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CHORDATES ( 脊脊脊脊脊

CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

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Page 1: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

CHORDATES ( 脊索动物门)

Page 2: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

Intruduction • Definition (脊索动物的定义)• The great phylum chordata (脊索动物门) derives its name

from one of the few common characteristics of this group --the notochord. This structure is possessed by all members of the phylum, either in the larval or embryonic stages or throughout life.

• The three distinctive characteristics that chordates apart from all other phyla are the notochord, dorsal tubular nerve cord, and pharyngeal gill slits. These characteristics are always found in the early embryo, although they may be altered or may disappear altogether in later stages of the life cycle. These four features are so important that each merits a short description of its own.

Page 3: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

• There are three subphyla under phylum Chordata. Two of these subphy1a are small, lack a vertebral column, and are of interest primarily as borderline or first chordates (protochordates ,原索动物 ).

• Subphylum Vertebrata (脊椎动物亚门):Bony or cartilaginous vertebrae surround spinal cord , notochord in all embryonic stages and persists in some of the fish.

Page 4: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

脊椎动物是和人类关系最密切的一类动物

1 人类本身就是一类特殊的脊椎动物

2 脊椎动物和人类的衣食紧密相关

3 提供了丰富的中医药

4 提供了满足各种研究需要的实验动物

5 要保护的大多数动物都是脊椎动物

6 给人类也带来很多危害

Page 5: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

二 如何学好脊椎动物学

1 以进化的观点来学习

2 形态特点和和生态环境紧密结合

3 理论教学和实验教学紧密结合

4 理论和实践紧密结合

5 以比较的方法来学习

Page 6: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

进化地位 是所有动物中最高等的一门动物,

包括尾索动物、头索动物和脊椎动物。 脊索动物由无脊椎动物演化而来,

与棘皮动物和半索动物具有共同的祖先。

脊椎动物是神经系统获得最充分发展的动物,并由此最后演化出具有自我意识的人。

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Characteristics of chordates(脊索动物的特征)

1 ) Notochord (a skeletal rod) present at some stage in life cycle• 2 ) Nerve cord dorsal and tubular: anterior end of cord usually enlarged to

form brain • 3 ) Pharyngeal gill slits present at some stage in life cycle and may or may

not be functional• 4 ) A postanal tail usua1ly projecting beyond the anus at some stage and

may or not persist• 5 ) Deuterostome• 6 ) Heart ventral, with dorsal and ventral blood vessels; closed blood

system• 7 ) Complete digestive system• 8 ) Exoskeleton often present; well developed in some vertebrates• 9 ) A cartilage or bony endoskeleton present in the majority of members

(vertebrates)• 10 ) Bilateral symmetry; segmented body; three germ layers; coelom well

developed

Page 8: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics
Page 9: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

脊索的出现在动物演化史上的意义

支持

保护

运动

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• DORSAL TUBULAR NERVE CORD. In the invertebrate phyla the nerve cord (often paired) is ventral to the alimentary canal and is solid, but in the chordates the cord is dorsa1 to the alimentary canal and is formed as a tube.The anterior end of this tube in vertebrates becomes enlarged to form the brain. The hol1ow cord is produced by the infoIding of ectodermal cells on the dorsal side of the body above the notochord. Among the vertebrates the nerve cord lies in the neural arches of the vertebrae, and the anterior brain is surrounded by a bony

or cartilaglnous cranlum.

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• PHARYNGEAL GILL SLITS. • Pharyngeal gill slits are perforated slitlike openings that lead from

the pharyngeal cavity to the outside. They are formed by the invagination of the outside ectoderm and the evagination of the endodermal lining of the pharynx. The two pockets break through when they meet, to form the slit. In higher vertebrates these pockets may not break through and only grooves are formed instead of slits; all traces of them usually disappear. In forms that use the slits for breathing, gills with blood vessels are attached to the margins of the slits and make the gaseous exchange with the water that enters the mouth and passes through the pharyngeal gill slits. The slits have in their walls supporting frameworks of gill bars. Primitive forms such as amphioxus have a large number of slits, but only six or seven are the rule in the fish. The transitory appearance of the slits in land vertebrates is often used as evidence for evolution.

