INVERTEBRATE BOTTOM FAUNA 



467 



Norway there are three common species : Laniinaria hyperborea, 

 L. digitata, and L. saccharina. The first of these occurs in 

 great thickets in open bays or places where the play of the 

 waves is felt, whereas the other two grow in more sheltered 

 localities. The fauna varies accordingly. On the stalks of 



Lanimaria hyperborea we 

 chiefly hydroids, bryozoans, 



^et numbers of attached forms, 

 synascidians (see Fig. 327), and 

 calcareous sponges. Halichondria 

 panicea, one of the few siliceous 

 sponges of the littoral zone, also 



Fig. 327. 



Synascidian : Polycycli/sficscus, 



Huitfeldt Kaas. 



Fig. 328. 

 Obelia ge7iiculata, L. (After Hincks. ) 



frequently forms a thick covering over long pieces of the stalks. 

 On the blades of the laminaria two forms are very common, 

 namely the bryozoan Membranipora nievibranacea, which makes 

 a white covering over large portions, and the little hydroid 

 Obelia genicidata (see Fig. 328). An unattached form, the 

 gasteropod belonging to the Patellid family [Nacel/a pelhicida), 

 is very conspicu- 

 ous, owing to its 

 handsome blue- 

 striped shell, and 

 lives exclusively 

 on the laminaria. 



Besides the fig. 329. 



I 1 c Caprella linearis, L. 



attached lorms, 



that often completely cover the lower parts of the laminaria, 

 there are unattached species in great abundance existing upon 

 or among them. The best way of observing them is to shake 

 a thickly overgrown laminaria stalk, placed in a large glass of 

 sea-water, when we may perceive swarms of amphipods, worms,^ 

 tiny mussels and snails, little starfishes, and other creatures. 

 The most noticeable of the amphipods are the elongated and 

 strangely built caprellids, of which Caprella linearis (see Fig. 329) 



^ A species of Nicolca is common. 



