Editing Sea butterfly

{{short description|Suborder of molluscs}}
{{use dmy dates|date=January 2022}}
{{Automatic Taxobox
| name = Sea butterflies
| fossil_range = {{fossil range|Late Paleocene|recent}}
| image = LimacinaHelicinaNOAA.jpg
| image_caption = ''[[Limacina helicina]]''
| taxon = Thecosomata
| authority = [[Henri Marie Ducrotay de Blainville|Blainville]], 1824
| subdivision_ranks = Families
| subdivision = [[Limacinidae]]<br />
[[Cavoliniidae]]<br />
[[Cliidae]]<br />
[[Creseidae]]<br />
[[Cuvierinidae]]<br />
[[Praecuvierinidae]]<br />
[[Peraclididae]]<br />
[[Cymbuliidae]]<br />
[[Desmopteridae]]
}}

The '''Thecosomata''' (collective/plural: ''thecosomes'',<ref name="Lalli1989" /> meaning "case/shell-body"),<ref>{{OED|theco-}} Sub-entry: "''thecoˈsomate'', ''thecoˈsomatous'' {{abbr|adjs.|adjectives}} [{{abbr|Gr.|Greek}} {{lang|grc|σῶµα}} body], belonging to the Thecosomata"</ref> or '''sea butterflies''', are a [[Taxonomy (biology)|taxonomic]] [[suborder (biology)|suborder]] of small, [[pelagic]], free-swimming [[sea snail]]s known as [[holoplankton]]ic [[opisthobranch]] [[gastropod]] [[mollusk]]s, in the [[Order (biology)|order]] [[Pteropoda]] (also included within the informal group [[Opisthobranchia]]). Most pteropods have some form of calcified [[gastropod shell|shell]], although it is often very light, even translucent.<ref name=Hunt-2007/>

The sea butterflies include some of the world's most abundant gastropod species;<ref name="Lalli1989">
{{cite book
 | author1 = Lalli, Carol M.
 | author2 = Gilmer, Ronald W.
 | year = 1989
 | title = Pelagic Snails: The Biology of Holoplanktonic Gastropod Mollusks
 | isbn = 978-0-8047-1490-7
 | url = https://books.google.com/books?id=yIAfwz5cxPMC&pg=PA6
}}
</ref> as their large numbers are an essential part of the ocean food chain, they are a significant contributor to the [[oceanic carbon cycle]].<ref name=Hunt-2007/><ref name=Comeau-Gorsky-etal-2009/> 

==Morphology==
Unlike other [[Sea snail|sea snails]], or even [[Land snail|land snails]], sea butterflies float and swim freely through the ocean, traveling along with the [[Ocean current|currents]]. This has led to a number of evolutionary [[Adaptation|adaptations]] in their bodies, including complete or near-complete loss of the shell and the [[gill]] in several families. Their [[gastropod]]al foot has also taken the form of two wing-like lobes, or ''[[parapodia]]'', which propel the animal through the sea by slow flapping movements.

[[file:sea butterfly.jpg|thumb|left|Unidentified thecosome]]
Most thecosomes have some form of calcified [[gastropod shell|shell]], although often very light.<ref name=Hunt-2007/>
They are rather difficult to see, since their shell, if present, is mostly transparent, fragile, and usually tiny (less than 1&nbsp;cm in length). Although their shell may be so fine as to be transparent, it is nevertheless [[calcareous]], and an important part of the oceanic [[calcium cycle]].<ref name=Comeau-Gorsky-etal-2009>
{{cite journal
 | last1 = Comeau  | first1 = S.    | last2 = Gorsky  | first2 = G.
 | last3 = Jeffree | first3 = R.    | last4 = Teyssié | first4 = J.-L.
 | last5 = Gattuso | first5 = J.-P.
 | year = 2009
 | title = Impact of ocean acidification on a key Arctic pelagic mollusc (''Limacina helicina'')
 | journal = Biogeosciences
 | volume = 6  | issue = 9  | page = 1877
 | doi = 10.5194/bg-6-1877-2009  | bibcode = 2009BGeo....6.1877C | doi-access = free 
| hdl = 10453/14721| hdl-access = free}}
</ref>
Their shells are [[symmetry (biology)#Bilateral symmetry|bilaterally symmetric]] and can vary widely in shape, ranging from coiled or needle-like to triangular or globular.

