Description: As a Sacoglossan, this nudibranch-like species has no external shell nor cephalic shield. Rhinophores, if present, are solid or rolled, not perfoliate, with longitudinal ridges, or with vertical pinnate plumes, and the clavus is not distinct from the stalk. The rhinophores, if present, cannot be retracted into a sheath. The dorsum of Sacoglossans may or may not have elongated outgrowths such as cerata. The anus is on the dorsal midline, just posterior to the rhinophores. Placida dendritica has up to about 50 well-developed cerata and also rhinophores, but the foot does not have parapodial outgrowths. The body is approximately cylindrical, and the posterior foot tapers gradually to form a pointed tail well behind the last cerata. The cerata are found on both the anterior and posterior half of the dorsum, and often occur in clusters of 3-5. The rhinophores are rolled tightly for nearly their entire length. The body is pale yellowish, with a branching green or red pattern on the dorsum and up into the cerata, formed by branches of the gut. Total length to 1.4 cm but usually 8 mm or smaller.
Geographical Range: Vancouver Island, Canada to Baja California, Mexico. Also has been found in Southeast Alaska. Also in Japan and much of the North Atlantic, and the Mediterranean.
Depth Range: Mid and low intertidal
Habitat: Generally on Bryopsis corticulans,Codium fragile,or C. setchelli algae.
sacoglossans, the radula
of this species is composed of individual, bladelike teeth used to slit
open algal cells. The animal sucks out the cell
found on C.
to strongly prefer that species and may starve on C.
setchelli, while those from C.
setchelli had little preference for one algal host over
Trowbridge (1991) found that the sacoglossan forms feeding groups when
feeding on C.
not when feeding on Bryopsis
Members of groups grew faster than isolated individuals if they were
the same size or if they were smaller than the other sacoglossans in
group. Evertsen and Johnsen (2009) found that they did not
functional chloroplasts from their food (C.
fragile). On the Oregon coast there is
of this species into protected bays, and peak abundance is in
The thalli of C.
could be heavily covered with new sacoglossans at a rate of 200 to 400
sacoglossans/thallus per month. The animals grew from initial
to sexual maturity in less than a month. Adults also moved
among different thalli of C.
Kozloff, 1987, 1996
McLean, N., 2005. Phagocytosis of chloroplasts in Placida dendritica (Gastropoda: Sacoglossa). Journal of Experimental Zoology 197:3 pp 321-329. DOI 10.1002.jez1401970304
Trowbridge, Cynthia D., 1991. Group membership facilitates feeding of the herbivorous sea slug Placida dendritica. Ecology 72:6 pp 2193-2201
Trowbridge, C.D., 1992. Phenology and demography of a marine specialist herbivore: Placida dendritica (Gastropoda: Opisthobranchia) on the central coast of Oregon. Marine Biology 114: pp 443-452
Vardaro, Rita, Vizenzo Di Marzo, and Guido Cimino, 1992. Placidenes: cyercene-like polypropionate y-pyrones from the mediterranean ascoglossan mollusck Placida dendritica. Tetrahedron letters 33:20 pp 2875-2878
General Notes and Observations: Locations, abundances, unusual behaviors:
We found this sacoglossan, probably not fully grown, in seawater from our seawater system in August, 2014. The animal must have been sucked into the seawater intakes, which are about 1.5 m off the bottom and 5-6 m from the surface, so it may have been pelagic or was feeding on algae coating the intake. I have not seen Codium fragile near the intakes so the animal was most likely pelagic. Trowbridge (1992) notes that the species has rapid recruitment and that adults are quite mobile as well, so I suspect it was traveling through the water column. The animal is very active and mobile--hard to photograph because it moves so fast.
Authors and Editors of
Salish Sea Invertebrates web site provided courtesy of Walla