LARVAE OF SERGESTES 19 



Hansen has noted that the sex is distinguishable at this stage by presence of a rudi- 

 mentary petasma. 



The dorsal spines of the abdomen may persist to the last Mastigopus stage (Fig. 1 1 a-d), 

 and the pleural hook of somite 5 is also retained. The penultimate segment of maxil- 

 lipede 3 in this stage is markedly dilated, and the propods of legs 2 and 3 have also a 

 characteristically dilated form in all the later stages. 



Colour. In the first and second mastigopus there is a large patch of vermilion in 

 thorax (several patches in later stages). Somites 4 and 5 have 3 chromatophores, and in 

 some cases these are expanded so that the whole of somite 4 is strikingly red. Antennal 

 flagellum at first colourless, later banded with red. Tips of maxillipede 3 and legs 2 

 and 3 red, the colour sometimes absent in the first stage. 



Sergestes arcticus Kroyer 



Dohrn, iSyor, PI. XVI, fig. 28, Elaphocaris 3. 

 Hansen, 1922, p. 68, Mastigopus; p. 70, Acanthosoma. 

 Illig, 1927, p. 308, Mastigopus. 



The development from the first Elaphocaris has been thoroughly described by 

 Wasserloos (1908), but we think it may be convenient to give some description of it 

 here. The Acanthosoma figured by Illig differs greatly from S. arcticus in the form of 

 the telson and length of the abdominal pleural spines. It appears to belong to S. robustus. 



Material. This species was not found at Bermuda. We are indebted to Mr F. S. 

 Russell for numerous specimens of all stages from Elaphocaris 2 taken in the Atlantic 

 (49° 53' N, 11° 3' W). We have also specimens of the Acanthosoma and Mastigopus 

 from Discovery Stations 100 (33° 21' S, 15° 18' E), 102 (35° 29' S, 18° 33' E), 278 (off 

 Port Gentil, French Congo), and 714 (35' 09' S, 47° 00' W). An Acanthosoma from 

 Terra Nova Station 251 (54° 2' S, 177" o' W, New Zealand) seems to be indistinguishable 

 from S. arcticus. Hansen (1903, p. 59) has identified S. arcticus in the Challenger collec- 

 tion from off Monte Video and south of Australia, while Stebbing has recorded it from 

 the Cape. The distribution of the larvae is therefore in agreement with that of the adult. 



Description. Elaphocaris 2 (Fig. 12 a). Length 1-2 mm. Rostrum 0-92 mm. 



Rostrum with three pairs of lateral spines, which are smooth but with the ends split 

 and brush-like. The spines of the lateral and posterior processes have also the same 

 brush-like ending which is most characteristic of the species. Lateral process with eight 

 spines. Posterior process with three pairs of lateral spines. Dorsal organ present, small. 

 Eye small, pear-shaped, with small inner ventral papilla. Maxillipede 3 without setae. 



Elaphocaris 3. Length 2-15 mm. Rostrum 1-34 mm. 



Rostrum without lateral or ventral spines. Supraorbital process long and slender, 

 with nine brush-ended spines. Posterior dorsal process with five pairs of similar spines. 

 Abdominal somites with pleural points. 



Telson arms very divergent, about twice as long as wide. 



3-2 



