Identify the INCORRECT statement regarding invertebrates from the options given below.

The correct answer is: They possess a backbone and an internal skeleton.

Step-by-Step Explanation:

1. Understanding Invertebrates:
Invertebrates are defined as animals that lack a vertebral column (spinal column or backbone). Their body structures are supported by other means, such as hydrostatic skeletons, exoskeletons (e.g., in arthropods), or simply flexible tissue layers.

2. Analyzing the Options:

• "They possess a backbone and an internal skeleton."
This statement is INCORRECT because invertebrates by definition do not possess a backbone or a vertebral column. Possessing a backbone and an internal bony endoskeleton is a characteristic feature of vertebrates (phylum Chordata, subphylum Vertebrata).

• "They have radial or bilateral body symmetry."
This statement is correct. Invertebrates display various body symmetries; for instance, cnidarians and echinoderms exhibit radial symmetry, while arthropods, annelids, and mollusks exhibit bilateral symmetry.

• "They have a pair of solid nerve cords, situated ventrally and bearing segmentally arranged ganglia."
This statement is correct. Non-chordates (invertebrates) like annelids and arthropods typically possess a ventral, solid, paired nerve cord with segmentally arranged ganglia, whereas chordates have a dorsal, hollow, single nerve cord.

• "They have open circulatory system as there is no organisation in the distribution."
This statement is generally accurate for many invertebrate groups (such as arthropods and most mollusks), which have an open circulatory system where blood/hemolymph pumps into open cavities (hemocoel).

Conclusion:
The statement claiming that invertebrates possess a backbone and an internal skeleton is false, making it the correct choice for the INCORRECT statement.