A newly discovered organism is observed to be triploblastic, bilaterally symmetrical, and coelomate, with a segmented body and a closed circulatory system. It possesses both longitudinal and circular muscles for locomotion. Which phylum does this organism most likely belong to?
Correct: C
Let's break down the characteristics:
- Triploblastic: Possesses three germ layers (ectoderm, mesoderm, endoderm). This is true for all options except Porifera and Cnidaria (which are not options here).
- Bilaterally symmetrical: Also true for all listed options.
- Coelomate: Possesses a true coelom derived from mesoderm. This excludes Platyhelminthes (acoelomate) and Aschelminthes (pseudocoelomate). So, Platyhelminthes is ruled out.
- Segmented body: This is a key distinguishing feature. Among the coelomates listed, Annelida and Arthropoda exhibit true segmentation (metamerism). Mollusca generally do not have externally segmented bodies.
- Closed circulatory system: Annelids possess a closed circulatory system. Arthropods and most Molluscs (except cephalopods) have an open circulatory system.
- Longitudinal and circular muscles for locomotion: This is characteristic of Annelids (e.g., earthworms) for peristaltic movement.
Combining these features, particularly true coelom, segmentation, closed circulatory system, and distinct muscle layers for locomotion, points unequivocally to Phylum Annelida.