WORMS (VERMES).—The hard, calcareous tubes of Sea-worms, the Polychaeta (“many bristles”) are often found in fossiliferous deposits, and sometimes form large masses, due to their gregarious habits of life; they also occur attached to shells such as oysters ([Fig. 26]). The burrows of the wandering worms are found in Silurian strata in Australia; and the sedentary forms likewise occur from the Devonian upwards.

ECHINODERMATA.—Sea-urchins (Echinoidea) possess a hard, calcareous, many-plated test or covering and, when living are covered with spines ([Fig. 27]). Both the tests and spines are found fossil, the former sometimes whole when the sediment has been quietly thrown down upon them; but more frequently, as in the Shepherd’s crown type (Cidaris), are found in disjointed plates, owing to the fact that current action, going on during entombment has caused the plates to separate. The spines are very rarely found attached to the test, more frequently being scattered through the marl or sandy clay in which the sea-urchins are buried. The best conditions for the preservation of this group is a marly limestone deposit, in which case the process of fossilisation would be tranquil ([Fig. 28]).


Fig. 26.—Fossil Worm Tubes (? Serpula.)
Attached to a Pecten. Slightly Enlarged.
Cainozoic (Balcombian).
Muddy Creek, Hamilton, Victoria.
(F.C. Coll.)
Fig. 27—A Regular Sea-Urchin
(Strongylocentrotus erythrogrammus, Val.)
About 2/3 nat. size.
Showing Spines attached.
Living. Victoria.
(F.C. Coll.)

Fig. 28.—Sea-Urchin (Linthia antiaustralis, Tate).
Test denuded of Spines.
About 2/3 nat. size.
Cainozoic (Janjukian):
Curlewis, Victoria.
(Nat. Mus. Coll.)
Fig. 29—Ophioderma egertoni, Broderip, sp.
About 1/2 nat. size.
A Brittle Star from the Lias
of Seaton, Devon, England.
(Nat. Mus. Coll.)

The true Starfishes (Asteroidea), are either covered with calcareous plates, or the skin is hardened by rough tubercles; and these more lasting portions are preserved in rocks of all ages. The shape of the animal is also often preserved in an exquisite manner in beds of fine mud or clay.

The Brittle-stars (Ophiuroidea) have their body covered with hard, calcareous plates. Their remains are found in rocks as old as the Ordovician in Bohemia but their history in Australia begins with the Silurian period ([Fig. 29]). From thence onward they are occasionally found in successive strata in various parts of the world.

The bag-like echinoderms (Cystidea) form a rare group, restricted to Palaeozoic strata. The plates of the sack, or theca, and those of the slender arms are calcareous, and are capable of being preserved in the fossil state. A few doubtful remains of this group occur in Australia.

The bud-shaped echinoderms (Blastoidea) also occur chiefly in Devonian and Carboniferous strata. This is also a rare group, and is represented by several forms found only in New South Wales and Queensland.

The well known and beautiful fossil forms, the Stone-lilies (Crinoidea) have a very extended geological history, beginning in the Cambrian; whilst a few species are living in the ocean at the present day. The many-jointed skeleton lends itself well to fossilisation, and remains of the crinoids are common in Australia mainly in Palaeozoic strata ([Fig. 30]). In Europe they are found abundantly also in Jurassic strata, especially in the Lias.

Fig. 30.
A Fossil Crinoid (Taxocrinus
simplex, Phillips sp.)
About 1/2 nat. size.
Wenlock Limestone (Silurian),
Dudley, England.
(Nat. Mus. Coll.)