A printhead module is provided for an inkjet printhead assembly. The printhead module includes a support defining a plurality of internal ink chambers. An elongate ink distributor is mounted to the support. A subassembly includes a micro-electromechanical integrated circuit (IC) configured to eject ink and mounted to the distributor so that ink from the ink chambers can be distributed to the IC by the distributor. The support, distributor and subassembly are shaped to define complementary formations on opposite sides of the printhead module so that a pair of the printhead modules can be mated together.