78 



Echinopluteus transversus nova forma. 



PI. XIII, Figs. 1—4. 



In the material collected by Mr. Blegvad in the West Indies in the 

 early part of 1911 there was a number of specimens of that most remark- 

 able Echinoid larva (Fig. 29) which I described in 1912 in the "Festschrift 

 fiir Spengel"!) and which I thought must be the larva of Echinometra 

 lucunter. That this reference was erroneous I have proved myself by 

 rearing the larva of that Echinoid from the egg through metamorphosis. 

 It therefore still remains an open question to which Echinoid this larva 

 belongs. — Meantime I have found in the plankton samples collected in 

 the Indian Ocean on my Expedition to Siam in 1900 a specimen of a larva 



_-^ 



Fig. 29. Echinopluteus transversus, species e. A. "/i, B. 'Vi- Figure A shows the excessive 



length of the postoral arms, wliich are not even quite complete here, the point being 



brolcen in the specimen from which the figure was drawn. 



exactly similar to the Westindian form, and another one was taken there in 

 1914 on my way to the Pacific. Furthermore two related forms were taken 

 in the Gulf of Panama in 1916, and two more were found in the material 

 collected in the West Indies by Mr. Blegvad and Mr. Faye. Thus I 

 have now no less than six different species of this interesting larval form, 

 which I shall designate as Echinopluteus transversus. The species described 

 in the paper quoted above is, together with the one from the Indian Ocean, 

 the most speziaUzed of all, the other forms showing more or less primitive 

 features. Still they all have so many characteristic features in common 

 that 1 have deemed it desirable to keep them together under the same 

 name, even though it may seem very probable that they will prove to 

 belong to different genera, but within the same family, beyond doubt. 



This larval type is eminently characteristic through the excessive devel- 

 opment of the postoral arms, while the other arms remain undeveloped, 



1) Th. Mortensen. Ober die Larve von Echinometra lucunter (L.) (?). Zool. Jahrb. 

 Suppl. XV. 2. Bd. 1912, p. 275—88. Taf. 19—20. 



