Why are malacostracans considered the most diverse group of crustaceans?

Malacostracans are considered the most diverse group of crustaceans because they represent more than two-thirds of all living crustacean species, comprising over 29,000 described species. Their success and diversity are attributed to several key evolutionary advancements:1

• Morphological Range: They exhibit the greatest variety of body forms and sizes, ranging from less than one millimeter to a limb spread exceeding three meters.1
• Anatomical Specialization: Evolution shifted food-gathering limbs and respiratory organs from the head to the thorax and abdomen. This transition freed the antennae to develop specialized sensory organs for detecting vibrations, sounds, and odors, while increasing the number of mouthparts (maxillipeds).1
• Adaptability: These developments, alongside the evolution of ambulatory legs and the suppression of free-living larval stages, have allowed malacostracans to thrive in diverse environments, including deep-sea abysses, subterranean waters, and terrestrial landmasses.12

This evolutionary trajectory has enabled them to efficiently exploit new food resources, such as those provided by the proliferation of vascular plants.1