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Temnosewellia

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Temnosewellia
Temnosewellia minor
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Platyhelminthes
Order: Rhabdocoela
Family: Temnocephalidae
Subfamily: Temnocephalinae
Genus: Temnosewellia
Damborenea & Cannon, 2001
Type species[1]
Temnocephala minor
Haswell, 1888
Diversity
52 species, see text

Temnosewellia is a genus of rhabdocoel worms in the family Temnocephalidae, native to Australia and parts of Asia. Members of this genus are ectosymbionts on usually freshwater crustaceans, although some are known from terrestrial hosts. Reaching up to 10 millimetres (0.39 in) in length, they are characterized by five anterior tentacles and a posterior adhesive disk, used for locomotion.

Taxonomy and history

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The genus Temnosewellia was erected by María Cristina Damborenea and Lester Robert Glen Cannon in 2001 to accommodate 15 Australian species formerly placed in the genus Temnocephala, with Temnocephala minor as the type species.[2]: 1115–1116 [3]: 3  A 2006 review described 31 additional species, all found in association with Euastacus crayfish.[4]

Ecology

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T. minor on the surface of a common yabby (Cherax destructor)

Temnosewellia species are specialised ectosymbionts associated with freshwater crustaceans, typically occurring on the external surface of the host or within its branchial chambers. Many species are known to occur only on a single host species,[5] with known hosts including species of shrimp (Caridina, Paratya, and Macrobrachium), crayfish (Cherax, Engaeus, Euastacus, and Parastacoides), crabs (Holthuisana, Villopotamon[6]), and isopods (Phreatoicopsis).[4]: 235  Of the 52 described Temnosewellia species, 32 are known from crayfishes in the genus Euastacus.[5] Some species are known to be capable of switching hosts, including to non-native host species, with T. minor having been documented in cultivation on Pontastacus leptodactylus in Turkey and Germany and on Potamonautes warreni in South Africa.[7]: 2901 

A few species occur on terrestrial hosts, namely T. caeca and T. geonoma on the burrowing isopod Phreatoicopsis terricola, and T. engaei on the land crayfish Engaeus fossor.[8]: 183 

Distribution

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Most Temnosewellia species are known from Australia. Four species are native to temperate and tropical environments in Asia. Of these, T. semperi has the widest range, spanning from South to East Asia, while T. rouxi is known from Aru Island in Indonesia, T. vietnamensis from Quảng Nam, Vietnam, and a still undescribed T. aff. vietnamensis from Kagoshima, Japan. Due to the variety of potential hosts in these regions, it is possible that the species diversity of Temnosewellia has been greatly underestimated.[9]: 10–11  Imported specimens of T. chaeropsis have been found in South Africa, while imported specimens of T. minor have been reported in Germany, Italy, Japan, Turkey, and South Africa.[9]: 1 [7]: 2901 

Evolutionary history

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A 2016 Bayesian phylogeny using molecular clock dating places the internal divergence of the genus at 106 Ma, during the Cretaceous period, close to the divergence of the widespread Australian host genus Euastacus.[5]: 5  Cophylogenetic correlations between host and symbiont indicate a shared evolutionary history across the five main clades of Temnosewellia species in Australia. The northernmost and earliest-diverging of these clades, which is estimated to have split 58 million years ago, maps onto two distinct clades of Euastacus forming a paraphyletic grade, providing evidence of host-switching.[5]: 5, 7 

A 2023 study found the genus to be polyphyletic, and recovered four distinct clades scattered throughout Temnocephalinae.[10]: 12 

Description

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Members of Temnosewellia are small worms growing to approximately 10 mm (0.39 in) long. They are characterised by having five anterior tentacles, a posterior adhesive disc, and an epidermis composed of five syncytial plates: an anterior tentacular plate, a single saddle-like post-tentacular plate, a body plate, a peduncular plate, and a posterior adhesive disc plate. The body and peduncular plates are split into dorsal and ventral sections by a shallow groove. A single pair of eyes is present at the base of the tentacles.[4]: 236  They may also exhibit some dark pigmentation in the body and/or eyes and lack any conspicuous ridges on the tentacles or body. The excretory pore is located on the body plate.[2]: 1115–1116 [11]: 386  Locomotion utilises the anterior tentacles and posterior adhesive disc in a looping leech-like motion.[3]: 1 [10]: 1  Eggs are laid on the surface of the host, and development is direct.[4]: 236 

Species

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The genus Temnosewellia includes 52 species:[12][13]

