The sponges are in contrast to all higher animals also in that; they lack a true mouth, the body being pierced by numerous minute incurrent pores connecting with canals and cavi- ties through which water flows to reach the outside by larger openings known as oscula (singular osculum . In the complicated sponges which constitute the vast majority of those encountered at the seashore and all those of fresh water, the choanocytes occur in small, scattered, spherical chambers. Sponges are attached, non-locomotor , nearly always colonial, and typically irregular in form, conforming to the surfaces on which they grow . In all save the simplest sponges the colony is so closely integrated that it is difficult or impossible to designate the individuals constituting it or at least to determine the limits of the individuals .
Except for a very few parasitic species all sponges are plankton feeders, the minute organisms and organic particles in the water currents being seized and taken in by the individual choanocytes. The skeletal system of calcareous or silicious spicules serves as a protection against predators and the unpleasant odor characteristic of number of sponges would seem to indicate the presence of distasteful chemical secretions. They lack, however, devices to protect against intertidal exposure and hence they are confined to protected situtions at, near, or below low-tide level. There they compete with other plankton feeders such as the Bryozoa and tunicates as also with the micropredators such as the hydroids and corals.
Until recently the identification of California marine sponges has not been possible. De Laubenfels' treatise (1932) makes this possible, but it requires study of spicule types and other internal characters and is not usually feasible for the average student.
Study pieces of a local encrusting sponge. Note its consistency. Is it hard and stony, soft and fragile, or leathery and spongy? What is the nature of the surface? Note the shape, size, and distribution of the oscula and the pores. The oscula are the larger, excurrent openings .The pores or ostia are the very small incurrent openings. Remove a small but characteristic portion, mount on a slide in a drop of water. Tease apart sufficiently to make a clear mount.
Examine under the microscope to make out the types of spicules. Spicules with a single point are termed monactinal . those with two, diactinal . Monaxon spiculeb are straight rods, needles, clubs, etc. Triaxons have three projecting points; if all are approximately equal they are triradiate or triaenes. Tetraxons may be quadriradiates or consist of three short rays radiating from a long axis. Hexactinal spicules have six (or five) rays radiating from a common cente
Siliceous spicules, found in all save the simple sponges, include, usually, two very different types, larger menascleres which make up the true skeleton, and the smaller microscleres in the softer tissues. The megasclera may be poly-di,-tylostyles.Oxeas are straight or somewhat curved, more or less fusiform and gradually pointed at the ends. Sub- tylostyles or monactinals have one of the ends rounded. These principal spicules may be sparsely spiny as in Lissodendoryx or extensively spined acanthostyles . Tylotes are diactinals with both heads rounded as in Plocamia.
Microscleres may be sigmas (S- or C-shaped, as in Lisso- dendoryx chelas.
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