Thorlaksonius platypus

Thorlaksonius platypus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Amphipoda
Family:	Pleustidae
Genus:	Thorlaksonius
Species:	T. platypus
Binomial name
Thorlaksonius platypus (Barnard & Given, 1960)
Synonyms [1]
Pleustes platypaBarnard & Given, 1960

Thorlaksonius platypus is a species of Pleustid amphipod native to southern California. It is thought to be an example of mimicry, as it resembles the gastropod Alia carinata . This was the first example of an arthropod mimicking a gastropod ever described. ^[2]

Taxonomy

Thorlaksonius platypus was originally described in 1960 as Pleustes platypa. ^[3] However, in 1994, it was redescribed under the new genus Thorlaksonius . ^[4]

Description

Thorlaksonius platypus ranges in size from 3.5–10 mm (0.14–0.39 in). ^[5] It has a variable color which closely resembles the variation of Alia carinata . The color of only a single specimen has been described. This individual displayed a brown and grey body with a singular yellow band across its dorsal plates, called the pereon. Its walking legs were light in color with some mottling, again resembling A. carinata. ^[2]

The way in which the amphipod holds its body also mimics the distinct shell of A. carinata. Its abdomen (pleon) is tucked underneath its body and is partially hidden by long protrusions of the pereon. The end of its body sticks up in the water at an angle. It walks slowly when in this position, but is capable of swimming. ^[2]

This species is quite similar to Thorlaksonius depressus and Thorlaksonius grandirostris . ^{[5] [6]} It may be distinguished by the shape of its dorsal pereon and pleon segments, which are sharp in T. platypus, and round in T. depressus. ^[5] Only the final (7th) segment of the pereon and pleon segments 1 and 2 have these tooth-like projections. The only other distinguishing characteristic is a broad rostrum that is longer than the head. ^{[3] [4]}

Distribution and habitat

Thorlaksonius platypus occurrences have been recorded from San Diego in the south to Gaviota State Park in the north. ^[2] Its range may extend up to Point Conception, which separates it from Thorlaksonius depressus (except at La Jolla Cove, where the two species are sympatric and likely interbreed). It is also found off the islands of Catalina and Santa Barbara. ^{[4] [5]}

This species is typically found living on algae, including Macrocystis and coralline algae, ^{[2] [4] [6]} but may also be found on other substrates. ^{[3] [5]}

References

1. WoRMS. "Thorlaksonius platypus (Barnard & Given, 1960)". World Register of Marine Species . Retrieved 5 February 2025.
2. Crane, Jules M. (1969). "Mimicry of the Gastropod 'Mitrella carinata' by the Amphipod 'Pleustes platypa'". The Veliger . 12: 200. Archived from the original on 2024-09-18. Retrieved 2025-02-09– via Biodiversity Heritage Library.
3. Barnard, J. Laurens; Given, Robert R. (April 15, 1960). "Common pleustid amphipods of southern california with a projected revision of the family". Pacific Naturalist. 1 (17): 41. OCLC   86074725.
4. Bousfield, E. L. (1994-05-24). "The amphipod superfamily Leucothoidea on the Pacific coast of North America. Family Pleustidae: subfamily Pleustinae. Systematics and biogeography". Amphipacifica. 1 (2): 38–49. Archived from the original on 2024-09-16. Retrieved 2025-02-09– via Biodiversity Heritage Library.
5. Barnard, J. Laurens (1969). "Gammaridean Amphipoda of the rocky intertidal of California: Monterey Bay to La Jolla". Bulletin of the United States National Museum. 258: 206–209. doi:10.5479/si.03629236.258.1. hdl:10088/9998. Archived from the original on 2025-01-08. Retrieved 2025-02-09.
6. Light, Sol Fetty (2007-05-07). "39: Amphipoda". In Chapman, John W. (ed.). Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon (4th ed.). University of California Press. p. 602. ISBN   9780520239395. OCLC   83758750. Archived from the original on 2025-01-19.