Chapter2phylumPorifera

1、 The porifera , or sponges , are primarily marine animals consisting of loosely organized cells. They vary in size from less than a centimeter to a mass that would more than fill your arms. Members are sessile and either asymmet-rical or radially symmetrical. There cell types: pinacocytes , mesen-ch

2、yme cells, and choanocytes . Central cavity, or a series of branching chambers, through which water circulates during filter feeding. No tissues or organs. 1.1 Simple multicellular animals, whose bodies consist of aggregations of cells. 1.2 mostly sessile, although a few are free swimming. 1.3 Their

3、 bodies mainly irregular, asymmetrical or some radially symmetrical Asymmetry, which is the absence of a central point or axis around which body parts are equally distributed, characterizes most protists and many sponges. Radial symmetry is the arrangement of body parts such that any plane passing t

4、hrough the central oral-aboral axis divides the animal into mirror images. 毛壺毛壺(Grantia) Pinacocytes: are thin, flat cells, line the outer surface of a sponge. Pinacocytes may be mildly contractile, and their contraction may change the shape of some sponges. In a number of sponges, some pinacocytes

5、are specialized into tubelike, contractile porocy-tes, which can regulate water circulation. Openings through porocytes are pathways for water moving through the body wall. mesenchyme cells : Just below the pinacocyte layer of a sponge is a jellylike layer called the mesohyl .Amoeboid cells called m

6、esenchyme cells move about in the mesohyl and are specialized for reproduction, secreting skeletal elements, trans-porting and storing food, and forming contract-ile rings around openings in the sponge wall. choanocytes: are below the mesohyl and lining the inner chamber(s), are flagellated cells th

7、at have a collarlike ring of microvilli surrounding a flagellum. Microfilaments connect the microvilli, forming a netlike mesh within the collar. The flagellum creates water currents through the sponge, and the collar filters microscopic food particles from the water.1.5 central cavity ( spongocoel海

8、綿腔海綿腔), or a series of branching chambers, through which water circulates during filter feeding. The simplest and least common sponge body form is the ascon . Ascon sponges are vaselike.In the sycon body form, the sponge wall appears folded. Leucon sponges have an extensively branched canal system.

9、Water enters the sponge through ostia and moves through branched incurrent canals. . Large populations of sponges play an important role in reducing the turbidity(混混濁度濁度) of coastal waters. A single leucon sponge, 1 cm in diameter and 10 cm high, can filter in excess of 20 liters of water every day!

10、 1.6 cells have not been organized into tis-sues or organs1.7 sponge skeleton: spicules and spongin Sponges are supported by a skeleton that may co-nsist of microscopic needlelike spikes called spicules. Spicules are made of calcium carbonate or silica , are formed by amoeboid cells, and may take on

11、 a variety of shapes. Alternatively, the skeleton may be made of spongin( a fibrous protein纖維狀蛋白纖維狀蛋白質質 made of collagen膠原質膠原質), which can produces a commercial sponge.海海綿綿動動物物骨骨針針1.8 Feeding: heterotrophic. Water flows through canals and chambers lined with collar cells in chambers, which generates

12、 water currents and traps food particles. Water currents created by choanocytes also bring oxygen and carry away metabolic and digestive wastes. - Food products partly digested in the choa- nocytes may be passed to amoeboid cells, and, soluble products diffuse through the sponge. Filtration is not t

13、he only way that sponges feed. Pinacocytes lining incurrent canals may phagocytize larger food particles . Sponges also absorb by active transport nutrients dissolved in seawater.1.9 respiration and excretion: simple diffusion Gas exchange takes place through the membranes of the cells by simple dif

14、fusion. 1.10 Osmoregulation: this occurs by means of a contractile vacuole. Freshwater sponges osmoregulate using contractile vacuoles in each cell. Simple diffusion removes other waste substances . 1.11 reproduction: asexual reproduction: budding and forming gemmules sexual reproduction: Most spong

15、es are monoexious (both sexes occur in the same individual) , but do not self-fertilize. Because individual sponges produce eggs and sperms at different times. gemmules: when the parent sponge dies in the winter, it releases gemmules, resistant capsules which can survive both freezing and drying. Wh

16、en favorable conditions return in the spring, amoeboid cells stream out of a tiny opening, organized into a sponge. development: the zygote firstly develop into a flagellate, free-living larva . some sponges possess remarkable powers of regeneration . Portions of a sponge that are cut or broken from

17、 one individual regenerate new individuals. 1.12 sponges do not have nerve cells to coordinate body functions. Most reactions result from individual cells responding to a stimulus . Class Calcarea Class Hexactinellida Class Demospongiae 2 the sponges taxonomy The Calcarea have spicules composed of c

18、alcium carbonate (e.g. Sycon sp.). Spicules are needle shaped or have three of four rays; all marine. Calcareous sponges. Grantia (scypha), Leucosolenia . Spicules composed of silica and usually six rayed; spicules often fuse into an intricate lattice ; cup or vase shaped; found at 450 to 900 m depths in tropical west Indies and eastern Pacific . Class sponges, Euplectella (Venus flower-basket) Brilliantly colored sponges with needle-shaped or four-rayed siliceous spicules or spongin or both; up to 1 m in height and diameter. Include one family of freshwater sponges,