| CAMBRIAN | The first geological period of the Palaeozoic era, during which marine invertebrates flourished (8) |
| ORDOVICIAN | Second period of the Palaeozoic era during which marine invertebrates flourished (10) |
| DEVONIAN | Fourth period of the Palaeozoic era, during which amphibians first appeared (8) |
| TRIASSIC | First and shortest geological period of the Mesozoic Era (8) |
| SILURIAN | Geologic period between the Ordovician and Devonian periods of the Palaeozoic era (8) |
| JURASSIC | Second period of the Mesozoic era during which dinosaurs flourished (8) |
| SEAHORSE | The male of which marine animal carries the young (8) |
| PERMIAN | Of or relating to the last period of the Palaeozoic era, between the Carboniferous and Triassic periods (7) |
| SEASTARS | Typically fivearmed marine invertebrates |
| ADAMSEDGWICK | 19th-century English geologist who proposed and named the Cambrian period, part of the Palaeozoic era (4,8) |
| PRECAMBRIAN | Era during which the earth's crust formed and life first appeared in the seas |
| VICTORIAN | Era during which the Great Exhibition in Crystal Palace took place, SS Great Britain was launched an |
| MIOCENE | First geological epoch of the Neogene period (7) |
| DELABECHE | Englishman whose years in Lyme Regis and acquaintance with fossil collector Mary Anning inspired his palaeontological interest and subsequent founding of the world's first geological survey (2,2,5) |
| WHALE | To which marine mammal group does the dolphin belong (5) |
| LIMPET | Which marine gastropod mollusc is found adhering to rocks (6) |
| EON | Geological period of time |
| AEON | Geological period of time (4) |
| MESOZOA | Wormlike parasites of marine invertebrates (7) |
| SPADEFISHES | Marine invertebrates named for their short-snouted, wide-finned shapes |
