MARINE ANIMALS THAT STING 



51 



of a foot or more. It is believed that the spines of some of these 

 species secrete a venom, but this has not been experimentally 

 demonstrated. The aboral spines of Asthenosoma are developed 

 into special venom organs carrying a single large gland. The point 

 is sharp and serves as a means of introducing the venom (Fig. 24) . 



Pedicellariae. Pedicellariae are small, delicate, seizing organs 

 which are found scattered among the spines of the shell. There 

 are several different types of pedicellariae. One of these, because 



spine tip 

 poison 



BAG 



SHEATH OF 

 MUSCLE & 

 CONNECTIVE 

 TISSUE 



Fig. 24. A venomous aboral spine of the sea urchin, Asthenosoma ijimai. 



(After Mortensen) 



of its globe-shaped head, is called the globiferous pedicellariae, and 

 serves as a venom organ. They are comprised of two parts, a ter- 

 minal, swollen, conical head, which is armed with a set of calcareous 

 pincer-like valves or jaws, and a supporting stalk (Fig. 25). The 

 head is attached to the stalk either directly by the muscles, or by a 

 long flexible neck. On the inner side of each valve is found a small 

 elevation provided with fine sensory hairs. Contact with these 

 sensory hairs causes the valves to close instantly. The outer sur- 

 face of each valve is covered by a large gland which in Toxopneustes 

 has two ducts that empty in the vicinity of a small tooth-like pro- 



