Cephalaspidea

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Headshield slugs
Chelidonura varians.jpg
A live individual of Chelidonura varians in the family Aglajidae, head end towards the lower left
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Cohort: Tectipleura
Order: Cephalaspidea
Superfamilies

See text

The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia. [1] Bubble shells is another common name for these families of marine gastropods, some of which have thin bubble-like shells. [2] This clade contains more than 600 species. [3]

Contents

Members of this worldwide clade used to be considered the most ancestral of the opisthobranchs, but now they are considered as derived and specialized members of the Euthyneura Spengel, 1881. [4]

Headshield slugs are the most morphologically diverse group of all the opisthobranchs.[ citation needed ]

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).

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 or bristleworms and foraminiferans. 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.

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. [3] The monophyly 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) and two genera ( Laona , Philinorbis ) are reinstated as valid

Linnaean taxonomy

2005 taxonomy

In the taxonomy of Bouchet & Rocroi (2005), the clade Cephalaspidea is arranged as follows:

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) [5] have rearranged taxonomy of Cephalaspidea sensu lato:

The taxonomy of Cephalaspidea sensu lato by Malaquias et al. (2009) [5] is arranged as follows (there are listed genera under molecular analysis; not analyzed families are under "incertae sedis"):

Architectibranchia Haszprunar, 1985

Runcinacea Burn, 1963

Cephalaspidea Fischer, 1887 – This means Cephalaspidea sensu stricto

2010 taxonomy

Subsequently, Malaquias (2010) [6] moved Bullacta exarata (formerly the only member of Bullactidae) into the family Haminoeidae. [6]

Jörger et al. (2010) [1] moved Cephalaspidea sensu stricto and Runcinacea into the Euopisthobranchia and they confirmed the placement of Acteonoidea within the Lower Heterobranchia. [1] 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.

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 [3]

The superfamily Bulloidea was not supported in the Bayesian phylogenetic hypothesis and Diaphanoidea was found polyphyletic. The superfamilies Haminoeoidea and Philinoidea were accepted. The composition of each of the superfamilies was drastically rearranged.

Related Research Articles

Diaphanoidea is a taxonomic superfamily of small sea snails, marine opisthobranch gastropod mollusks or micromollusks in the Cephalaspidea, the headshield slugs and bubble snails.

Notodiaphana fragilis is a species of marine snail, gastropod mollusk in the clade Architectibranchia.

<span class="mw-page-title-main">Haminoeoidea</span> Superfamily of gastropods

Haminoeoidea is a taxonomic superfamily of small sea snails or bubble shells, marine opisthobranch gastropod mollusks in the clade Cephalaspidea, the headshield slugs and bubble snails.

<span class="mw-page-title-main">Haminoeidae</span> Family of gastropods

Haminoeidae, commonly known as the haminoeid bubble snail family, is a taxonomic family of sea snails, marine opisthobranch gastropod mollusks in the superfamily Haminoeoidea.

<span class="mw-page-title-main">Philinoidea</span> Superfamily of gastropods

Philinoidea is a taxonomic superfamily of sea slugs, specifically headshield slugs, marine gastropod mollusks in the order Cephalaspidea.

<span class="mw-page-title-main">Aglajidae</span> Family of gastropods

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.

<span class="mw-page-title-main">Bulloidea</span> Superfamily of gastropods

Bulloidea is a superfamily of sea snails, or bubble snails, marine gastropod mollusks.

<span class="mw-page-title-main">Philinidae</span> Family of gastropods

Philinidae is a family of medium-sized sea slugs, marine opisthobranch gastropod mollusks. These are headshield slugs, in the order Cephalaspidea.

<span class="mw-page-title-main">Cylichnidae</span> Family of gastropods

Cylichnidae, common name the "chalice bubble snails" or "canoe bubble snails" is a family of sea snails or bubble snails, marine gastropod mollusks in the superfamily Cylichnoidea.

Runcinoidea is a taxonomic superfamily or a clade Runcinaecea of sea slugs, marine gastropod mollusks in the order Runcinida

This overview lists proposed changes in the taxonomy of gastropods at the family level and above since 2005, when the taxonomy of the Gastropoda by Bouchet & Rocroi (2005) was published. In other words, these are recent updates in the way various groups of snails and slugs are classified.

<span class="mw-page-title-main">Scaphandridae</span> Family of gastropods

Scaphandridae is a family of sea snails, marine gastropod mollusks in the superfamily Philinoidea.

