Accepting the homology of these apical systems with the calycinal system, the theory would regard the aboral pole of a sea-urchin or starfish as corresponding in everything, except its relations to the sea-floor, with the aboral pole of a fixed echinoderm.
1 The EXevoSep,ua, or "urchin-skinned" animals, have long been a favourite subject of study with the collectors of sea-animals or of fossils, since the lime deposited in their skins forms hard tests or shells readily preserved in the cabinet.
- Supposed calycinal systems of free-moving Echinoderms. A, regular sea-urchin (Cidaris); B, sea-urchin with a suranal plate (Salenia); C, developing ophiurid (Amphiura); D, young starfish (Zoroaster).
Neumayr adduced the Triassic sea-urchin Tiarechinus, in which the apical system forms half of the test, as an argument for the origin of Echinoidea from an ancestor in which the apical system was of great importance; but a genus appearing so late in time, in an isolated sea, under conditions that dwarfed the other echinoid dwellers therein, cannot seriously be thought to elucidate the origin of pre-Silurian Echinoidea, and the recent discovery of an intermediate form suggests that we have here nothing but degenerate descendants of a well-known Palaeozoic family (Lepidocentridae).