| Neopilina | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Monoplacophora |
| Order: | Tryblidiida |
| Superfamily: | Tryblidioidea |
| Family: | Neopilinidae |
| Genus: | Neopilina |
| Species | |
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Neopilina is a highly derived genus of modern monoplacophoran.[1] However, molecular methods show that they fall within the polyplacophoran clade,[2] and fossil and morphological data show that they are rather derived and bear very little resemblance to an 'ancestral mollusc'.[1]
Its anatomy[3] led researchers to believe that the cephalopods evolved from the monoplacophora.[3]
Its pair of preoral tentacles are considered homologous to those of gastropods; like prosobranch gastropod tentacles, their nerves connect to the cerebal ganglia of the brain.[3] The post-oral tentacles are equated with bivalves' labial flaps, cephalopods' arms, and scaphopods' captacula.[3]
Cuticular hardenings around the mouth of the organism are considered to be jaw-like and very not far removed from the beaks of cephalopods, or the jaws of many gastropods.[3]
The presence of a single shell prompts comparisons to the cephalopod Nautilus, but besides its bilateral symmetry and direction of coiling, there is not a clear equivalence; Nautlius' shell is notably different in the possession of septa (and thus a sphuncle).[3]:64 It bears a similar degree of similarity to most other mollusc groups, leading to speculation that it may reflect a relatively unchanged ancestral mollusc.[3] The shell itself is aragonitic, consisting mainly of a prismatic layer,[4] lined with nacre.[3]
The organism bears five pairs of ctenidia, unusually for molluscs; the rear two are homologous to the two pairs in Nautilus. This is unlike the polyplacophora, who have a number of pairs of ctenidia, but this number varies and is not related to the number of their body 'segments'.[3]
The foot and pallial groove are very difficult indeed to discriminate from the polyplacophora,[3] supporting its placement in this group by molecular methods[2]
Its radula is not unlike that of the polyplacophora; notably, its fifth tooth is modified to be comb-like.[5]
Neopilina is a bottom feeder, probably a deposit feeder; whilst alive, its shell is covered by a layer of mucus that might be involved in feeding or locomotion.[6]