Question

The given statement describes a group of organisms.
(i) Instead of a cell wall they have a protein-rich pellicle making their body flexible.
(ii) They have 2 flagella, a short and a long one.
(iii) They show mixotrophic nutrition.
(iv) They are connecting links between plants and animals.
Which of the following groups is referred to here?
(a) Dinoflagellates
(b) Slime molds
(c) Desmids and diatoms
(d) Euglenoids

Answer 1

Unicellular protists are normally found in new water. They have a protein-rich cell film known as a pellicle rather than a cell divider and they also bear two flagella on the front end of the body. Photosynthesizing chloroplasts can be found in most types of Euglena inside the body of the cell, which empowers them to bolster via autotrophy like plants as well as they sometimes can take sustenance heterotrophically like creatures.

Complete answer:
Almost a billion years or more before the origins of plants and animals, Euglenoids form a diverse group of eukaryotic organisms that have arisen. With only one genus they are largely unicellular flagellates, and they also form colonies. Nearly 2,900 nominal species are present in the major photosynthetic taxa, but among them, only about 800 are accepted as taxonomically valid. In euglena taxonomy, modern phylogenetics has brought numerous changes that keep the number of accepted species in constant transition. Among all photosynthetic taxa, the majority live in freshwater, also only a few taxa can be found in seas and oceans and their most common habitats are eutrophic small water bodies such as ditches, canals, ponds. By the presence of a type of cell covering called a pellicle.

Euglenoids are mainly distinguished which is the most diverse morphological feature within its taxon. The pellicle can be found underneath the cell membrane which is composed of proteinaceous strips that are supported by dorsal and ventral microtubules but this varies from rigid to flexible, and this structure gives the cell its shape, often it also gives its distinctive striations. The strips are seen sliding past one another in many euglenoids which causes an itching motion called metabolic or otherwise, they move from place to place with the help of their flagella.

Additional information:

1. Otto Bütschli first defined the euglenids in 1884 as the flagellate order Euglenida, as an animal. Subsequently, the botanists created the algal division as Euglenophyta; and as they share characteristics with both they were classified as both animals and plants.
2. As we know they were originally classified as animals as euglenoids share several common characteristics with animals, but no evidence has been found of euglenids ever using sexual reproduction and that’s why they could no longer be classified as animals.
3. Euglenids reproduce through asexual reproduction where binary fission takes place where the cells replicate and divide during mitosis and cytokinesis.

Note: These Euglenoids more than a billion years ago split from other Euglenozoa, and are assumed to descend from an ancestor that took up a red alga by secondary endosymbiosis which was lost since then. The result of secondary endosymbiosis between a phagotrophic eukaryovorous euglenid and a Pyramimonas-related green alga is the plastids that can be found in all extant photosynthetic species.