Nucleic acid molecule comprising a nucleic acid sequence which codes for a haemocyanin, a haemocyanin domain or a variant of claim 1(c), the nucleic acid sequence being: (a) a nucleic acid sequence which is selected from a DNA sequence shown below or a corresponding RNA sequence: SEQ ID NO:4 (HtH1 Domain d), SEQ ID NO:5 (HtH1 Domain e), SEQ ID NO:7 (HtH1 Domain g), SEQ ID NO: 8 (HtH1 Domain h), SEQ ID NO: 16 (partial KLH1 Domain b), SEQ ID NO: 17 (KLH1 Domain c), SEQ ID NO: 18 (KLH1 Domain d), SEQ ID NO: 19 (partial KLH1 Domain e), SEQ ID NO: 54 (KLH1 Domain e'), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 83 (HtH1 Domain d"), SEQ ID NO: 84 (HtH1 Domain e"), SEQ ID NO: 86 (HtH1 Domain g"), SEQ ID NO: 87 (HtH1 Domain h"), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 96 (partial KLH1 Domain b"), SEQ ID NO: 97 (KLH1 Domain c"), SEQ ID NO: 98 (KLH1 Domain d"), SEQ ID NO: 99 (KLH1 Domain e"), SEQ ID NO: 100 (KLH1 Domain f"), and SEQ ID NO: 101 (KLH1 Domain g"); (b) a nucleic acid sequence which encodes a polypeptide comprising at least one amino acid sequence which is selected from the group of:: SEQ ID NO: 28 (HtH1 Domain d), SEQ ID NO: 29 (HtH1 Domain e), SEQ ID NO: 31 (HtH1 Domain g), SEQ ID NO: 32 (HtH1 Domain h), SEQ ID NO: 40 (partial KLH1 Domain b), SEQ ID NO: 41 (KLH1 Domain c), SEQ ID NO: 42 (partial KLH1 Domain d), SEQ ID NO: 43 (partial KLH1 Domain e), SEQ ID NO: 64 (HtH1 Domain h'), SEQ ID NO: 69 (partial KLH1 Domain b'), SEQ ID NO: 70 (KLH1 Domain e'), SEQ ID NO: 71 (KLH1 Domain f), SEQ ID NO: 72 (KLH1 Domain g), and SEQ ID NO: 73 (KLH1 Domain h); or (c) a nucleic acid sequence which encodes a polypeptide, which is at least 60% homologous to one of the sequences of (b), wherein the homology is calculated over a stretch of at least 90 amino acids. (a) a nucleic acid sequence which is selected from a DNA sequence shown below or a corresponding RNA sequence: SEQ ID NO:4 (HtH1 Domain d), SEQ ID NO:5 (HtH1 Domain e), SEQ ID NO:7 (HtH1 Domain g), SEQ ID NO: 8 (HtH1 Domain h), SEQ ID NO: 16 (partial KLH1 Domain b), SEQ ID NO: 17 (KLH1 Domain c), SEQ ID NO: 18 (KLH1 Domain d), SEQ ID NO: 19 (partial KLH1 Domain e), SEQ ID NO: 54 (KLH1 Domain e'), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 83 (HtH1 Domain d"), SEQ ID NO: 84 (HtH1 Domain e"), SEQ ID NO: 86 (HtH1 Domain g"), SEQ ID NO: 87 (HtH1 Domain h"), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 96 (partial KLH1 Domain b"), SEQ ID NO: 97 (KLH1 Domain c"), SEQ ID NO: 98 (KLH1 Domain d"), SEQ ID NO: 99 (KLH1 Domain e"), SEQ ID NO: 100 (KLH1 Domain f"), and SEQ ID NO: 101 (KLH1 Domain g"); SEQ ID NO:4 (HtH1 Domain d), SEQ ID NO:5 (HtH1 Domain e), SEQ ID NO:7 (HtH1 Domain g), SEQ ID NO: 8 (HtH1 Domain h), SEQ ID NO: 16 (partial KLH1 Domain b), SEQ ID NO: 17 (KLH1 Domain c), SEQ ID NO: 18 (KLH1 Domain d), SEQ ID NO: 19 (partial KLH1 Domain e), SEQ ID NO: 54 (KLH1 Domain e'), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 83 (HtH1 Domain d"), SEQ ID NO: 84 (HtH1 Domain e"), SEQ ID NO: 86 (HtH1 Domain g"), SEQ ID NO: 87 (HtH1 Domain h"), SEQ ID NO: 55 (KLH1 Domain f), SEQ ID NO: 56 (KLH1 Domain g), SEQ ID NO: 96 (partial KLH1 Domain b"), SEQ ID NO: 97 (KLH1 Domain c"), SEQ ID NO: 98 (KLH1 Domain d"), SEQ ID NO: 99 (KLH1 Domain e"), SEQ ID NO: 100 (KLH1 Domain f"), and SEQ ID NO: 101 (KLH1 Domain g"); (b) a nucleic acid sequence which encodes a polypeptide comprising at least one amino acid sequence which is selected from the group of:: SEQ ID NO: 28 (HtH1 Domain d), SEQ ID NO: 29 (HtH1 Domain e), SEQ ID NO: 31 (HtH1 Domain g), SEQ ID NO: 32 (HtH1 Domain h), SEQ ID NO: 40 (partial KLH1 Domain b), SEQ ID NO: 41 (KLH1 Domain c), SEQ ID NO: 42 (partial KLH1 Domain d), SEQ ID NO: 43 (partial KLH1 Domain e), SEQ ID NO: 64 (HtH1 Domain h'), SEQ ID NO: 69 (partial KLH1 Domain b'), SEQ ID NO: 70 (KLH1 Domain e'), SEQ ID NO: 71 (KLH1 Domain f), SEQ ID NO: 72 (KLH1 Domain g), and SEQ ID NO: 73 (KLH1 Domain h); or SEQ ID NO: 28 (HtH1 Domain d), SEQ ID NO: 29 (HtH1 Domain e), SEQ ID NO: 31 (HtH1 Domain g), SEQ ID NO: 32 (HtH1 Domain h), SEQ ID NO: 40 (partial KLH1 Domain b), SEQ ID NO: 41 (KLH1 Domain c), SEQ ID NO: 42 (partial KLH1 Domain d), SEQ ID NO: 43 (partial KLH1 Domain e), SEQ ID NO: 64 (HtH1 Domain h'), SEQ ID NO: 69 (partial KLH1 Domain b'), SEQ ID NO: 70 (KLH1 Domain e'), SEQ ID NO: 71 (KLH1 Domain f), SEQ ID NO: 72 (KLH1 Domain g), and SEQ ID NO: 73 (KLH1 Domain h); or (c) a nucleic acid sequence which encodes a polypeptide, which is at least 60% homologous to one of the sequences of (b), wherein the homology is calculated over a stretch of at least 90 amino acids.