Cephalaspidea

Source: Wikipedia, the free encyclopedia.
This article is about the gastropod taxon. For the prehistoric fish taxon, see
Cephalaspida
.

Headshield slugs
A live individual of Chelidonura varians in the family Aglajidae, head end towards the lower left
Scientific classification Edit this classification
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

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]

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).

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

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.

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)

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

polyphyletic. The superfamilies Haminoeoidea and Philinoidea
were accepted. The composition of each of the superfamilies was drastically rearranged.

References

Wikispecies has information related to Cephalaspidea.
  1. ^
    doi:10.1186/1471-2148-10-323
    .
  2. ISBN 0-86318-811-7
    .
  3. ^ a b c 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
  4. ^ H. Wägele, A. Klussmann-Kolb, E. Verbeek, M. Schrödl, Flashback and foreshadowing – a review of the taxon Opisthobranchia; Org. Divers. Evol., 14 (2014), pp. 133–149
  5. ^
    doi:10.1111/j.1463-6409.2008.00354.x
    .
  6. ^
    doi:10.1080/00222933.2010.487574
    .
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