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1、Chapter 2 phylum Porifera The porifera 多孔动物门多孔动物门 or sponges 海绵海绵 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 Characteristics of the phylum Porifera include Members are sessile 固着的固着的 a
2、nd either asymmet rical 不对称不对称 or radially 辐射状地辐射状地 symmetrical There cell types pinacocytes 扁平细胞扁平细胞 mesen chyme 间质间质 cells and choanocytes 领细胞 领细胞 Central cavity or a series of branching chambers through which water circulates during filter feeding No tissues or organs 1 Characteristics of the phy
3、lum Porifera include 1 1 Simple multicellular 多细胞的多细胞的 animals whose bodies consist of aggregations of cells 1 2 mostly sessile although a few are free swimming 1 3 Their bodies mainly irregular asymmetrical or some radially symmetrical Asymmetry which is the absence of a central point or axis aroun
4、d 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 through the central oral aboral axis divides the animal into mirror images 毛壶 Grantia 1 4 Cells have differentiated 分化分化 three cell typ
5、es pinacocytes 扁平细胞扁平细胞 who line the outer surface some are specialized into porocytes孔细胞 mesenchyme 间质间质 cells and choanocytes 领细胞领细胞 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 I
6、n a number of sponges some pinacocytes 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
7、 mesohyl 中质中质 Amoeboid cells called mesenchyme 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 cham
8、ber s are flagellated cells that 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 ce
9、ntral cavity spongocoel海绵腔 or a series of branching chambers through which water circulates during filter feeding The simplest and least common sponge body form is the ascon 单沟型单沟型 Ascon sponges are vaselike In the sycon 双沟型双沟型 body form the sponge wall appears folded Leucon 复沟型复沟型 sponges have an e
10、xtensively branched canal system Water enters the sponge through ostia 流入口流入口 and moves through branched incurrent canals 1 Characteristics of the phylum cont 1 Characteristics of the phylum cont Large populations of sponges play an important role in reducing the turbidity 混 浊度 of coastal waters A s
11、ingle leucon sponge 1 cm in diameter and 10 cm high can filter in excess of 20 liters of water every day 1 6 cells have not been organized into tis sues or organs 1 7 sponge skeleton spicules 骨针骨针 and spongin 海绵丝海绵丝 Sponges are supported by a skeleton that may co nsist of microscopic 微观的微观的 needleli
12、ke spikes called spicules Spicules are made of calcium carbonate 碳酸钙碳酸钙 or silica 二氧化硅二氧化硅 are formed by amoeboid cells and may take on a variety of shapes Alternatively the skeleton may be made of spongin a fibrous protein纤维状蛋白 质 made of collagen胶原质 which can produces a commercial sponge 1 Characte
13、ristics of the phylum cont 1 Characteristics of the phylum cont 海 绵 动 物 骨 针 1 8 Feeding heterotrophic Water flows through canals and chambers lined with collar cells in chambers which generates water currents and traps food particles Water currents created by choanocytes also bring oxygen 氧氧 and car
14、ry away metabolic 代谢的代谢的 and digestive wastes Food products partly digested in the choa nocytes may be passed to amoeboid cells and soluble products diffuse through the sponge 1 Characteristics of the phylum cont 1 Characteristics of the phylum cont Filtration is not the only way that sponges feed P
15、inacocytes 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 diffusion 1 10 Osmoregulation this occ
16、urs by means of a contractile vacuole Freshwater sponges osmoregulate using contractile vacuoles in each cell Simple diffusion removes other waste substances 物物 质质 1 11 reproduction asexual reproduction budding and forming gemmules 芽球芽球 sexual reproduction Most sponges are monoexious 雌雄同体的雌雄同体的 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 gemmu
