Many of our marine animals are truly beautiful but there are some which are just fascinatingly weird. The peanut worm (Phascolosoma noduliferum) belongs to the second group.

Peanut worms can often be found in water under stones where sand or gravel is present. When first discovered they will look like soft, pale brown blobs about the size of peanuts. Their leech-like bodies will be in their contracted form since you will have disturbed them.

If you stay to watch, the peanut worm it will slowly push out a thin extension like a miniature elephant’s trunk except that the worm’s trunk ends in short tentacles. This part of the peanut worm is called the introvert, not because of its personality but because it can be pulled back into the main part of the animal. The introvert ends in a mouth around which are the tentacles that can also be retracted.

The peanut worm feeds like an earthworm. It burrows in the sediment with the aid of hooks on the introvert and draws in detritus adhering to its tentacles. Luckily for the peanut worm it can regenerate these vital parts of its body if they are bitten off by predators.

Sexes are separate in peanut worms. The sperm and eggs are released into the sea; fertilization takes place there, and the larvae live for a while in the plankton.

Taxonomists found peanut worms a bit of a nightmare. They don’t fit neatly into any of the other major biological groups. They are not segmented like many other marine worms, the polychaetes. However, their nervous systems, body wall construction and larvae resemble those of polychaetes. Eventually peanut worms were given their own phylum – Sipuncula.