Spirula
| Spirula Temporal range:
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| Dorsal view of female | |
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| Ventral view of female (chromatophoresof mantle missing) | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Spirulida |
| Family: | Spirulidae Owen,1836 |
| Genus: | Spirula Lamarck,1799 |
| Species: | S. spirula
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| Binomial name | |
| Spirula spirula | |
| Synonyms | |
Spirula spirulais aspeciesof deep-watersquid-likecephalopodmollusk.It is the onlyextantmember of thegenusSpirula,thefamilySpirulidae,and theorderSpirulida.Because of the shape of its internal shell, it is commonly known as theram's horn squid[3]or thelittle post horn squid.Because the live animal has a light-emitting organ, it is also sometimes known as thetail-light squid.
Live specimens of this cephalopod are very rarely seen because it is a deep-ocean dweller. The small internal shell of the species is, however, quite a familiar object to manybeachcombers.The shell ofSpirulais extremely light in weight, very buoyant, and surprisingly durable; it very commonly floats ashore onto tropical beaches (and sometimes even temperate beaches) all over the world. Thisseashellis known toshell collectorsas theram's horn shellor simply asSpirula.
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Side view of aSpirulashell -
Taxonomy
[edit]Swedish botanistCarl LinnaeusdescribedNautilus spirulaLinnaeus, 1758 in his bookSystema Naturae.[4]In 1799, French naturalistJean-Baptiste Lamarckdescribed the genusSpirulaand transferred this species to it, andSpirula spirulais the name still used today for the ram's horn squid.[5][6]S. spirulais the only species in the monotypic genusSpirula.A morphometric study published in 2010 showed that shell characteristics ofS. spirulavary with geography, but no subspecies or additional species were proposed.[7]
Description
[edit]S. spirulahas asquid-like body between 35 mm and 45 mm long. It is adecapod,with eightarmsand two longertentacles,all with suckers. The arms and tentacles can all be withdrawn completely into themantle.
The species lacks a radula[8]: 110 [9]: 26 (or, at most, has a vestigial radula).[10]
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Female with dissected mantle cavity -
Immature specimens at various stages of development -
Immature specimen
Shell
[edit]The most distinctive feature of this species is its buoyancy organ, an internal, chambered, endogastrically coiled shell in the shape of an open planispiral (a flat spiral wherein the coils do not touch each other), and consisting of two prismatic layers. The shell functions toosmoticallycontrolbuoyancy.[10]Unlike the nautilus, which exchange air and liquid only in the three most adoral chambers (the remaining chambers always being gas-filled), spirula can bring cameral fluid into all of their chambers.[11]Another trait is that it is mineralized, a feature only seen incuttlefishand thenautilusamongst extant species of cephalopods.[12]
The siphuncle is marginal, on the inner surface of the spiral.[13]
Behaviour
[edit]
S. spirulais capable of emitting a green light from aphotophorelocated at the tip of its mantle, between theear-shaped fins.[10] Evidently this seems as acounter-illuminationstrategy, asin situobservations have captured footage of animals in a vertical stance, with photophore pointing downward and head up.[14]
Habitat and distribution
[edit]
By day,Spirulalives in the deep oceans, reaching depths of 1,000 m. At night, it rises to 100–300 m.[15][5] Its preferred temperature is around 10 °C, and it tends to live around oceanic islands, near the continental shelf.[10]
Most sources cite this species astropicaland they are observed to be plentiful in thesubtropicalseas around theCanary Islands.Shells are regularly found along the western coasts ofSouth Africa.In 2022, records of the species have also been confirmed in theArabian Sea.[16]However, significant quantities of shells from dead spirula are washed ashore even in temperate regions, such as coasts ofNew Zealand.Because of the great buoyancy of the shells, these may possibly have been carried long distances by ocean currents.
Much of the organism's life history has not been observed; for instance, they are thought to spawn in winter in deeper water, yet no spawnlings have been directly seen. They must occasionally venture into the upper 10 m of the sea, for they are sometimes found in albatross guts.[17]
The species was observed for the first time in its natural habitat in 2020, when anROVof theSchmidt Ocean Instituterecorded it in the depths near the northernGreat Barrier Reef.[14][18]
Evolutionary relationships
[edit]The orderSpirulidaalso contains two extinct suborders:Groenlandibelina(including extinct familiesGroenlandibelidaeandAdygeyidae), andBelopterina(including extinct familiesBelemnoseidaeandBelopteridae).
