| Acaenoplax | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | incertae sedis |
| Family: | †Heloplacidae |
| Genus: | †Acaenoplax |
| Species: | †A. hayae |
| Binomial name | |
| †Acaenoplax hayae Suttonet al, 2001 | |
Acaenoplax is an extinct worm-shapedmollusc known from theCoalbrookdale Formation ofHerefordshire, England. It lived in theSilurian period. It was a couple of centimetres long and half a centimetre wide, and comprises serially repeated units with seven or eight shells, and rings of 'spines'.[1][2]
Some of its characters are reminiscent of thepolychaete worms, and the character combinations do not place it obviously in the stem of any modern mollusc group,[3] but although it was originally interpreted as a polychaete,[1] this position is untenable for a number of reasons.[4]
The organism resembles a bristled worm, but bears a number of shells on its upper surface. The first shell is cap-like, whereas the others are saddle-shaped. The rearmost shell is almost rectangular, whereas the others are more circular, with spines on the rear surface of the third to sixth shells. The originally-aragonitic shells do not overlap.[1] There are eighteen rows of spines projecting from ridges in the body surface, which encircle the body except for its bottom surface,[1] which presumably bore a molluscan foot. Its straight gut was preserved in phosphate.[2]
Heloplax,Enetoplax andArctoplax are genera of shell that are closely related toAcaenoplax, but whose soft tissue is not preserved.[1]
