Arbacia lixula

Sea urchin, Arbacia lixula Soft parts, Italy ... 

Basic proteins of the histone type, or of a type intermediate between histone and protamine, are usually found in various amounts in cell nuclei of immature fish testes, often together with a protamine. Similar basic proteins of the histone type, but not protamines, are reported to be present in mature sperm cell nuclei of several fish and marine animals such as codfish (Stedman and Stedman, 1951), halibut, shad, sea urchin (Arbacia lixula and Stronglocentrotus lividus) starfish (Astropecten auran-tiacus and Echinaster spositus) (Kossel and Staudt, 1926), octopus (Eledone cirrosa) and some shellfish (Palau and Subirana, 1967). The same is true for some land animals such as Drosophila [Das et aL, 1964 (1,2,3)], grasshopper (Bloch and Brack, 1964 Das et al. 1965), and cricket (Kaye and McMaster-Kaye, 1966). No basic proteins can be readily extracted from mammalian sperm nuclei by acids (Dallam and Thomas, 1953). Nevertheless, there appears to exist in mammalian semen a basic keratin-like protein containing cystine in combination with DNA in a molecular ratio... 

Bibring, T. J., Bracket, J., Gaeta, F. S., and Graziosi, F. (1965). Some physical properties of cytoplasmic deoxyribonucleic acid in unfertilized eggs of Arbacia lixula. Biochim. Biophys. Acta 108, 644-651. 

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