Architectibranchia is a clade of marine snails, gastropod molluscs.

<span class="mw-page-title-main">Rhizoridae</span> Family of gastropods

Rhizoridae is a family of very small sea snails, barrel-bubble snails, marine opisthobranch gastropod molluscs. These are headshield slugs, in the superfamily Bulloidea.

<span class="mw-page-title-main">Tornatinidae</span> Family of gastropods

Tornatinidae is a family of very small sea snails, barrel-bubble snails, marine opisthobranch gastropod molluscs. These are headshield slugs, in the superfamily Bulloidea.

<i>Smaragdinella</i> Genus of sea snails

Smaragdinella is a genus of medium-sized sea snails or bubble snails, marine opisthobranch gastropod molluscs in the family Haminoeidae, the haminoea bubble snails, part of the clade Cephalaspidea, the headshield slugs and bubble snails.

<i>Biuve fulvipunctata</i> Species of gastropod

Biuve fulvipunctata, the white-speckled headshield slug, is a species of sea slug or headshield slug, a marine opisthobranch gastropod mollusc in the family Aglajidae. This species is widespread in the Indian and Pacific Oceans but has invaded the Mediterranean Sea since 1961, despite apparently being absent from the Red Sea until recorded there in the 21st century. It is the only species in the monotypic genus Biuve.

<span class="mw-page-title-main">Cylichnoidea</span> Superfamily of gastropods

Cylichnoidea is a superfamily of sea snails or bubble snails, marine gastropod molluscs in the order Cylichnidae, the "chalice bubble snails".

Laonidae is a family of small marine snails belonging to the superfamily Philinoidea, though Laonidae and Philinoidea are genetically distinct. They are monophyletic, meaning they are developed from a single ancestor. Laonidae also has the synonymised name Laoninae, which is largely unaccepted in the modern day scientific community. The name Laoninae is introduced by Alice Pruvot-Fol who proposes it as the subfamily to the genea Loana, A.Adams 1865.

<i>Phanerophthalmus</i> Genus of gastropods

Phanerophthalmus is a genus of medium-sized sea snails or bubble snails, marine opisthobranch gastropod molluscs in the family Haminoeidae, the haminoea bubble snails, part of the clade Cephalaspidea, the headshield slugs and bubble snails.

References

  1. 1 2 3 Jörger, Katharina M; Stöger, Isabella; Kano, Yasunori; Fukuda, Hiroshi; Knebelsberger, Thomas; Schrödl, Michael (2010). "On the origin of Acochlidia and other enigmatic euthyneuran gastropods, with implications for the systematics of Heterobranchia". BMC Evolutionary Biology. 10 (1): 323. Bibcode:2010BMCEE..10..323J. doi: 10.1186/1471-2148-10-323 . PMC   3087543 . PMID   20973994.
  2. ↑ Dance, S. P. (1996). Shells. The visual guide to over 500 species of seashell from around the world. Dorling Kindersley. pp. 200–203. ISBN   0-86318-811-7.
  3. 1 2 3 Oskars, Trond R.; Bouchet, Philippe; Malaquias, Manuel António E. (2015). "A new phylogeny of the Cephalaspidea (Gastropoda: Heterobranchia) based on expanded taxon sampling and gene markers". Molecular Phylogenetics and Evolution. 89: 130–150. Bibcode:2015MolPE..89..130O. doi:10.1016/j.ympev.2015.04.011. PMID   25916189.
  4. ↑ Wägele, Heike; Klussmann-Kolb, Annette; Verbeek, Eva; Schrödl, Michael (2014). "Flashback and foreshadowing—a review of the taxon Opisthobranchia". Organisms Diversity & Evolution. 14: 133–149. doi:10.1007/s13127-013-0151-5.
  5. 1 2 3 4 5 Malaquias, Manuel António E; Mackenzie-Dodds, Jacqueline; Bouchet, Philippe; Gosliner, Terrence; Reid, David G (2009). "A molecular phylogeny of the Cephalaspidea sensu lato (Gastropoda: Euthyneura): Architectibranchia redefined and Runcinacea reinstated". Zoologica Scripta. 38 (1): 23–41. doi:10.1111/j.1463-6409.2008.00354.x.
  6. 1 2 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 44(33 & 34): 2015-2029. doi : 10.1080/00222933.2010.487574.
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