This small box jellyfish grows up to 7 cm (2.8 in) across and may have tentacles of up to 2 m (6.6 ft) in total length. It has a transparent box-shaped bell with a very long tentacle trailing from each corner.
The C. branchi is described as being robust and having a well sculpted in particular, single rooted with multiple stems, velarial canals 2 per octant, pedalia knee bend upwards turned volcano shaped. Also known to have a brownish pigmentation of the phacellae and pedalia. 
This jellyfish is found from the north of Namibia and around the South African coast to Port Elizabeth from the surface to a depth of at least 35 m (115 ft) underwater.
This jellyfish is often seen in swarms. The tentacles have a painful sting, although the sting is not known to be fatal. It is eaten by the sunfishes, Mola mola and Mola ramsayi, as well as the slender sunfish, Ranzania laevis.
3. Acevedo et al. 2019. Revision of the genus Carybdea (Cnidaria: Cubozoa: Carybdeidae): clarifying the identity of its type species Carybdea marsupialis. Zootaxa.