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• 其他与无脊椎动物的区别– 肛后尾:即尾在肛门后方;– 闭管式循环系统;– 心脏位于消化道腹面;– 后口;– 分节的肌节;– 生物化学比较 ( 无 : 精氨酸 ; 脊椎 : 肌酸 )

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• 与部分无脊椎动物的共同点

– 后口

– 三胚层

– 真体腔

– 身体分节

– 两侧对称

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ANCESTRY AND EVOLUTION(脊索动物的祖先和进化)

• The great chasm between vertebrates and invertebrates seems nearly as wide today as it did 150 years ago when zoologists began serious speculation on the issue. The most serious obstacle to progress is the almost total absence of fossi1 material for reconstructing lines of descent. The earliest protovertebrates were in all probability soft-bodied forms that stood litt1e chance of being preserved even under the most ideal conditions. Consequently, speculations must come from the study of living organisms, especially from an analysis of how they develop. But well. over 600 million years have elapsed since the vertebrates had their beginnings, and even the highly conservative early developmental stages of animals cannot be expected to remain unchanged over such an enormous span of time.

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EARLY THEORIES OF CHORDATE EVOLUTION

• . The earliest speculations about vertebrate origins understandably focused on the most successful, and in may respects most advanced, of invertebrate groups.

• the Arthropoda. It was quickly recognized that if one took an arthropod with its segmented body, ventral nerve cord and dorsal heart and turned it over, one has the basic plan of a vertebrate. The idea was first proposed by St. Hilaire in 1818 and received detailed support by subsequent zoologists.

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• Later, in 1875 Semper and Dohrn independently transferred the ancestral award to the Annelida, because this group shares a basic body plan with the arthropods and in addition has an excretory system that strikingly resembles that of primitive vertebrates. The anne1id-vertebrate theory continued to receive support as late as 1922 when the Dutch biologist Delsman published his e1aborate arguments in a book. The principal difficulty with the annelid theory was that an inverted annelid has its brain and mouth in the wrong relative positions. The annelid's nerve cord is ventra1 but connects to a dorsal brain via circum pharyngeal connectives through which the digestive tube passes (Fig. 16-4, A). When an annelid is inverted, as was required for the annelid-vertebrate theory, the mouth ends up on top of the head, and the brain below.

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ECHINODERM THEORY• When, early in 20 century, further theorizing became rooted in developmenta1

patterns of animals, it immediate1y became apparent that on1y the echinoderms deserved serious consideration as the vertebrate's ancestor.

• Echinoderms and chordates belong to the deuterostome branch of the animal kingdom in which the mouth is formed as a secondary opening and the b1astopore of the gastrula becomes the anus.

• The coelom of these two phyla is primitive1y enterocoelous: • Furthermore, there is a great resemb1ance between the bipinnaria larvae of

certain echinoderms and tornaria larvae of the hemichordates, a phylum bearing some chordate characteristics. Both have similar ciliated bands in loops, sensory cilia at the anterior end, and a complete digestive system of ventral mouth and posterior anus.

• Both echinoderm and chordate embryos show indeterminate cleavage• These characteristics are shared by brachiopods and pterobranchs (a

hemichordate group) as well as by echinoderms, protochordates, amphioxus, and vertebrates. This is probably a natural grouping and almost certainly indicates interrelationships. However the absence of biochemical support and the uncertainty of fossil evidence in no way invalidates the embryologic evidence for a remote kinship between echinoderms and chordates.

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• 脊索动物的祖先可能类似尾索动物的幼体,后向两个方向发展,一是经过变态,成体为固着生活,具鳃裂作为取食和呼吸器官;另一个是幼体期延长并适应新的生活环境,不再变态,出现生殖腺并进行繁殖(即幼体性成熟),进而发展出新的一类动物,即具有脊索、背神经管和鳃裂的自由运动的脊索动物。

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系统发育研究的方法• 1 形态学 形态特征的形似性• 2 幼虫(系统发育) 幼虫具有的特征为

祖征,而成虫具有的为衍征。• 3 分子生物学 蛋白质的氨基酸序列或核

酸序列分析。目前最流行的方法。

Page 21: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

分子系统学• 主要在分子水平,利用分子生物学手段探索生物遗传物质 ----DNA 的分子差异,探讨物种之间及大的类群之间的亲缘关系,以促进合理的、自然的分类系统,揭示生命系统的奥秘。在这一方面, 20 世纪 90 年代作了许多基础工作,在脊索动物方面也作了大量工作。例如 Russo 等人( 1996 )对 11 种脊椎动物的线粒体 DNA(mt DNA 的完整序列)测序分析。这些种的 mtDNA 包括 13 个编码蛋白质的基因。这 11 种物种中共有的密码子的数目从 52 个到 582 个不等,这是随基因的不同而不同的。对这些基因中的每一个都构建了系统树,并对全部基因( 3682 个密码子)也构建了系统树。他把这些树与真实树进行了比较。这里,我们考虑的是用氨基酸序列,而不是核苷酸序列所获得的结果,因为前者比后者获得的树更可信。

