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List of animals featuring external asymmetry

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The beak of a wrybill is bent towards the right

This is a list of animals that markedly feature external asymmetry in some form. They are exceptions to the general pattern of symmetry in biology. In particular, these animals do not exhibit bilateral symmetry which permits streamlining and is common in animals.[1]

Birds

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The crossbill has an unusual beak in which the upper and lower tips cross each other.[2]

The wrybill is the only species of bird with a beak that is bent sideways (always to the right).[2]

Many owl species, such as the barn owl, have asymmetrically positioned ears that enhance sound positioning.[3]

Fish

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Fish: Dorsal view of right-bending (left) and left-bending (right) jaw morphs[4]

Many flatfish, such as flounders, have eyes placed asymmetrically in the adult fish. The fish has the usual symmetrical body structure when it is young, but as it matures and moves to living close to the sea bed, the fish lies on its side, and the head twists so that both eyes are on the top.[5]

The jaws of the scale-eating cichlid Perissodus microlepis occur in two distinct morphological forms. One morph has its jaw twisted to the left, allowing it to eat scales more readily on its victim’s right flank. The other morph has its jaw twisted to the right, which makes it easier to eat scales on its victim’s left flank. The relative abundance of the two morphs in populations is regulated by frequency-dependent selection.[4][6][7]

Mammals

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The narwhal has a helical tusk on its upper left jaw. Odobenocetops, an extinct toothed whale, may have possessed similar asymmetrical dentition, though it differed from the narwhal in possessing two erupted, rear-facing tusks with the right significantly longer than the left.[8]

The sperm whale (Physeter macrocephalus) has a single nostril on its upper left head. The right nostril forms a phonic lip. The source of the air forced through the phonic lips is the right nasal passage. While the left nasal passage opens to the blow hole, the right nasal passage has evolved to supply air to the phonic lips. It is thought that the nostrils of the land-based ancestor of the sperm whale migrated through evolution to their current functions, the left nostril becoming the blowhole and the right nostril becoming the phonic lips.[citation needed]

The fin whale (Balaenoptera physalus) has complex and asymmetrical coloration on its head, with the jaw dark grey on one side and white on the other.[9]

The caribou or reindeer (Rangifer tarandus) has asymmetrical antlers. Adult males, in particular, usually possess one brow tine formed into a "shovel" shape.[10] Suggestions for its function include eye protection during antler-threshing courtship displays[11] or as an offensive weapon during the mating season.[12]

Honey badgers of the subspecies signata have a second lower molar on the left side of their jaws, but not the right.[13]

Humans show a systematic aurofacial asymmetry, meaning that the face (eyes, nose and mouth) are displaced to the left with respect to the midplane between the ears. In young children this asymmetry is on average 4 degrees and is easily recognized (See also: Axial Twist theory).[14]

Reptiles

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Skull of Pareas iwasakii

Iwasaki's snail-eater snake (Pareas iwasakii) is a snail-eating specialist; even newly hatched individuals feed on snails. It has asymmetric jaws, which facilitates feeding on snails with dextral (clockwise coiled) shells. A consequence of this asymmetry is that this snake is much less adept at preying on sinistral (counterclockwise coiled) snails. [15] [16] [17] [18] [19] [20] [21] [22]

Invertebrates

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Fiddler crabs and hermit crabs have one claw much larger than the other, which in hermit crabs is used as a makeshift "door" to block the opening of the shell when it retracts inside. If a male fiddler loses its large claw, it grows another on the opposite side after molting.[23] A soft abdomen is also present in a hermit crab as an asymmetrical modification due to the asymmetrical nature of the snail shells they inhabit.[24]

All gastropods are asymmetrical. This is easily seen in snails and sea snails, which have helical shells. At first glance slugs appear externally symmetrical, but their pneumostome (breathing hole) is always on the right side. The origin of asymmetry in gastropods is a subject of scientific debate.[25] Other gastropods develop external asymmetry, such as Glaucus atlanticus that develops asymmetrical cerata as they mature.

