Abstract

The six species of this genus all have the primitive moiabine karotype (2n male = 17, male XO) modified as a result of two dissociations (numbered D9 and D10) that have fragmented the original AB and CD metacentric chromosomes into acrocentrics A,B, C and D. This has produced a 2n male = 21 karyotype in four of the species. In the two remaining species (H. spinipinnis and H. longirostris), which have a somewhat more westerly distribution in northern Australia. a fusion (F20) between two of the small chromosomes is present; this has reduced the chromosome number to 2n males = 19. All the species are XO in the male sex. From the limited material available, five of the species appear to be chromosomally monomorphic, but the rather widespread H. obtusipinnis is polymorphic for several structural chromosome rearrangements.