1921.] 



Fauna of the Chilka Lake : Polychaeta. 



633 



slit — the mouth — between them. These lips may possibly represent the proboscis as it 

 begins to be extruded. No eyes were observed. The intestine is full of sand grains. 



The ist foot (text-fig. 18a) has dorsally a nu- 

 merous group of capillary setae, with serrated 

 blades, diminishing in size from above down- 

 wards. They are guarded in front by a low in- 

 significant fillet, behind by a rather more conspi- 

 cuous one. The ventral bundle consists of three 

 or four rows of stout hooks (fig. 19F). Above 

 and below the hooks, and posterior to them are 

 two groups of capillary setae like those in the 

 dorsal bundle. The whole ventral bundle is sur- 

 rounded by a low and inconspicuous fillet. The 

 2nd foot is similar. In the 3rd foot the dorsal 

 bundle is relatively a little smaller, and has a 

 small flat cirrus behind it. No cirrus was noted 

 in the ventral division. 



In the 4th foot (fig. 19B) there is a conical cir- 

 rus behind the middle of the ventral division, as 

 well as the flat finger-shaped dorsal cirrus. 



The short ventral hooks are only present in 

 numbers in the anterior 8 setigerous segments. 

 In the 9th segment only 2 were observed, and in 

 the 10th, none. This type of seta has a number 

 of coarse serrations beneath the rounded tip, which is guarded by two very delicate 

 wings. The shaft shows a double curvature. In the anterior segments the ventral 

 capillary setae are shorter and stouter than the dorsal setae, and the blade is more 

 abruptly widened. 



No further change occurs in the feet till the 13th setigerous segment, where the 

 branchiae appear as minute papillae, and the dorsal cirrus commences to elongate. 

 At the 17th foot (fig. 19c) the dorsal cirrus and branchia are very similar in size and 

 shape, but the ventral cirrus is still small. In the 18th and 19th feet (fig. 19D) 

 marked changes commence. The dorsal cirrus and dorsal setae are much longer. 

 The ventral cirrus is longer also, and behind and beneath it is a large thin membrane 

 shaped like a pocket. The latter commences on the 18th segment, and increases a 

 little in size in the succeeding segments. All the setae are now longer, slenderer, and 

 with finer serrations than those in the anterior region, the dorsal setae being longer 

 than the ventral. Each bundle is supported by a number of pale spines. The ven- 

 tral cirrus, however, still remains entire, and the area from which the ventral setae 

 emerge is still elongate, as in the preceding feet. 



In the 20th foot the metamorphosis is complete. The ventral cirrus is bifid at 

 the tip, and the setae emerge in a small area in front of and between the two lobes. 

 The dorsal cirrus is constricted near the base. The ventral setae have also changed 



a, 



Tëxt-fig. 18. — Parapodial diagrams of 

 Scoloplos marsupialis, sp. nov. 



a. ist foot ; b. 30th foot. 

 ■ = capillary setae ; x = short hooks. 



