LARVAE OF SERGESTES S3 



Sergestes vigilax Stimpson 



Claus, 1863, PI. XXVII, fig. 43, Acanthosoma ; fig. 44, Mastigopus. 



Claus, 1876, Pis. V, VI, Elaphocaris and Acanthosoma. 



Hansen, 1922, p. 165, Mastigopus and Acanthosoma. 



Gurney, 1924c, p. 80, fig. 17, Elaphocaris 2; p. 81, fig. 18, Elaphocaris 3 (?). 



lUig, 1927, p. 344, fig. 127, Elaphocaris 3 (?). 



Cecchini, 19286, Acanthosoma i and 2 referred to. 



Material. The species is common at Bermuda. Moults have been obtained of 

 Elaphocaris i to stage 2; Elaphocaris 3 to Acanthosoma; Acanthosoma i to stage 2; 

 Acanthosoma 2 to Mastigopus. In addition, several moults of the Mastigopus have been 

 observed. The connection of Elaphocaris 2 to stage 3, which is the only gap in the 

 sequence of moults, is established by general similarity in form and colour, and by 

 capture in association with later stages in the Discovery material. 



The larvae have been recognized in the material from the following Discovery 



Stations: _ 34- 33' N, 14° 32' W, 703. 7° 17' N, 28° 02' W, 



100. 33° 20' S, 15° 18' E, 704. 3° 37' N, 29" 14' W, 



701. 14° 39' N, 25° 51' W, 708. 10° 26' S, 34° 57' W, 



702. 10° 59' N, 27° 04' W, 714. 35" 09' S, 47" 00' W. 



Among the numerous specimens of the Acanthosoma examined from various stations 

 in the Atlantic differences have been noted in the form of the pleural spines. These 

 differences may point to the presence of distinct races or species within a vigilax group ; 

 but the material does not justify an attempt to define such races. 



Description. Elaphocaris i (Fig. 45 a). Length i-i6 mm. 



Anterior processes about as long as carapace, trifurcate, the median branch with 

 denticles; base with four small spines. Lateral and posterior dorsal processes simple, 

 with a few denticles, the lateral process a little longer than carapace. Telson branches 

 short and stout, diverging, with four very long spines and two short ones ; spine 5 much 

 the longest, and exceeding length of whole body. Thorax containing numerous yolk 

 globules. 



Elaphocaris 2 (Fig. 45 b). Length 1-47-1 7 mm. Rostrum i-o mm. 



Rostrum very broad at base over eye, with four pairs of lateral and two ventral spines. 

 Lateral processes large and stout, with ten dorsal and lateral spines and one ventral. 

 Posterior process with two pairs of lateral spines. Telson branches divergent, longer 

 and more slender than in stage i. Carapace with dorsal organ minute or absent. Eyeball 

 not markedly asymmetrical, with slight indentation in centre, the diameter about half 

 length of eye. 



Elaphocaris 3 (Fig. 45 c). Length 2-6 mm. Rostrum i-i mm. 



Rostrum as long as carapace, with one pair of lateral and two unpaired ventral spines 

 (three seen in one specimen). Supraorbital spines large, with 15-17 spines. Lateral 



