MYSTACOCARIDA, A NEW ORDER OF CRUSTACEA 

 FROM INTERTIDAL BEACHES IN MASSACHU- 

 SETTS AND CONNECTICUT 



By ROBERT W. PENNAK 

 Biology Department, University of Colorado 



AND 



DONALD J. ZINN 



Oshorn Zoological Laboratory 

 Yale University 



(With 2 Plates) 



During the course of recent investigations on the ecology of the 

 micrometazoa inhabiting the capillary waters of intertidal beaches in 

 Massachusetts and Connecticut (Pennak, 1942a, 1942b; Zinn, 1942), 

 more than 65 specimens of a small peculiar entomostracan were found. 

 When these organism? were first examined superficially it was thought 

 that they were copepods. In size, in their basic i6-segmented struc- 

 ture, in the general organization of the body into head, thorax, and 

 abdomen, and in the number and arrangement of the appendages (see 

 pi. I, fig. 3), they appeared to be an aberrant species of Harpacticoida. 

 A more detailed study, however, revealed that in certain fundamental 

 anatomical features they were markedly different from copepods — so 

 different, in fact, as to warrant the erection of a new order, the order 

 Mystacocarida. A brief diagnosis of this group is given in the follow- 

 ing paragraph. 



ORDER MYSTACOCARIDA 



The Mystacocarida are microscopic Entomostraca inhabiting the 

 interstitial waters of intertidal beaches. Only females are known. 

 The body is colorless, distinctly segmented, cylindrical, vermiform, 

 and elongate ; it is divided into a large head, a single-segmented post- 

 cephalosome, a 4-segmented thorax, and a 6-segmented abdomen. The 

 head is elongate, with a cephalic shield, prominent rostrum, and ocelli ; 

 it bears two pairs of antennae, a labrum, a pair of mandibles, and two 

 pairs of maxillae. The first antennae are large, elongate, uniramous, 

 and sensory. The second antennae are prominent, biramous, sensory, 

 and elongate. The large labrum is flat, broad, and movable; it is at- 



Smithsonian Miscellaneous Collections, Vol. 103, No. 9 



