  The purported observation of a state $\Theta^+$ with strangeness S = +1 led
to its quark model interpretation in terms of a pentaquark combination
involving a triquark-diquark structure -- the Karliner-Lipkin model. In this
work, the proper colour-spin symmetry properties for the $q q \bar{q}$ triquark
are elucidated by calculating the SU(6) unitary scalar factors and Racah
coefficients. Using these results, the colour-spin hyperfine interactions,
including flavour symmetry breaking therein, become straight-forward to
incorporate and the pentaquark masses are readily obtained. We examine the
effect on the pentaquark mass of (a) deviations from the flavour symmetric
limit and (b) different strengths of the doublet and triplet hyperfine
interactions. Reference values of these parameters yield a $\Theta^+$ mass
prediction of 1601 MeV but it can comfortably accommodate 1540 MeV for
alternate choices. In the same framework, other pentaquark states $\Xi$ (S=--2)
and $\Theta^c $ (with charm C=--1) are expected at 1783 MeV and 2757 MeV,
respectively.
