Top 20 Characteristics of Archimollusc (With Diagram)

The following points highlight the top twenty characteristics of Archimollusc.

1. The archimollusc was a sluggish animal, creeping slowly over the hard surfaces in shallow water.

2. Archimollusc had a flattened body which was perfectly bilateral in symmetry.

3. There was no trace of segmentation but it had an anterior mouth and a posterior anus.

4. It had a distinct head, situated antero-ventrally, with a pair of tentacles and a pair of eyes.

5. Archimollusc had a large, muscular ventral foot; its edges were provided with small delicate tactile tentacles.

6. Its postero-dorsal part was raised into a hump.

7. Its visceral mass was covered in pallium or mantle.

8. Dorsally, it had an oval, convex shell secreted by the mantle.

9. Mantle cavity lying between the visceral mass and mantle was in direct communication to external environment.

10. Respiration was performed by one or more pairs of ctenidia or gills.

11. An olfactory organ, osphradium was present close to gills.

12. Its alimentary canal was somewhat straight; pharynx had horny jaws, odontophore was present which had chitinous radula.

13. Archimollusc was microphagous and herbivore.

14. Its heart was three chambered, having one mid-dorsal ventricle and two ventro-lateral auricles.

15. The body cavity was haemocoel and original coelom in the form of pericardium and gonocoel.

16. Archimollusc had a pair of tubular nephridia or kidneys for excretion.

17. Its nervous system was very simple; nerve ring around oesophagus, visceral and pedal nerve cords.

18. Paired tentacles, eyes, osphradium, statocysts were the sensory organs.

19. Sexes were separate and fertilisation was external.

20. A free swimming trochophore larva developed during development which metamor­phosed directly into adult without undergoing in veliger stage.