Cephalaspidea
| Headshield slugs | |
|---|---|
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| A live individual of Chelidonura varians in the family Aglajidae, head end towards the lower left | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): |
clade Heterobranchia clade Euthyneura |
| Superfamilies | |
|
See text |
|
clade Euthyneura
clade Euopisthobranchia
clade Cephalaspidea
See text
The clade 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.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 primitive of the opisthobranchs, but now they are considered as derived and specialized members of the Euthyneura Spengel, 1881
Headshield slugs are the most morphologically diverse group of all the opisthobranchs.
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.
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