Photo Andrew Taylor
Photo Andrew Taylor
Photo Guido Zsilavecz
Photo Guido Zsilavecz
Janolus longidentatus eggs on left, Janolus capensis eggs on right.
Photos Guido Zsilavecz.
There are two very closely related "silvertip" nudibranchs in Cape Town waters: Janolus capensis, the "classical" silvertip mentioned in Two Oceans, and Janolus longidentatus. Reading through the species description there does not seem to be anything through which the two can be distinguished from each other, using the naked eye, or even a macro photograph. The differences are largely internal, with the species name of J. longidentatus referring to "to the elongate cust of the lateral radular teeth which characterizes this species." This is something you can only see under a scanning electron microscope. The distribution of the two species differs, with J. capensis occurring on both sides of the Peninsula, whereas J. longidentatus only seems to occur seasonally in False Bay, with specimens not having been found between February to July. Looking at all the photos from both sides of the Peninsula, from different times of the year, it is still not possible to see a difference, and even the photos in the paper describing the two species do not conclusively allow for differentiation.
The only way the two differ quite radically is in their egg mass, with J. capensis having a globular cluster, while J. longidentatus having a flat mass, as shown in the photographs. This, of course, does not allow for differentiation of the adults, and the mystery of which is which thus remains, and while SURG believes all photos shown are J. capensis, this could be wrong! As can be seen, the amount of silver on the cerata is variable, as is their shape.
Nudibranchs of Southern Africa - a guide to the opisthobranch molluscs of southern Africa, T Gosliner, 1987.
Two Oceans, A guide to the marine life of Southern Africa, GM Branch, CL Griffiths, ML Branch and LE Beckley, 1994.
The South African Janolidae (Mollusca, Nudibranchia) with the description of a new genus and two new species, TR Gosliner, Annals of the South African Museum, Volume 86 Part 1, September 1981.