CAMBRIAN PERIOD 17 



nellids). The work, however, had not ended in spicule-making. 

 In some cases the spicules were artistically joined together, 

 forming a beautifully outlined framework. The builders 

 were, therefore, artists as well as artisans. 



Jelly-fishes have left impressions of their flimsy shapes jelly-fishes 

 (Medusites). Corals were in the waters, and were widely corals 

 distributed (Archceocyathus) ; but no reef -builders had yet 

 made their appearance. Some forms, however, allied to corals 

 were living in more or less large colonies (Cladophora). The cladophora 

 majority of these communities were rooted to the ground on a 

 stem, and the zooids or individuals were borne on one side 

 (only) of numerous branches and branchlets (Bryograptus). 

 Other colonies enjoyed a somewhat free existence, and floated 

 about attached by threads to seaweeds (Didyonema). The 

 zooid-communities of our own time, known as " sea-firs " (Ser- 

 tularians), retain close affinities with these ancient colonies. 



Little bud-shaped animals, rooted in the sea-floor, were CYSTIDS 

 numerous. The box or cista which contained their vitals 

 was protected by tiny plates rudely arranged, and rendered 

 prickly by a deposit of Ume. These little creatures — known as 

 cystids — were not, as a rule, provided with arms (Protocystis, 

 Stromacystis), and were therefore short of the facilities for 

 obtaining food which later cystids generally possessed. 

 Cystids, no doubt, dated far back into the Foundational 

 Ages ; for a few closely allied but more highly organised 

 forms, known as crinoids or " sea-hlies," were living in sea-lilies 

 Cambrian seas (Palceocrinus). The " spiny-skinned " stock 

 was also represented on another line of evolution. Star- starfishes 

 fishes were a fruit of this departure (Palesterina). For long 

 periods during the Foundational Ages starfishes were probably 

 — hke their cousins the cystids and " sea-hlies " — fixed to the 

 ground ; but by a gradual wasting away of their stalks 

 emancipation was in course of time obtsdned. The arms or 

 rays of the Cambrian starfishes do not appear to have been 

 so sharply defined as in later forms ; and the animals, no 

 doubt, had other peculiar features. So far as is known no 

 animals in Cambrian seas had become so far developed as to be 

 describable as sea-urchins (echinoids); but sea-cucumbers 

 (holothurians) were probably in existence (Eldonia). 



