The narrow abdomen or tail is very flexible, and can be doubled up under the body or stretched out behind; it ends in a forked telson. There are two pairs of swimming limbs, each with endopodite and exopodite, and the short antennules and antennæ are seen on either side of the rostrum. There are a pair of very large compound eyes, which are not set on movable stalks, but are under the front part of the carapace. The two-branched swimming feet are really the first and second maxillipeds (the mandibles, maxillulæ, and maxillæ, can be found in front of them), but none of the other thoracic limbs are yet developed, and, although the somites of the abdomen are distinct, there are no swimmerets. This type of larva is known as a zoëa, a name which was given to it when it was supposed to be an independent species of Crustacean. As a matter of fact, the zoëa just described is not quite the earliest stage of the Shore Crab, for when hatched from the egg it is without the spines on the carapace, and is slightly different in other respects. A few hours after hatching, however, it casts its skin for the first time, and becomes a fully-formed zoëa. It swims rapidly about at the surface of the sea, feeding on the minute floating animals and plants which are found there, and growing in size with repeated castings of its skin. In the later stages of the zoëa the rudiments of the hinder thoracic limbs and of the swimmerets appear as little buds. In the next stage ([Fig. 25], B) all the appendages are present, the dorsal spine of the carapace has disappeared, the eyes are stalked and movable, and the animal has all the appearance of a little Crab, except that the abdomen is stretched out instead of being tucked up under the body, and the swimmerets are used as paddles in swimming. In this stage the larva, which is known as a megalopa, swims at the surface of the sea, but later it sinks to the bottom, and, moulting again, appears as a little Crab ([Fig. 25], C), with tucked-up abdomen and swimmerets no longer adapted for locomotion.
Fig. 26—Last Larval Stage of the Common Porcelain Crab (Porcellana longicornis—see [Fig. 41], p. 113). × 9. (After Sars.)
![[View larger image]](#8391965335141687956_fig_026lg.png.id-9031586198046875127.wrap-0.html.html){kind=link}
Fig. 27—First Larval Stage of Munida rugosa (see [Plate VI].). × 10. (After Sars.)
![[View larger image]](#8391965335141687956_fig_027lg.png.id-8617677066549587863.wrap-0.html.html){kind=link}
Most of the true Crabs (Brachyura) have a larval history similar to that just described, and pass through zoëa and megalopa stages which differ only in details from those of Carcinus. The Anomura are also hatched as zoëæ, and one of the most remarkable forms common in tow-nettings in British waters is the zoëa of the little Porcelain Crabs (Porcellana—[Fig. 26]). In this larva the carapace has two long spines behind, and a rostral spine which is several times as long as the body of the animal. A great development of spines also characterizes the larva of Munida ([Fig. 27]).