The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major
taxon
In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
of sea slugs and bubble snails,
marine gastropod
Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, freshwater, and fro ...
mollusk
Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...
s within the larger clade
Euopisthobranchia
Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura.
This clade was established as a new taxon by Jörger et al. in October 2010. Euopisthobranchia is a monophyletic portion of the ...
.
Bubble shells is another common name for these families of marine gastropods, some of which have thin bubble-like shells. This clade contains more than 600 species.
Members of this worldwide clade used to be considered the most ancestral of the
opisthobranch
Opisthobranchs () 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.
Euopistho ...
s, but now they are considered as derived and specialized members of the
Euthyneura
Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia.
Euthyneura are characterised by several autapomorphies, bu ...
Spengel, 1881.
Headshield slugs are the most morphologically diverse group of all the opisthobranchs.
Anatomy
The vast majority possess a shell, although it may be reduced or internal. They have a well-developed headshield, a characteristic broadening at the head, which is used to plow beneath the surface of the sand. This headshield prevents the sand entering the mantle cavity. There is a muscular foot with or without parapodia (fleshy wing-like flaps).
Life habits and related anatomical structures
Headshield slugs often live just beneath the surface of the sand and can also be seen crawling on rocks. They have well-developed
sensory structures to detect prey, which may be other opisthobranchs,
polychaetes
Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...
or bristleworms and
foraminifera
Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
ns. Several species are voracious carnivores.
Members of the brightly colored genus ''
Chelidonura'' also have well-developed eyes on the anterior end of the head and bundles of sensory cilia around the mouth. With these cilia they are able to track their prey by following the victim's mucous trail.
The
Hancock's organ is a
chemosensory organ situated between the foot and the headshield. It plays a role in olfactory and sensory detection. It is visible as a dark brown pit at the base of the right
rhinophore
A rhinophore is one of a pair of Chemoreceptor, chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, Marine (ocean), marine gastropod opisthobranch mollusks suc ...
.
Taxonomy
The taxonomy of the shelled cephalaspideans, the bubble snails, like that of many shelled mollusks, used to be based very simply on shell characteristics. But because there are some similarities in shell morphology throughout this group, more recently taxonomists have taken other anatomical characteristics into consideration, such as the radula, gizzard, penis, and Hancock's organ.
In 2015 a new study based on molecular phylogenetics has changed significantly the taxonomy of the Cephalaspidea.
The
monophyly
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent comm ...
of the Cephalaspidea was confirmed, but the families Cylichnidae, Diaphanidae, Haminoeidae, Philinidae, and Retusidae were found non-monophyletic. This had led to the creation of new families ((
Alacuppidae,
Colinatydidae,
Colpodaspididae,
Mnestiidae,
Philinorbidae) ) and one new genus (''
Alacuppa''). Two family names (
Acteocinidae,
Laonidae
Laonidae is a family of small marine snails belonging to the superfamily Philinoidea,MolluscaBase eds. (2021). MolluscaBase. Laonidae Pruvot-Fol, 1954. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php? ...
) and two genera (''
Laona'', ''
Philinorbis'') are reinstated as valid
Linnaean taxonomy
* Suborder Cephalaspidea P. Fischer, 1883
** Superfamily
Acteonoidea D'Orbigny
Alcide Charles Victor Marie Dessalines d'Orbigny (6 September 1802 – 30 June 1857) was a French naturalist who made major contributions in many areas, including zoology (including malacology), palaeontology, geology, archaeology and anthropol ...
, 1835
** Superfamily
Bulloidea Lamarck
Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biolo ...
, 1801
** Superfamily
Cylindrobulloidea Thiele, 1931 – These are now included in the suborder
Sacoglossa
Sacoglossa are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia known as sacoglossans. There are 284 valid species recognized within this superorder. Sacoglossans live by ingestin ...
** Superfamily
Diaphanoidea Odhner, 1914
** Superfamily
Haminoeoidea Pilsbry, 1895
** Superfamily
Philinoidea J.E. Gray, 1850
** Superfamily
Ringiculoidea Philippi, 1853
2005 taxonomy
In the
taxonomy of Bouchet & Rocroi (2005), the
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
Cephalaspidea is arranged as follows:
* Superfamily
Bulloidea: family
Bullidae
* Superfamily
Diaphanoidea: families
Diaphanidae and
Notodiaphanidae,
* Superfamily
Haminoeoidea: families
Haminoeidae,
Bullactidae and
Smaragdinellidae
* Superfamily
Philinoidea: families
Philinidae,
Aglajidae
Aglajidae is a family of often colorful, medium-sized, sea slugs, marine opisthobranch gastropod mollusks. These are not nudibranchs; instead they are headshield slugs, in the clade Cephalaspidea
The order Cephalaspidea, also known as the ...
