200 
K.J. McNamara 
concave; peristome a little sunken. Food grooves 
relatively long, extending about one-third of the 
way to the ambitus in larger specimens. Peristome 
and periproct small. Periproct situated at least two 
periproct diameters from posterior margin. 
Description 
Test small, reaching up to 35 mm test length (TL); 
subcircular, with a broadly rounded ambitus; 
posterior generally truncate (Figure 5A,B,H); 
highest at mid-test length at apical system; height 
19-26%TL; large adults relatively lower than 
smaller adults; at margin test height varies between 
12-20%, being higher in small individuals; test 
slightly longer than wide, width ranging between 
91-99%TL. Aboral surface rises gently and evenly 
from broadly rounded lateral margin up to apex. 
Apical system slightly anterior of centre; 
tuberculate, with four gonopores. Petals almost 
closed or slightly open distally. Paired petals of 
equal length (17-24%TL, but slightly shorter than 
anterior petal in ambulacrum III (20-28%TL); 
extend about half of the way to the ambitus; petals 
broad, with maximum width varying between 10- 
16%TL; relatively broad in juveniles (Figure 5G), 
narrowing slightly during ontogeny; petals widest 
at about mid-petal length. Interporiferous region 
6-10%TL, being widest in smallest specimens. 
Inner pores of each pair circular; outer pore slightly 
elongate; connected by shallow interporiferous 
furrow. 
Adoral surface gently concave, sloping at low 
angle to slightly sunken peristome. Peristome small 
in adults, 6—10%TL; larger in juveniles, up to 
18%TL in specimen of 8 mm TL; circular and 
surrounded by weakly developed bourrelets; 
central or slightly anterior of centre. Food grooves 
of moderate length and well-impressed (Figure 
5H,I), extending about one-third of the way to the 
ambitus. Periproct circular to transversely oval, 
with a width similar to peristome diameter; 
situated at least twice its length from the posterior 
border (9-15%TL). 
Discussion 
The living Peronella orbicularis occurs in the 
shallow intertidal zone in Western Australian 
waters from the far north of the state at a latitude 
of 14°S, south to Shark Bay at a latitude of 26°S. It 
extends further south only offshore, reaching to 
31°34'S, some tens of kilometres off Guilderton. 
Although Rowe and Gates (1995) give its 
bathymetric range as 0-70 m, it has been collected 
off Guilderton in water depths of 106-110 m, 40 
km west of Jurien Bay (latitude 30°21'S) at 165 m, 
and off Green Head (latitude 30°S) from between 
190 and 238 m. Its presence offshore this far south, 
but absence inshore, can be attributed to southerly 
dispersal in the offshore Leeuwin Current (see 
McNamara 1992 for a discussion of the effect of this 
current on the southerly dispersal of echinoids). It 
occurs in Late Pleistocene deposits in the Shark Bay 
region, but is absent from coeval deposits in the 
Perth Basin. However, four specimens from a 
Middle Pleistocene unit at Dumbarton, near 
Busselton in the Perth Basin (WAM 94.266), 
although poorly preserved, probably belong to this 
species, having, like P. orbicularis, a relatively broad 
test, relatively short petals and periproct that is not 
less than two diameters from the posterior ambitus. 
The living species occupies a range of habitats, 
specimens in the collections of the Western 
Australian Museum recording its presence from 
intertidal reef flats to at least 200 m. It inhabits a 
variety of substrates, from coarse gravel to sand, 
muddy sand to silt. In shallow water it is found in 
assoociation with mangroves or seagrass, but with 
coralline algae nodules and bryozoa in deeper 
water off the coast. 
Peronella orbicularis can be distinguished from 
another living northwest Australian species, P. 
tuberculata, in having shorter petals and periproct 
situated closer to the posterior margin. 
PLIOCENE TO HOLOCENE DISTRIBUTION 
OF PERONELLA IN WESTERN AUSTRALIA 
Peronella is today a Tropical Indo-West Pacific 
genus, having been recorded from near-shore 
environments around Australia, Japan, Taiwan, 
Malaysia, Philippines, Polynesia and Indonesia 
(Mortensen 1948). Seven species are known from 
Australian waters (Rowe and Gates 1995). The 
stratigraphic distribution of Peronella is essentially 
from the Pliocene to the Recent. Species recorded as 
Peronella from the Eocene of Trinidad, Cuba and the 
southeastern United States (Cooke 1942) are now 
placed in Weisbordella, a neolaganid (Durham 1954). 
Pliocene species have previously been described 
from Japan (Cooke 1954), the Philippines (Israelsky 
1933) and South Australia (Tate 1893). 
Eucla Perth Carnarvon 
Figure 6 Biostratigraphical distribution of fossil 
species of Peronella in the Eucla, Perth and 
Carnarvon Basins in Western Australia. 
