A new family of fusiform, semi-planktonic harpacticoid copepods is described from two anchihaline caves, Caye Chapel Cave and Columbus Caye Blue Hole, on the Belize Barrier Reef. The Novocriniidae fam. n. is proposed to accommodate Novocrinia trifida gen. et sp. n. and is placed in the tisbidimorph complex of families (Tisboidea) by virtue of its maxilliped morphology. The new genus shares several characters with other tisbidimorph families but cannot be placed in any of them without an unnatural extension of their diagnoses. The Novocriniidae display a suite of plesiomorphic character states in most appendages from the antennules to the PS, indicating their basal position on the tisbidimorph phylogenetic tree. They exhibit a unique sexually dimorphic modification of the antennae, involving the transformation of two setal elements into filamentous sensory tufts. The unusual presence of supernumerary elements on the male PS baseoendopod is briefly discussed as well as the presence of a genuine but incipient oral cone derived from the labrum and medially fused paragnaths.