The shell is present in all life cycle stages of the [[Cavolinioidea]] (euthecosomata). In the [[Cymbulioidea]] (pseudothecosomata), adult Peraclididae also bear shells; the [[Cymbuliidae]] shed their larval shells and develop a cartilaginous ''pseudoconch'' in adulthood. Only the [[Desmopteridae]] lack any rigid covering when mature.

== Behavior and distribution ==
=== Swimming kinematics ===
Molluscan pteropods develop their feet into a pair of wing-like parapodia in the growing phase. These 'wings' are highly flexible, as the orientation of the muscles is different, and they have a [[hydrostatic skeleton]] filled with a pressurized fluid. Thus, the high bending-angle supports the parapodia to diminish the [[Drag (physics)|drag forces]] generated by the classic "[[Insect flight|clap-and-fling]]" maneuver; additionally, it aids in carrying the extra weight of a shell and ascending the water column for the [[diel vertical migration]].<ref>Karakas, F., Maas, A. E., & Murphy, D. W. (2020). A novel cylindrical overlap-and-fling mechanism used by sea butterflies. Journal of Experimental Biology, 223(15), jeb221499.</ref>

The power-stroke for ''L. helicina'' starts with a sharp rotation of it is body accompanied by an increase in swimming speed; it then rotates its shell in the opposite direction to initiate the recovery-stroke and swims upward, with a speed less than the power phase. There is a drop in overall speed between power and recovery strokes, which develop a [[Sawtooth wave|sawtooth]] trajectory in the [[sagittal plane]]. The hyper-pitch of the round shell of ''L. helicina'' diminishes the rotational drag and the moment of [[inertia]]; the extreme shell rotation also assists in raising the wingtips at the end of each stroke to create a figure-eight pattern, common for [[Pterygota|flying insects]]. In contrast, flying insects and shell-less pteropods encounter higher resistance forces that limit the body rotation.<ref>Murphy, D. W., Adhikari, D., Webster, D. R., & Yen, J. (2016). Underwater flight by the planktonic sea butterfly. Journal of Experimental Biology, 219(4), 535-543.</ref>  

Sea butterflies range from the tropics<ref name=ParraFlores2009/> to the poles.<ref name=Seibel2007/>
They are "[[holoplankton]]ic"—they spend all their lives floating amongst [[plankton]], rather than remaining planktonic during their [[larva]]l stage.{{efn|Compare the sea butterflies unusual whole-life residence in the [[plankton]] with the more common behavior of most other [[marine (ocean)|marine]] gastropods, whose [[veliger]] larvae are part of the [[meroplankton]], but who leave the plankton once they reach adult form.}} Thus, thecosomans are most common in the top {{Convert|25|m}} of the ocean—in terms of diversity, species richness, and abundance—and become scarcer with increased depth.<ref name=ParraFlores2009>
{{cite journal
 |author1 = Parra-Flores, A.
 |author2 = Gasca, R.
 |year = 2009
 |title = Distribution of pteropods (Mollusca: Gastropoda: Thecosomata) in surface waters (0–100&nbsp;m) of the Western Caribbean Sea (winter, 2007)
 |journal = Revista de Biología Marina y Oceanografía
 |volume = 44  |issue = 3  |pages = 647–662
 |doi = 10.4067/s0718-19572009000300011  |doi-access = free
}}
</ref>

Occasionally, thecosomans swarm in large numbers, and can sometimes be found washed ashore in [[flotsam]], especially along the coastline of [[eastern Australia]].

