How does the carapace differ among branchiopod groups?

Within the class Branchiopoda, the presence and structure of the carapace vary significantly across different groups:

• Absent: The orders Anostraca (fairy and brine shrimp) and the extinct order Lipostraca lack a carapace entirely.12
• Enclosing the Trunk: In the suborders Spinicaudata and Laevicaudata, as well as the infraorders Ctenopoda and Anomopoda, the carapace is bivalved and encloses the trunk. Notably, in the Laevicaudata, Ctenopoda, and Anomopoda, the carapace leaves the head exposed. In contrast, the Spinicaudata possess a large carapace that encloses both the head and the trunk.12
• Reduced to a Brood Pouch: In the infraorders Onychopoda and Haplopoda, the carapace is reduced to a dorsal brood pouch and does not enclose the trunk limbs.12
• Partial Coverage: The order Notostraca (tadpole shrimp) and the extinct order Kazacharthra feature a large, domed carapace that covers only a portion of the trunk.23