Question

Animals in the genus Xenoturbulla have extremely simple body parts, they have a gut with only one opening and no brain. Propose a hypothesis to explain how this simple organism evolved in the clade with other deuterostomes.

Answer 1

Answer-This simple organism evolved in the cl ade with other De ute ros tome.In 2009, a p hy l o genomic study covering 94 taxa across the animal kingdom suggested that Xe not ur bella is not a de ute ros tome, but rather a sister group to the Ac o el o mo r p ha, and that this group (Xe not u r b ella + Ac o el o mo r p ha) forms a sister cl ade to all other bi later an s.

The latest p hy l og eno mic study supports a somewhat compromising hypothesis. This 2011 study adopted mitochondrial protein sequences from this genus and to construct a phylogenetic tree. Independent analysis was also performed from a p hy l og eno mic. data set of 38,330 amino-acid positions. These two independent analyses both showed that the basal position of Ac o e l o morph a within the bil atria n s is probably due to long-branch attraction.Deuterostomes constitute a super phylum of animals. It is a sister cl ade of Pro to st o mi a, with which it forms the N e p hr o zoa cl ade.

Xe not ur be l la is a genus of very simple bila teri an s up to a few centimeters long. It contains a small number of marine benthic worm-like species. The nervous system is composed by a net of interconnected neurons beneath the epidermis, without any concentration of neurons forming ganglia or nerve cords.

Species of Xe n o t u r bella also lack a respiratory, circulatory and excretory system. In fact, there are no defined organs, except for a Stat o cyst containing flagellated cells.There are no organized gonads, but gametes are produced. Adults producing sperm are very rarely observed, but eggs and embryos are known to occur in follicles.Eggs of Xe not ur be l la are 0.2 millimetres (0.0079 in) wide, pale orange and opaque.Newly hatched embryos are free-swimming (tending to stay close to water surface) and ciliated. They feature no mouth and they do not apparently feed.From this type Xe not ur b u l l a evolved in the cl ade with other de ute ros tomes.