Succulents . . . that ambiguous group of plants so in vogue right now because they are fool proof cast iron sure to succeed . . . do have pest problems.
This cotyledon fell prey to a major aphid infestation. The meristem here is covered with aphids which will likely deform the leaves as they grow.
It's easy to brush or wash the pesky suckers off of succulents thanks to the lack of leaves and stuff. Another reason to like 'em.