316 
K.J. McNamara 
aimed at clarifying the number of species of 
Schizaster. 
The other aspect of this study is to document the 
ontogenetic development of the species, as both 
juvenile and adult specimens are present within 
the population that was collected. McNamara and 
Philip (1980a) documented a number of 
ontogenetic changes in another Australian species, 
Schizaster (Ova) myorensis. Defining the characters 
that undergo morphological change during 
ontogeny in the northwestern Australian species of 
Schizaster will assist in determining the universality 
of ontogenetic change in suites of characters within 
the genus Schizaster and so aid the elucidation of 
the phylogenetic history of the genus. 
MATERIALS AND METHODS 
Measurements were carried out on 26 specimens. 
These are registered in the collections of the 
Western Australian Museum under the numbers 
132-93 to 135-93. Measurements were made using 
electronic callipers to an accuracy of 0.1 mm. 
Measurements were made of test length; maximum 
test width; maximum test height; centre of apical 
system to anterior ambitus; width of aboral 
ambulacrum III; length and width of anterior 
petals; length and width of posterior petals; width 
and length of peristome; width and length of 
periproct; length from anterior of peristome to 
anterior ambitus; maximum width of plastron. 
Furthermore, counts were made of the number of 
gonopores and number of pore pairs in ambulacra 
I, II and III aborally. For the purposes of 
ascertaining the number of gonopores present in 
the species 27 specimens were studied. 
SYSTEMATIC PALAEONTOLOGY 
Order Spatangoida Claus, 1876 
Family Schizasteridae Lambert, 1905 
Genus Schizaster L. Agassiz, 1836 
Type species 
Schizaster studeri L. Agassiz 1836, by subsequent 
designation of the Thirteenth International 
Congress of Zoology in Paris; opinion 209,1954. 
Subgenus Schizaster L. Agassiz, 1836 
Emended diagnosis 
Moderate to deeply incised ambulacrum III 
aborally, in which pore pairs are numerous (more 
than 15 in each row), occur in regular, single series 
and are aligned transversely, or only slightly 
obliquely. 
Remarks 
In his description of the fossil spatangoid 
echinoids of Cuba, Kier (1984) addressed the 
question of the validity of the taxon Paraster. 
Traditionally, Schizaster and Paraster had been 
distinguished on the basis of the number of genital 
pores, Paraster having four, Schizaster having two 
(Mortensen 1951). The two taxa had either been 
regarded as being of separate generic status 
(Mortensen 1951; Chesher 1966, 1972; Kier 1975) or 
only subgeneric status (Kier 1957; Henderson 1975) 
on the basis of this character. 
With the discovery that within a single 
population of Schizaster (Ova) myorensis the number 
of genital pores may vary between two, three and 
four (McNamara and Philip 1980b), other criteria 
were employed to distinguish Paraster from 
Schizaster. McNamara and Philip (1980a,b) 
regarded the two as subgenera and characterised 
Paraster as having a more shallow ambulacrum III 
than Schizaster, with fewer, oblique pore pairs; a 
more circular test; more central apical system; and 
straighter, more divergent anterior petals. They 
noted, however, that tire two subgenera lie at either 
end of a morphological continuum, and that some 
species are therefore likely to be transitional 
between the two subgenera. 
In their analysis of the evolution of the Australian 
species of Schizaster (s.l.) in the Tertiary, 
McNamara and Philip (1980b) noted that those 
species with the Paraster morphology were 
restricted to coarser sediments than those species 
with the Schizaster (s.s) morphology. They 
suggested that this indicated evolution of the finer- 
grained sediment dwelling Schizaster (s.s.) 
morphotype from the coarser-grained sediment 
inhabiting Paraster morphotype. A similar 
evolutionary trend has been observed in the genus 
in the Pyrennees (J. Villatte, pers. comm.). 
Although both the Australian living and fossil 
species of Schizaster (s.l.) can be accommodated 
comfortably within the two subgenera Schizaster 
and Paraster on the basis of characters suggested 
by McNamara and Philip (1980a,b), Kier (1984) was 
unable to separate all of the 16 Cuban species of 
Schizaster (s.l.) into the subgenera Schizaster and 
Paraster. 
However, it may be possible to subdivide 
Schizaster (s.l.) on the basis of the nature of 
ambulacrum III aborally, principally using a 
combination of the depth of ambulacrum III and 
the number and orientation of pore pairs. In those 
species with very shallow ambulacrum III, the 
number of pore pairs is much fewer than in those 
species with a deeper, broader ambulacrum III. 
Furthermore, the pore pairs are much more 
obliquely aligned, with the inner pore of each pair 
set much farther forward than the corresponding 
outer pore, such as in the sand-inhabiting Paraster 
