Opisthobranchia sentence example
- The Euthyneura comprises two orders, Opisthobranchia and Pulmonata.
- The heart lies in front of, instead of to the side of, the attachment of the ctenidium - hence Opisthobranchia as opposed to " Prosobranchia," which correspond to the Streptoneura.
- Many Opisthobranchia have by a process of atrophy lost the typical ctenidium and the mantleskirt, and have developed other organs in their place.
- The variety of special developments of structure accompanying the atrophy of typical organs in the Opisthobranchia and general degeneration of organization is very great.
- In many respects the sea-hare (Aplysia), of which several species are known (some occurring on the English coast), serves as a convenient example of the fullest development of the organization characteristic of Opisthobranchia.Advertisement
- Such parapodia are common, though by no means universal, among Opisthobranchia.
- The development of many Opisthobranchia has been examined - e.g.
- Euthyneurous Gastropoda, probably derived from ancestral forms similar to the Tectibranchiate Opisthobranchia by adaptation to a terrestrial life.
- The demonstration which it affords of the extreme shortening of the Euthyneurous visceral nerve-loop is most instructive and valuable for comparison with and explanation of the condition of the nervous centres in Cephalopoda, as also of some Opisthobranchia.
- It is clear enough that the sac is of a different origin from that of Aplysia (described in the section treating of Opisthobranchia), being primitive instead of secondary.Advertisement
- A single otolith is present as in the veliger embryos of Opisthobranchia.
- The members of the order present the same wide range of superficial appearance as do the Pectinibranchiate Streptoneura, forms carrying well-developed spiral shells and large mantle-skirts being included in the group, together with flattened or cylindrical slug-like forms. But in respect of the substitution of other parts for the mantle-skirt and for the gill which the more degenerate Opisthobranchia exhibit, this order stands alone.
- Some Opisthobranchia are striking examples of degeneration (some Nudibranchia), having none of those regions or processes of the body developed which distinguish the archaic Mollusca from such flat-worms as the Dendrocoel Planarians.