References

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  1. ↑ "Genus Temnosewellia Damborenea & Cannon, 2001". Australian Faunal Directory. Department of Climate Change, Energy, the Environment and Water. Retrieved 18 July 2026.
  2. 1 2 Cristina Damborenea, M.; Cannon, Lester R. G. (2001). "On neotropical Temnocephala (Platyhelminthes)". Journal of Natural History. 35 (8): 1103–1118. doi:10.1080/00222930152434454. ISSN 0022-2933. OCLC 49668173.
  3. 1 2 Sewell, Kim B. (2013). "Key to the genera and checklist of species of Australian temnocephalans (Temnocephalida)". Museum Victoria Science Reports. 17: 1–13. doi:10.24199/j.mvsr.2013.17. ISSN 1833-0290. OCLC 224727920.
  4. 1 2 3 4 Sewell, Kim B.; Cannon, Lester R. G.; Blair, David (2006). "Review of Temnohaswellia and Temnosewellia (Platyhelminthes: Temnocephalida: Temnocephalidae) ectosymbionts from Australian crayfish Euastacus (Parastacidae)". Memoirs of the Queensland Museum. 52 (1): 199–279. ISSN 2204-1478. OCLC 892910542 – via Biodiversity Heritage Library.
  5. 1 2 3 4 Hoyal Cuthill, Jennifer F.; Sewell, Kim B.; Cannon, Lester R. G.; Charleston, Michael A.; Lawler, Susan; Littlewood, D. Timothy J.; Olson, Peter D.; Blair, David (2016). "Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?". Proceedings of the Royal Society B: Biological Sciences. 283 (1831) 20160585. doi:10.1098/rspb.2016.0585. ISSN 1471-2954. LCCN 92656221. OCLC 1764614.
  6. ↑ Damborenea, Cristina; Brusa, Francisco (2009). "A new species of Temnosewellia (Platyhelminthes, Temnocephalida) ectosymbiont on Villopotamon thaii (Crustacea, Decapoda, Potamidae) from Vietnam". Zoosystema. 31 (2): 321–332. doi:10.5252/z2009n2a5.short. ISSN 1280-9551. OCLC 930608541.
  7. 1 2 Sibraa, Lachlan; Barton, Diane; Shamsi, Shokoofeh (2021). "Occurrence of Temnocephalidae flatworms in Australia". Journal of Natural History. 55 (45–46): 2879–2907. doi:10.1080/00222933.2022.2033869. ISSN 0022-2933. OCLC 49668173.
  8. ↑ Williams, Joan Bowman (1980). "Morphology of a species of Temnocephala (Platyhelminthes) ectocommensal on the isopod Phreatoicopsis terricola". Journal of Natural History. 14 (2): 183–199. doi:10.1080/00222938000770181. ISSN 0022-2933. OCLC 49668173.
  9. 1 2 Uyeno, D.; Kaneko, T.; Uyeno, H.; Miyazaki, W.; Tosuji, H. (2022). "Temnosewellia aff. vietnamensis (Platyhelminthes: Rhabdocoela: Temnocephalidae) associated with freshwater crabs from Kagoshima, southern Japan, with review of records of the genus from East to South Asian countries". Journal of Helminthology. 96 e58. doi:10.1017/S0022149X22000190. ISSN 0022-149X. OCLC 1754614. PMID 35912882.
  10. 1 2 Blair, David; Cannon, Lester R.G.; Littlewood, D. Timothy J.; Olson, Peter D.; Sewell, Kim B. (2023). "The Temnocephalidae (Platyhelminthes): molecular data illuminate the evolution of an ancient group of symbiotic flatworms". Systematics and Biodiversity. 21 (1). doi:10.1080/14772000.2023.2174611. ISSN 1477-2000. OCLC 52503894.
  11. ↑ Cannon, Lester R. G.; Sewell, Kim B. (2001). "A review of Temnosewellia (Platyhelminthes: Temnocephalida) ectosymbionts of Cherax (Crustacea: Parastacidae) in Australia". Memoirs of the Queensland Museum. 46 (2): 385–399. ISSN 2204-1478. OCLC 892910542 – via Biodiversity Heritage Library.
  12. ↑ Tyler S, Artois T, Schilling S, Hooge M, Bush LF (eds.). "Temnosewellia Damborenea & Cannon, 2001". World List of turbellarian worms: Acoelomorpha, Catenulida, Rhabditophora. World Register of Marine Species. Retrieved 18 July 2026.
  13. ↑ Tyler, S.; Schilling, S.; Hooge, M.; Bush, L. F. (eds.). "Temnosewellia Damborenea & Cannon, 2001". Turbellarian Taxonomic Database. Version 2.3. Retrieved 18 July 2026.
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