THE THORNY OYSTERS FAMILY SPONDYLIDAE Genus SPONDYLUS, Linn.
Shell irregular, attached by right valve, rarely free; valves radiately ribbed, set with spiny or leaf-like scales; hinge of two curved, interlocking teeth in each valve; mantle open; gills separate; foot small, cylindrical. Inhabits warm seas. Living species seventy; fossil eighty.
The thorny oysters were known by name, admired and eaten by the early Greeks long before most shell families had been discovered. The warm Mediterranean shores harboured the royal-hued Ass's Foot Spondylus, S. gadaropus, Linn., and others. The Swedish systematist retained the name given it by Aristotle, who saw under the sharp prickles and curving flat spines two valves shaped like a compact little hoof. 1 he purple of the upper valve contrasts oddly with the orange that is mingled with white on the under valve. The combination is peculiarly rich and attractive.
Collectors have always desired to have these showy bivalve shells. They are all striking in ornamentation and colouring.
Even the distortion of form that results from their crowding as they grow, attached firmly to rocky formations or to other shells, adds interest, for it tells something of the life they live.
We shall not find any species nearer than the Bermudas and West Indies, Mexico and the Gulf of California. The adjectives before their names will indicate the striking character of some of the species: dyed, variegated, painted, strawberry, orange, yellow, crimson-dyed, amber, dusky, violet, white-spined, many-spined, bearded, cat's tongue, leafy, hedge-hog, porcupine, branched, fingered, crumpled. Some aristocrats are called royal, princely and imperial.
The Variable Thorny Oyster (S. varians, Sby.) is great in size and thickness, weighing several pounds. Its oval valves, 404 The Thorny Oysters sometimes two or three inches thick, have their dense cover of flat spines entirely overlaid with a chalky lime deposit. Only a remnant of colour, orange or purple, remains tinging the fluted lips inside, and the beak. Wide ruffles extend out from the sides of some specimens. The white lining is china-like, with deep muscle scars.
The peculiarity of the attached valve is that it contains water chambers, flat, extensive, between the layers of the growing shell. The border of the mantle deposits material faster than the hinge area. In early stages the upper valve is bright rose colour, with three narrow dark ridges. Subsequent growth is colourless. Length, 5 to 6 inches.
Habitat.— Pacific Islands.
The Lime-Carrier (S. calcifer, Cpr.), with ruby lips, has its orange-coloured spiny face quite buried under burdensome depos its of lime. This species seems much like its predecessor, but is more compactly built. Diameter, 5 to 8 inches.
Habitat.— Panama to California.
The American Thorny Oyster (S. Americanus, Lam.) varies in its shape and the character of its spines. The scallop like, eared valves are whitish or brightly painted with yellow, and shades of red. The valves are ribbed, the area sub-divided by six extra ribs of greater size. The spines vary from needles, long and short, to broad, laminate frills, irregularly formed and distributed on a given specimen. The texture throughout these forms is china-like. Length, 3 to 6 inches.
Habitat.— Bermuda, West Indies.
The Imperial Thorny Oyster (S. imperialis, Chemn.), one of the most beautiful of its tribe, is fortunately abundant, and quite common in collections. Its valves are similar, round and eared like a scallop shell. Six main ridges separate the low ribs into groups of threes. Sharp spines, a single row on each ridge, cover the surface. The short ones on the secondary ridges are re-curved and each has a basal pair of minute points. The long primary spines overlap each other. This species never attaches itself, but remains free through life. The rosy flesh tint of these elegant shells deepens between the ridges. Diameter, 2 to 3 inches.
Habitat.— China.
The Royal Thorny Oyster (S. regius, Linn.) larger, more 405 The Thorny Oysters ventricose, the upper beak quite overhanging its mate, is rather more elaborate in ornamentation than the previous one, though made on the same plan. The primary spines are longer, and flung out at various angles. More and finer ridges separate the six principal. ones. The colour is rose purple. This species has the longest spines of all. Diameter, 3 inches.
Habitat. —Pacific Islands.
The Painted Spondylus (S. pictorum, Chernn.) has its six main ribs very regularly set with tongue-shaped spines. Inter vening ridges have similar spines or sharp pointed prickles; Some are coloured with shades of rose. More commonly they are rose and orange, or a rich salmon yellow. Some that begin life with a coloured shell abandon the scheme and produce a white border. No species is more variable in colouring than this. It is fastened to coral rocks at a depth of fifteen to eighteen fathoms. Length, 3 to 5 inches. Lower California, Mexico, Colombia.