Question: From NCERT 100% NCERT covered from Particular Keyword. NEET 2014 Explanations are 100% from NCERT | [Difficult level: Easy]
Select the taxon mentioned that represents both marine and freshwater species
(1) Echinoderms
(2) Ctenophora
(3) Cephalochordata
(4) Cnidaria
Answer:(4) Cnidaria
👉Phylum – Coelenterata (Cnidaria)
They are aquatic, mostly marine, sessile or free-swimming, radially
symmetrical animals (Figure 4.6). The name cnidaria is derived from the
cnidoblasts or cnidocytes (which contain the stinging capsules or
nematocysts) present on the tentacles and the body. Cnidoblasts are used
for anchorage, defense and for the capture of prey (Figure 4.7). Cnidariansexhibit tissue level of organisation and are diploblastic. They have a central
gastro-vascular cavity with a single opening, mouth on hypostome.
Digestion is extracellular and intracellular. Some of the cnidarians, e.g.,
corals have a skeleton composed of calcium carbonate. Cnidarians exhibit
two basic body forms called polyp and medusa (Figure 4.6). The former
is a sessile and cylindrical form like Hydra, Adamsia, etc. whereas, the
latter is umbrella-shaped and free-swimming like Aurelia or jelly fish.
Those cnidarians which exist in both forms exhibit alternation of
generation (Metagenesis), i.e., polyps produce medusae asexually and
medusae form the polyps sexually (e.g., Obelia).
Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone),
Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral).
👉Phylum – Ctenophora
Ctenophores, commonly known as sea walnuts or comb jellies
are exclusively marine, radially symmetrical, diploblastic
organisms with tissue level of organisation. The body bears
eight external rows of ciliated comb plates, which help in
locomotion . Digestion is both extracellular and
intracellular. Bioluminescence (the property of a living
organism to emit light) is well-marked in ctenophores. Sexes
are not separate. Reproduction takes place only by sexual
means. Fertilisation is external with indirect development.
Examples: Pleurobrachia and Ctenoplana.
👉Phylum – Echinodermata
These animals have an endoskeleton of calcareous ossicles
and, hence, the name Echinodermata (Spiny bodied)
All are marine with organ-system level of organisation.
The adult echinoderms are radially symmetrical but larvae
are bilaterally symmetrical. They are triploblastic and
coelomate animals. Digestive system is complete with mouth
on the lower (ventral) side and anus on the upper (dorsal)
side. The most distinctive feature of echinoderms is the
presence of water vascular system which helps in
locomotion, capture and transport of food and respiration.
An excretory system is absent. Sexes are separate.
Reproduction is sexual. Fertilisation is usually external.
Development is indirect with free-swimming larva.
Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon
(Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).
👉Subphyla Urochordata and
Cephalochordata are often referred to as
protochordates and are
exclusively marine. In Urochordata, notochord
is present only in larval tail, while in
Cephalochordata, it extends from head to tail
region and is persistent throughout their life.
Examples: Urochordata – Ascidia, Salpa,
Doliolum; Cephalochordata – Branchiostoma
(Amphioxus or Lancelet).
