LARVAE OF SERGESTES 13 



Acanthosoma 2 (Figs. 3 c, J, 4 a). Length 3 •34-4-0 mm. Rostrum 0-83 mm. 



General form as in stage i. Antennal scale differing little from that of stage i, 

 but having a relatively larger outer distal spine. Pleopods large, with rudiment of 

 endopod on pleopod 5 only. Exopod of uropod Vi^ith setose part 1-3 times as long as 

 bare part. 



Mastigopus I (Figs. 46, 5). Length 3-9 mm. Rostrum 07 mm. 



Rostrum nearly reaching end of segment i of antennule, basal spine large. Supra- 

 orbital and hepatic spines large. Posterior dorsal spine present, small. Dorsal organ a 

 small papilla. 



Abdominal somites with small dorsal and pleural spines, the dorsal spines increasing 

 somewhat in length from in front backwards. Telson slender, nearly three times as long 

 as wide, with small apical fork. There may be one, or two, small spines on outer margin 



at end. 



Eye with very long slender stalk and very asymmetrical eyeball. In preserved material 

 the pigment is very pale, sometimes almost absent. Antennal scale very long and slender, 

 about fourteen times as long as wide ; flagellum about twice as long as body. 



Mandibular palp absent, or represented by a very minute papilla. Legs with vestiges 

 of exopods ; endopods of legs 4 and 5 absent. Pleopods very long, with setose endopod 

 on pleopod 5 ; pleopod 4 may have a rudiment of endopod, but there is no trace of it 

 on 1-3. Exopod of uropod very slender, about ten times as long as wide, the bare part 

 a little longer than the setose part (1-25 : i). 



Colour as in Acanthosoma; colourless except for vermilion mass in gastric region, 

 and red bands on antennal flagellum. 



Fig. 5 shows a specimen of 5-2 mm. (rostrum -6 mm.) in stage 2 or 3, in which the 

 antennal flagellum is very much longer and sharply bent, but with the curved setae 

 not yet fully developed. Legs 4 and 5 are beginning to regenerate. The mandibular 

 palp is present, though still rudimentary. 



A Mastigopus of about 12 mm. mouhed to a young male with rudiment of petasma. 

 The two pairs of "organs of Pesta" were noted in the last Mastigopus. 



Sergestes cornutus Kroyer 



Sund, 19206, PI. I, fig. I, Acanthosoma 2. 

 Hansen, 1922, p. 57, Mastigopus. 

 lUig, 1927, fig. 123, Elaphocaris 3. 



Material. Common at Bermuda. The three Elaphocaris stages can be connected 

 with each other with certainty by their characteristic colour. The connexion of 

 Elaphocaris with Acanthosoma and Acanthosoma with Mastigopus was established by 

 moult. 



Description. Elaphocaris i (Fig. 6 a). Length 0-9 mm. 



Anterior process trifid, the branches with long spinules at end, and posterior branch 