Histioteuthis is a genus of squid, commonly known as the cock-eyed squid, because in all species the right eye is normal-sized, round, blue and sunken; whereas the left eye is at least twice the diameter of the right eye, tubular, yellow-green, faces upward, and bulges out of the head.

Sponges are asymmetrical.[1]

Corals build colonies that are not symmetrical, but the individual polyps exhibit radial symmetry.[26]

Alpheidae feature asymmetrical claws that lack pincers, the larger of which can grow on either side of the body, and if lost can develop on the opposite arm instead.[27]

Certain polyopisthocotylean monogeneans are asymmetrical, as an adaptation to their attachment to the gill of their fish hosts.[citation needed]

Certain parasitic copepods[which?] which live inside the gill chamber of their fish hosts are asymmetrical.[citation needed]

Lobsters of the genera Homarus, Nephrops, and Homarinus have dimorphic claws, a crushing one and a cutting one.[28]

Thrips have asymmetrical mouthparts, unique among insects.[29]

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See also

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References

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  1. ^ a b Symmetry, biological, cited at FactMonster.com from The Columbia Electronic Encyclopedia (2007).
  2. ^ a b Ngutuparore, the wrybill. Narena Olliver, New Zealand Birds Limited. Retrieved 8 February 2012.
  3. ^ Krings, Markus; Castanhinha, Rui; Müller-Limberger, Elena; Wipfler, Benjamin; Wagner, Hermann (August 2020). "Ear asymmetry in Tengmalm's owl (Aegolius funereus): Two phases of asymmetrical development of the squamoso-occipital wing". Zoology. 141: 125814. doi:10.1016/j.zool.2020.125814. PMID 32629330. S2CID 219784846.
  4. ^ a b Lee, H. J.; Kusche, H.; Meyer, A. (2012). "Handed Foraging Behavior in Scale-Eating Cichlid Fish: Its Potential Role in Shaping Morphological Asymmetry". PLOS ONE. 7 (9): e44670. Bibcode:2012PLoSO...744670L. doi:10.1371/journal.pone.0044670. PMC 3435272. PMID 22970282.
  5. ^ American Plaice, Canadian Fisheries. Retrieved 8 February 2012.
  6. ^ Hori, M. (1993). "Frequency-dependent natural selection in the handedness of scale-eating cichlid fish". Science. 260 (5105): 216–219. Bibcode:1993Sci...260..216H. doi:10.1126/science.260.5105.216. PMID 17807183. S2CID 33113282.
  7. ^ Stewart, T. A.; Albertson, R. C. (2010). "Evolution of a unique predatory feeding apparatus: functional anatomy, development and a genetic locus for jaw laterality in Lake Tanganyika scale-eating cichlids". BMC Biology. 8 (1): 8. doi:10.1186/1741-7007-8-8. PMC 2828976. PMID 20102595.
  8. ^ Muizon, CHRISTIAN de; Domning Fls, Daryl P. (April 2002). "The anatomy of Odobenocetops (Delphinoidea, Mammalia), the walrus-like dolphin from the Pliocene of Peru and its palaeobiological implications". Zoological Journal of the Linnean Society. 134 (4): 423–452. doi:10.1046/j.1096-3642.2002.00015.x.
  9. ^ Clark (2008). "Fin Whale" (PDF). Alaska Department of Fish & Game. Retrieved 2021-07-06.
  10. ^ Goss, Richard J. (1990-06-01). "Interactions between asymmetric brow tines in caribou and reindeer antlers". Canadian Journal of Zoology. 68 (6): 1115–1119. doi:10.1139/z90-165. ISSN 0008-4301.
  11. ^ William O. Pruitt, Jr (1966-01-01). "The Function of the Brow-Tine in Caribou Antlers". Arctic. 19 (2): 110–113. doi:10.14430/arctic3419. ISSN 1923-1245.
