In which of the following phylum distinct Cephalization is absent ?

Options

A. Mollusca
B. Arthropoda
C. Chordata
D. Echinodermata

Answer

To solve the question regarding the absence of distinct cephalization in certain phyla, we can follow these steps:

### Step 1: Understand Cephalization
Cephalization refers to the evolutionary trend where sensory organs and nerve tissues become concentrated at one end of the body, forming a distinct head region. This is commonly seen in many animal phyla.

**Hint:** Think about how animals are organized and where their sensory organs are located.

### Step 2: Identify the Phyla in Question
The question asks which phylum lacks distinct cephalization. We need to consider the characteristics of various phyla, particularly those known for their body organization.

**Hint:** Recall the major phyla and their body structures, especially focusing on those that are less complex.

### Step 3: Analyze Echinodermata
Echinoderms, such as starfish and sea urchins, are known for their unique body plan. They exhibit radial symmetry in adults and do not have a distinct head region. Instead, their nervous system is decentralized, lacking concentrated neural ganglia.

**Hint:** Remember that echinoderms have a different symmetry in adulthood compared to their larval stages.

### Step 4: Compare with Other Phyla
Other phyla, such as Chordata, exhibit distinct cephalization with a clear head and trunk division. In contrast, echinoderms do not have this feature, which makes them stand out.

**Hint:** Consider how the body is organized in other phyla and whether they have a head region.

### Step 5: Conclude the Answer
Based on the analysis, the phylum in which distinct cephalization is absent is **Echinodermata**.

**Final Answer:** Echinodermata