This “case” features the Giant Nudibranch (Dendronotus iris to 30 cm long) and the Tube-Dwelling Anemone (Pachycerianthus fimbriatus).
The Giant Nudibranch’s favourite snack is this anemone species. It is not impacted by the anemone’s stinging cells (nematocysts).
The Tube-Dwelling Anemone is therefore adapted to be able to withdraw into its tube (which can be up to 1 m long) in an attempt to get away from the predator sea slug.
And the battle is on! The Giant Nudibranch patrols the sandy ocean plains “looking” for the Tube-Dwelling Anemone. When it finds one, it rears up and pounces, mouth parts extended in the hopes of grabbing onto the anemone. When the anemone senses the nudibranch’s attack, it withdraws into its tube.
Wait till you see what happens to the Giant Nudibranch!
See below for a short clip of such an attack.
But that’s not all, this nudibranch species also swims.
By lifting off, it may land somewhere with better chances for feeding and mating. See video below.
As is also generally the way with sea slugs, they also lay their eggs on their prey.
And oh the diversity in colour among Giant Nudibranchs. See photos below.
Note: Dendonotids are not known to utilize the stinging cells (nematocysts) of their prey. From the Sea Slug Forum “There has been some confusion in the literature concerning the presence of branches of the gut in the ‘gills’ or ‘cerata’ of species of Dendronotus. Firstly there is no evidence to suggest that any species of Dendronotus has cnidosacs at the tip of its dorsal processes in which to store nematocysts. In fact there is no evidence that they store nematocysts from their prey anemones in any part of their body.“