Moving down from the aboral to the oral side, the following internal and external structures can be identified, amongst others (Additional files 3, 4, 5, 6): madreporic plate, gonads, spines, intestine, compass elevator muscles, Aristotle's lantern with corresponding muscles, and the stomach.
Such unusual fossils as Hallucigenia, a creature with a long tubular body and two rows of tall dorsal spines; Wiwaxia, an oval creature with two rows of spines down its plated back; and Opabinia, which had five eyes and a long nozzle, have led many scientists to conclude that the Cambrian Period may have produced many unique phyla.
g gut, h head, l legs/lobopods, p plates, sp spines.
This results in much faster book scanning since each page doesn't need to be flattened by glass plates and spines don't need to be broken.
In these unfamiliar environments, the fish lost their bony plates and spines and developed novel behaviors and physiology.
Bony lateral plates and spines enhance protection from gape-limited predators, which are the main threat in open water (it makes stickleback more difficult to swallow and improves the chances of survival after escape) (Reimchen 1992, 2000).
The sea stars first developed lesions, then began to lose their arms, and finally decayed into piles of skeletal ossicles (bits of calcium carbonate such as a star's plates and spines).
They also have body armour in the form of hard plates and spines.
Butterfield has also described Wiwaxia′s armor plates and spines as similar in internal structure to the chetae ("hairs") of polychaetes.
Most fossils of Wiwaxia are just a jumble of armor plates and spines, but after examining dozens of them Conway Morris reconstructed them as slug-like animals covered in rows of overlapping armor plates, with two rows of longer spines projecting upwards.
Here we show that freshwater EDA alleles have cis-acting regulatory changes that reduce expression in developing plates and spines.
