Dendronotus cf. frondosus
- East Coast, Nth America (Ascanius, 1774)

Family: Dendronotidae

I have placed a number of photos of Dendronotus from the east coast of North America. It is possible that they are all colour varieties of Dendronotus frondosus but as is discussed in the messages it will probably require a better understanding of the local fauna before these animals can be identified from photographs.

Note added 30 Jan 2002: Since receiving Chad Sisson's message I have moved two messages from this page to the D. frondosus page.

Authorship details
Rudman, W.B., 2001 (June 28) Dendronotus cf. frondosus - East Coast, Nth America (Ascanius, 1774). [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

Re: Tiny Dendronotus from southern Maine

January 31, 2002
From: Chad Sisson

Dear Dr. Rudman,
I realize this response is a bit delayed, but I've just gotten around to reviewing some of the past messages on the forum. I have been working with Dendronotus frondosus in the Gulf of Maine for the past five years during my graduate work at the University of New Hampshire, so I am familiar with the photos on this message string.

The smaller animals with small white spots are definitely D. frondosus judging from the pigmentation and branching patterns of the cerata. [message 1, message 2] The pale coloration is probably in part due to whatever they have been eating. These animals have planktotrophic veliger larvae and a radula typical for this species as described by Robilliard (1970).

The larger reddish-purple animals are definitely not D. robustus, as you mentioned [message 3]]. I have found D. robustus in a small tidal rapids on Mount Desert Island, and it has a remarkably large oral veil and flared anterior end of the foot. In my experience, they are also not D. dalli, judging by the morphology of the rachidian teeth (Robilliard 1970), although Dr. Bleakney's guide might suggest that. These animals probably should not be considered D. frondosus as we know it, so your placement on this page is justified.

These animals have lecithotrophic larvae and a radula very similar to D. frondosus. I am trying to sort out the systematics of these two types in this geographical area, so please stay tuned as I finish my thesis! For now, a description of the two larval types can be found in a paper I have in press with The Veliger (please pardon the personal plug).

There is certainly lots to be learned about the systematics and ecology of this genus in the northeast Atlantic and all northern waters.

Thanks to the underwater photographers for these great observations.

Chad Sisson

Sisson, C., 2002 (Jan 31) Re: Tiny Dendronotus from southern Maine. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Chad,
Thanks for the information - its never too late to solve a problem. I look forward to your article in The Veliger appearing. Any information and photos of nudibranchs from the Gulf of Maine you would like to share with us would be very welcome.
Best wishes,
Bill Rudman

Re: Dendronotus from New England

June 26, 2001
From: Jussi Evertsen

Regarding Paul Young's dendronotids [message 1, message 2], I would suggest you look up Robilliard (1970) and (1972):
• Robilliard, G. A. 1970. The systematics and some aspects of the ecology of the genus Dendronotus (Gastropoda: Nudibranchia). The Veliger, 12(4): 433-479.
• Robilliard, G. A. 1972. A new species of Dendronotus from the northeastern Pacific with notes on Dendronotus nanus and Dendronotus robustus (Mollusca: Opisthobranchia). Canadian Journal of Zoology, 50(4): 421-432.

Jussi Evertsen

Evertsen, J., 2001 (Jun 26) Re: Dendronotus from New England. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jussi,
I wish it were so simple! My first move was to read Gordon Robilliard's work but that only made it more confusing, particularly when I have only photos to work from. If we first consider the yellow/white spotted species;
Robilliard (1970) reviews two species which have been reported from the north western Atlantic and could be this species.
D. frondosus is highly variable in colour many mottled with various proportions of brown, white and yellow.
D. robustus (Verrill, 1870). Robilliard has seen no live animals but he cites from Verrill's description that the animal has "a pale greyish ground color liberally sprinkled with small yellow spots..."

In Robilliard's 1972 paper he describes another possibly relevant species, from the northeast Pacific:
D. albopunctatus Robilliard, 1972. This has small white spots but also ahsa scattering of larger red brown spots as well.

And concerning Paul Young's brown dendronotid, it certainly doesn't fit Verrill's colour description of D. robustus. It could possibly be D. frondosus but I fear I am only guessing.

For these reasons I was hoping that there is someone out there with a knowledge of the fauna of the Nth American east coast who had a personal knowledge of these species and could stop me blundering around in the literature. And as a final comment I refer to Sherman Bleakney's book:
" In Atlantic Canada we have two large pale orange, essentially identical bushy-backed slugs. If your specimen is from intertidal or shallow water it probably is Dendronotus frondosus. If it is from depths greater then 18m, it probably is Dendronotus dalli. Anything from in between needs to have its teeth examined ..."

Bill Rudman

Rudman, W.B., 2001 (Jun 26). Comment on Re: Dendronotus from New England by Jussi Evertsen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dendronotus frondosus? from New England

June 24, 2001
From: Paul Young

Locally these are called Bushy-Back Nudibranches. This isi the second of the two species we think we have here. The first I sent in a separate message

We think this heavier set animal is Dendronotus robustus.

They are common in central Maine. They are about 4 cm long and are usually found on kelp. These were photographed off Mount Desert Island.
Paul Young

Young, P., 2001 (Jun 24) Dendronotus frondosus? from New England. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Paul,
As I asked in the first message, can someone please say something intelligible about Dendronotus on the east coast of North America.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Jun 24). Comment on Dendronotus frondosus? from New England by Paul Young. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from