Boone, Echinodermata, Cruises of "Ara" and "Alva" 193 



Remarks: Specimen A represents the Pentacula stage of a 

 Synapta, It has the five interradial circumoral tentacles and when 

 cut open longitudinally shows the slightly curved gut terminating 

 in the aboral anus. The body is marked into the five radial sec- 

 tions, of which the dorsal two, composing the bivium, are more 

 developed than the two lateral radii of the trivium (ventral in 

 position), which possess nerves, muscles and tube-feet and later 

 develop oral tentacles. 



Specimen B represents a seldom seen larval Synaptid, in an 

 excellent state of preservation, the oral end being expanded disk- 

 like and showing the twelve digitate tentacles, each of which is 

 distally quadridigitate and internally beneath the muscular disk 

 each tentacle communicates with a tube, which converge like the 

 spokes of a wheel, uniting in a circular ring from which also 

 arises the Polian vesicle. These radial water canals of the larval 

 Synaptid are especially interesting because they are absent in the 

 adult. 



The central aperture to the aesophagus is controlled by a 

 strong muscular ring. The intestine is large and well filled with 

 detritus, the lower gut being broken from the aboral aperture and 

 extruded. 



The five rays are definitely developed, but unequally so, as they 

 are in the mature larva, specimen A. 



Externally the body-wall is so constricted in the dead speci- 

 men that it appears to be a soft-textured skin continuously paved 

 with small rounded verrucae. Posteriorly the body-wall is rounded 

 and externally near and adjacent to the aboral aperture the body- 

 wall is developed into slightly branched processes, resembling the 

 pseudanchrorhagi of an actinian. 



The Synaptidae are considered to be an early offshoot of the 

 Holothuridean ancestor. The adult Sytmptid has an elongated, 

 cylindrical body with the oral and aboral apertures terminal; 

 tentacles pennate or digitate and supplied direct from the circular 

 canal, no radial tubes being present. 



Reference: Goodrich, E. S., in Lancaster, E. Ray, editor of: A 

 Treatise in Zoology, pt. Ill, 1900, chapter XIII, The Eleuthe- 

 roza-Holothuroidea, p. 234. 



