Of the republic of kazakhstan state university

1 Sponges are sessile aquatic animals, mostly marine and largely inhabitants of hard substrates.

2 They are primitive in their lack of organs, in­cluding mouth and gut. There are different kinds of cells, but cellular differentiation has not fol­lowed the common designs of other animals.

The Sponges

3 The bodies of sponges are organized around a system of water canals, a specialization correlated with sessility.

4 The small, vase-shaped asconoid body form, in which flagellated choanocytes line an interior atrial chamber, is the primitive sponge form. The evolution of the common leuconoid form, in which the flagellated cells are distributed within a vast number of minute chambers, has permitted the at­tainment of much larger size and great diversity of shape, since each addition to the sponge body brings with it all of the units necessary to provide the required additional water flow.

5 The growth form of sponges is, in part, an adaptive response to the availability of space, the inclination of the substrate, and the current velocity.

6 Support is provided by a skeleton of organic spongin fibers or siliceous or calcareous spicules, or a combination of spongin fibers and siliceous spicules.

7 Feeding, gas exchange, and waste removalde pend on the flow of water through the body. Thi ability of the choanocyte collar to remove d tremely small particles from the water stream has probably been an important factor in the long, successful history of sponges.

8 Probably because of their sessility, mosi sponges are hermaphroditic. Sperm leave Offi sponge and enter another in the currents flowing through the water canals. Eggs in the mesophylan fertilized in situ. They may then be released by wq of the water canals or brooded up to the larva stage. In most sponges the flagellated larva is a blastula, and reorganization equivalent to gastrulatioin occurs following settling.

9 Sponges are probably an early evolution! side branch that gave rise to no other groups of animals.

Lecture #5. Species diversity and structural features of the type Coelenterates.

1. 
   Increase the general level of organization cnidarians compared with sponges.
   
2. 
   General characteristics of the type of coelenterates. Class Hydroids.
   
3. 
   Class Scyphozoa-Scyphozoa. Coral polyps class-Antozoa.
   

The phylum Cnidana, or Coelenterata, includes the familiar hydras, jellyfish, sea anemones, and corals. The bright coloring of many species, com­bined with a radial symmetry, creates a beauty that is surpassed by few other animals. The radial sym­metry is commonly considered justification for uniting the cnidarians and the ctenophores within a division of phyla of the Animal Kingdom called the Radiata.

The cnidarians possess two basic metazoan structural features. There is an internal space for digestion, called in cnidarians a gastrovascular cav­ity (Fig. 5-1). This cavity lies along the polar axis of the animal and opens to the outside at one end to form a mouth. The presence of a mouth and digestive cavity permits the use of a much greater range of food sizes than is possible in the protozoa and sponges. In cnidarians a circle of tentacles, rep­resenting extensions of the body wall, surrounds the mouth to aid in the capture and ingestion of food.

The cnidarian body wall consists of three basic layers (Fig. 5-1): an outer layer of epidermis, an inner layer of cells lining the gastrovascular cavity, and between these a layer called mesoglea. Thei soglea ranges from a thin, noncellular membranetl a thick, fibrous, jelly-like, mucoid material with Л without wandering cells. The mesoglea probably evolved from a basement membrane, and in forms like Hydra it has hardly progressed beyond thJ level. In others it is more like connective tissue] but the cells appear to be derived from the epidel mis. Thus, cnidarians are diploblastic; i.e., tbl body is constructed from only two germ layers, eel toderm and endoderm.

Histologically, the cnidarians have remained I rather primitive, although they anticipate some el the specializations that are found in higher meta­zoans. A considerable number of cell types conJ pose the epidermis and gastrodermis, but there J only a limited degree of organ development.

Although all cnidarians are basically tentaculate and radially symmetrical, two structural types are encountered within the phylum. One type, which is sessile, is known as a polyp. The other form is free swimming and is called a medusa. Typically, the body of a polyp is a tube or cylinder, in which the oral end, bearing the mouth and tentacles, is directed upward, and the opposite, or aboral, end is attached (Fig. 5-L4).

The medusoid body resembles a bell or an um­brella, with the convex side upward and the mouth located in the center of the concave undersurface (Fig. 5-IB).


The tentacles hang down from the mar­gin of the bell. In contrast to the polypoid mesoglea (middle layer), which is more or less thin, the me­dusoid mesoglea is extremely thick and constitutes the bulk of the animal. Because of this mass of jelly-like mesogleal material, these cnidarian forms arc commonly known as jellyfish. Some cnidarians exhibit only the polypoid form, some only the me­dusoid form, and others pass through both in their life cycle. Colonial organization has evolved nu­merous times within the phylum, especially in po­lypoid forms.