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图 3-1( A )已知的 11 种脊椎动物物种的系统发育树( B )加入七鳃鳗和海胆的序列后推断的系统发育树。

Page 23: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

图 3-2 用线粒体细胞色素 b 基因的核苷酸和氨基酸序列构建的11 种脊椎动物的系统发育树。

TL :树长; PC :泊松校正距离; Kimura: Kimura距离

Page 24: CHORDATES ( 脊索动物门). Intruduction Definition (脊索动物的定义) The great phylum chordata (脊索动物门) derives its name from one of the few common characteristics

The Divesity of Chordates (第二节 脊索动物门的多样性)

• . CHORDATE SUBPHYLA• There are three subphyla under phylum Chordata.

Two of these subphy1a are small, lack a vertebral column, and are of interest primarily as borderline or first chordates (protochordates ,原索动物 ). Since these subphyla lack a cranium, they are also referred to as Acrania (无头类) . The third subphylum is provided with a vertebral column and is cal1ed Vertebrata. Since this phylum has a cranium, it is also called Craniata (有头类) .

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• Protochordata (Acrania)• Subphylum Urochordata (尾索动物亚门):

(Tunicata 海鞘 ). Notochord and nerve cord on1y in free--swimming larva; adults sessile and encased in tunic. Example:Molgula.

• Appendiculariae (尾海鞘纲)• Ascidiacea (海鞘纲)• Thaliacea(樽海鞘纲 )• Subphylum Cephalochordata (头索动物亚门):

Notochord and nerve cord found aIong entire length of body and persist throughout life; fishlike in form. Example: Branchiostoma (Amphioxus 文昌鱼 ).

• Cephalochorda (头索纲 )

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• Craniata • Subphylum Vertebrata (脊椎动物亚门): Bony or

cartilaginous vertebrae surround spinal cord, notochord in all embryonic stages and persists in some of the fish. This subphylum may also be divided into two great groups (superclasses) according to whether they have jaws (颌) .

• Superclass Cyclostomata (圆口总纲): (Agnatha 无颌类 ). Without true jaws or appendages. Example: Pltromyzon.

• Cyclostomata (圆口纲 )• Superclass Cnathostomata (有颌类) : With jaws and

(usually) paired appendages. Example: Homo (人类) .• Pisces (鱼纲) (软骨鱼纲 Chondrichthyes ,硬骨鱼纲

Osteichthyes )• Amphibia (两栖纲 )• Reptilia (爬行纲)• Aves (鸟 纲)• Mammalia (哺乳纲)

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中国和世界脊椎动物物种数比较

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脊椎动物主要类群上下颌 附肢 胚膜 体温

圆口纲 无颌类软骨鱼纲硬骨鱼纲

鱼形类

两栖纲

无羊膜类

爬行纲

变温动物

鸟纲哺乳纲

有颌类 (颌口类 )

四足类羊膜类

恒温动物

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Urochordata ( 尾索动物亚门)

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Adult ascidian—Molgula(海鞘 )

Molgula is globose in form and is attached by its base to piles and stones. Lining the test or tunic is a membrane or mantle. On the outside are two projections: the incurrent and excurrent siphons. Water enters the incurrent siphon and passes into the pharynx (branchial sac) through the mouth. On the mid-ventral side of the pharynx is a groove, the endostyle(内柱) , which is ciliated and secretes mucus. Food materia1 in the water is entang1ed by the mucus in this endostyle and carried into the esophagus (食道) and stomach. The intestine leads to the anus near the excurrent siphon.

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• The water passes through the pharyngeal slits in the walls of the pharynx into the atrial cavity (围鳃腔) . As the water passes through the slits, respiration occurs.

• The circulatory system contains a ventral heart near the stomach and two large vessels, one connected to each end of the heart. The action of the heart is peculiar in that it drives the blood first in one direction and then in the other. This reversal of blood flow is found in no other animal.

• The excretory system is a type of nephridium (肾管) near the intestine.

• The nervous system is restricted to a nerve ganglion and a few nerves that lie on the dorsal side of the pharynx.

• A notochord is lacking. • The animals are hermaphroditic (雌雄同体) , for both ovaries

and testes are found in the same anima1. Ducts lead from the gonads close to the intestines and empty near the anus. The germ cells are carried out the excurrent siphon into the surrounding water, where cross-fertilization occurs.

