Opisthobranchia
Opisthobranchia Temporal range:
| |
---|---|
Notodoris minor | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Gastropoda
|
Subclass: | Heterobranchia |
Informal group: | Opisthobranchia Milne-Edwards, 1848 |
Included groups | |
clade Cephalaspidea Thecosomata clade Gymnosomata clade Aplysiomorpha group Acochlidiacea clade Sacoglossa group Cylindrobullida clade Umbraculida clade Nudipleura |
Opisthobranchs (/əˈpɪsθəˌbræŋks, -θoʊ-/[2]) is a now informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping.[3]
Euopisthobranchia is a taxon containing a revised collection of opisthobranchs, and that taxon is considered monophyletic. Euopisthobranchia does not include some "traditional" opisthobranchs such as the Sacoglossa and the Acochlidiacea.[4] The subclass Heterobranchia now contains all the species which used to be assigned to Opisthobranchia, plus all the species in the Pulmonata.
The subclass Opisthobranchia included species in the order
Opisthobranch means "gills behind" (and to the right) of the heart. In contrast, Prosobranch means gills in front (of the heart). Opisthobranchs are characterized by two pairs of tentacles and a single gill behind and to the right of the heart. With the lack of a heavily mineralized shell, there has been very little fossil record of the group. However, molecular clock studies have suggested that Opisthobranchia emerged as early as the Carboniferous.[5][6]
Taxonomy
Under the 1931 classification system drawn up by Johannes Thiele, the class Gastropoda was divided into three subclasses; Prosobranchia, Pulmonata and Opisthobranchia. The latter two were later combined into a single order.[7]
The current classification of the gastropods is more nuanced, with the following subclasses:[8]
- Subclass Caenogastropoda
- Subclass Cocculiniformia
- Subclass Heterobranchia
- Subclass Neomphalina
- Subclass Neritimorpha
- Subclass Patellogastropoda
- Subclass Vetigastropoda
- Subclass Gastropoda incertae sedis
As a non-monophyletic taxon
It was speculated as far back as 1985 that the Opisthobranchia were
Because the Pulmonata are a sibling group to an opisthobranch taxon, some authors argued that the Opisthobranchia are therefore not a monophyletic group and can no longer be accepted as a valid taxon.[10] The opisthobranchs are now included within the subclass Heterobranchia, although many manuals and websites still use the old classification.
A phylogenetic study published in November 2004,[11] gave new definitions of the seven main lineages of the Opisthobranchia.
However, in 2005, a study of
Subsequent taxonomic classification in 2005 overturned the Opisthobranchia as a valid clade, reclassifying it as an informal group within the Heterobranchia.[3] Accordingly, articles no longer use the term Opisthobranchia, replacing it with Heterobranchia to emphasise a different concept.[4]By 2011, the "Opisthobranchia" were declared artificial and obsolete and were replaced by new phylogenetic hypotheses.
Linnean taxonomy
Order Opisthobranchia Milne-Edwards, 1848 – sea slugs
- Suborder Cephalaspidea P. Fischer, 1883 – headshield slugs and bubble shells
- Suborder Sacoglossa H. von Ihering, 1876 – sap-sucking slugs and bivalved gastropods
- Suborder AplysiomorphaP. Fischer, 1883 – sea hares
- Suborder Notaspidea P. Fischer, 1883 – sidegill slugs
- Suborder Thecosomata Blainville, 1824 sea butterflies with shells
- Suborder Gymnosomata Blainville, 1824 – sea angels, no shells
- Suborder Nudibranchia Blainville, 1814 – nudibranchs
- Infraorder Anthobranchia Férussac, 1819
- Infraorder Cladobranchia Willan & Morton, 1984
Description
The reduction or loss of the shell, the elaboration of the head, foot or mantle, and the acquisition of chemical defences are evolutionary trends shared by most opisthobranch taxa.[15]
The loss of shell in the group is an example of parallel evolution and has occurred on multiple independent occasions.[16]
Opisthobranchs have undergone detorsion, an evolutionary reversal of the half revolution
There is no marked distinction between head and mantle. The
Their eyes are simple
Ecology
Opisthobranchia represents a morphologically diverse group of gastropods occupying a great variety of
Defense
Principally soft-bodied marine creatures with a reduced or absent
Opisthobranchs secrete irritants such as
Diet
Opisthobranchs may be
Communication
Like most lifeforms, they use chemical cues for much of their life cycle. The
Reproduction
Opisthobranchs are hermaphrodites and have complex reproductive strategies, typically involving reciprocal sperm transfer and storage until the eggs are ready for fertilisation.[21] Eggs are commonly laid in ribbons of varying structure. The egg ribbons are usually unique to each species and in some cases are the only means of differentiating them.[22]
See also
The dictionary definition of opisthobranchia at Wiktionary
- Symposia and workshops on opisthobranchs
- Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)
- Changes in the taxonomy of gastropods since 2005
References
This article incorporates CC-BY-2.0 text from reference[15]
- S2CID 30138345.
- ^ "Opisthobranch". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 26 August 2022.
- ^ ISSN 0076-2997.
- ^ PMID 20973994.
- ISBN 80-7067-599-3.
- PMID 21429465.
- PMID 16230032.
- ^ Gofas, S. (2014). Gastropoda. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=101 on 2015-02-12
- .
- ^ Schroedl, Michael; Jörger, Katharina; Klussmann-Kolb, Annette; Wilson, Nerida (1 July 2011). "Bye bye 'Opisthobranchia'! A review on the contribution of Mesopsammic sea slugs to euthyneuran systematics". Thalassas. 27: 101–112.
- PMID 15336672.
- .
- ^ Schrödl M; Jörger KM; Klussmann-Kolb A; Wilson NG. "Bye bye "Opisthobranchia"! A review on the contribution of mesopsammic sea slugs to euthyneuran systematics" (PDF). Thalassas. 27 (2): 101–112.
- ^ MolluscaBase eds. (2020). MolluscaBase. Opisthobranchia. Accessed through: World Register of Marine Species at: http://marinespecies.org/aphia.php?p=taxdetails&id=382226 on 2020-12-23
- ^ PMID 20205753.
- ^ PMID 15715915.
- S2CID 40169600.
- ISBN 978-3-319-15452-7, retrieved 15 November 2021
- ISBN 0-930118-13-8
- ISBN 0-930118-13-8
- ^ Debelius, Helmut (2001) Nudibranchs and Sea Snails Indo-Pacific Field Guide p. 7 Ikan, Frankfurt
- ISBN 0-930118-13-8
Further reading
- Bieler R. (1990). "Haszprunar's "clado-evolutionary" classification of the Gastropoda—a critique". Malacologia 31(2): 371–380, 2 tabs. [28 May; G, Haszprunar's response published in Malacologia, 1990, 32(1): 195–202].
- Bieler R. (1992). "Gastropod phylogeny and systematics". Annual Review of Ecology and Systematics. 23: 311–338. .
External links
- The Sea Slug Forum, a resource from the Australian Museum.
- Sea slugs of Hawaii
- Born to be Wild: Sea Slugs, retrieved 30.4.2008
- Various opisthobranch species from Indonesia, Philippines and Thailand
- Nudi Pixel Nudi Pixel is a web-based identification tool for opisthobranchs worldwide