Perlucin from H. laevigata was first purified and characterised as a water-soluble protein of 155 amino acids from the nacreous layer. Based on the amino acid sequence a synthetic gene has been designed, although the natural coding sequence has not yet been determined. Perlucin comprises a C-type lectin with a lectin domain spanning the first 130 amino acids followed by two repeats of ten amino acids each. It has one predicted N-glycosylation site at position 84. Furthermore, it is able to bind lactose and mannose, most likely via its lectin domain. However, the physiological function of this activity has not yet been investigated. Together with other proteins of the organic matrix, one function proposed for Perlucin is the nucleation of aragonite crystals by binding to aragonite instead of calcite. In calcium carbonate precipitation experiments, native Perlucin clearly leads to faster precipitation of CaCO3. Using atomic force microscopy it has been demonstrated that 100 mg/mL Perlucin supports nucleation on calcite in saturated CaCO3 solutions. Moreover, if Perlucin is dialysed against a saturated CaCO3 solution, the CaCO3 crystals formed incorporated Perlucin, which has recently been confirmed by Weber et al. using green fluorescent protein tagged Perlucin. Purified native Perlucin always appears very heterogeneous. This observation raised the idea that additional variants exist beside the described protein. Here we describe the cloning and expression of cDNAs encoding Perlucin from the mantle epithelia of H. laevigata. Three new splice variants of Perlucin were identified, which differ mainly in the number of a 10 amino acid repeating unit at their C-termini. Recently, it has been assumed that aragonite-associated proteins have evolved signature sequence traits of intrinsic disorder and a predicted “disordered domain” within the repeating region of a Perlucin variant described here has been identified. Interestingly, in recombinant Perlucin the number of repeats strongly influences the precipitation behaviour of CaCO3, suggesting specific physiological roles of the splice variants in the regulation of crystal growth. In addition to alternative splicing, posttranslational modifications clearly lead to heterogeneity. One motif for N-glycosylation has been identified in Perlucin. Our MALDI-ToF MS data demonstrate that the non-glycosylated protein also occurs, since the corresponding non-glycosylated peptide was identified in the peptide map of spot 4. Obviously, this does not exclude the existence of glycosylated forms of Perlucin exist. Since the glycan structures of Haliotis are unknown, the molecular masses of the corresponding glycopeptides cannot be predicted and no evidence for the non-glycosylated peptide was found in any of the other spots.