DESCRIPTION OF SPECIES 57 



' Discovery ' specimens belong, without much doubt, to D. studeri. The nearest existing records of the 

 species are from Tierra del Fuego and the Strait of Magellan. It is not surprising to find it at the 

 Falkland Islands, but the record from Gough Island is considerably farther north, where the tempera- 

 ture at 150 m. is about 4 C. higher. 



Table 15 



Hartmeyer Michaelsen Kott 



'Discovery' 191 1 1919 1954 



No. of follicles 2-4 3 2-3 3 



No. of spiral turns 4-7 At least 7 7-8 7-10 



Didemnum biglans (Sluiter) (Text-fig. 11) 



Leptoclinum biglans Sluiter, 1906, p. 29, pi. 2, figs. 27, 28. 

 For synonymy see Kott, 1954, p. 159. 



Occurrence. St. 182: Palmer Archipelago, 273-500 m. St. 187: Palmer Archipelago, 259-354 m - 



Colony. The colony from St. 182 is attached to the sandy tube of a worm, and measures about 

 5 cm. in length. It is thick and fleshy, and, preserved, is of a pale buff-grey colour, the zooids forming 

 paler spots on the surface. Four round or oval common 

 cloacal openings are found scattered over the surface of 

 this colony. Although the zooids are grouped there is no 

 very obvious arrangement in systems. No spicules 

 whatever are present in the common test, but the 

 superficial layer has round empty spaces very like the 

 cavities occupied by sp icules in other didemnids, and I 

 am inclined to believe that this colony may originally 

 have had a layer of spicules near the surface and that 

 these have been destroyed after the specimen was 

 collected, possibly by acid in the preserving liquid. 

 This explanation of the superficial empty spaces is 

 supported by Sluiter's (1906) statement that no vesicular 

 cells are present in this species. On the other hand, it 

 may be that the colony had no spicules in life. Within 

 the colony there are very large cavities, especially in the 

 upper half of the test, the thoraces of the zooids being 

 contained in strands of test which pass from the upper 

 layer down to the basal layer of common test, a con- 

 dition very like that found in Diplosoma. 



The specimen from St. 187 is in all essentials like that 

 from St. 182, but is smaller and was growing on the test 

 of a specimen of Pyura discoveryi. 



Zooid (Text-fig. 11). The zooids are small, having 

 an average length of 2 mm. The oral siphon is short 

 with six indistinct lobes. Much of the dorsal surface of the branchial sac is exposed by the large 

 atrial opening which extends, in well-expanded zooids, from the 1st to the 4th row of stigmata. The 

 opening is surmounted by a short triangular atrial languet (a.L). There is no trace of lateral thoracic 

 organs. 



0.5 mm 



Text-fig. 11. Didemnum biglans (Sluiter) 

 (St. 182): Zooid. 



