942Polymorphus fatimaae Khan, Dharejo, Birmani and Bilqees, 2008Polymorphus fulicai Birmani, Dharejo and Khan, 2011Polymorphus gavii Hokhlova, 1965Polymorphus inermis Travassos, 1923Polymorphus karachiensis Polymorphus kostylewi Petrochenko, 1949Polymorphus magnus Skrjabin, 1913Polymorphus marchii Polymorphus marilis Van Cleave, 1939Polymorphus mathevossianae Petrochenko, 1949Polymorphus meyeri Lundström, 1942Polymorphus miniatus Polymorphus minutus Polymorphus mohiuddini Muti-ur-Rahman, Khan, Bilqees and Khatoon, 2008Polymorphus mutabilis Polymorphus nickoli Khan and Bilqees, 1998Polymorphus obtusus Van Cleave, 1918Polymorphus paradoxus Connell and Corner, 1957Polymorphus paucihamatus Heinze, 1936Polymorphus phippsi Kostylew, 1922Polymorphus piriformis Polymorphus pupa Polymorphus sichuanensis Wang and Zhang, 1987Polymorphus sindensis Khan, Ghazi and Bilqees, 2002Polymorphus spindlatus Amin and Heckmann, 1991Polymorphus striatus Polymorphus strumosoides Lundström, 1942Polymorphus swartzi Schmidt, 1965Polymorphus trochus Van Cleave, 1945

Morphology

A distinguishing feature of Polymorphus species is their vivid red to orange pigmentation, which becomes particularly pronounced within transparent intermediate hosts, such as amphipod crustaceans . This conspicuous coloration enhances the visibility of infected hosts to predatory definitive hosts, thereby increasing the efficiency of trophic transmission . The pigmentation arises from the parasite's unique ability to sequester carotenoids from its amphipod hosts, resulting in the characteristic reddish coloration of the organism .

General morphological features

  • Proboscis: The proboscis is a defining structure, armed with 20 to 22 longitudinal rows of 11 to 13 hooks per row, enabling firm attachment to the intestinal wall of the definitive host .
  • Trunk: The body is cylindrical, with anterior expansions. The fore-trunk bears spines, and the neck region is conical in shape .
  • Internal anatomy includes a prominent ganglion, clavate lemnisci, and simple roots anchoring the proboscis apparatus .

Sexual dimorphism and reproductive morphology

Males

  • Possess well-developed testes .
  • The posterior extremity is dramatically rounded, terminating in a terminal genital pore .
  • A distinctive copulatory bursa is present, characterized by numerous sensory pits. The length of the bursa is variable and depends on the degree of eversion, playing a crucial role in reproductive behaviour .

Females

  • The reproductive system features a vaginal complex, ovarian balls, and developing eggs .
  • Eggs are elongated with a polar prolongation of the middle membrane, a taxonomically significant trait within the genus .

Endoparasitic lifestyle

Worms within the genus Polymorphus are well known for their obligate endoparasitic lifestyle, particularly their ability to manipulate intermediate hosts . Polymorphus species utilize invertebrates, including amphipods and decapods, as intermediate hosts and vertebrates such as waterfowl and fish-eating birds as their final hosts. An example of this interaction is the relationship between Polymorphus paradoxus and its intermediate host, Gammarus lacustris. These parasites manipulate G. lacustris by modifying its behavior, causing the amphipod to be drawn to light and swim toward the surface . Such manipulation ultimately enhances the likelihood that P. paradoxus will be consumed by the parasite's final host. Additionally, Polymorphus species exhibit the ability to steal carotenoids from their amphipod hosts, leading to the characteristic red colouration of the organism . By leaching carotenoids from G. lacustris, this causes the amphipod to appear blue opposed to brown, which once again increases the probability of being detected by waterfowl or fish-eating birds.

Previous names

Polymorphus used to be called by many names such as: Profilicollis Meyer, 1931, Falsifilicollis Webster, 1948, Parafilicollis Petrochenko, 1956, Subfilicollis Hoklova, 1967, Subcorynosoma Hoklova, 1967, Arhythmorhynchus Lühe, 1911, Hexaglandula Petrochenko, 1950 or as subgenera.