ECHINOIDEA 301 



red-brown and white lines, which jirobably represent growth- 

 lines. Spines usually reddish at the base, white in the point ; 

 but they may be more greenish. Grows to about the same size 

 as Ech. escidentus, at least to 150 mm. horizontal diameter. 



It is a very variable form and has given rise to the estabhsh- 

 ment of several "species ", some of which may be kept as more 

 or less distinct varieties. The typical form, as described above, 

 has been named Echinus Flemingii Forbes. A fairly character- 

 istic small form, depressed, with long and slender spines 

 and with five conspicuous red-brown spots around the 

 apical system, is the Var. norvegicus Diiben and Koren, and 

 another likewise very depressed form, characterised bv its 



Fig. 170. — Echinus acutus, in side view. About nat. size. 

 (After Koehler ; from Danmark's Fauna.) 



exceptionally small peristome, is the Var. microstoma Wyv. 

 Thomson. 



Hybrids between this species and Ech. escidentus are not 

 rare in places where these two species live together. The 

 parasitic Planarian Symlesmis echinorum also occurs in this 

 species. 



The breeding season is in the summer months. The larva 

 very much resembles that of Ech. esculentus. In the I. stage 

 it is easily recognisable by its rather strongly spiny body- rods, 

 which are slightly thickened and only slightly in\^ards bent 

 (Fig. 148, 2) ; the II. stage is hardly to be distinguished with 

 certainty from that of Ech. esculentus ; generally the arms are 

 a little more slender and more diverging than in the latter. 



