SUB-KINGDOM _ECHINODERMATA_ +-------------------------------------------+-------------+--------------+ |Body star-shaped. |Body glob- |Body | +------------+------------------------------+ ular, sub- | elongated, | |Body |Body not stalked. | globular, | and covered | | stalked, |Tube-feet used for locomotion.| or heart- | with a | | at least |=Class:= _Stelleridæ._ | shaped, | soft skin | | during +--------------+---------------+ and cov- | containing | | early |Arms jointed |Arms contin- | ered with | calcareous | | stage. | to disc, and | uous | a con- | spicules. | | Feet not | not contain- | with disc, | tinuous | | | used for | ing prolong- | and contain- | shell. |=Class:= | | loco- | -tions of the| ing processes | | _Holothu- | | motion. | internal | of the |=Class:= | roidea_ | | | organs | viscera. | _Echinoidea_| (Sea | |=Class:= | | | (Sea Ur- | Cucumbers). | | _Crinoidea_|=Order:= |=Order:= | chins). | | | (Feather | _Ophiuroidea_| _Asteroidea_ | | | | Star). | (Brittle | (Common | | | | | Stars). | Stars). | | | +------------+--------------+---------------+-------------+--------------+ CHAPTER XI _MARINE WORMS_ Some groups of animals are so well defined that the individual species contained in them can be assigned their proper place without any difficulty, the main characteristics by which the group is distinguished running with more or less precision throughout the series; but, unfortunately this is not the case with the ‘worms,’ which constitute the sub-kingdom _Vermes_. Here we have a most heterogeneous assemblage of animals, collectively exhibiting exceedingly wide variations in both form and structure. We have already referred to the sea cucumber as wormlike in form, and this creature is only one of a large number of wormlike animals that are not worms; and it is also a fact that a considerable number of the worms are not wormlike. It appears as if the sub-kingdom Vermes were a kind of receptacle into which we may throw almost any invertebrate animal that does not readily fall in line with the general characteristics of the other important groups; for in it we have such a varied assemblage of creatures that, speaking of them collectively as worms, it becomes most difficult, if not absolutely impossible, to say exactly what a worm is; and it is a question whether the sub-kingdom ought not to be divided into at least two or three groups of the same standing.