Protochordata | Animalia | Diversity in Living Organisms

7.5.8 ECHINODERMATA In Greek, echinos means hedgehog, and derma means skin. Thus, these are spiny skinned organisms. These are exclusively free-living marine animals. They are triploblastic and have a coelomic cavity. They also have a peculiar water-driven tube system that they use for moving around. They have hard calcium carbonate structures that they use as a skeleton. Examples are starfish and sea urchins (see Fig. 7.19). Aranea(Spider) Palaemon (Prawn) Palamnaeus (Scorpion) Butterfly Pariplaneta (Cockroach) Musca (House fly) Scolopendra (Centipede) Fig. 7.17: Arthropoda 7.5.7 MOLLUSCA Antedon Holothuria In the animals of this group, there is bilateral symmetry. The coelomic cavity is reduced. There is little segmentation. They have an open circulatory system and kidney-like organs for excretion. There is a foot that is used for moving around. Examples are snails and mussels (see Fig. 7.18). (feather star) (sea cucumber) Echinus (sea urchin) Asterias (star fish) Fig. 7.19: Echinodermata 7.5.9 PROTOCHORDATA These animals are bilaterally symmetrical, triploblastic and have a coelom. In addition, they show a new feature of body design, namely a notochord, at least at some stages during their lives. The notochord is a long rod-like support structure (chord=string) that runs along the back of the animal separating the nervous tissue from the gut. It provides a place for muscles to attach for ease of movement. Protochordates may not have a proper notochord present at all stages in their Chiton Octopus Unio Pila Fig. 7.18: Mollusca lives or for the entire length of the animal. Protochordates are marine animals. 7.5.10 (i) PısCES These are fish. They are exclusively water- living animals. Their skin is covered with scales/plates. They obtain oxygen dissolved in water by using gills. The body is streamlined, and a muscular tail is used for Examples are Balanoglossus, Herdemania and Amphioxus (see Fig. 7.20). movement. They are cold-blooded and their hearts have only two chambers, unlike the four that humans have. They lay eggs. We can think of many kinds of fish, some with skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of Proboscis Collarette Collar both bone and cartilage, such as tuna or rohu [see examples in Figs. 7.21 (a) and 7.21 (b)]. Anus -Branchial region Gill pores Dorsally curved Posthepatic region genital wings Middosrsal ridge Synchiropus splendidus (Mandarin fish) Caulophyryne jordani (Angler fish) -Нерatic caecа Hepatic region Pterois volitans Fig. 7.20: A Protochordata: Balanoglossus (Lion fish) Eye 7.5.10 VERTEBRATA Spiracle These animals have a true vertebral column and internal skeleton, allowing a completely different distribution of muscle attachment points to be used for movement. Vertebrates are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs. All chordates possess the following Pelvic fin Dorsal fin -Tail Caudal fin Sting ray Electric ray (Torpedo) Dorsal fin Eye Tail features: (i) have a notochord (ii) have a dorsal nerve cord (iii) are triploblastic (iv) have paired gill pouches (v) are coelomate. Vertebrates are grouped into five classes. Mouth Gills Pectoral Pelvic fin fin Scoliodon (Dog fish) Fig. 7.21 (a): Pisces