=== Diurnal vertical migration ===
Thecosomata beat their wing-like parapodia to "fly" through the water.<ref name=Seibel2007/><ref>
{{cite journal
 |author1=Murphy, D.   |author2=Adhikari, D.
 |author3=Webster, D.  |author4=Yen, J.
 |year=2016
 |title=Underwater flight by the planktonic sea butterfly
 |journal=Journal of Experimental Biology
 |volume=219 |issue=4 |pages=535–543
 |doi=10.1242/jeb.129205 |doi-access=free
 |pmid=26889002
}}
</ref>
When descending to deeper water, they hold their wings up.

They [[migrate vertically]] from day to night, so the community structure changes on a 24&nbsp;hour cycle; during the day many organisms take refuge at water depths in excess of 100&nbsp;m.<ref name=ParraFlores2009/>

===Feeding===
Little is documented of the dietary habits or behaviour of sea butterflies, yet they are known to have a peculiar way of feeding.<ref name=Hunt-2007/> Being generally [[Herbivore|herbivorous]], and mostly passive [[plankton]]-feeders, they live their lives according to the currents and find food by floating [[ventral]]-side up; some may more actively forage, at times.<ref name="Hunt-2007" /> They feed secreting a fine mucus web to capture the plankton and organic particles suspended in water columns.<ref>{{cite web |last=Andringa |first=J. |title=The glass slipper of Cymbulia: the sea butterfly wonder of the ocean |url=https://www.naturetoday.com/intl/en/nature-reports/message/?msg=28866 |website=Nature Today |access-date=2025-04-29}}</ref> Measuring up to 5&nbsp;cm wide—many times larger than their own bodies. If disturbed, they simply abandon the web and flap slowly away.

Each day, they embark on a regular [[diel vertical migration]] through the water column in their pursuit of planktonic prey. At night, they forage at the surface and return to deeper waters by the morning.<ref>
{{cite web
 |title=Sea Butterfly
 |website=Our Breathing Planet
 |url=http://www.ourbreathingplanet.com/sea-butterfly/
 |access-date=12 October 2016
}}</ref>

== Fossil record ==
Geologically-speaking, Thecosomata is a rather young group, being known from the Late [[Paleocene]] of the [[Cenozoic]] Era.<ref>
{{cite book
 | last1= Bé    |first1=A.W.H.
 |last2=Gilmer  |first2=R.W.
 |year=1977
 |chapter=A zoogeographic and taxonomic review of euthecosomatous pteropoda
 |volume=1 |pages=733–808
 |title=Oceanic Micropaleontology
 |editor-first=A.T.S. |editor-last=Ramsey
 |publisher=Academic Press
 |place=London, UK
}}
</ref>

[[File:Sea butterfly pseudoconch (12286).jpg|thumb|Sea butterfly pseudoconch]]
The group is known within the fossil record from shells of those groups within the clade that mineralized.<ref>
{{Cite journal
 | author = Janssen, A.W.
 | year = 2008
 | title = Heliconoides linneensis sp. nov., a new holoplanktonic gastropod (Mollusca, Thecosomata) from the Late Oligocene of the Aquitaine Basin (France, Landes)
 | journal = Zoologische Mededelingen
 | volume = 82 | issue = 9 | pages = 69–72
}}
</ref><ref>
{{cite journal
 | author1 = Lokho, K.
 | author2 = Kumar, K.
 | year = 2008
 | title = Fossil pteropods (Thecosomata, holoplanktonic Mollusca) from the Eocene of Assam-Arakan Basin, northeastern India
 | journal = Current Science
 | volume = 94 | issue = 5 | pages = 647–652
}}
</ref> These carbonate shells are a major contributor to the oceanic carbon cycle, making up as much as 12% of global carbonate flux.<ref name=Hunt-2007/> However, the low stability of their [[aragonitic]] shells means that few end up being preserved within sediments as viable fossils; rather, they are mostly deposited in shallow, tropical seas.<ref name=Hunt-2007/>