,
Cylichnidae,
Gastropteridae,
Philinoglossidae,
Plusculidae and
Retusidae
* Superfamily
Runcinoidea: families
Runcinidae and
Ilbiidae
The superfamily
Acteonoidea has been included into the new Informal Group "Lower Heterobranchia" and the superfamily Cylindrobulloidea becomes part of the Group Cylindrobullida.
2009 taxonomy
Malaquias et al. (2009)
have rearranged taxonomy of Cephalaspidea ''sensu lato'':
* reinstated
Architectibranchia
* reinstated
Runcinacea as a valid name outside Cephalaspidea.
* reinstated
Scaphandridae
Scaphandridae is a family (biology), family of sea snails, marine (ocean), marine gastropod mollusks in the superfamily Philinoidea.
Taxonomy
Scaphandridae was considered as a synonym of Cylichnidae in the Taxonomy of the Gastropoda (Bouchet & ...
as a valid family.
* they did not use superfamilies in the classification scheme.
The taxonomy of Cephalaspidea ''
sensu lato
''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...
'' by Malaquias et al. (2009)
is arranged as follows (there are listed genera under molecular analysis; not analyzed families are under "
incertae sedis
or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
"):
Architectibranchia Haszprunar, 1985
* Family
Acteonidae d'Orbigny, 1843 – ''
Acteon'', ''
Mexacteon'', ''
Pupa
A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...
''
* Family
Aplustridae
The Aplustridae is a Taxonomy (biology), taxonomic family (biology), family of sea snails or bubble snails, Marine (ocean), marine gastropod mollusks in the superfamily Acteonoidea.
The former name of this family, Hydatinidae (Pilsbry, 1893) has ...
Gray, 1847 – ''
Hydatina'', ''
Micromelo''
* Family
Bullinidae Gray, 1850 incertae sedis
* Family
Ringiculidae
Ringiculidae are a family (biology), family of small deep water sea snails, marine (ocean), marine gastropod mollusks or micromollusks in the informal group Lower Heterobranchia.Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., ...
Philippi, 1853 incertae sedis
* Family
Notodiaphanidae Thiele, 1931 incertae sedis
Runcinacea Burn, 1963
* Family
Runcinidae H. Adams & A. Adams, 1854 – ''
Runcina''
* Family
Ilbiidae Burn, 1963 incertae sedis
Cephalaspidea Fischer, 1887 – This means Cephalaspidea ''
sensu stricto
''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
''
* Family
Diaphanidae Odhner, 1914 – ''
Diaphana'', genus ''
Colpodaspis'' is incertae sedis
* Family
Cylichnidae H. Adams & A. Adams, 1854 – ''
Cylichna''
* Family
Scaphandridae
Scaphandridae is a family (biology), family of sea snails, marine (ocean), marine gastropod mollusks in the superfamily Philinoidea.
Taxonomy
Scaphandridae was considered as a synonym of Cylichnidae in the Taxonomy of the Gastropoda (Bouchet & ...
G. O Sars, 1878 – ''
Scaphander
''Scaphander'' is a genus of sea snails, marine (ocean), marine gastropod molluscs in the family (biology), family Scaphandridae, the canoe bubbles.
Description
(Described as ''Meloscaphander'') The shell is ovate, convex in its upper part, and ...
''
* Family
Retusidae Thiele, 1925 – ''
Retusa'', ''
Pyrunculus''
* Family
Rhizoridae Dell, 1952 – ''
Volvulella''
* Family
Bullidae Gray, 1827 – ''
Bulla''
* Family
Philinidae Gray, 1850 – ''
Philine''
* Family
Aglajidae
Aglajidae is a family of often colorful, medium-sized, sea slugs, marine opisthobranch gastropod mollusks. These are not nudibranchs; instead they are headshield slugs, in the clade Cephalaspidea
The order Cephalaspidea, also known as the ...
