THE PLANKTON OF EASTERN NOVA SCOTIA WATERS 



15 



SESSIONAL PAPER No. 22a 



HARPACTICIDAE. 



Microsetella atlantica Brady and Robertson (fig. 12) was frequently taken in the 

 beginning of July. Eipe females are readily recognized by tbe long setae, as long as 

 the body (547/^ ), the orange-red colouring which extends to the eggs disposed in a single 

 packet underneath the abdomen, and the denticulation on the segments. 



HarpacHcus chelifer (fig. 13) is also common. 



AMPHIPODA. 



The commonest member of this order in the Canso plankton is Euthemisio com- 

 pressa Goes, Plate YI. fig. 14. It was most abundant in June. 



DECAPODA. 



Throughout the month of July there was plenty of opportunity of observing the 

 various larval phases of Cancer and two species of Pagurus. One of the latter which 

 occurred towards the end of the month differed from the figures I have studied by 

 the presence of sixteen setae on the telson, and a rostrum which only reached to the 

 middle of the basal joint of the antennulse. 



UNIDENTIFIED EGGS. 



Two pelagic eggs are of very frequent occurrence. One of these (Plate VII., figs. 

 1 and 2) is that of a gastropod and is contained in a horny capsule which suggests in 

 its shape a low wide-brimmed hat, and resembles closely the figures given by Hensen 

 (l.c. Taf . IV., fig. 25-30) of his ' Barbierbecken-statoblast.' 



A further resemblance to his figure 25 is that two eggs are frequently found in 

 the cavity of the capsule. The dimensions, however, of these structures do not agree 

 for whereas the whole capsule of Hensen's statoblast merely measures 200/' , that of 

 the egg in question is 675 — 775, a, the flat rim measuring 140 — 160/' or so, the capsule 

 proper some 400// ; its cavity, (or cavities if there are two eggs) 140 — 150 /' , and the 

 unsegmented egg about 120/^-. Segmentation had begun towards the end of June, the 

 spheres having a certain pinkish hue by reflected light. By the eighth of July the 

 shell and velar cilia could be made out. Larvae ready to escape were observed up till 

 the middle of August, but were not recognized in the plankton nor referred to the 

 parent mollusc. Pig. 3 is a rough sketch of the shelled larva. I have not found any 

 pelagic gastropod egg-capsules referred to in any of the literature accessible to me. 



The second egg-capsule, commoner than the foregoing, I have not been able to 

 localize even as definitely. It has something of the same form (fig. 4), viz., a 

 Bubglobular capsule of 120 // in diameter, with a thin rim 100/^. broad, which, however, 

 unlike the former, does not lie entirely in the same plane, but is often much curled. 

 The capsule is yellowish in colour and the rim shows a network of fine fibres (fig. 5). 

 Empty capsules were common, and embryos (fig. 6) were observed in July and August 

 within others, but I did not succeed in diagnosing them. These egg-capsules, when 

 deserted, were frequently occupied by a species of Chytridium. 



Among the numerous gastropod veligers found at Canso that of Aeolis despecta 

 (fig. 7) was particularly common and attracted attention by its pellucid shell. Larvse of 

 the following Pteropods were also found, Clione aurantiaca (fig. 8) and two species of 

 Hyalaeacese (figs. 9 and 10). 



TUNIGATA. 



Although this Phylum furnishes a very large number of interesting forms belong- 

 ing to the plankton, the only members of it found at Canso belong to the class Cope- 

 lata, which permanently retain the tail and notochord of the larval Tunicate. 