• It will be seen that, of the four chief characteristics of chordates, adult tunicates have only one, the pharyngeal glll slits. However, the larval form gives away the secret of their true relationship.

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Ascidian tadpole (海鞘幼虫)• The tadpole larvae among the different ascidians vary in certain details, but the

basic plan is much the same in all. • The deve1opment of the egg through the blastula and gastrula stages is somewhat

similar to that of amphioxus. After a development of about 2 days the embryo hatches out into an elongated transparent larva about 1 to 5 mm. long. Its tail, four or five times longer than its trunk, is provided with a slender cuticular fin and contains the following structures:

• a notochord of vacuolated cells arranged in a single row; a hollow dorsal nerve chord extending from the tip of the tail to the sensory vesicle and made up of small cells; and a striated muscle band on each side of the notochord.

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• In the larger head and trunk regions are found the three adhesive papillae a digestive system of dorsal mouth, short esophagus, large pharynx with endostyle and gill slits (which open into the atrium), stomach, intestine, and anus (which opens into the atrium): the brain, which is a continuation of the nerve cord of the tail: a sensory vesicle containing an otolith for balance; and a dorsal median eye with lens and pigmented cup. A coelom and a circulatory system are present, but the heart is not formed until after metamorphosis. The larva does not feed but swims around for some hours, during which time it is at first positively phototactic( 趋光性 ) and negatively geotactic but later becomes negatively phototatic and positively geotactic. By its adhesive papi1lae it now fastens itself vertically to some solid object and then undergoes retrograde metamorphosis to become an adult. In this process the tail is absorbed by phagocytes; the notochord, muscles, and nervous system (except a trunk ganglion) degenerate; the branchial sac enlarges with many gill slits; and the alimentary canal and circulatory system (with a heart) enlarge and develop. The body also undergoes a rotation so that the mouth and atrial openings (siphons) are shifted to the upper unattached end. Gonads and ducts arise in the mesoderm, and the who1e animal becomes enclosed in a test or tunic.

• The evolutionary significance of the ascidian tadpole has already been discussed.

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• 2 幼体和变态

幼体具脊索动物 3 大特征,尾内有脊索;脊索背部有中空的背神经管,神经管前端膨大成脑泡,并具眼点和平衡器;消化道前端分化成咽,咽壁上有鳃裂。尾在肛门后方,心脏位于腹面。

变态期间:尾部连同脊索逐渐萎缩消失,神经管退化成神经节,感觉器官消失 , 裂数增加,体壁分泌被囊素形成被囊,开始营固着生活。

这种从幼体至成体结构更为简单化的变态称为逆行变态或退化变态 (retrogressive metamorphosis) 。

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尾索动物分

类尾海鞘纲 ( 幼形纲 )

海鞘纲

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樽海鞘纲

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Subphylum Cephalochordata (头索动物亚门)

• Amphioxus (文昌鱼)• Subphylum Cephalochordata is the most interesting of all the

protochordates, for one of its members is the lancelet Branchiostoma (Amphioxus) , one of the classic animals in zoology. This group is found mainly on the sandy beaches of southern waters, where they burrow in the sand, with the anterior-end projecting out. One American species, B. virginiae. is found from Florida to the Chesapeake Bay. Altogether there are 28 species, of which 4 are North American, scattered over the world. They can swim in open water by swift lateral movements of the body. B. belcheri is found in China.

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• Amphioxus is especial1y interesting, for it has the four distinctive characteristics of chordates in simple form, and in other ways it may be considered a blueprint of the phylum. It has a 1ong, slender, laterally compressed body 2 to 3 inches long, with both ends pointed. There is a long dorsal fin, which passes around the tail end to form the caudal fin. A short ventral fin is also found. These fins are reinforced by fin rays of connective tissue. The ventral side of the body is flattened and bears along each side a metapleural fold (腹褶) . There are three openings to the outside; the ventral anterior mouth, the anus near the base of the caudal fin, and the atriopore (腹孔) just anterior to the ventral fin.

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• The body is covered with a soft epithelium one layer thick resting upon some connective tissue. The notochord, which extends almost the entire length of the body, is made up of cells and gelatinous substance enclosed in a sheath of connective tissue. Above the notochord is the tubular dorsal nerve cord, with a slight dilation at the anterior end known as the cerebral vesicle.

