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Notoplax crocodila (Torr & Ashby, 1898)

Description: Animal ovate, broadly elongate, girdle moderately broad. Median valves with jugal area triangular, either smooth or longitudinally striate, sometimes edged with sawtooth effect (Fig. 2). Lateral and pleural areas separated by diagonal rib in SA specimens, barely so in NSW specimens; sculptured with curved rows of round or triangular nodules. Girdle densely spiculose with short sutural tufts. Colour variable.

Size: Up to 19 mm in length.

Distribution: Endemic to Australia: NSW, around southern Australia to south-western WA.

Habitat: On, under or at the edge of stones in sand or mud, below low water mark (Iredale & Hull, 1927, p. 76). Uncommon.

Comparison: This species is characterised by the triangular nodules on the valves, and the densely spiculose girdle.

Synonymy: Acanthochiton crocodilus debilior Iredale & Hull, 1925, was described as a subspecies from Sydney Harbour. The authors said "This subspecies differs from the South Australian shell in the generally weaker sculpture, and the obsolescence of the ribs on the anterior and median valves". 

Remarks: The original description of N. crocodila from SA gave the colour as olive-green. Iredale & Hull (1927, p. 76) described the colour of NSW specimens as "variable, white with a few faint markings chiefly towards the beaks; uniform purple and dark red are some of the variations observed".

Fig. 1: HOLOTYPE of Acanthochiton crocodilus debilior (C. 051551 Bottle & Glass Rocks, Sydney Harbour). The specimen is not flat, causing the anterior and posterior valves to appear shortened. It was collected before 1925, and is probably faded. The sutural tufts are broken and hardly visible in the image.

Fig. 2: HOLOTYPE of Acanthochiton crocodilus debilior showing half of one valve, with triangular nodules and the sawtooth edge to the jugal ridge.


Copyright Des Beechey 2019