FISHERY BOARD FOR SCOTLAND. 



REPORT ON THE LARVAL AND LATER STAGES OF PORTUNUS 

 HOLSATUS, Fabr.; PORTUNUS RUBER, L. ; PORTUNUS 

 LEPURATOR,'Lesich; EYAS ARENEUS {'L.); EUPAGURUS 

 BERNHARDUS, L. ; GALATHEA BISPERSA, Spence Bate; 

 CRANGONTRISPINOSUSiKsiihtone) ; GANGER PAGURUS,'L. 



BY 



H. CHAS. WILLIAMSON, M.A., D.Sc, F.R.S.E.,/^\ 

 Marine Laboratory, Aberdeen. 



{Plates I.-r.) 



Zoe£e, etc. , of Portunus, 



,, ,, Portunus Jiolsatus, 

 ,, ,, Portunus puber, . 

 Zoea of Portunus depurator, 

 Zoese, etc. , of Hyas areneus, 

 Zoea of Eivpagurus hernhardus, 

 Protozoea of Galafhea dispersa, 

 Zoea of Crangon trispinosus, 

 ,, Cancer pagurus. 



CONTENTS. 



The following pages contain observations made on Plankton Zoese which 

 have been obtained fi'om the Moray Firth and Aberdeen Bay. 



While dealing chiefly with the structure of these forms, I purpose to 

 devote some atteation to the colours of these larvae. 



While only slight structural difl[erences can sometimes be made out 

 between Zoese, the jngmentation affords an igaportant aid to specific 

 identification. The Zoese are usually well supplied with pigment, and, 

 when alive, may in some cases be separated into species by the naked 

 eye. The jdgmentation is specific, and remains constant through all the 

 Zoea and Megalops stages. 



The colouration does vary considerably, but not, so far as I have noticed, 

 sufficiently to confuse the identity of the form, when attention is also paid 

 to the main structural features. 



It is therefore easy to select from a tow-net collection the Zoese of one 

 species, even although they are in different stages. It is thus possible to 

 connect two Zoea stages wliich are structurally different. The later Zoea 

 stages of Portunus have long spinous processes projecting- from the hind 

 lateral boi^der of three of the abdominal segments. These are not present 

 in the earliest Zoea stage. 



The material upon which this research is founded was obtained almost 

 wholly from the plankton. The Zoese were brought to the Laboratory, 

 and, after being separated into different stages, were kept alive in order 

 that their moults might serve to connect the stages. 



