Cephalopods became common animals near the water surface, and animals like snails and mussels appear.

Carpoids

It is not quite understood which is the front and which is the back of this animal, but they lived in groups with all the individuals pointing in the same direction.

Carpoids were echinoderms whose bodies did not have a symmetry based on the number 5, as starfish do for example. They had an irregular body, with one small and one large arm at opposite ends.

Trochonema

Trochonema fed on algae it scraped from the ocean floor, amidst or near the limestone reefs in what is now Dalarna during the late Ordovician.

Gastropods were not very common during that time.

Asaphus

This trilobite species was very common during the middle of the Ordovician in what is now Sweden. It was probably a scavenger that searched for dead animals such as large cephalopods on the ocean floor.

Like most trilobites, Asaphus had a hard shell on its back and a softer underside with many legs. If threatened, it could curl into a ball to protect its belly and vulnerable legs. Trilobites were often in that position when buried in sediment.

Asaphus

This trilobite species was very common during the middle of the Ordovician in what is now Sweden. It was probably a scavenger that searched for dead animals such as large cephalopods on the ocean floor.

Like most trilobites, Asaphus had a hard shell on its back and a softer underside with many legs. If threatened, it could curl into a ball to protect its belly and vulnerable legs. Trilobites were often in that position when buried in sediment.

Echinosphaerites grandis

These round balls are fossils of animals that lived together in large groups, firmly attached to the ocean floor by a short, narrow stem.On their upper sides, they had some simple arms with which they captured small animals in the ocean water.

They were common during the Ordovician and are sometimes called crystal apples because their fossils are often filled with calcite crystals.

Echinosphaerites grandis

These round balls are fossils of animals that lived together in large groups, firmly attached to the ocean floor by a short, narrow stem.On their upper sides, they had some simple arms with which they captured small animals in the ocean water.

They were common during the Ordovician and are sometimes called crystal apples because their fossils are often filled with calcite crystals.

Echinosphaerites aurantium

These round balls are fossils of animals that lived together in large groups, firmly attached to the ocean floor by a short, narrow stem.On their upper sides, they had some simple arms with which they captured small animals in the ocean water.

They were common during the Ordovician and are sometimes called crystal apples because their fossils are often filled with calcite crystals.

Endoceras

Their shells were filled with gas, water and calcium carbonate, which made them well balanced in the water. Endoceras species were therefore able to swim straight.

They were predators whose main prey were other cephalopods. But as they were rather slow and clumsy, scientists believe that they hunted by lying in ambush. Endoceras species were among the largest animals of the Ordovician Period. 

Michelinoceras

Michelinoceras was a medium-sized squid-like cephalopod with a long, straight shell. It lived almost vertically in the water, with its head and arms pointing downward.

It may have hunted small trilobites and other animals by crawling across the ocean floor with the help of its arms. Or it may have floated higher up in the water, feeding on plankton.

Endoceras

This fossil shows part of the shell with chamber walls and a tube, the siphuncle, which was located on the underside of the animal.

The siphuncle was thick and heavy, making the shell well balanced so that Endoceras could swim horizontally in pursuit of prey animals. Endoceras was common during the Ordovician in the area that is now Sweden. 

Anthoceras

This squid-like cephalopod had a slightly curved shell. Growth rings can be clearly seen on this fossil, and it can also be seen that the animal was severely injured on at least one occasion.

Part of the shell has broken off, perhaps in an attack by a larger cephalopod. But the animal survived and the shell healed. Such repaired shell injuries are fairly common in Ordovician cephalopods. 

Trocholites

Trocholites was a genus of squid-like cephalopods with coiled shells that were not very stable. They were therefore clumsy swimmers, and scientists believe that they hunted small animals by moving over the ocean floor with the help of their arms.

Tragoceras

This small squid-like cephalopod had an open, spiral-shaped shell that was not suitable for rapid movement. It probably lived mainly in sheltered habitats.

Lituites

Lituites was a small and fairly common squid-like cephalopod during the Ordovician Period. Fossils are often found with many Lituites individuals together.

Its shell was originally spiral-shaped; but at some point, the growth pattern changed and the shell of adults became almost straight. Lituites was probably a predator that lived in small groups.

Cameroceras

This large squid-like cephalopod had a slightly curved shell and was among the slower species of its kind during the Ordovician. It stayed near the ocean floor, near the extensive limestone reefs in what is now Dalarna.

Species of the genus Cameroceras were among the largest cephalopods found in Ordovician fossils; they could be up to eight metres long. You can see a model of a large Cameroceras cephalopod hanging from the ceiling.