The strontium-calcium atom ratio in carbonate-secreting marine organisms 23 



The average strontium-calcium atom ratio of calcareous sponges, Caicarea, 

 containing measurable quantities of strontium, was 2-99 x 10 * (Table 1 (C)). The 

 calcium content in silicious sponges, Demospongiae, was minute; only traces of 

 strontium were detected. 



4. Coelenterata: The high strontium content in corals was observed by Noll ( 1 934). 

 He reported the following results as percentage of strontium in their ash: hydrozoan 

 Millepora alcicornis, 0-43%; alcyonarian Cora/Hum ruhrum, 0-17%; and madrepor- 

 arian Porites clavaria, 0-42%. Odum (1951 b) reported an average strontium-calcium 

 atom ratio of 10-6 X 10^^ for corals. The calcium carbonate of Hydrozoa and 

 Madreporaria was reported as aragonite, whereas that of Alcyonaria was calcite. 



In Table I (D) are the results of analysis on calcareous portions of Coelenterata. 

 In Hydrozoa, the Hydrocorallina possess calcareous skeletons. Except Errinopora 

 zarhyncha, all the analyses yielded high strontium-calcium atom ratios which averaged 

 9-49 X 10-'. 



The soft corals, Alcyonaria, contained less strontium than other corals, and 

 magnesium was present in the skeletons. However, Heliopora coerulea, which has 

 the calcium carbonate in the form of aragonite, showed a much higher atom ratio 

 than other Alcyonaria. The Heliopora with their external tube-like skeletons differ 

 morphologically from all other Alcyonaria. With the high content of organic matter 

 and their strontium-calcium atom ratios comparable to Porifera (Caicarea), it is 

 interesting to note that the skeletons of Alcyonaria also have much in common 

 morphologically with those of Porifera. 



The solitary corals, Madreporaria, were found to have consistently high strontium- 

 calcium atom ratios with an average of 9-86 x 10'. This is one of the orders of 

 marine organisms to show the atom ratio equal to or greater than that of sea water, 

 8-9 x 10-3. 



5. Minor Phyla: Specimens of these skeletonless marine organisms were analyzed. 

 They were Bolinopsis microptera (Ctenophora), 7Vo/o/7/fl«a ac/Zco/a (Platyhelminthes), 

 Micrura verrilli (Nemertea), Urechis caupo (Echiuroidea), Phascolosoma agassizii 

 (Sipunculoidea), and Phoronopsis viridis (Phoronidea). Being non-carbonate secreting, 

 these organisms contained 85 to 99 % of organic matter which varied considerably 

 among specimens. Calcium was always present in the ash of the organisms, and only 

 traces of strontium could be detected. 



6. Phylum Annelida: Many members of Annelida such as Polychaeta possess 

 calcareous tubes which serve to shelter them. Lowenstam (1954 a) reported from 0-2 

 to 0-9% of strontium in the calcareous tubes of Serpulidae. Chave (1954) showed 

 that the°calcium carbonate in Polychaeta varies from pure calcite in specimens collected 

 in the north Pacific and Behring Sea to almost pure aragonite in specimens collected 



in tropic areas. 



Analyses of calcareous annelid tubes given in Table I (E) showed strontium-calcium 

 atom ratios ranging from 3-86 to 8-22 X lO-^ This is the only group of marine 

 organisms that demonstrated a wide range for the strontium-calcium atom ratio. 



7. Phylum Arthropoda: The Arthropoda are represented in the ocean mainly by 

 species of Crustacea. The majority of Crustacea possesses chitinous exoskeletons. 

 The Cirripedia is the only group in this phylum which possesses calcareous skeletons 