Pilsbry, 1895–96 – ''
Aglaja'', ''
Chelidonura'', ''
Navanax'', ''
Odontoglaja'', ''
Philinopsis''
* Family
Philinoglossidae Hertling, 1932 – ''
Philinoglossa''
* Family
Gastropteridae Swainson, 1840 – ''
Gastropteron'', ''
Sagaminopteron'', ''
Siphopteron''
* Family
Plusculidae Odhner, 1968 incertae sedis
* Family
Haminoeidae Pilsbry, 1893 – ''
Atys'', ''
Haminoea'', ''
Phanerophthalmus'', ''
Smaragdinella'', ''
Ventomnestia'' incertae sedis
* Family
Bullactidae Thiele, 1826 incertae sedis
2010 taxonomy
Subsequently, Malaquias (2010)
[Malaquias M. A. E. (2010). "Systematics, phylogeny, and natural history of ''Bullacta exarata'' (Philippi, 1849): an endemic cephalaspidean gastropod from the China Sea". '']Journal of Natural History
The ''Journal of Natural History'' is a scientific journal published by Taylor & Francis focusing on entomology and zoology. The journal was established in 1841 under the name ''Annals and Magazine of Natural History'' (''Ann. Mag. Nat. Hist.'') an ...
'' 44(33 & 34): 2015-2029. . moved ''
Bullacta exarata'' (formerly the only member of Bullactidae) into the family
Haminoeidae.
Jörger et al. (2010)
moved Cephalaspidea ''
sensu stricto
''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
'' and Runcinacea into the
Euopisthobranchia
Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura.
This clade was established as a new taxon by Jörger et al. in October 2010. Euopisthobranchia is a monophyletic portion of the ...
and they confirmed the placement of
Acteonoidea within the
Lower Heterobranchia
Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly evolved sea slugs and sea snails, marine (ocean), marine gastropod mollusc, mollusks within the Subclass (biology), subclass Heterobranchia.WoRMS (20 ...
.
All families of Architectibranchia were already within the Lower Heterobranchia in the taxonomy of Bouchet & Rocroi, except for the
Notodiaphanidae, which has been placed in the Lower Heterobranchia since 2010, in order that the Architectibranchia can be considered to be
monophyletic
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
.
2015 taxonomy
The publication by Oskars T.R., Bouchet P. & Malaquias M.A. (2015)''. A new phylogeny of the Cephalaspidea (Gastropoda: Heterobranchia) based on expanded taxon sampling and gene markers.'' in the journal Molecular Phylogenetics and Evolution. 89 came to the following conclusion, with the creation of new families
*
Acteocinidae Dall, 1913 – type genus: ''
Acteocina'' Gray, 1847
*
Alacuppidae Oskars, Bouchet, and Malaquias, 2015 – type genus: ''
Alacuppa'' Oskars, Bouchet, and Malaquias, 2015
*
Mnestiidae Oskars, Bouchet, and Malaquias, 2015 – type genus: ''
Mnestia'' H. Adams and A. Adams, 1854
*
Colpodaspididae Oskars, Bouchet, and Malaquias, 2015 – type genus: ''
Colpodaspis'' M. Sars, 1870
*
Colinatydidae Oskars, Bouchet, and Malaquias, 2015 – type genus: ''
Colinatys'' Ortea, Moro and Espinosa, 2013
*
Philinorbidae Oskars, Bouchet, and Malaquias, 2015 – type genus: ''
Philinorbis'' Habe, 1950
*
Laonidae
Laonidae is a family of small marine snails belonging to the superfamily Philinoidea,MolluscaBase eds. (2021). MolluscaBase. Laonidae Pruvot-Fol, 1954. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php? ...
Pruvot-Fol, 1954 (formerly Laoninae) – type genus:
Laona A. Adams, 1865
*
nassignedCephalaspidea (temporary name) with the genera ''
Cylichnium''
Dall, 1908, ''
Micratys''
Habe, 1952 and ''
Noalda''
Iredale, 1936.
The superfamily
Bulloidea was not supported in the
Bayesian phylogenetic hypothesis and
Diaphanoidea was found
polyphyletic
A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
. The superfamilies
Haminoeoidea and
Philinoidea were accepted. The composition of each of the superfamilies was drastically rearranged.
Image:Bulla ampulla 01.JPG, '' Bulla ampulla'' ( Bullidae).
Image:Haminoea cymbalum Réunion.JPG, '' Haminoea cymbalum'' ( Haminoeidae).
Image:Chelidonura varians.JPG, '' Chelidonura varians'' (Aglajidae
Aglajidae is a family of often colorful, medium-sized, sea slugs, marine opisthobranch gastropod mollusks. These are not nudibranchs; instead they are headshield slugs, in the clade Cephalaspidea
The order Cephalaspidea, also known as the ...
).
Image:Siphopteron quadrispinosum copulating.png, Couple of '' Siphopteron quadrispinosum'' ( Gastropteridae).
References
Oskars T.R., Bouchet P. & Malaquias M.A. (2015). A new phylogeny of the Cephalaspidea (Gastropoda: Heterobranchia) based on expanded taxon sampling and gene markers. Molecular Phylogenetics and Evolution. 89: 130-150
{{Authority control
Protostome unranked clades