Spirulais likely the closest living relative of the extinctbelemnitesandaulacocerids.These three groups as a unit are closely related to thecuttlefish,as well as to the true squids.
See also
[edit]References
[edit]- ^Hayward, B.W. (1977)."Spirula(Sepioidea: Cephalopoda) from the Lower Miocene of Kaipara Harbour, New Zealand (note) "(PDF).New Zealand Journal of Geology and Geophysics.19:145–147.doi:10.1080/00288306.1976.10423557.
- ^Barratt, I. & Allcock, L. (2012).Spirula spirula.The IUCN Red List of Threatened Species. Version 2014.2.
- ^Norman, M.2000.Cephalopods: A World Guide.Hackenheim, ConchBooks.
- ^Linné, Carl von (1758).Systema naturae, per regna tria naturae: secundum classes, ordines, genera, species cum characteribus, differentiis, synonymis, locis(in Latin). Vol. v. 1, pt. 2 (Ed. 13. ed.). Vindobonae [Vienna]: Typis Ioannis Thomae. p. 1163.
- ^ab"Critter of the week: Spirula spirula | NIWA".niwa.co.nz.Retrieved2024-04-25.
- ^Lamarck, Jean-Baptiste (1799).Mémoires de la Société d'Histoire Naturelle de Paris(in French). Vol. 1. p. 80.
- ^Neige, Pascal; Warnke, Kerstin (2010)."Just how many species of Spirula are there? A morphometric approach".Cephalopods - Present and Past:77–84.
- ^ Nixon, M. (1985), "The buccal mass of fossil and recent Cephalopoda", in Wilbur, Karl M. (ed.),The Mollusca,New York: Academic Press,ISBN0-12-728702-7
- ^ Landman, Neil H.; Tanabe, Kazushige; Davis, Richard Arnold (1996).Ammonoid Paleobiology.ISBN978-0-306-45222-2.
- ^abcd Warnke, K.; Keupp, H. (2005)."Spirula– a window to the embryonic development of ammonoids? Morphological and molecular indications for a palaeontological hypothesis "(PDF).Facies.51(1–4): 60.doi:10.1007/s10347-005-0054-9.S2CID85026080.
- ^Evolution of the Ammonoids
- ^ Lemanis, R.; Korn, D.; Zachow, S; Rybacki, E.; Hoffmann, R. (2016)."The evolution and development of cephalopod chambers and their shape".PLOS ONE.11(3): e0151404.Bibcode:2016PLoSO..1151404L.doi:10.1371/journal.pone.0151404.PMC4786199.PMID26963712.
- ^"Spirula spirula".Tree of Life (tolweb.org).
- ^abc Lindsay, Dhugal; Hunt, James; McNeil, Mardi; Beaman, Robin; Vecchione, Michael (27 November 2020)."The firstin situobservation of the Ram's Horn squidSpirula spirulaturns "common knowledge" upside down ".Diversity.12(449): 449.doi:10.3390/d12120449.
- ^ Clarke, M.R. (2009). "Cephalopoda collected on the SOND Cruise".Journal of the Marine Biological Association of the United Kingdom.49(4): 961–976.doi:10.1017/S0025315400038042.S2CID86329056.
- ^Sajikumar, K.K; Rajeeshkumar, M.P; Vellathi, Venkatesan (June 2022)."Rediscovery of Ram's horn squid, Spirula spirula (Cephalopoda: Spirulidae), from the Arabian Sea".
- ^ Price, G.D.; Twitchett, R.J.; Smale, C.; Marks, V. (2009). "Isotopic analysis of the life history of the enigmatic squidSpirula spirula,with implications for studies of fossil Cephalopods ".PALAIOS.24(5): 273–279.Bibcode:2009Palai..24..273P.doi:10.2110/palo.2008.p08-067r.S2CID131523262.
- ^ Fox, Alex (3 November 2020)."See strange squid filmed in the wild for the first time".Smithsonian Magazine.Retrieved2021-04-25.
External links
[edit]- "Spirula Spirula".Tree of Life web project.
- "Spirulidaeforum ".TONMO.com.Archived fromthe originalon 2006-03-16 – via Internet Archive (archive.org).