Except for the hydras and a few other freshwa­ter hydrozoans, cnidarians are marine. Most are in­habitants of shallow water; sessile forms abound on rocky coasts or on coral formations in tropical waters. The phylum is composed of approximately 9000 living species, and a rich fossil record dates from the Cambrian period.

1 Cnidarians are aquatic, radially symmetrical animals with tentacles encircling the mouth at one end of the body. The mouth is the only opening into the gut cavity.

2 Cnidarians exhibit two body forms: the me­dusa, which is adapted for a pelagic existence, and the polyp, which is adapted for an attached, benthic existence. Colonial organization has evolved in many polypoid groups.

3 The body wall consists of an outer epidermis, an inner gastrodermis, and an intervening mesoglea. The latter may be thin or thick, acellularor cellular.

4 Cnidarians are primitive in their lack of orl gans theii lack oi fully differentiated epithelil and muscle cells, and the diploblastic origin of Л adult body.

5 Most feed on zooplankton, although son utilize larger animals and some are suspension! feeders on fine particulate matter. Prey is caugbJ with the tentacles and immobilized by ехркші cells, called cnidocytes, which are unique to tfj phylum. Digestion is initially extracellular, thd intracellular.

6 The neurons arc usually arranged as a nervel net at the base of the epidermal and gastrodenol layers, and impulse transmission tends to be ] dialing. Synaptic junctions are common^ nonpolarized.

7 A ciliated, free-swimming stereogastrula, I called the planula larva, occurs in the life cycleif most cnidarians.

The few known freshwater cnidarians belong to to the class Hydrozoa. They include the hydras and some small, freshwater jellyfish.

Hydrozoans display either the polypoid or the medusoid structure, and some species pass through both forms in their life cycle. Three characteristic unite the members of this class. The mesoglea is never cellular; the gastrodermis lacks cnidocytes and the gonads are epidermal, or if gastrodermal, the eggs and sperm are shed directly to the outside and not into the gastrovascular cavity.

SYSTEMATIC RESUME OF CLASS HYDROZOA

Order Trachylina. Medusoid hydrozoans lacking a polypoid stage. Medusa develops directly from an actinula. This order contains perhaps the most primitive members of the class. Liriope, Aglaura.

Order Hydroida. Hydrozoans with a well-devel­oped polypoid generation. Medusoid stage pres­ent or absent. The majority of hydrozoans belong to this order.

Suborder Limnomedusae. Mostly freshwater hy­drozoans possessing small solitary polyps and free medusae. The marine Gonionemus; the freshwater Craspedacusta.

Suborder Anthomedusae. Skeletal covering, when present, does not surround hydranth (athecate). Free medusae, which are tall and bell-shaped, are commonly present. Tubularia, Vermana, Syncoryne, Eudendrium, Hydracti-nia, Polyorchis, Branchiocerianthus, the fresh­water hydras.

Suborder Leptomedusae. Hydranth surrounded by a skeleton (thecate). Free medusae are com­monly absent, but when present, they are more or less flattened. Obelia, Campanularia, Abie-tinaria, Sertularia, Plumularia, Aglaophenia. Suborder Chondrophora. Pelagic, polymorphic, polypoid colonies. (These cnidarians can also be interpreted as large, single, inverted polyps.) Velella, Porpita. Order Actinulida. Tiny, solitary hydrozoans resem­bling actinula larvae. No medusoid stage present. Interstitial inhabitants. Halammohydra, Oto-hydra.

Order Siphonophora. Pelagic hydrozoan colonies of polypoid and medusoid individuals. Colonies with float or large swimming bells. Largely in warm seas. Physalia (Portuguese man-of-war), Stephalia, Nectalia. Order Hydrocorallina. Colonial polypoid hydro­zoans that secrete a calcium carbonate skeleton. Suborder Milleporina. Stinging, or fire, coral. Skeleton covered by only a thin epidermal layer. Defensive polyps arising from separate pores encircling a central gastrozooid. MiJIe-pora is the only genus.

Suborder Stylasterina. A thick layer of tissues overlying skeleton. Defensive and feeding pol­yps located within star-shaped openings on the skeleton. Stylaster, Allopora.

