Class Nuda These are sponges that lack intercellular jelly. In other words, the star-shaped cells and the amoeba cytes form a network through which water percolates, and there are no inhalant or exhalant canals. Glass sponges (Order Hexactinellida) Sponges of this order are characterized by siliceous spicules based on a hexaradiate or six-rayed plan. Suborder … Read more
Calcareous sponges are largely confined to the littoral and the shallow seas, although a few have been dredged at depths down to 600 ft. or beyond, to a maximum depth of 2,700 ft. Hexactinellida is typically deep-sea, the majority of species living at depths greater than 600 ft., but around the Indo-Pacific islands they seem … Read more
With few exceptions, the body of a sponge is supported by a skeleton made up either of spongin fibers, usually forming a network, as in the bath sponges (Spongia), or of spicules (little spikes) of silica or carbonate of lime. Although we speak of the spicules as constituting a skeleton there are some remarkable differences … Read more
Reproduction in sponges [Phylum Parazoa] This is by both sexual and a variety of non-sexual methods. All sponges appear to bear both ova and spermatozoa, although there has recently been a suggestion that this is not invariable, and fertilization may be internal or external. With internal fertilization the embryos develop inside the sponge, which is … Read more
Body structure [Phylum Parazoa] Probably the best way to describe the body of a sponge is to define its various parts: The skin or ectosome is the outer layer or layers of cells; usually this is a single or double-layer but in a few species it takes the form of a thick cortex made up … Read more
Hymenostomes (Order Hymenostomatida) This order marks the starting point for the elaborations found in the remaining ciliates. The feeding apparatus is described in some detail here and the names of structures are applicable later. The first of these structures is the buccal cavity between the cytostome and the buccal overture, which is a line of … Read more
Gymnostomes (Order Gymnostomatida) – Protozoans As the name suggests the mouth is without ciliary organelles. This is a most diverse group of structurally simple ciliates. But diversity has led to considerable changes in classification in recent years. A comparison of current classifications shows that no general agreement has yet been reached. Most species in the … Read more
Ciliates (Class Ciliata) – Protozoans These protozoans have many cilia and nuclei of two sizes. Because the mastigophoran Opalina also has many flagella (or cilia), it is the nuclei that act as the criterion and establish the true ciliates as a distinct group. Other features include a kinety. Holotrichs (Subclass Holotricha) This group is regarded … Read more
Protozoa Subclass Coccidiomo Subclass Coccidiomo This group is distinguished from the previous one by spending the whole of its trophozoite life intracellularly, and by effecting massive reproduction with schizogony. There is only one major order which contains three suborders. These are markedly different from one another. Order Eucoccidia These are parasites of epithelial cells of … Read more
Subclass Gregarinomorpha In this group are placed various parasites with reproductive similarities. The trophozoite is large and feeds in the lumen of the host’s gut or between cells Genetic exchange is achieved by a union of two sporonts (mature trophozoites) prior to gametogenesis. This union and the formation of gametocysts ensures that gametes can find … Read more