Isopods and Amphipods

General

Two successful groups of Crustaceans are the Isopods and Amphipods, with about 350 - 400 thousand species in each group. Members of both groups are poor swimmers and live their lives as bottom crawlers and beach scavengers.

Features which all members of these two groups have in common are:

• lack of a carapace,
• sessile eyes, not on stalks,
• highly specialised limbs,
• respiratory pleopods, and the
• uropods not forming a tail-fan.

The Isopods are all dorsoventrally flattened
(top = dorso) (bottom = ventrally)
with all thoracic limbs similar and all abdominal limbs similar. The common example is the Marine Slater, Ligia australiensis. On rocky ocean shores, it seems to become more common, the more southerly the shore. It always seems to be abundant in estuaries.

The Amphipods are laterally (side to side) compressed with the thoracic and abdominal limbs, each arranged in at least two groups, differing in form and function so that there are between 4 - 6 different limb sets. Sand Hoppers are the common example. They are often found under broken clumps of algae stranded on the shore, especially along southern shores.