664 THE BIOLOGY OF MARINE ANIMALS 



POISONS AND VENOMOUS DEVICES 



The use of toxic and noxious substances for offence and defence is wide- 

 spread among marine animals. The substances involved act as repellents, 

 deterrents or are definitely poisonous. We find them incorporated in the 

 tissues, or associated with stings, darts, etc. An account of venomous 

 animals has been prepared by Phisalix (102). 



Some species of dinoflagellates are toxic, and have been regarded as being 

 responsible for the death of marine fish, mass mortalities associated with 

 "red-tides," and paralytic shell-fish poisoning. Toxin extracted from 

 Gymnodinium veneficum affects the nervous system of animals, especially 

 ganglionic synapses. Its mode of action appears to involve membrane 

 depolarization (1). 



Sponges are said to be repellent to most other animals, but this has not 

 prevented lodgers from making use of sponge cavities (see Chapter 14), 

 or certain animals from feeding upon sponges. Sponge-eaters are generally 

 specialized in feeding habits and restricted to this particular food, e.g. 

 various snails and nudibranchs (38). 



Coelenterates, as a group, are characterized by stinging nematocysts, 

 which are poisonous to other animals (101a). These independent effectors 

 have already been described (p. 373). 



Various worms and molluscs possess noxious properties, frequently in 

 conjunction with bright warning coloration. Brightly coloured dorids 

 and a terebellid Polycirrus caliendrum are distasteful to predatory fish. 

 A tectibranch Pleurobranchus membranaceus secretes acid (H 2 S0 4 ) from 

 the body-surface and is repellent to fish. The cerata of nudibranchs (Aeoli- 

 diella, Facelina, etc.) enclose cnidophorous sacs. These contain nemato- 

 cysts derived from the coelenterates on which these nudibranchs feed, and 

 have a protective function. Cone-shells (Conidae) of tropical Indo-Pacific 

 shores are venomous : the radula is used for wounding and as a penetrant 

 for introducing a poison with curare-like properties. Other gastropods re- 

 garded as venomous are dog-whelks and allies (Nucella, Murex). Murex is 

 the source of Tyrian purple, which is produced by a hypobranchial gland 

 in the mantle cavity. Extracts of this gland are highly toxic when injected 

 into test animals (crabs, fish, frogs). Apart from the colouring material, 

 the hypobranchial gland contains serotonin, choline esters and substances 

 with curare-like activity (15, 33, 63, 64, 122). 



Poisonous and Repellent Devices in Echinoderms. Poisonous echinoderms 

 include certain sea-urchins and sea-cucumbers. Urchins of the family 

 Toxopneustidae bear poisonous pedicellariae ; other echinoids have poison- 

 ous spines, e.g. the tropical urchin Asthenosoma (31, 86, 101). 



Defensive structures, known as organs of Cuvier, are peculiar organs 

 occurring in certain holothurians (Holothuria, Actinopyga). They consist of 

 short tubes opening into the cloaca, and represent modified basal branches 

 of the respiratory tree. The walls of the tubes contain muscles, spirally 

 wound connective-tissue fibres and glandular cells capable of discharging 



