Creature of the week
Burrowing acorn worm
Balanoglossus australiensis
200 – 250 mm
The burrowing worm’s sand-mucus tube exposed.
Photo David Gray@MERC
Burrowing acorn worm
Balanoglossus australiensis
200 – 250 mm
Description:
This worm has no segments. Its front parts are bright yellow, consisting of a small pointed or acorn
shaped head followed by a collar, sex organs, gills, gut and then a long featureless body.
The acorn part is muscular and does the burrowing by expanding and contracting – just like the
tuatua does with its tongue to dig into the soft sand.
The collar part excretes a mucus which holds the sand particles together to form a U-shaped tube
or burrow.
Habitat:
Common at Long Bay. Between low and mid tide. Look for a little “dump” of excreted sand and
nearby will be a conical funnel “dip” or hollow. Very gentle excavation alongside (parallel to) the dip and
dump will expose the U-shaped mucus tube with the worm inside. See photo.
Diet:
Grazing on fine algal matter on sand particles.
Reproduction:
Can be sexual but more commonly it just breaks up behind the sex organs into tiny pieces that contain
some cells of each type in the adult body These pieces grow into small replicas of the adult worm, within
the parents’ burrow.
References:
Morton and Miller “The New Zealand Sea Shore”
Diagram : part of Fig.185, page 501.