  12. ^ Bubenik, A. B. (1975). "Significance of antlers in the social life of barren ground caribou". Biol Pap Univ Alaska Spec Rep.
  13. ^ *Rosevear, D. R. (1974). The Carnivores of West Africa. London: British Museum (Natural History). pp. 114–16. ISBN 978-0-565-00723-2.
  14. ^ de Lussanet, M.H.E. (2019). "Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis". PeerJ. 7: e7096. doi:10.7717/peerj.7096. PMC 6557252. PMID 31211022.
  15. ^ Götz M, 2002. The feeding behavior of the snail-eating snake Pareas carinatus Wagler 1830 (Squamata: Colubridae). Amphibia-Reptilia 23:487-493.
  16. ^ Hirata T, Ota H, 1993. Predation on snails by the pareatine snake Pareas iwasakii. Japanese Journal of Herpetology 15:90-91.
  17. ^ Hori M, 1993. Frequency-dependent natural selection in the handedness of scale-eating cichlid fish. Science 260:216-219
  18. ^ Hoso M, 2007. Oviposition and hatchling diet of a snail-eating snake Pareas iwasakii (Colubridae: Pareatinae). Current Herpetology 26:41-43.
  19. ^ Hoso, M., T. Asami, and M. Hori. 2007. Right-handed snakes: convergent evolution of asymmetry for functional specialization. Biology Letters 3:169-172.
  20. ^ Hoso M, Hori M, 2006. Identification of molluscan prey from feces of Iwasaki’s slug snake, Pareas iwasakii. Herpetological Review 37:174–176.
  21. ^ Hoso M, Kameda Y, Wu SP, Asami T, Kato M, Hori M, 2010. A speciation gene for left-right reversal in snails results in anti-predator adaptation. Nature Communications 1:133.
  22. ^ Ota H, Lin JT, Hirata T, Chen SL, 1997. Systematic review of colubrid snakes of the genus Pareas in the East Asian Islands. Journal of Herpetology 31:79-87.
  23. ^ Reaney, Leeann T.; Milner, Richard N.C.; Detto, Tanya; Backwell, Patricia R.Y. (April 2008). "The effects of claw regeneration on territory ownership and mating success in the fiddler crab Uca mjoebergi". Animal Behaviour. 75 (4): 1473–1478. doi:10.1016/j.anbehav.2007.09.021. hdl:1885/53242. S2CID 44159791.
  24. ^ Schwab, I R; Nilsson, Dan‐E (June 2007). "A stranger in his own home". The British Journal of Ophthalmology. 91 (6): 709. ISSN 0007-1161. PMC 1955607. PMID 17563928.
  25. ^ Louise R. Page (2006). "Modern insights on gastropod development: Reevaluation of the evolution of a novel body plan". Integrative and Comparative Biology. 46 (2): 134–143. doi:10.1093/icb/icj018. PMID 21672730.
  26. ^ Gateño, D.; Rinkevich, B. (May 2003). "Coral polyp budding is probably promoted by a canalized ratio of two morphometric fields". Marine Biology. 142 (5): 971–973. doi:10.1007/s00227-003-1009-8. S2CID 82438045.
  27. ^ Pereira, Ariane; Tracey, Erica; Cooney, Patricia C.; Korey, Christopher A.; Hughes, Melissa (4 May 2014). "Post-autotomy claw regrowth and functional recovery in the snapping shrimp Alpheus angulosus". Marine and Freshwater Behaviour and Physiology. 47 (3): 147–159. doi:10.1080/10236244.2014.928460. S2CID 84475452.
  28. ^ Angermeier, W. F. (1 April 1991). "Behavioral expression of the asymmetry in lobster claws". Bulletin of the Psychonomic Society. 29 (4): 311–312. doi:10.3758/BF03333928. ISSN 0090-5054. S2CID 145058162.
  29. ^ Childers, Carl C.; Achor, Diann S. (1991). "Structure of the mouthparts of Frankliniella bispinosa (Morgan) (Thysanoptera: Thripidae)". USDA Forest Service: Northern Research Station. Archived from the original on 20 October 2011.
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