Described as a "typical slice of the Hauraki Gulf" by the East Coast Bays Coastal Protection Society.(who led the MPA process back in the day), the Long Bay-Okura marine reserve hosts a good variety of nudibranches. Nudibranches are a group of marine gastropods that loose their shells soon after transitioning from their larvae stage. Therefore their nomenclature "nudi", from the Latin "nudus". Nudibranches are well known for their colorful appearance, which varies greatly among species and is due to a variety of reasons, including camouflag and toxicity (see aposematism).
The following list includes the species that I have personally sighted at the reserve and for which I have obtained decent footage. I have observed more species that I hope to add over time as I spend more time underwater, which hopefully will translate into more good footage and pictures.
Dendrodoris krusensternii (Gray, 1850). This species holds the title of New Zealand's "loveliest nudibranch" and it's easy to see why. It can be found all over the east coast of the North Island and is very common at the reserve.
Dendrodoris arborescens (Collingwood, 1881). Perhaps the less attractive of the species from a color perspective. Sometimes you can appreciate the red margin which highly contrasts against the rest of the dark body. Occurs throughout the whole of the North Island.
Dendrodoris citrina (Cheeseman 1881). Another easy-to-spot species due to its bright color. Very common inside the reserve and along the coast.
If you want to know more about New Zealand nudibranches, I highly recommend the NIWA's Super Sea Slug guide.