156 

 Ophiopluteus serratus Mrtsn. 



PL XXVIII, Figs. 1—2. 



In the memoir "Die Echinodermenlarven der deutschen Siidpalar Ex- 

 pedition 1901—3" p. 96 (Taf. XIII, Fig. 1) an Ophiurid larva was described 

 under this name, characterized especially by its very large median process 

 with a series of more or less branched prominences along its outer side. 

 In the material collected during my expeditions to Siam 1899 — 1900 and 

 to the Pacific in 1914 — 16 there is a considerable number of Ophiurid 

 larvae which belong, evidently, to the same type. They may possibly re- 

 present two different species or even more; but as they show considerable 

 variation, especially in regard to the size of the median processes, it is 

 hardly possible to come to a definite result as to their specific limits. I 

 have therefore preferred to designate them all simply as Ophiopluteus ser- 

 ratus. Only the study of living material and tracing their origin to the 

 parental forms will give the clue to the question of the specific limits 

 within this, evidently, very variable larval type. 



This larva is characteristic through the great length of the inner arms and 

 the nearly upright position of the posterolateral arms. These latter arms 

 are ca. 5 times, the inner arms about 3 times the body length. There appears 

 to be a very slight widening at the tip of the arms. The preoral area is 

 very low; it may be distinct in its whole width or only at the corners. 

 This is possibly a specific difference, which cannot, however, be decided 

 from the preserved material. The preoral band is more or less covered by 

 the postoral band, the whole oral area being almost totally covered up 

 by the postoral or anal lobe^). A conspicuous feature in some of the spec- 

 imens is the very large size of the stomach (PI. XXVIII, Fig. 1), which 

 fills the whole space inside the posterolateral rods. In other specimens it 

 is much smaller, occupying only the space inside the rods of the inner 

 arms (PI. XXVI II, Fig. 2). It is very well possible that this is really a 

 specific character, but in the preserved material it is too often impossible 

 to decide, what is due to preservation and what not, so that, although 

 there would seem to be no doubt in some cases that we really have to 

 do with two different species, it is better to leave the species question 

 undecided at present. 



In the skeleton (Fig. 84) there appears to be no distinct characters 

 eventually corresponding to the mentioned differences in the size of the 

 stomach and the preoral area. A noteworthy fact is the very great variation 

 in the size of the median processes from the transverse rods. In some 

 specimens they are quite small and inconspicuous, in others as large as 



1) The suggestion given in tlie original description tiiat tlie peculiar feature of tlie oral 

 region of tlie type specimen was due to compression is certainly correct. 



