Phronima sedentaria anatomy
After finding some higher-quality images/videos with some views of the creature from the front, I can say that the image I linked is mostly accurate, if lacking in detail. There does appear to be a set of antennae, though they are significantly shorter than the legs, the front two pairs of legs are shorter than the others and end in small claws, and are positioned more 'underneath' than 'to the side of' the body relative to the other legs. The reason for the confusion seems to have been a combination of the different position of the front four legs, some pictures of other Phronima species misnamed as sedentaria, and that the antennae appear to be able to fold in close to the head, making them nearly invisible.