SUMMARY

1 Members of the class Hydrozoa are medu­soid or polypoid or exhibit both forms in their life cycle. The mesoglea is acellular, cnidocytes are re­stricted to the epidermis, and gametes develop in the epidermis. Hydrozoans may be the most prim­itive of the three classes of cnidarians.

2 Hydromedusae are usually small and planktonic.

3 The most primitive hydrozoans are probably medusoid species, in which the pelagic actinula de­velops directly into an adult medusa. Such a life cycle may also be primitive for the phylum.

4 The polypoid form may have arisen in some medusoid species in which the actinula passed through a period of attachment prior to develop­ment into a pelagic adult; i.e., the attached actinula was the first polyp.

5 Early polypoid stages, including the attached actinula, probably reproduced asexually by bud­ding. Persistent attachment of the buds led to co­lonial polypoid species, called hydroids, which now compose the majority of hydrozoans.

6 Associated with colonial organization has been the evolution of a skeleton (support) and polymorphism (division of labor).

7 Naked solitary species, such as hydras and the Gonionemus polyp, probably stem from early polypoid forms that were not colonial.

8 Suppression of the medusa through attach­ment to the polyp and subsequent reduction has evolved independently in different hydrozoan lines, and living species exhibit all degrees of re­duction in the medusoid form.
3. Class Scyphozoa-Scyphozoa. Coral polyps class-Antozoa.

Scyphozoans are the cnidarians most frequently re­ferred to as jellyfish. In this class the medusa is the dominant and conspicuous individual in the life cycle; the polypoid form is re­stricted to a small larval stage. In addition, scyphozoan medusae are generally larger than hydrome­dusae. The majority of scyphozoan medusae have a bell diameter ranging from 2 to 40 cm; some spe­cies are even larger.

Although the Cubomedusae have, in this edi­tion, been discussed with the Scyphozoa, the na­ture of their nematocysts, the possession of a velum, and their life cycle are considered evidence that they are not closely related to the other scy­phozoans and should be placed within a separate class, the Cubozoa (Werner, 1975; Calder and Pe­ters, 1975).

1 Members of the class Scyphozoa are pelagic cnidarians in which the medusa is the dominant and conspicuous form. A polypoid larva, equiva­lent to an actinula, follows the planula. Assuming the primitive nature of the medusoid form, scy­phozoans are primitive in their life cycle and per­haps evolved early from the ancestral hydrozoans.

2 Within the Scyphozoa, specialization has led to complexities in medusoid structure, as evi­denced by such features as the following: larger size than that of most hydromedusae, more highly developed manubrium, cellular mesoglea, septate gut or at least a gut with gastric filaments, gastro­dermal cnidocytes, and some development of sense organs.

3 The gonads are gastrodermal, and the eggs, which are shed through the mouth, develop into planula larvae. Following settling, the planulae de­velop into polypoid larvae, which feed and may re­produce asexually.

4 In some species the polypoid larva trans­forms directly into a young medusa, which can be taken as additional evidence that the polypoid form was derived from a larval stage in the evolu­tion of the cnidarians. In most species of scypho­zoans, young medusae are budded off transversely from the oral end of the polypoid larva.
Class Anthozoa

This is the largest of the сnidarian classes and contains over 6000 species,

Although the anthozoans are polypoid, they differ considerably from hydrozoan polyps The I mouth leads into a tubular pharynx that cxtendil more than halfway into the gastrovascular cavil (Fig. 5-34). The gastrovascular cavity is divideded longitudinal mesenteries, or septa, into radiating compartments, and the edges of the mesentery bear nematocysts. The gonads, as in the scyphozoans are gastrodermal, and the fibrous mesoglea contains cells. The nematocysts, unlike those of hydrozoans and scyphozoans, do not possess an opercullum, or lid. Some anthozoan nematocysts have a | three-part tip that folds back on expulsion; іn оthers, the thread appears to rupture directly through) the end of the capsule.

In order to simplify the survey of this class, we will deal with the sea anemones, the stony corals and the octocorallian corals separately.

1 Members of the class Anthozoa are polypoid cnidarians; the medusoid stage is entirely lacking.

2 The anthozoan polyp is more specialized than that of hydrozoans, and its cellular mesoglea, septate gastrovascular cavity, cnidocytes in gastric filaments, and gastrodermal gonads indicate a closer phylogenetic relationship with the Scypho­zoa than with the Hydrozoa.

3 The difference in the body form of the Scy­phozoa and the Anthozoa (medusa versus polyp) may be reconciled if the anthozoans are derived through the polypoid larva of scyphozoans.

