190 



THE BIOLOGY OF MARINE ANIMALS 



are variable. In the decapods Homarus, Cancer and Maia, haemocyanin 

 shows minimal affinity for 2 below pH 7, whereas in Busycon (conch) 

 and Limulus (king crab) minimal affinity lies above neutrality. The normal 

 reactions of all these bloods lie slightly above pH 7. 



The blood of Limulus appears reduced under normal conditions when 

 drawn and contains about the same amount of 2 as ordinary sea water. 

 Oxygen capacities of Limulus and Busycon blood are 2-6 times that of 

 sea water, indicating maximal amounts of 2 which can be taken up under 

 optimal conditions. In Busycon about 80 % of the 2 is utilized in passage 

 through the tissues, and most of this 2 is carried by haemocyanin. The 

 increased oxygen affinity which attends rise in C0 2 may be of value in 

 promoting loading in oxygen-deficient environments, but it is otherwise 



c: 



o 



100 



80 



bO 



40 



10 



10 



20 30 40 50 60 10 80 90 WO 110 120 

 Oxygen Tension (mm Hg) 



Fig. 4.23. Oxygen Dissociation Curves for Haemocyanin 

 in Blood of the Cuttlefish Sepia officinalis at 14°C 



Curves: 1: pH 7-97, C0 2 , 0-6 mm; 2: pH 7-85, CO,, 1-95 mm; 3: pH 7-60, CO a , 

 2-8 mm; 4: pH 7-35, C0 2 , 9-75 mm; 5: pH, 7-24, CO,, 161 mm Hg. (From Wolvekamp 

 et al. (169).) 



rather difficult to understand. Lobster haemocyanin, like that of Loligo, 

 shows fairly high affinity for 2 in the normal physiological range (t u 

 Panulirus 6-5 mm at 15°C). About 0-5 c.c. of oxygen is delivered to the 

 tissues by 100 c.c. of blood, and haemocyanin accounts for 80-90% of the 

 oxygen exchange {Panulirus). The Bohr effect appears to be of slight signific- 

 ance in the blood of decapod Crustacea (45, 100, 130, 131). 



TRANSPORT OF CARBON DIOXIDE 



Normally sea water contains about 4-8 vols% C0 2 and fluid of similar 

 composition could serve adequately as a transport medium in many 

 sluggish invertebrates. Sea water and body fluids in general contain a 

 surplus of strong cations over strong anions, which combine with C0 2 

 to make up the alkali reserve. For such fluids carbon-dioxide dissociation 

 curves have been obtained (Fig. 4.24). 



In vertebrate bloods buffering is provided by bicarbonates, phosphates, 

 plasma proteins and haemoglobin. Among invertebrates the phosphate 

 content of the blood is usually low, and high buffering capacity, when 



