Cleavage in the egg of the jellyfish Aglantha digitale is different from most other cnidarian eggs in that it isn't unilateral (for examples of unilateral cleavage in cnidarians, see videos of the siphonophore Nanomia and the hydromedusae Phialidium and Sarsia).  Instead, it’s circumferential: as in a sea urchin egg or a mouse egg or most other eggs, the cleavage furrow ingresses from the entire circumference at once.  The egg of Aglantha is filled with large clear yolk droplets which, rather than being infuriating as very yolky eggs often are to folks interested in intracellular activities, actually help make the mitotic apparatus more visible.  Notice that spindles form near cell centers, rather than at the periphery as they would in most other cnidarian embryos.

The unusual cleavage pattern of Aglantha is not the only thing that differentiates it from other jellyfish.  It is also one of the few hydrozoans that does not have a biphasic life cycle (see the text accompanying a movie of Sarsia's embryo for more information).  This means that its entire life cycle takes place in the water column, in contrast to hydrozoans which spend the polyp portion of their life cycle attached to a hard substrate, necessitating very different strategies for larval form and behavior.

— text by Katie Bennett