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• Along each side of the body and tail are the numerous < shaped myotomes (肌节) , or muscles, which have a metameric arrangement. The myotomes are separated from each other by myosepta of connective tissue. The myotomes of the two sides alternate with each other. The anterior end of the body is called the rostrum. Just back of this and slightly below is a median opening surrounded by a membrane, the oral hood, which bears some twenty oral tentacles (buccal cirri 触须 ). The oral hood encloses the chamber known as the vestibule, at the bottom of which lies the true mouth with a membrane, the velum, around it. Around the mouth are 12 velar tentacles. The cirri and tentacles serve to strain out large particles and have sensory functions. Ciliated patches on the walls of the buccal cavity in front of the velum produce a rotating effect and are called the wheel organ, which propels water currents.

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• On the dorsal side of the oral hood is hatschek's groove and pit, an embryonic relic from the first coelomic sac on the left. It may be homologous with the pituitary of vertebrates. Just behind the mouth is the large compressed pharynx with more than a hundred pairs of gill slits, which act as strainers in filter feeding as well as in respiration. From the pharynx the narrow tubular intestine extends backward to the anus.

• On the ventral side of the intestine is a large diverticu1um, the hepatic cecum.

• The coelom is reduced and is confined to the region above the pharynx and around the intestine . Connecting the coelom to the atrium are about a hundred pairs of ciliated nephridia of the solenocyte type, a modified kind of flame cell. The big cavity around the pharynx is the atrium; it is lined with ectoderm and is therefore not a coelom. The pharynx has a mid-dorsal groove, the hyperbranchial (epipharyngeal) groove, and a mid-ventral one, known as the endostyle. Both of these grooves are lined with cllia and gland cells. Food is entangled by the mucus of the endostyle and is carried to the intestinei the water passes through the gill slits into the atrium and gives up oxygen to the blood vessels in the gill bars.

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• Although there is no heart, the blood system similar to that of higher chordates . The blood moves posteriorly in the dorsal aorta and anteriorly in the ventral aorta; a hepatic portal vein leads from the intestines to the liver. Blood is propelled by contractions of the ventral aorta and is carried to the dorsal aorta by vessels in the gill bars. The blood is almost colprless, with a few red corpuscles.

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• The nervous system is above the notochord an. consists of a single dorsal nerve cord, which is hollow. This nerve cord gives off a pair of "nerves" alternately to each body segment, or myotome, as dorsal and ventral roots. Although this arrangement resembles the vertebrate spinal cord, the ventral root actually does not contain nerves but rather the drawn-out extensions of myotomic muscle fibers.

• Ciliated cells with sensory functions are found in various parts of the body. Sexes are separate, and each sex has about 25 pairs of gonads located on the wall of the atrium. The sex cells are set free in the atrial cavity and pass out the atriopore to the outside, where fertilization occurs. Cleavage is total (holoblastic) and a gastrula is formed by invagination. The larva hatches soon after deposition and gradually assumes the shape of the adult.

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• No other chordate shows so well the basic diagnostic chordate characteristics as does the amphioxus. Not only are the four chief characters of chordatese, dorsal nerve cord, notochord, pharyngeal gill slits, and postanal tail--well represented but also secondary characteristics, such as liver diverticulum, hepatic portal system, and the beginning of a ventral heart. Indicative also of the condition in vertebrates is the much thicker dorsal portion of the muscular layer. This is in contrast to the invertebrate phyla in which the muscu1ar layer is about the same thickness around the body cavity. The metameric arrangement of the muscles suggests a similar p1an in the embryos of vertebrates. Just where it is placed in the evolutionary blueprint of the chordates and the vertebrates is a controversial point.

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头索动物是典型的桥梁动物:

除终生具有以上脊索动物的三个主要特征外,还具有A.与脊椎动物相似的特征 具肌节、有奇鳍、肛后尾、闭管式循环系统,其

胚胎发育和三个胚层的分化也与脊椎动物相似。B.比脊椎动物原始的特征: 无头、无骨骼、无心脏、排泄器官为肾管。C.比无脊椎动物进化的特征: 躯体两侧有一对腹褶,为脊椎动物成对附肢的雏形。

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思 考 题1.脊索动物门有何共同特征?与无脊椎动物

比较有何功能和进化意义?2. 何为逆行变态?了解逆行变态有何意义?3. 文昌鱼为什么被称为头索动物?简述文昌鱼结构的原始性、特化性和进步性。4. 试述脊索动物的起源。5. 试述脊索动物门中亚门和纲的分类及各类

群的主要特征。