346 



3. The "Suckers" of the Myzostomidae. 



By Charles L. Boulenger, M. A. 



Lecturer on Zoology in the University of Birmingham. 



[With 2 Figures.; 



eingeg. 25. Januar 1911. 



The large collection of Annelida made by Mr. Cyril Crossland in 

 the Red Sea in 1905 included several species of Myzostomids. These, 

 together with the Polychaetes, were sent to Mr. F. Potts of Trinity 

 Hall, Cambridge who very generously handed them over to me for exa- 

 mination. 



As the material contains a large number of specimens my full re- 

 port on the collection will not be ready for some time; in this note, 

 however, I desire to call attention to one species which presents certain 

 peculiarities of considerable morphological importance. 



The specimens I refer to present most of the features characteristic 

 of the old established species My^.ostoma costatum founded in 1836 by 

 F. S. Leuckhart ^ for forms obtained from Comaiula nmltiradtata Lam. 

 in the Red Sea, and it is my intention to call them by that name, at 

 least provisionally. 



Von Graff, in his well-known monograph ^ on the group, defines 

 M. costatum as follows: — "Corpus ovale depressum, incisura antica 

 triangulari, griseo- aut nigro-brunneum, supra costatum. Costa una 

 longitudinalis mediana qua communicantes 10 — 14 costae transversales 

 ad marginem productae. Margine orientes inter has costae breviores 

 secundariae et tertiarae illam longitudinalem non attingentes margi- 

 nemque crenulantes. Parapodia crassitudine uncinorumque forma M. 

 glabrwn, longitudine Jf. cirriferum aequantia. Acetabula elliptica. 

 Os ad basin incisurae triangularis, ventrale, papilla cloacalis ventralis. 



Longit. ad 31/2 ^m- 



In mari rubro Comatulae multiradiatae Lam. in mari prope Bohol 

 Actinometrae Solaris Lam. incolae". 



Mr. Crossland's specimens differ from previously described exam- 

 ples in being devoid of the triangular incision of the anterior margin, the 

 latter being transparent and deeply indentated to form a number of broad, 

 blunt processes. Whilst examining the oral region of a small mounted 

 specimen under the microscope I was surprised to find that, in addition 



1 F. S. Leuckart, »In Beziehung auf . . . das Schmarotzertier auf Coma- 

 fnla*, Proriep s Notizen. No 1087. Bd. öOj. S. 130. 



2 L. V. Grraff, Das Genus Myxostoma F. S. Leuckart^ Leipzig, 1877. S. 22. 