4 The two subclasses, the Zoantharia and the Octocorallia, reflect different levels of structural evolution within the Anthozoa. The Octocorallia have retained an arrangement of eight complete mesenteries and eight tentacles, which may be the primitive anthozoan condition. Colonial organiza­tion is characteristic of almost all octocorallians, and the polyps are interconnected through a com­plex mass of mesoglea and gastrodermal tubes. The zoantharia display a more complex system of mes­enteries, which always exceed eight in number. There are many solitary forms, and colonial species are connected by more or less simple outfoldings of the body wall.

5 Sea anemones are the principal group of sol­itary anthozoans, and perhaps because of their sol­itary condition, many species have evolved a larger size than most other anthozoan polyps. The num­ber and complexity of their mesenteries, providing a large surface area of gastric filaments, may be re­lated to the utilization of larger prey.

6 The majority of .anthozoans are colonial, and this type of organization has evolved indepen­dently a number of times within the class. Al­though colonies may reach a large size, the individ­ual polyps are generally small. There are some groups with polymorphic colonies, but this condi­tion is not as widespread as in the hydrozoans.

7 Scleractinian corals, although similar to sea anemones, are largely colonial and are unique in their secretion of an external calcareous skeleton. The skeleton provides the colony with a uniform substrate on which the living colony rests. The sclerosepta may contribute to the adherence of the polyps within the thecal cups and provide some protection against grazing predators when the polyps are withdrawn.

8 The majority of scleractinian corals are trop­ical reef inhabitants (hermatypic) and harbor zoo­xanthellae. Zooxanthellae are found in many other anthozoans as well as some scyphomedusae and some hydrozoans.

9 The colonial alcyonaceans, or soft corals, which are most abundant on Indo-Pacific reefs, in many ways parallel the scleractinian corals, for the massive coenenchymal mass forms the substrate from which the individual polyps arise.

10 The branching, rodlike colonies or gorgon­ian corals are adapted for exploiting the vertical water column while using only a small area of the substrate for attachment. Flexible support is pro­vided by a central, organic skeletal rod and separate calcareous spicules embedded in the coenenchyme.

11 The pennatulaceans, which include sea pens, sea feathers, and sea pansies, are adapted for life on soft bottoms. A large, primary polyp, which determines the form of the colony, not only pro­vides anchorage in the sand but also acts as the sub­strate from which the small, secondary polyps arise.

12 A planula larva is characteristic of most an­thozoans and develops into the polyp. Colonial forms are derived by budding from the first polyp.

Lecture # 6. Section right - symmetric animals. Several protostomes. Systematic position worms, external morphology, covers.

1. 
   Systematic position type worm flat, round and Annelida.
   
2. 
   The external morphology of of flat, round and annelids.
   
3. 
   Distinctive features of flat sheets, and round worms.
   

Sub- Kingdom: Metazoa

Phylum: Plathyhelminthes

Phylum: Nemathelminthes

Phylum: Annelida
What are flatworms?

Flatworms are soft, flattened worms that have tissues and internal organs. They are the simplest animals to have:

• 
  three germ layers – in other words they are triploblastic,
  
• 
  bilateral symmetry, and
  
• 
  cephalization.
  

The three main groups of flatworms include the:

• 
  Turbellaria (freeliving),
  
• 
  Cestoda (parasitic tapeworms), and
  
• 
  Trematoda (parasitic flukes).
  

The phylum was created by Gegenbaur in 1859 for unsegmented round worms but now phylum Nematoda is commonly used instead. The phylum includes bilaterally symmetrical triploblastic and pseudocoelomate animals with organ system of organization. Excretion involves a giant excretory cell called Renette cell. They have tube-within-tube type of body plan.

It includes round worms that are both free living and parasitic, containing about 28,000 species, of which 16,000 are parasitic. They are slender and unsegmented worms having bilateral symmetry and their skin consists of a syncytium covered by a thick layer of cuticle. They possess only longitudinal muscles. Most of the species are dioecious and lay shelled eggs.

The Annelida are a medium sized phylum of more than 9,000 species of worms. Most species prefer aquatic environments, but there are also a number of well know terrestrial species. Only a few species of annelids are commonly known to human beings, these include the delightful Rain, Dew or Earthworms that work so hard to make our soils healthy, the Ragworms and Lugworms used by marine fishermen and the much smaller Tubifex or Red worms used by aquarists to feed their fish. In many countries people are still familiar with Medicinal leeches, and people who live closer to nature are naturally more familiar with a much wider range of Annelids than those who live in cities.