Class Crustacea: Order Decapoda. 

 Sub-order MACRURA, Dana. 



Dana, U. S. Expl. Exped. CruBt. pt. I. p. 497. 



Although there are some Anomala, such as Pylocheles, and some Macrura, 

 such as Thalassina, that occupy a sort of borderland between the Macrura and 

 Anomala, and although in another direction there are some Brachyura, such as 

 Arachnodromia, that almost cross the boundary line between the Macrura and 

 Brachyura, yet I still think it more convenient to fall in with the older authors 

 in recognizing three groups of Decapod Crustacea — Macrura, Brachyura, and 

 Anomala — than to follow Boas, who separates the Peneids and Caridids as 

 Natantia and leaves all the other Decapods — Brachyura, Anomala and a large 

 section of Macrura — together as Reptantia. 



The Macrura may be distinguished from all other Decapod Crustacea by 

 the following characters : — 



The body is elongate, the cephalothorax is less than half its total length, 

 and the front is not fused with the epistome. The abdomen is large and 

 symmetrical : it is more or less completely extended behind the cephalothorax 

 and is never folded beneath it, and it ends in a symmetrical tail-fan the lateral 

 lobes of which (caudal swimmerets) are almost without exception foliaceous. 



Except in a very few forms, and those for the most part small pelagic and 

 nectic species, the 4th and 5th pairs of thoracic legs are not reduced in size, nor 

 are they ever folded within the branchial chambers. 



The genital ducts never open on the sternum. 



In addition the following points are characteristic of the sub-order, but are 

 not invariably constant : — 



The carapace is generally produced anteriorly into a rostrum and generally 

 covers the ophthalmic somite. 



The thoracic sternum is generally narrow. 



The abdominal pleura, at any rate behind the 1st, are generally well 

 developed : and the terga commonly overlap one another. 



It is very unusual for the eyes to be lodged in orbits. 



The antennular peduncle is generally rigid (i.e., its joints not folded) and 

 generally shorter than the flagella. 



The antennal peduncle commonly has all 5 joints distinct and movable : its 

 2nd joint very often carries an exopodite, which is usually large and foliaceous 

 (antennal scale), but is sometimes spiniform: the antennal flagellum is almost 

 always very long. 



