Nudibranch species found during intertidal exploration
KNOW YOUR NUDIBRANCHS : NUDIBRANCHS FROM NEW ENGLAND
This is a fun post about the four nudibranch species I found in the intertidal rocks of Nahant, MA while tidepooling in the Spring 2025.
NUDIBRANCHS (nudus: Naked; brankhia: gills)
Nudibranchs are marine soft-bodied mollusks which have two main characteristics. They lack a shell unlike any other snail/mollusk and have external gills either in the form of gill plume or cerata.
There are typically two kinds of nudibranchs:
A. Dorid Nudibranch- Flat disc shaped body, external gills on the back looking like a plume or tree. Sometimes when they feel threatened, they retract their gills inside the body.
Image: A Dorid Nudibranch( Goniobranchus trimarginatus ) in the intertidal of India (2021); Image Credit: Datta Pednekar.
B. Aeolid Nudibranch- Unlike dorids, aeolids have a narrow mantle with finger like extensions/projections called as the cerata (external gills in aeolids). The tips of the ceratas stored cnidosacs containing nematocysts obtained from their food sources like sea anemones, hydroids or other cnidarians.
Image: A aeolid Nudibranch( Coryphella trilineata ) on the Friday Harbor Laboratory Docks, WA (2023).
1. Dendronotus frondosus-Bushy-backed nudibranch
- Feeds on a variety of hydroids in the mid intertidal to shallow sublittoral.
- Commonly found nudibranch on the pacific and east coast of the United States
- Mantle comprises of eight-nine branched processes/cerata.
Image : Nudibranch in the intertidal grazing over substratum (2025).
Image : Headshot of the nudibranch where you could see the ribbed pine cones rhinophores which are chemosensory in function (2025).
2. Ancula gibbosa-Humped Ancula Sea Slug
- It is a dorid nudibranch with rhinophores and gills having colored tips.
- They are known to feed on colonial ascidians like that of Botryllus, Botrylloides sp. but can also feed on bryozoans.
- The Humped Ancula Sea slug has several processes rising around the gill cluster.
Image : Ancula sea slug (2025)
Image : Ancula gibbosa on a hydroid colony (2025)
3. Archidoris pseudoargus-Sea Lemon
- They are known to feed on sponges found in the east coast waters.
- Archidoris pseudoargus been a dorid nudibranch, have its external gills arranged in a circle.
- The adult individuals could depict several hues of yellow with red, pink as well as purple patterns on the body.
Image : A gorgous sea lemon aganist a crustose coralline algae (2025).
Image : Extended gills of the dorid which looks like a plume (2025).
4. Aeolidia papillosa-Shag-rug nudibranch/ Shaggy mouse nudibranch
- The shaggy mouse nudibranch has two dense rows of cerata.
- As they are very cryptic to the surrounding because of their color, they often go unnoticed and misinterpreted for anemones.
- This nudibranch species feeds on sea anemones and sometimes on hydroids.
Image : A individual of the shaggy mouse nudibranch found on a mussel bed (2025).
Lastly, nudibranchs are cool and so are you!!! This post was just to enlighten cool creatures like the nudis that exists in the intertidals of the world and often go unnoticed.
All the images included in this post are clicked by me through the Olympus TG-6 camera apart from the cool click of the Goniobranchus trimarginatus by my dad.