58 



DISCOVERY REPORTS 



As Hansen has shown, the Mastigopus phase with long stalked eyes persists up to 

 about 16 mm., and the dorsal spines of the abdomen are retained to about 10 mm. 

 These spines may be lost at 8 mm., but are generally to be found on somites 5 and 6, 

 while the posterior dorsal spine of the thorax may be retained up to 9 mm. The smallest 

 specimen in which we have seen the rudiment of the petasma (Fig. 50) is 10-9 mm., 

 whereas Hansen found it in one of 9 mm. The mandibular palp develops very late, being 

 absent up to about 6 mm. and not fully formed in a male of 11 -8 mm. The endopods 

 of the pleopods also develop late. We find in a specimen of 8 mm. the endopods very 

 small, with few setae on 3-5 and no setae on 2. 



Sergestes diapontius Bate 



Hansen, 1922, p. 173, Mastigopus. 



Illig, 1927, p. 338, fig. 117, Mastigopus; fig. 118, Acantiiosoma. 



Material. No specimens referable to this species were taken at Bermuda. The 



following descriptions are from specimens taken at Discovery Stations 282, 701, 702. 



The identification is somewhat doubtful (see p. 47). / 



Description. Acanthosoma i (Fig. 51 b-d). Length 

 3-0 mm. Rostrum i-i mm. 



Rostrum much longer than antennule. Supraorbital 

 spine longer than eye, not very spiny. Hepatic spine 

 long and prickly ; anterior lateral spine with very long 

 spinules ; posterior lateral spine thick, coarsely prickly. 

 Dorsal spine large, prickly, nearly vertical. Dorsal 

 organ minute. 



Abdominal somites with dorsal spines long, the third 

 the longest; lateral spines very long and prickly. 

 Somites i and 2 with median ventral spines. Telson 

 short, parallel-sided, with lateral spines and small fork, 

 the branches of which are slender and nearly parallel. 



Eye large, asymmetrical, less than one-fifth length 

 of body, the eyeball about two-thirds total length. 

 Labral spine minute. Antennal flagellum very long 

 (no entire specimen seen). Mandibular palp absent. 

 Maxillipede 3 not much larger than legs. Exopod of 

 uropod with setose margin 2-7 times as long as bare 

 part. 



Acanthosoma 2 (Fig. 51 «). Length 3-5 mm. Ros- 

 trum 1-42 mm. Fig. 51. S. diapontius. «, Acantho- 



General form as in stage i . Length of eye i -7 times the soma 2 ; b-d, Acanthosoma i, telson, 

 greatest diameter of eyeball ; total length of eye about ""'"""^' ''^^^^ ""^ "y"' 

 one-sixth of body length. Pleopod 5 only with rudiment of endopod. Uropod unchanged. 



