Which blastula is seen in amphioxus?

Which blastula is seen in amphioxus?

As a result of cleavage in Amphioxus, a ‘blastula is formed which has a large blastocoele and a blastoderm consisting of a single layer of columnar cells. The cells at the vegetal pole are somewhat larger than at the animal pole, and the blastoderm therefore is thicker.

Which type egg of amphioxus is?

Egg : 1 : The egg of Amphioxus is microlecithal and isolecithal type. 2 : The nucleus is almost centric because the yolk content is very less and does not affect the nucleus of the egg considerably.

How does gastrulation occur in amphioxus?

Gastrulation in Amphioxus � begins by the flattening of the blastula, loss of the blastocoel, and formation of the archenteron – the embryonic gut cavity that is lined with endoderm. After flattening, two cell layers can be distinguished – ectoderm and endoderm.

What are the stages of development of amphioxus?

Embryonic Development From the Zygote to the Tailbud Stages. The early embryonic development is subdivided into four developmental periods: zygote period (AMPHX:0000008), cleavage period (AMPHX:0000009), blastula period (AMPHX:0000010), and gastrula period (AMPHX:0000011) (Figure 1 and Table 1).

What is the larva of amphioxus?

The amphioxus contain two larva such as Branchiostoma( around 23 species) and other one is Asymmetron(around six species). The basic name lancelet, or amphioxus, is commonly utilized for all cephalochordates.

What are the general characteristics of amphioxus?

GENERAL CHARACTERSTICS OF AMPHIOXUS Adult is less than 5 cm long and has superficially fish-like structural make up. Body is elongated, flattened, non-pigmented and pointed at both ends as the name implies. Anterior end projects forwards as the rostrum. Dorsal, ventral and caudal fins are low and continuous.

What is Mesolecithal and Meiolecithal egg?

A Telolecithal egg is one that has one large yolk that is found at one pole of the egg. In meiolecithal eggs, the yolk will take up nearly the entire ooplasm. In a mesolecithal egg, the yolk will be concentrated in one of the hemispheres of the egg.

What is Polylecithal egg?

Macrolecithal or Megalecithal or Polylecithal egg: When the egg contains large amount of yolk it is said to be macrolecithal or megalecithal egg. It is also called Polylecithal egg. E.g. Reptiles, Birds, Prototheria (Monotremata) Egg laying mammals.

Why is amphioxus called lancelet?

Lancelets are also called amphioxus, which translates to “both ends pointed,” because of the shape of their elongated bodies, as shown in Figure below. Unlike many of the tunicates, the lancelets are capable of swimming, however, they spend most of their time buried in sandy, shallow regions of the ocean.

What is the structure of amphioxus?

Summary. The excretory organs of Amphioxus occur as segmentally arranged structures throughout the pharyngeal region and may be divided into three components: the solenocytes, the renal tubule, and the renal glomerulus.

What is Meiolecithal egg?

Meiolecithal Eggs In Meiolecithal type of egg, area of the egg except a small portion for the cytoplasm will be yolk. The yolk will be concentrated in one hemisphere. Eggs of Fish & frogs are examples for Meiolecithal egg.

What is Cleidoic egg and non Cleidoic egg?

Cleidoic egg is a terrestrial adaptation. For example – Birds & Reptiles, Prototherian mammals, and insects. Non-Cleidoic egg – Egg membranes are squashy in these eggs e.g. All viviparous animals and in oviparous animals that put down eggs in water.