Trichoplax adhaerens (Tp) is the only living species in the phylum Placozoa. Individuals are about 1 mm wide and only 27 μm high, are irregularly shaped, and consist of a total of about 2,000 cells, which are diploid (2n = 12). There are four types of cells, none of which are nerve or muscle cells, and none of which have cell walls. They move using cilia, and any "edge" can lead. Tp feeds on marine microbes, mostly unicellular green algae, by crawling atop the algae and trapping it between its ventral surface and the substrate. Enzymes are then secreted onto the algae, and the resulting nutrients are absorbed. Tp sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage.
-On the basis of information in the previous paragraph, which of these should be able to be observed in Tp?
A) the act of fertilization
B) the process of gastrulation
C) eggs
D) All three of the responses above are correct.
E) Two of the responses above are correct.

Question

Quizplus · Accepted Answer

Since Trichoplax adhaerens reproduces, eggs must be present even though sperm cells and embryos past the 64-cell stage have not been observed. The absence of observed sperm cells and embryos past the blastula stage suggests that fertilization and gastrulation have not been observed, making eggs the correct answer.

Trichoplax Adhaerens (Tp) Is the Only Living Species in the Phylum