==Importance in the food chain==
These creatures, which range from [[lentil]]- to orange-sized, are eaten by various marine species, including a wide variety of fish that are, in turn, consumed by [[penguin]]s and [[polar bear]]s. The sea butterflies form the sole food source of their relatives, the [[Gymnosomata]].<ref name=Seibel2007>
{{Cite journal
 | last1 = Seibel    | first1 = B.A.
 | last2 = Dymowska  | first2 = A.
 | last3 = Rosenthal | first3 = J.
 | year  = 2007
 | title = Metabolic temperature compensation and coevolution of locomotory performance in pteropod molluscs
 | journal = Integrative and Comparative Biology
 | volume = 47 | issue = 6 | pages = 880–891
 | pmid =  21669767
 | doi = 10.1093/icb/icm089  | doi-access = free
}}
</ref> They are also consumed by sea birds, whales, and commercially important fish. However, if sea butterflies are consumed in large quantities fish can get "black gut", which makes them unsellable.<ref name="Lalli1989"/>

==Taxonomy==
Along with its sister group, the sea angels ([[Gymnosomata]]), the sea butterflies (Thecosomata) are included in the [[order (biology)|order]] [[Pteropoda]].<ref name=Hunt-2007/>
The validity of the [[pteropod]] order is not universally accepted; it fell out of favour for a number of years, but recent molecular evidence suggests that the taxon should be revived.<ref>
{{cite journal
 | last1 = Klussmann-Kolb | first1 = A.
 | last2 = Dinapoli       | first2 = A.
 | year = 2006
 | title = Systematic position of the pelagic Thecosomata and Gymnosomata within Opisthobranchia (Mollusca, Gastropoda) - revival of the Pteropoda
 | journal = Journal of Zoological Systematics and Evolutionary Research
 | volume = 44 | issue = 2 | pages = 118
 | doi = 10.1111/j.1439-0469.2006.00351.x
| doi-access = free
 }}
</ref> 
Although most Thecosomata have some form of calcified [[gastropod shell|shell]], mature Gymnosomata have none.<ref name=Hunt-2007/>

=== Ponder & Lindberg ===
Order '''Thecosomata''' <small>[[de Blainville]], 1824</small>
* Infraorder [[Euthecosomata]]
** Superfamily [[Limacinoidea]]
*** Family [[Limacinidae]] <small>[[de Blainville]], 1823</small>
** Superfamily [[Cavolinioidea]]
*** Family [[Cavoliniidae]] <small>H. and A. Adams, 1854</small>
*** Family [[Cliidae]]
*** Family [[Creseidae]]
*** Family [[Cuvierinidae]]
*** Family [[Praecuvierinidae]]
* Infraorder [[Pseudothecosomata]]
** Superfamily [[Peraclidoidea]]
*** Family [[Peraclidae]] <small>Tesch, 1913</small>
** Superfamily [[Cymbulioidea]]
*** Family [[Cymbuliidae]] <small>[[John Edward Gray|Gray]], 1840</small>
*** Family [[Desmopteridae]] <small>[[W.H. Dall|Dall]], 1921</small>

=== Bouchet & Rocroi ===
In the new [[Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)|taxonomy of Bouchet & Rocroi]] (2005) Thecosomata is treated differently :

