9.3.1 Phylum Porifera
(Greek: Poros means channels, Latin: Ferre means The name Porifera was given by Robert E. Grant in 1836. Phylum Porifera is also known as sponges and possesses the following characteristics.
Habitat:
Their larval stage is motile while the adult is sessile (attached to submerged rock), about 10,000 species have been recorded. Their size ranges from a few millimeters wide to more than a meter long (e.g. scolymastra joubini from Antarctica).
Body:
Poriferans are the simplest multicellular animals having no tissues and organ organization. Asymmetrical or radially symmetrical. The body wall is formed of an outer dermal layer known as pinacoderm, which contains pinacocytes, and an inner layer, the choanoderm, which contains flagellated collar cells known as choanocyBetweenetween these two terms is a gelatinous matrix, the mesenchyma containing wandering cells. They have a single body cavity, the spongocoel, divided into canals. The body contains numerous incoming or incurrent pores, the ostia, and a single large excurrent pore, the osculum.
Nutrition:
Sponges are heterotrophic and depend on food coming to their body with water current through ostia and moved in by flagella of choanocytes, where intracellular digestion takes place, and the digested foods are transported by mesenchymal cells. The waste material either diffuse out of the sponges directly through the body wall or through the osculum.
The nervous system is absent, but neuron and neurosensory cells help to coordinate water flow. The skeleton is formed of needle-like structures the spicules (either calcareous or silicious) while some sponges, like bath sponges, possess sponging fibers, and osculum, and Ostia also contain spicules. The sponges possess both asexual and sexual reproduction.
Asexual, either by external budding or internal budding (gemmule formation), regeneration is also common. Sponges are mostly hermaphrodite (Bisexual) and protandrous (male gametes develop before the female). Fertilization is internal and occurs in mesenchymal.
The sponges have probably evolved from flagellated protists known as choanoflagellates. Examples: second (marine sponge), Leucosolenia (erect tube shaped), Euplectella (glassy framework), and Spongilla (freshwater sponge).
Evolutionary adaptation in Porifera:
Sponges have intracellular digestion, which is facilitated by flagellated collar cells. Respiration occurs by diffusion because almost each body cell is in contact with water. Zouston and 10% due propritur in doad maner.
Transportation of substances (food, excretory products) either by diffusion or by water current through canal systems. "Water enters through ostia into spongocoel and goes out of the body through the osculum." They have weak coordination, only some neurosensory cells and neurons coordinate water flow.
Importance of sponges:
The bath sponges are used for washing and bathing by humans. Sponges can greatly absorb water and thus are used in surgical operations for absorbing fluid and blood. In large buildings, sponges are used for sound absorption, to prevent echo. They are also used for decorative purposes and used in shoe or vehicle polishing.
9.3.2 Phylum Cnidaria
The name Cnidaria is given to this phylum due to the presence of specialized stinging cells called cnidocytes all over the body which give rise to nematocysts. The nematocyst is a capsule with paralyzing venom which acts as an offensive and defensive organ. Phylum Cnidaria exhibits the following characteristics.
Habit and Habitat:
Cnidarians are either sessile e.g., hydra, or free-living motile e.g., jellyfish). Many are colonial (e.g., Obelia). Most of them are carnivores. All cnidarians are aquatic (both marine and freshwater).
Size:
May be from microscopic (Hydra) to very large (e.g., Brachioceranthus, up to two meters (in length.)
Body:
Cnidarians are radially symmetrical, and most are diploblastic i.e. outer ectoderm and inner endoderm between these two layers, there is a gelatinous cementing substance, called mesoglea.
Enteron or gastrovascular cavity with a single opening called mouth (act both as mouth and anus). The mouth is surrounded by tentacles.
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