POLYCERIDAE, Alder & Hancock, 1845

Mead, A., Carlton, J. T., Griffiths, C. L. & Rius, M., 2011, Introduced and cryptogenic marine and estuarine species of South Africa, Journal of Natural History 45 (39 - 40), pp. 2463-2524 : 2494-2495

Family POLYCERIDAE

Polycera hedgpethi Marcus, 1964 Cryptogenic

Gosliner (1982) extended the range of this nudibranch, which eats the bryozoan Bugula , from the North American Pacific coast to South Africa, where it was found in 1980 in the Keurbooms River Estuary, near Plettenberg Bay (on the southeast coast). Willan (1984) suggested that this species was introduced to South Africa (also repeated by Wilson 2006), whereas Gosliner (1987) suggested that “it is unlikely that this species has been introduced to southern Africa,” arguing that the Keurbooms Estuary “is shallow and certainly is not subject to international shipping.” However, Polycera may have arrived in the Plettenberg Bay area by secondary coastal dispersal from larger bays in South Africa supporting international shipping, suggesting ship fouling and ballast water as the most likely vectors.

Thecacera pennigera (Montagu, 1815) Cryptogenic (= Thecacera lamellata Barnard, 1933 )

Now occurring in the Pacific, Atlantic and Indian Oceans, this nudibranch has been dispersed globally along with its bryozoan prey, Bugula , in ship fouling communities and, in more modern times, probably with ballast water. This species was first collected and inadvertently re-described as a new species, Thecacera lamellata by Barnard (1933). Gosliner (1987) noted that this species is “commonly found along the coast of southern Africa from Cape Town to Umgazana in the Transkei (east coast). As several localities, including Umgazana, are over 250 km from the nearest harbour, it is difficult to attribute the distribution of this species in southern Africa solely to introduction by shipping.” However, introduced species can spread long distances along coastlines after their introduction, far from their initial point of entry. Hence the occurrence of this species at distant points does not argue against its being non-native.