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Austrocochlea porcata (Adams, 1851)

Description: Shell solid, heavy, relatively (in comparison with A. constricta) weakly spirally ribbed, with 3-4 ribs on the penultimate whorl and 8-12 on the body whorl. Aperture heavily ribbed internally, porcelain-white, overlaying a nacreous layer, the edge of which can be seen on the outer lip. External coloration white, with diagonal black or reddish-brown stripes. Columella smooth, with a weak tooth at anterior end. Umbilicus closed.

This species is extremely variable. The colour pattern varies in the number, width, and angle of the stripes, the apertural lirae may be strong or obsolete, and the columellar tooth may be absent.

Size: Average 25 mm, maximum 43 mm high.

Distribution: Endemic to Australia; Whitsunday Passage, Qld, to Houtman Abrolhos, WA, including Tas.

Habitat: Lives exposed in a wide range of habitats from exposed rocky shores to sand, seagrass and mangroves in sheltered estuaries, around the mid-tide zone; abundant.

Comparison: This species is very similar to Austrocochlea constricta. The following table showing the differences between the two species is slightly modified from that given by Parsons and Ward (1994) for four populations they examined from southern Tasmania and one population from southern NSW. More populations needs to be examined to be sure that these difference apply over the ranges of the species on mainland Australia.

Character A. porcata A. constricta
Spiral ribs Weakly spirally ribbed, 3-4 ribs on penultimate whorl, 8-12 on body whorl Pronounced shell ribbing, 2-3 ribs on penultimate whorl, 6-8 on body whorl
Shell colour and pattern Longitudinally striped on the spire and last whorl with parallel, alternate bands of off-white and black to red; intensity of banding pigmentation uniform over the shell surface Shell unicoloured, off white, or weakly striped
Snout Orange stripe on black snout Black, no stripe
Cephalic lappets Green/orange, frondose, positioned anteriorly on the head Black, solid, positioned at the sides of the head
Mantle fringe Black Cream

Remarks: Creese & Underwood (1976a, 1976b) have investigated the ecology and mechanisms responsible for colour banding in this species. They investigated population densities, size class distributions, growth rates, and variations in banding patterns at six sites near Sydney. They report the food to be diatoms and algal spores scraped from the rock surface, and the colour banding to be due to the pigment uroporphyrin I, laid down by groups of cells at the edge of the mantle. Shell colouration was determined to be an environmental, not a genetic factor; heavily pigmented individuals from Mona Vale, grown in cages at Warumbul showed a less dense pigmentation pattern when they laid down new shell. Quantitative measurement of the amount of pigment in the shell and the amount of chlorophyll in the substrate showed a linear relationship. The amount of dark banding in the shell is proportional to the amount of chlorophyll present in the food supply.

The animal is described and figured by Hedley (1917).

Figs. 1,2: Bondi, Sydney, NSW (C.326312)