72 allan hancock pacific expeditions vol. 8 



Characters Used for Identification 



Macroscopical characters 



Size. — Where full-grown specimens are available, size constitutes a 

 fairly good character, although some caution must be used, as many species 

 are able to contract their bodies to an unbelievable degree, while others 

 rarely change much. Most Den drochi rotes are small forms, that is, less 

 than 10 cm. long, a number measure between 10-15 cm., and few are 

 large, above 20 cm. The largest forms are known to reach a length of 

 50 cm. when fully expanded. The chief difficulty about using size for 

 identification is that one so often encounters young individuals. Speci- 

 mens 1 cm. long are usually difficult to identify; the feet are frequently 

 not distributed in their tj^pical pattern, and the spicules may be very 

 different from what they are in more mature individuals. Where very 

 young specimens are involved, the characters, "feet ambulacral" or "feet 

 interambulacral," cannot be used, as all the forms with interambulacral 

 feet begin with feet in the ambulacra only. In some species the inter- 

 ambulacral feet begin to appear when the animal is less than 1 cm. long, 

 but in others they appear much later, when the animal is 2-3 cm. long. 



For that matter, veiy little is known about the growth rate of the 

 Dendrochi rotes or any order of seacucumbers. Mitsukuri found that the 

 Japanese Aspidochirote form Stichopus japonicus reaches the unbelievable 

 length of 25 cm. in a little over a year, but such a rapid growth is prob- 

 ably an exception, and under no circumstances can it be assumed to be 

 the normal in the Dendrochirotes without definite proof. Smaller species 

 may probably reach their full length in one or two years; larger forms, 

 as, for example, Thyone briareus (Lesueur), require undoubtedly four 

 to five years to reach their full size. 



Tentacles. — The full number is quickly reached in the "dekachirote" 

 forms. In the "polychirote" forms (those which have tentacles arranged 

 in 2 well-defined circles and definitely of two sizes) seem to develop the 

 full number before they have reached the length of about 1 cm., while 

 in the species which have the 2 circles indistinctly set off and with ten- 

 tacles of varying size the full number seems to be reached rather late. 

 In many "dekachirote" forms the two ventral tentacles are much smaller 

 than the others, and the difference in size is retained throughout the 

 animal's life. In a few species the number of tentacles falls below ten in 

 various deep sea forms and in that case the tentacles are often unbranched. 



Tube feet. — ^The arrangement of the tube feet is of importance in 

 reasonably mature individuals and constant for the different species. The 



