Cephalaspidea
From Wikipedia, the free encyclopedia
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 The sea slug Chelidonura varians
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The suborder Cephalaspidea, also known as the headshield slugs and bubble shells, is a suborder of sea slugs and bubble snails, marine opisthobranch gastropod mollusks.
Members of this worldwide suborder are considered the most primitive of the Opisthobranchs. They most closely resemble their prosobranch ancestors. Cephalispideans are therefore traditionally considered to be a transitional group between prosobranch gastropods, the majority of which have a shell, and the mostly shell-less opisthobranchs.
Headshield slugs are the most morphologically diverse group of all opisthobranchs.
[edit] 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 winglike flaps).
[edit] Life habits and related anatomical structures
Headshield slugs 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.
[edit] Taxonomy
The taxonomy of headshield slugs, 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.
- Suborder Cephalaspidea P. Fischer, 1883
- Superfamily Acteonoidea D'Orbigny, 1835
- Superfamily Bulloidea Lamarck, 1801
- Superfamily Cylindrobulloidea Thiele, 1931 (These are now included in the suborder Sacoglossa)
- Superfamily Diaphanoidea Odhner, 1914
- Superfamily Haminoeoidea Pilsbry, 1895
- Superfamily Philinoidea J.E. Gray, 1850
- Superfamily Ringiculoidea Philippi, 1853
In the new taxonomy of Bouchet & Rocroi (2005), the clade Cephalaspidea is arranged as follows :
- Superfamily Bulloidea : family Bullidae
- Superfamily Diaphanoidea : family Diaphanidae, family Notodiaphanidae,
- Superfamily Haminoeoidea : family Haminoeidae, family Bullactidae, family Smaragdinellidae
- Superfamily Philinoidea : family Philinidae, family Aglajidae, family Cylichnidae, family Gastropteridae, family Philinoglossidae, family Plusculidae, family Retusidae
- Superfamily Runcinoidea : family Runcinidae, family Ilbiidae
The superfamily Acteonoidea has been included into the new Informal Group "Lower Heterobranchia" and the superfamily Cylindrobulloidea becomes part of the Group Cylindrobullida.
