225 



as an establislu-d fad lhi()ii,t>Ii llic "'Brachioldiid hibernicd" of Gemmill, 

 affords anoUior iinpoiiaiil aid for settling Iht' question of the parentage of 

 the larva. Aslerias Icnuispina does not occur in the Atlantic to the North 

 of 10' I.at. X. Accordingly its larva could hardly be found olT Ireland. 

 On the other hand Pcdirctlaslcr sc.rradialus is not known to occur farther 

 North than the Hiscayan (luU: l)iil il is by no means improbable that it 

 does, however, occur in I he deep-sea off Ireland. The result is then that 

 it seems highly probable liiat llu' "Slvllosphn'id inirdbilis" is the laiva of 

 Pcdicclliislcr scxradidliis. 



The Ophioplu t eus. in spite of the great number of ■■s|)ecies" known, 

 appears to show only uiiiin|)()ilanl dcNialioiis from the original simple 

 type, which may perhaps be most nearly represented by the Opliiothri.r- 

 larva. In the shape of the body there are only few features which may be 

 regarded as a higher specialization: such feature is the presence of vibratile 

 lobes at the base of the posterolateral arms in the OphiocoiiidAavva. The 

 presence of a ciliated tuft at the posterior end of the body, occurring in 

 various forms, may also be a sjjecialized feature, probably acquired separ- 

 ately in various groups. Hut too little is known for forming a dcfmite judg- 

 ment of the value of this character. The ciliated ring in the posterior end of 

 the body of Ophiopliileus corondtus ("bk-hinodermen-Larven d. IMankton- 

 b>xpe(l." Taf. VI, Fig. (i), as yet quite a unique feature in Ophiurid-larvae, 

 may perhaps represent a further specialization of the apical tuft. But so 

 long as we do not know anything about the affinities of thai larva ( its 

 skeletal structure is still unknown — ) this question must remain unsettled. 



The length of the arms varies very considerably. The jiosterolateral arms 

 are generally much the longer and form the main floating ajjparatus of 

 the larva: this is especially evident in the Ophiolhri.vAnyxn and Ophiopl. 

 opuli'nlus. whei'e these arms are entirely unaltered during metamorphosis, 

 the young Ophiurid remaining attached to them and simply leaving them 

 by the time it is giving up pelagic life. The arms of ()|)hiurid-larva' never 

 become actively movable swimming organs, no muscles connecting the 

 two parts of the body skeleton being present, contrary to what is often 

 the case in Echinoid larvae. Generally the arms are very thin and narrow, 

 more rarel\ bioad and Hat (as in Ophiopl. pdiridoxus and the Ophioconvi- 

 larva). The widening of the arm points often found in preserved si)eci- 

 mens is probably only due to preservation. It is a curious fact thai the 

 right anterolateral arm is often longer than the left one. 



A very conspicuous feature is the absence of poslerodorsal arms in the 

 larva of Arnphiura fUiformis (Ophiopliileus numciis). .\lso in Ophiopliileus 

 r/»ftn/.s (Kchinodermen-l.ai\en d. IMankton-Kxped. Taf. I\ . I'ig. 9 — 10) the 



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