'''Clade Thecosomata :''' <ref name="Thecosomata">{{cite book | title=Pseudothecosomata, Gymnosomata and Heteropoda (Gastropoda)| last=van der Spoel| first=S.| year=1976| pages=484 pp| publisher=Bohn, Scheltema & Holkema| location=Utrecht | isbn=90-313-0176-0}}</ref>
*Superfamily Cavolinioidea <small> Gray, 1850 </small> ( = Euthecosomata)
**Family Cavoliniidae <small> Gray, 1850 (1815) </small>
***Subfamily Cavoliinae  <small> Gray, 1850 (1815) </small> (formerly Hyalaeidae <small> Rafinesque, 1815 </small>)
***Subfamily Clioinae <small> Jeffreys, 1869 </small> (formerly Cleodoridae <small> Gray, 1840 </small> - ''nomen oblitum'')
***Subfamily Cuvierininae <small> van der Spoel, 1967 </small> (formerly : Cuvieriidae <small> Gray, 1840 </small> (nom. inv.); Tripteridae <small> Gray, 1850 </small>)
***Subfamily Creseinae <small>Curry, 1982 </small>
**Family Limacinidae <small> Gray, 1840 </small> (formerly : Spirialidae <small> Chenu, 1859 </small>; Spiratellidae <small> Dall, 1921 </small>)
** † Family Sphaerocinidae <small> A. Janssen & Maxwell, 1995 </small>
*Superfamily Cymbulioidea <small> Gray, 1840 </small> ( = Pseudothecosomata)
**Family Cymbuliidae <small> Gray, 1840 </small>
***Subfamily Cymbuliinae <small> Gray, 1840 </small>
***Subfamily Glebinae <small> van der Spoel, 1976 </small>
**Family Desmopteridae <small> Chun, 1889 </small>
**Family Peraclidae <small> Tesch, 1913 </small> (formerly Procymbuliidae <small> Tesch, 1913 </small>

Bouchet & Rocroi (2005) move the family Limacinidae into the superfamily Cavolinioidea, making redundant the superfamily Limacinoidea erected for it in Ponder & Lindberg's taxonomy. The families Creseidae and Cuvierinidae are demoted to subfamilies of Cavoliniidae (Creseinae and Cuvierininae). The infraorder Pseudothecosomata becomes the superfamily Cymbulioidea. The family Peraclididae is included in the superfamily Cymbulioidea as the family Peraclidae, making the superfamily Peraclidoidea redundant.

==See also==
* [[Ocean acidification]]
* ''[[Clione antarctica]]''

==Footnotes==
{{notelist}}

==References==
{{reflist|25em|refs=

<ref name=Hunt-2007>
{{cite journal
 | last1 = Hunt  | first1 = B.P.V.   | last2 = Pakhomov | first2 = E.A.
 | last3 = Hosie | first3 = G.W.     | last4 = Siegel   | first4 = V.
 | last5 = Ward  | first5 = P.       | last6 = Bernard  | first6 = K.
 | year = 2008
 | title = Pteropods in Southern Ocean ecosystems
 | journal = Progress in Oceanography
 | volume = 78  | issue = 3  | pages = 193
 | doi = 10.1016/j.pocean.2008.06.001
| bibcode = 2008PrOce..78..193H }}
</ref>

}} <!-- end "refs=" -->

==Sources==
* {{cite book
 |first1=A.W.H. |last1=Bé 
 |first2=R.W.   |last2=Gilmer
 |year=1977
 |section=A zoogeographic and taxonomic review of [[euthecosomatous]] [[pteropoda]]
 |volume=1 |pages=733–808
 |title=Oceanic Micropaleontology
 |editor-first=A.T.S. |editor-last=Ramsey 
 |publisher=Academic Press
 |place=London, UK
}}

* {{cite thesis
 |first=S. |last=van der Spoel
 |year=1967
 |title=Euthecosomata, a group with remarkable developmental stages (Gastropoda, Pteropoda)
 |publisher=University of Amsterdam
 |quote=Gorinchem (J. Noorduijn)
}}

* {{cite book
 |first=S. |last=van der Spoel
 |year=1976
 |title=Pseudothecosomata, Gymnosomata, and Heteropoda (Gastropoda)
 |place=Utrecht
 |publisher=Bohn, Scheltema & Holkema
}}

* {{cite journal
 |author={{grey|[no author cited]}}
 |journal=Cainozoic Research
 |volume=2 |issue=1–2 |pages=163–170
 |year=2003
 |title=Regarding the raising of ranks
}}

* {{cite web
 |title=Sea Butterfly
 |website=Our Breathing Planet
 |url=http://www.ourbreathingplanet.com/sea-butterfly/
 |access-date=12 October 2016
}}

{{Commons category|Thecosomata}}
{{taxonbar|from=Q772011}}

[[Category:Euopisthobranchia]]
[[Category:Extant Thanetian first appearances]]