Axiidea can range a variety of colors, including white, pink, red, orange, and dark brown. The rostrum can range from being nearly invisible, to fairly rigid and extending past the eyes. The carapace also ranges from fairly rigid to transparent, showing the organs underneath. Axiidea can range from having a well-calcified exoskeleton, to barely calcified elongated exoskeletons, which show an adaptation to burrowing in certain species. The sex of the Axiidea can be determined by the pleopod structure on the underbelly of the organism. This structure is underdeveloped or absent in the males. The sex ratio in most species of Axiidea tends to be 1:1, although in certain habitats one sex can slightly outnumber the other. Duration of egg incubation periods, and therefore also larval development, is dependent on the environmental factors surrounding the habitat of each individual species. Environmental factors tend to include developmental constraints, salinity of the marine environment, and temperature of the water. Furthermore, the duration of the zoeal, or larval, phase ranges quite a bit, and has been estimated to last as little as 2 to 3 days in some species of Axiidea, to 5 to 6 months in other species. The pre-zoeal hatching stage is marked by poor swimming ability and lack of setae, and the zoeal stages are planktonic. The megalopa stage represents the transition from plankton to their benthic habitats, and morphological development is marked by the growth of functional mouthparts resembling those of juveniles or adults. Burrows Burrows can be divided into two groups in terms of external characteristics, depending on the existence of a mound of sediment around the entrance of the burrow. These two groups can be further divided based on whether they contain plant material within the burrow. Burrows tend to be narrow, and can range from Y or U shaped in certain species, to intricate branching tunnels and deep wells in other species. Burrows can also differ within the classifications of external characteristics, based on the feeding mode for each organism. There are three general trophic groups that the families within the infraorder Axiidea can fall into. The first trophic group are the detritophages, or deposit feeders. The other two trophic groups are the drift catchers, which collect plant matter that drifts based on ocean currents, and the suspension feeders, which feed on plant matter that is suspended in the water. Drift catcher burrows tend to lack the