- Kingdom: Animalia
- Phylum: Mollusca
- Class: Gastropoda
- Subclass: Heterobranchia
- Order: Nudibranchia
- Suborder: Dexiarchia
- Infraorder: Dendronotida
- Superfamily: Tritonioidea
- Family: Dendronotidae
- Scientific name: Dendronotus frondosus
- Norwegian: busksnegl
This is one of the bigger nudibranchs in Norway, as it can reach a length of 10 cm. It comes in many different colors. Yellow, brown, red and even entirely white individuals exist. The color cannot be used for identification. A typical characteristic for the Dendronotus species is the bushy appearance of the gills on the back of the body. It can be difficult to distinguish D. frondosus from the two other Dendronotus species known, from Norwegian waters:
- D. frondosus has between 6 and 12 lamellae on the rhinophores (organ on the top of the head, used to "smell" chemical compounds in the water). The gills are moderately branched, they usually have secondary, but sometimes even tertiary branches. The secondary and tertiary branches have rounded tips. Most specimens have pigmented spots or stripes. In the waters of Trøndelag, where many of the pictures on seawater.no is taken, specimens with a heavy reddish brown pigmentation seem to be common.
- D. lacteus has between 10 and 14 lamellae on the rhinophores. The gills tends to be more heavily branched. The tertiary branches are short. The tip of the secondary branches are shaped like spikes, in contrast to the rounded branches of D. frondosus. The color variation is as great as the D. frondosus, but white specimens seems to be common in Trøndelag waters. This is also reported from Sweden, by Thollesson.
- D. robustus has shorter, not so heavily branched gills, compared to the two species above. The flattened, not so slender body gives this species a more robust appearance. It is often heavily pigmented, making the body look reddish brown. White pigmented spots are scattered out over the entire body and tentacles. Close-ups will reveal fine wrinkles in the skin.
It is often seen feeding on hydroids among seaweeds and algae, often on sheltered locations where there are not too much disturbance from the waves.
The frond eolis is common in Northern parts of both the Atlantic and Pacific oceans. In Europe it has been registered as far north as Siberia and Greenland and as far south as France.
D. frondosus and D. lacteus has been regarded as the same species for a period of time, but recent genetic studies by Thollesson (from Sweden), Ekimova (from the North East Atlantic and North West Pacific) and Stout (from the Eastern Pacific) show that these are indeed two separate species.