Understanding Animals with Spiny Skin and Water System

The question asks to identify a group of animals characterized by two main features: spiny skin and a peculiar water-driven tube system used for movement. Let's examine the options provided to see which group fits this description.

Analyzing the Options

We need to look at the defining characteristics of each phylum listed:

• Hemichordata: This phylum consists of worm-like marine animals. They have a proboscis, collar, and trunk. They do not have spiny skin or a water-driven tube system for locomotion like the one described.
• Aschelminthes (or Nematoda and other related phyla): This group includes roundworms. They are typically cylindrical, unsegmented worms. Their body surface is usually smooth, and they use muscular contractions for movement, not a water-driven tube system.
• Echinodermata: This phylum includes animals like starfish, sea urchins, sea cucumbers, and brittle stars. The name "Echinodermata" comes from the Greek words 'echinos' meaning 'spiny' and 'derma' meaning 'skin'. A key feature of this group is their spiny body surface or calcareous plates under the skin. Another unique characteristic is the presence of a water vascular system, which consists of canals and tube feet used for locomotion, feeding, respiration, and excretion. This system is driven by water pressure.
• Mollusca: This phylum includes snails, slugs, clams, octopuses, and squids. Molluscs typically have a soft body, often enclosed in a shell. They move using a muscular foot. They do not have spiny skin or a water vascular system.

The Correct Identification: Echinodermata

Based on the analysis, the group of animals that are named because of their spiny skin and possess a water-driven tube system for moving around is Echinodermata. Both the spiny skin and the water vascular system are hallmark features of this phylum.

The table clearly shows that Echinodermata is the only phylum among the options that exhibits both spiny skin and a water-driven tube system.

Revision Table: Key Phyla Features

Additional Information on Echinodermata

Echinoderms are exclusively marine animals. Besides spiny skin and the water vascular system, other important characteristics include:

• Radial Symmetry: Adult echinoderms typically show pentamerous radial symmetry, meaning their body parts are arranged in five sections around a central axis. Larvae, however, are bilaterally symmetrical.
• Endoskeleton: They possess an internal skeleton made up of calcareous plates or ossicles, often bearing spines.
• Digestive System: Complete, but with mouth on the lower (oral) side and anus on the upper (aboral) side. Some like brittle stars have an incomplete digestive system.
• Reproduction: Mostly sexual, with external fertilization. They have remarkable regenerative abilities.

Examples of echinoderms include Starfish (Asterias), Sea Urchins (Echinus), Sea Cucumbers (Cucumaria), Brittle Stars (Ophiura), and Sea Lilies (Antedon).