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Spirula

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Spirula
Temporal range: Miocene–Recent[1]
Spirula spirula1.jpg
Dorsal view of female
Spirula spirula2.jpg
Ventral view of female
(chromatophores of mantle missing)
Scientific classification edit
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Spirulida
Family: Spirulidae
Owen, 1836
Genus: Spirula
Lamarck, 1799
Species:
S. spirula
Binomial name
Spirula spirula
Synonyms

Spirula spirula is a species of deep-water squid-like cephalopod mollusk. It is the only extant member of the genus Spirula, the family Spirulidae, and the order Spirulida. Because of the shape of its internal shell, it is commonly known as the ram's horn squid[3] or the little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the tail-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 many beachcombers. The shell of Spirula is 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. This seashell is known to shell collectors as the ram's horn shell or simply as Spirula.

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Species

Species

In biology, a species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour, or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.

Squid

Squid

True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.

Cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Genus

Genus

Genus is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.

Family (biology)

Family (biology)

Family is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between order and genus. A family may be divided into subfamilies, which are intermediate ranks between the ranks of family and genus. The official family names are Latin in origin; however, popular names are often used: for example, walnut trees and hickory trees belong to the family Juglandaceae, but that family is commonly referred to as the "walnut family".

Order (biology)

Order (biology)

Order is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. An immediately higher rank, superorder, is sometimes added directly above order, with suborder directly beneath order. An order can also be defined as a group of related families.

Spirulida

Spirulida

Spirulida is an order of cephalopods comprising one extant species and several extinct taxa.

Beachcombing

Beachcombing

Beachcombing is an activity that consists of an individual "combing" the beach and the intertidal zone, looking for things of value, interest or utility. A beachcomber is a person who participates in the activity of beachcombing.

Seashell

Seashell

A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another animal.

Conchology

Conchology

Conchology is the study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs; however, malacology is the study of molluscs as whole organisms, whereas conchology is confined to the study of their shells. It includes the study of land and freshwater mollusc shells as well as seashells and extends to the study of a gastropod's operculum.

Siphuncle

Siphuncle

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the septa (walls) dividing the camerae (chambers). Some older studies have used the term siphon for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a mollusc organ of the same name.

Phragmocone

Phragmocone

The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae.

Description

S. spirula has a squid-like body between 35 mm and 45 mm long. It is a decapod, with eight arms and two longer tentacles, all with suckers. The arms and tentacles can all be withdrawn completely into the mantle.

The species lacks a radula[4]: 110 [5]: 26  (or, at most, has a vestigial radula).[6]

Shell

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 to osmotically control buoyancy.[6] Another trait is that it is mineralized, a feature only seen in cuttlefish and the nautilus amongst extant species.[7]

The siphuncle is marginal, on the inner surface of the spiral.[8]

Illustration showing the position of the shell inside the mantle
Illustration showing the position of the shell inside the mantle
End of mantle showing the photophore
End of mantle showing the photophore

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Squid

Squid

True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.

Decapodiformes

Decapodiformes

Decapodiformes is a superorder of Cephalopoda comprising all cephalopod species with ten limbs, specifically eight short arms and two long tentacles. It is hypothesized that the ancestral coleoid had five identical pairs of limbs, and that one branch of descendants evolved a modified arm pair IV to become the Decapodiformes, while another branch of descendants evolved and then eventually lost its arm pair II, becoming the Octopodiformes.

Tentacle

Tentacle

In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainly like muscular hydrostats. Most forms of tentacles are used for grasping and feeding. Many are sensory organs, variously receptive to touch, vision, or to the smell or taste of particular foods or threats. Examples of such tentacles are the eyestalks of various kinds of snails. Some kinds of tentacles have both sensory and manipulatory functions.

Mantle (mollusc)

Mantle (mollusc)

The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.

Osmosis

Osmosis

Osmosis is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential to a region of low water potential, in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a selectively permeable membrane separating two solutions of different concentrations. Osmosis can be made to do work. Osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.

Buoyancy

Buoyancy

Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.

Cuttlefish

Cuttlefish

Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of buoyancy.

Nautilus

Nautilus

The nautilus is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.

Behaviour

Dated illustration of a live animal, but shown upside down; the photophore on a live animal points downward.[9]
Dated illustration of a live animal, but shown upside down; the photophore on a live animal points downward.[9]

S. spirula is capable of emitting a green light from a photophore located at the tip of its mantle, between the ear-shaped fins.[6] Evidently this seems as a counter-illumination strategy, as in situ observations have captured footage of animals in a vertical stance, with photophore pointing downward and head up.[9]

Habitat and distribution

Oral view of the left tentacular club
Oral view of the left tentacular club

By day, Spirula lives in the deep oceans, reaching depths of 1,000 m. At night, it rises to 100–300 m.[10] Its preferred temperature is around 10 °C, and it tends to live around oceanic islands, near the continental shelf.[6]

Most sources cite this species as tropical and they are observed to be plentiful in the subtropical seas around the Canary Islands. Shells are regularly found along the western coasts of South Africa. In 2022, records of the species have also been confirmed in the Arabian Sea.[11] However, significant quantities of shells from dead spirula are washed ashore even in temperate regions, such as coasts of New 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.[12]

The species was observed for the first time in its natural habitat in 2020, when an ROV of the Schmidt Ocean Institute recorded it in the depths near the northern Great Barrier Reef.[9][13]

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Canary Islands

Canary Islands

The Canary Islands, also known informally as the Canaries, are a Spanish autonomous community and archipelago in Macaronesia in the Atlantic Ocean. At their closest point to the African mainland, they are 100 kilometres west of Morocco. They are the southernmost of the autonomous communities of Spain. The islands have a population of 2.2 million people and are the most populous special territory of the European Union.

