The “Imperial Thorny Oyster” is a splendidly spinous spondylid widely distributed in the Indo-West Pacific, ranging from India to South China Sea to Taiwan to Philippines. Typically uniform white in colouration (umbo is often pink), spines very long spines especially in young specimens; larger specimens often have shorter spines in proportion to the shell. It is in fact a very variable species and in some specimens the pink colouration persists and the whole shell may be tinged in pink. The depicted specimen is an uncommon form with very well-developed fine spines and pink hue persisting to adult size. Generally a common species, it is a filter-feeding bivalve normally found on shell debris and dead corals of shallow to moderate depths between -10~100m. Typical shell length including spines around 90mm, very large specimens may exceed 150mm. Some large specimens, especially the depicted form, are very similar to S. victoriae Sowerby II, 1860 (better known as S. wrightianus Crosse, 1872) from Australia; but S. victoriae has five to seven minor interstice ribs each carrying one row of smaller spines between the principal ribs compared to three minor interstice ribs in S. imperialis each carrying three rows of smaller spines, one from the centre and weaker ones from either side. S. victoriae also usually has much thicker and stronger spines on the principal ribs in the early growth stage. – From Chong Chen’s post

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