Pleurobrachia (Gr. pleuron, side, + L. brachia, arms) is about 1.5 to 2 cm in diameter. The oral pole bears the mouth opening, and the aboral pole has a sensory organ, the statocyst. Comb Plates On the surface are eight equally spaced bands called comb rows, which extend as meridians …

Sponges feed primarily by collecting suspended particles from water pumped through internal canal systems. Water enters canals through a multitude of tiny incurrent pores in the outer layer of cells, a pinacoderm. Incurrent pores, called dermal ostia, have an average diameter of 50 µm. Inside the body, water is directed …

Ctenophora (te-nof´o-ra) (Gr. kteis, ktenos, comb, +phora, pl. of bearing) is composed of about 150 species. All are marine forms occurring in all seas but especially in warm waters. They take their name from eight rows of comblike plates used for locomotion. Common names for ctenophores are “sea walnuts” and …

A typical hydroid has a base, a stalk, and one or more terminal zooids. The base by which colonial hydroids attach to the substratum is a rootlike stolon, or hydrorhiza, which gives rise to one or more stalks called hydrocauli. The living cellular part of the hydrocaulus is a tubular …

Sponges originated before the Cambrian period. Two groups of calcareous spongelike organisms occupied early Paleozoic reefs. The Devonian period saw rapid development of many glass sponges. Phylogenetic studies 2 using sequence data from large subunit rRNA, small subunit rRNA, and protein kinase C, indicate that sponges with calcareous spicules in …

One of the most interesting—and sometimes puzzling—aspects of this phylum is the dimorphism and often polymorphism displayed by many of its members. All cnidarian forms fit into one of two morphological types (dimorphism): a polyp, or hydroid form, which is adapted to a sedentary or sessile life, and a medusa, …

Phylum Cnidaria (ny-dar´e-a) (Gr. knide, nettle, + L. aria [pl. suffix], like or connected with) is an interesting group of more than 9000 species. It includes some of nature’s strangest and loveliest creatures: branching, plantlike hydroids; flower like sea anemones; jellyfishes; and those architects of the ocean floor, horny corals …

Sponge cells are loosely arranged in a gelatinous matrix called mesohyl, or mesenchyme. The mesohyl is the connective tissue of sponges; in it are found various fibrils, skeletal elements, and ameboid cells. The absence of tissues or organs means that all fundamental processes must occur at the level of individual …

Asconoids Asconoid sponges have the simplest organization. Water is drawn into the sponge through microscopic dermal pores by the beating of large numbers of flagella on the choanocytes. These choanocytes line the internal cavity known as the spongocoel. As the choanocytes filter the water and extract food particles from it, …

Paramecia are often described as slipper shaped. Paramecium caudatum is 150 to 300 µm in length and is blunt anteriorly and somewhat pointed posteriorly. The organism has an asymmetrical appearance because of the oral groove, a depression that runs obliquely backward on the ventral side. The pellicle is a clear, …