Discovery reports (1941) Discovery reports discoveryreports20inst Year: 1941 LARVAE OF SERGESTES 27 apical fork very slender, parallel, or even bending slightly inwards, not reaching end of uropods. Each arm with two outer spines and with or without one inner spine near apex. Eye about one-seventh length of body, its length nearly twice the diameter of the eyeball, which is nearly round. Antennal scale widening towards the end, about five times as long as wide; flagellum about half length of body. Mandibular palp rudi- mentary, but with apical setae. Legs with vestiges of exopods. Pleopods v
Discovery reports (1941) Discovery reports discoveryreports20inst Year: 1941 LARVAE OF SERGESTES 27 apical fork very slender, parallel, or even bending slightly inwards, not reaching end of uropods. Each arm with two outer spines and with or without one inner spine near apex. Eye about one-seventh length of body, its length nearly twice the diameter of the eyeball, which is nearly round. Antennal scale widening towards the end, about five times as long as wide; flagellum about half length of body. Mandibular palp rudi- mentary, but with apical setae. Legs with vestiges of exopods. Pleopods very long, with rudiment of endopod on 2-5. Exopod of uropod with bare part a little longer than setose (i : o-8) and six times as long as wide. The stout, broad body is characteristic of this species, and is retained in all stages. The dorsal spines of abdominal somites 4 and 5 remain up to a length of about 8 mm. The mandibular palp is still unsegmented in stage 2. At a length of about 7 mm. it is Fig. 19. S. crassus. Mastigopus telson. a, 4-2 mm.; b, 4-85 mm.; c, 4-68 mm.; (f, 5-45 mm.; e, 6-95 mm.;/, 14mm.; », 15 mm. large, two-segmented, and setose. The transformation of the telson is shown in Fig. 19. The largest Mastigopus is about 10 mm., and there is an immature phase, according to Hansen, up to about 20 mm., during which the petasma is formed. Colour. Red in thorax, but abdomen colourless. Red patches in antennae and all limbs, and in exopod of uropods. Sergestes robustus Smith Lo Bianco, 1903, p. 182, PI. vii, fig. 9, Acanthosoma 2. Hansen, 1922, pp. 114, 117, Mastigopus and Acanthosoma. Illig, 1927, fig. 62, Acanthosoma (as S. arcticus). Cecchini, 19286, p. 34, Mastigopus. Material. Larvae of this species were taken but rarely at Bermuda, and only over very deep water, at depths of about 250 m. Moults were obtained of first to second Acanthosoma and of Acanthosoma to Mastigopus, but the identity of the Elaphocaris was not proved by moult. 4-2
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