Orders: Decapoda (Sub-orders: Brachyura, Macrura), Schizopoda (including Anaspides), Stomatopoda, Sympoda (Cumacea), Isopoda (including Tanaidacea), Amphipoda.
There are at least seven orders: the stalk-eyed Brachyura, Macrura, Schizopoda, Stomatopoda, and the sessile-eyed Sympoda, Isopoda, Amphipoda.
Stomatopoda.-ThiS order, at one time a medley of heterogeneous forms, is now confined to the singularly compact group of the Squillidae.
A remarkable feature found only in the Stomatopoda is the reappearance of segmentation in the anterior part of the cephalic region.
- Squilla mantis bases tends to show that the primitive (Stomatopoda), showing the type of appendage was more complex last four thoracic (leg-bearthan the simple biramous limb, and ing) somites free from the some authorities have regarded the carapace.
In the Malacostraca, the antennules are often biramous, but there is considerable doubt as to whether the two branches represent the endopodite and exopodite of the other limbs, and three branches are found in the Stomatopoda and in some Caridea.
In the Malacostraca, an elongated heart with numerous segmentally arranged ostia is found only in the aberrant group of Stomatopoda and in the transitional Phyllocarida.
It is most typically developed in the most specialized Decapoda, the Brachyura, while the more primitive groups of Malacostraca, the Euphausiidae, Penaeidea and Stomatopoda, retain the primitive order of appearance C FIG.
Stomatopoda of a very modern-looking type, and even their larvae, occur in Jurassic rocks.