South Africa

South Africa

South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres (1,739 mi) of coastline that stretches along the South Atlantic and Indian Oceans; to the north by the neighbouring countries of Namibia, Botswana, and Zimbabwe; and to the east and northeast by Mozambique and Eswatini. It also completely enclaves the country Lesotho. It is the southernmost country on the mainland of the Old World, and the second-most populous country located entirely south of the equator, after Tanzania. South Africa is a biodiversity hotspot, with unique biomes, plant and animal life. With over 60 million people, the country is the world's 24th-most populous nation and covers an area of 1,221,037 square kilometres. Pretoria is the administrative capital, while Cape Town, as the seat of Parliament, is the legislative capital. Bloemfontein has traditionally been regarded as the judicial capital. The largest city, and site of highest court is Johannesburg.

Arabian Sea

Arabian Sea

The Arabian Sea is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel and the Arabian Peninsula, on the southeast by the Laccadive Sea and the Maldives, on the southwest by Somalia, and on the east by India. Its total area is 3,862,000 km2 (1,491,000 sq mi) and its maximum depth is 4,652 meters (15,262 ft). The Gulf of Aden in the west connects the Arabian Sea to the Red Sea through the strait of Bab-el-Mandeb, and the Gulf of Oman is in the northwest, connecting it to the Persian Gulf.

List of marine molluscs of New Zealand

List of marine molluscs of New Zealand

This is a list of the marine molluscs of the country of New Zealand, which are a part of the molluscan fauna of New Zealand, which is a part of the biodiversity of New Zealand.

Remotely operated underwater vehicle

Remotely operated underwater vehicle

A remotely operated underwater vehicle is a tethered underwater mobile device, also commonly called an underwater robot.

Schmidt Ocean Institute

Schmidt Ocean Institute

Schmidt Ocean Institute (SOI) is a 501(c)(3) non-profit operating foundation established in March 2009 by Eric Schmidt and Wendy Schmidt. The Institute's goal is to advance innovative oceanographic research and discovery through technological advancement, collaborative research, outreach and education, and open sharing of information. SOI supports oceanographic research by providing collaborators with free ship time aboard their research vessel Falkor (too) and expert technical shipboard support. Collaborating researchers and institutions utilizing Falkor commit to openly share and communicate the outcomes of their research, including raw observations and data. Research proposals are reviewed through a peer-reviewed process and assessed based on their potential for technological innovation, oceanographic research, and overall impact. Since its inception in 2009, SOI has supported over 60 expeditions all around the globe.

Great Barrier Reef

Great Barrier Reef

The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres (1,400 mi) over an area of approximately 344,400 square kilometres (133,000 sq mi). The reef is located in the Coral Sea, off the coast of Queensland, Australia, separated from the coast by a channel 100 miles wide in places and over 200 feet deep. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981. CNN labelled it one of the Seven Natural Wonders of the World in 1997. Australian World Heritage places included it in its list in 2007. The Queensland National Trust named it a state icon of Queensland in 2006.

Source: "Spirula", Wikipedia, Wikimedia Foundation, (2023, February 25th), https://en.wikipedia.org/wiki/Spirula.

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See also
References
  1. ^ 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.
  2. ^ Barratt, I. & Allcock, L. (2012). Spirula spirula. The IUCN Red List of Threatened Species. Version 2014.2.
  3. ^ Norman, M. 2000. Cephalopods: A World Guide. Hackenheim, ConchBooks.
  4. ^ Nixon, M. (1985), "The buccal mass of fossil and recent Cephalopoda", in Wilbur, Karl M. (ed.), The Mollusca, New York: Academic Press, ISBN 0-12-728702-7
  5. ^ Landman, Neil H.; Tanabe, Kazushige; Davis, Richard Arnold (1996). Ammonoid Paleobiology. ISBN 978-0-306-45222-2.
  6. ^ a b c d 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. S2CID 85026080.
  7. ^ 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. PMC 4786199. PMID 26963712.
  8. ^ "Spirula spirula". Tree of Life (tolweb.org).
  9. ^ a b c Lindsay, Dhugal; Hunt, James; McNeil, Mardi; Beaman, Robin; Vecchione, Michael (27 November 2020). "The first in situ observation of the Ram's Horn squid Spirula spirula turns "common knowledge" upside down". Diversity. 12 (449): 449. doi:10.3390/d12120449.
  10. ^ 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. S2CID 86329056.
  11. ^ Sajikumar, K.K; Rajeeshkumar, M.P; Vellathi, Venkatesan (June 2022). "Rediscovery of Ram's horn squid, Spirula spirula (Cephalopoda: Spirulidae), from the Arabian Sea".
  12. ^ Price, G.D.; Twitchett, R.J.; Smale, C.; Marks, V. (2009). "Isotopic analysis of the life history of the enigmatic squid Spirula spirula, with implications for studies of fossil Cephalopods". PALAIOS. 24 (5): 273–279. Bibcode:2009Palai..24..273P. doi:10.2110/palo.2008.p08-067r. S2CID 131523262.
  13. ^ Fox, Alex (3 November 2020). "See strange squid filmed in the wild for the first time". Smithsonian Magazine. Retrieved 2021-04-25.
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