176 



quite possible that other species may have a Pluteus-larva, corresponding 

 to the fact shown in this work that within the genus Asterina some species 

 have a typical Bipinnaria-larva, while others have a shortened, direct 

 development as in the classical case of Asterina gibbosa. - 



The larva of Ophionereis squamulosa belongs to the same type as that 

 of Ophioderma brevispina, described by Caswell Grave. There are some 

 minor differences in the shape of these two larvae, that of Ophionereis squa- 

 mulosa having the anterior lobe distinctly longer than that of Ophioderma 

 brevispina. Also the arrangement of the vibratile bands is somewhat dif- 

 ferent, especially the posterior band, as a comparison of PI. XXXI, Fig. 3 

 with PI. Ill, Fig. 22 of Grave's Memoir will make evident. 



The statement of Grave (Op. cit. p. 83) that the usual Pluteus skeleton 

 is formed in the larva of Ophioderma brevispina, while there is no trace 

 of a larval skeleton in Ophionereis squamulosa, would appear to indicate 

 a very important difference between these two larvae. Later on, however, 

 Grave has announced 1 ) that he mistook the beginning skeletal plates of 

 the Ophiuricl for the larval skeleton. There is thus no larval skeleton in 

 the larva of Ophioderma brevispina either. 



A larva closely resembling that of 0. brevispina was taken pelagically 

 atTaboga, Gulf of Panama, 18/XI. 1915. Probably it belongs to one of the 

 Panamic species of Ophioderma. It would seem superfluous to give a closer 

 description or figures of it. - To the same larval type belongs that describ- 

 ed by Joh. Mil Her 2 ) from Triest under the designation "wurmformige 

 Asterienlarve", and also those described from Madeira by Krohn 3 ). It 

 may perhaps be suggested that the Mediterranean form belongs to Ophio- 

 derma longicauda. 



In the "Echinodermenlarven d. Plankton-Exped." I designated also 

 these worm-shaped larvae as Ophiopluteus. Hamann 4 ) objects to this 

 designation, because there is neither a ciliated band nor a larval skeleton 

 in these larvae, not to mention that the usual larval arms are totally lacking. 

 I would, however, still think it justifiable to use this designation. In the 

 larva of Ophiura ajfmis b ), Ophiopluteus Metschnikoffi and 0. Claparedei we 

 have different stages of the reduction of the typical Pluteus-shape. From 



1 ) Caswell Grave. On the occurrence among Echinoderms of larvae with cilia arranged 

 in transverse rings; with a suggestion as to their significance. Biol. Bull. V. 1903. p. 173. 



2 ) Joh. Miiller. Uber die Larven u. die Metamorphose d. Holothurien u. Asterien. 

 III. Abhandlung. Abh. d. Akad. Berlin. 1850. p. 26. Taf. VI. 812. VII. 14. 



3 ) A. Krohn. Uber einen neuen Entwicklungsmodus d. Ophiuren. Miiller's Archiv. 

 1857. p. 369, 373. Taf. XIV. B. Fig. 14. 



Th. Mortensen. Echinodermenlarven d. Plankton-Exp. p. 65 66. 



4 ) O. Hamann. Die Schlangensterne. Bronn. Klassen u. Ordn. III. 1901. p. 860. 



6 ) Th. Mortensen. Notes on the development and the larval forms of some Scandinavian 

 Echinoderms. p. 135. 



