More than 50,000 known species of molluscs can be found on land, in freshwater, and in marine habitats. One of the most well-known terrestrial species is the snail, which belongs to a family that also includes mussels and clams.
Echinodermata is the largest phylum without any freshwater or terrestrial creatures and has at least 6,000 species. Echinoderms, on the other hand, are marine-only organisms. Sea urchins and sea stars are well-known echinoderms.
Table of Contents
- Phylum Mollusca
- Phylum Echinodermata
- Difference between Mollusca and Echinodermata
- Frequently Asked Questions (FAQs)
Phylum Mollusca
Bilaterally symmetrical, triploblastic organisms are a part of the Phylum Mollusca, a subclass of the Kingdom Animalia. The Mollusca phylum contains species that have distinctive segmentation. The three distinct body parts are the head, visceral mass, and ventral foot. The ventral foot also helps in movement. Molluscs can be found both on land and in water.
Phylum Mollusca comprises six classes: Gastropoda, Bivalvia, Cephalopoda, Amphineura, Monoplacophora, and Scaphopoda. Therefore, the phylum Mollusca includes creatures like octopuses, clams, cuttlefish, squid, and others.
Molluscs possess a complete digestive system that includes a radula structure for eating. An associated pair of ganglia and their accompanying nerves make up the nervous system. Molluscs also have a heart and aorta as part of their open circulatory system. Molluscs breathe through unique gill structures called ctenidia. Additionally, they have metanephridia for excretion. Molluscs are also bisexual creatures and can fertilise internally or externally.
Phylum Echinodermata
Triploblastic coelomates are a part of the Phylum Echinodermata, a Kingdom Animalia subclass. They only exist in marine habitats. They also exhibit radial symmetry, particularly pentaradial symmetry similar to that of starfish. But they do not display segmentation. Their bodies might be flat, elongated, or star-shaped. Echinoderms are known for having tube feet, a water vascular system, a mouth on the ventral side, an anus on the dorsal side, and a papula for respiration.
The phylum Echinodermata’s five classes are Ophiuroidea, Asteroidea, Holothuroidea, Echinoidea, and Crinoidea. Echinoderms include the sea cucumber, starfish, and sea urchin.
Echinoderms are bisexual and exhibit external fertilisation. These creatures possess appropriate organisation and a fully functional digestive system. They are responsive to stimuli even though they lack a complete nervous system. Additionally, they have a reduced circulatory system and colourless blood.
Difference between Mollusca and Echinodermata
The differences between Mollusca and Echinodermata are given in the table below.
| MOLLUSCA | ECHINODERMATA |
|---|---|
| Definition | |
| Molluscs are triploblastic haemocoelomates that can survive on land and in water. | Echinoderms are triploblastic coelomates that survive primarily in marine environments. |
| Habitat | |
| Live in both terrestrial and aquatic environments. | Live only in marine environments. |
| Segmentation | |
| Exhibit distinct segmentation. | Do not exhibit segmentation. |
| Symmetry | |
| Show bilateral symmetry. | Show radial symmetry. |
| Respiration | |
| Breathe and respire through structures known as ctenidia. | Respire through respiratory structures known as papula. |
| Excretion | |
| Possess excretory structures known as metanephridia. | Do not possess any excretory structure. |
| Vascular System | |
| Neither has a water vascular system nor tube feet. | Possess water vascular system and tube feet. |
| Examples | |
| Octopuses, clams, cuttlefish, squid, and others | Sea cucumber, starfish, and sea urchin |
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Related Links:
- MCQs on Mollusca
- Animal Kingdom- Animalia Phylum, Subphylum
- Kingdom Animalia: Higher Invertebrate Animals
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