Evolution & Classification — Animal Phyla & Key Concepts

1.Protostomes: blastopore becomes the mouth first. Spiral cleavage, schizocoely coelom formation. Phyla: Mollusca, Annelida, Arthropoda, plus Platyhelminthes and Nematoda.

原口動物：原口先發育為口。螺旋卵裂，裂體腔形成。代表門：軟體、環節、節肢，加上扁形和線蟲。

2.Deuterostomes: blastopore becomes the anus first; mouth forms later. Radial cleavage, enterocoely. Phyla: Echinodermata and Chordata. Humans are deuterostomes — meaning your anus developed before your mouth in the embryo.

後口動物：原口先發育為肛門，口後來才形成。輻射卵裂，腸體腔。代表門：棘皮動物和脊索動物。人類是後口動物——胚胎發育時你的肛門比嘴巴先成形。

3.Porifera, sponges: asymmetric, no true tissues. Choanocytes drive water flow with flagella; intracellular digestion. Skeleton: spicules of calcium carbonate or silicon dioxide, or spongin protein. Trap: sponges look like plants but are heterotrophic animals that filter feed.

海綿動物 Porifera：不對稱，無真正組織。領細胞鞭毛驅動水流，細胞內消化。骨架：碳酸鈣或二氧化矽骨針，或海綿絲蛋白。陷阱：海綿看似植物但其實是異營動物，靠濾食維生。

4.Cnidaria: radial symmetry, diploblastic. Key feature is cnidocytes containing nematocysts — stinging cells. Two body forms: polyp like sea anemones, and medusa like jellyfish. Examples: jellyfish, coral, sea anemone.

刺絲胞動物 Cnidaria：輻射對稱，雙胚層。關鍵特徵是含刺絲胞 nematocyst 的刺絲胞細胞——刺細胞。兩種型態：水螅型如海葵，水母型如水母。例：水母、珊瑚、海葵。

5.Platyhelminthes, flatworms: bilateral, triploblastic, acoelomate — no body cavity. Flat body, no circulatory or respiratory system, flame cells for excretion. Examples: planaria, tapeworm, fluke.

扁形動物 Platyhelminthes：兩側對稱、三胚層、無體腔。扁平體型、無循環無呼吸系統、焰細胞排泄。例：渦蟲、絛蟲、吸蟲。

6.Nematoda, roundworms: bilateral, triploblastic, pseudocoelomate — false body cavity. Cylindrical body, cuticle with molting, complete digestive tract from mouth to anus. Examples: Ascaris, pinworm, C. elegans.

線蟲動物 Nematoda：兩側對稱、三胚層、假體腔。圓柱形、有角質層蛻皮、完整消化管從口到肛門。例：蛔蟲、蟯蟲、線蟲 C. elegans。

7.Mollusca: bilateral, true coelom, protostome. Key features: mantle, radula (rasping tongue), open circulatory system except in cephalopods. Examples: snail, clam, octopus.

軟體動物 Mollusca：兩側對稱、真體腔、原口。關鍵特徵：外套膜、齒舌、開放式循環（頭足類除外）。例：蝸牛、蛤蜊、章魚。

8.Annelida, segmented worms: bilateral, true coelom, protostome. Key features: segmentation, setae or chaetae (bristles), closed circulatory system. Examples: earthworm, leech, polychaete.

環節動物 Annelida：兩側對稱、真體腔、原口。關鍵特徵：體節、剛毛、閉鎖式循環。例：蚯蚓、水蛭、沙蠶。

9.Arthropoda: bilateral, true coelom, protostome. Key features: chitin exoskeleton, jointed appendages, molting, open circulatory system. Most diverse phylum. Examples: insects, spiders, shrimp and crabs.

節肢動物 Arthropoda：兩側對稱、真體腔、原口。關鍵特徵：幾丁質外骨骼、附肢分節、蛻皮、開放式循環。最多樣的動物門。例：昆蟲、蜘蛛、蝦蟹。

10.Echinodermata: larva is bilateral, adult is RADIAL — secondary radial symmetry. True coelom, deuterostome. Key features: calcium carbonate endoskeleton, water vascular system, tube feet. Examples: sea star, sea urchin, sea cucumber.

棘皮動物 Echinodermata：幼體兩側對稱、成體輻射對稱——次生輻射。真體腔、後口。關鍵特徵：碳酸鈣內骨骼、水管系統、管足。例：海星、海膽、海參。

11.Chordata: bilateral, true coelom, deuterostome. Four chordate features: notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail. Examples: tunicate, lancelet, all vertebrates.

脊索動物 Chordata：兩側對稱、真體腔、後口。脊索動物四大特徵：脊索、背神經管、咽裂、肛後尾。例：海鞘、文昌魚、所有脊椎動物。

12.Natural selection has four conditions: variation exists in the population; overproduction of offspring; competition for limited resources; differential survival and reproduction based on heritable traits. Result: descent with modification.

天擇有四個條件：族群內存在變異、過度繁殖、競爭有限資源、可遺傳性狀的差異存活繁殖。結果：有修飾的傳承。

13.Endosymbiosis theory: mitochondria and chloroplasts originated from free-living bacteria engulfed by ancestral eukaryotes. Six lines of evidence: double membrane, circular DNA, seventy-S ribosomes (like prokaryotes), binary fission for replication, comparable size to bacteria, ribosomal RNA sequences cluster with bacteria.

內共生學說：粒線體和葉綠體源自自由生活的細菌，被原始真核細胞吞噬而來。六大證據：雙膜、環狀 DNA、70S 核糖體（似原核）、二分裂繁殖、細菌大小、rRNA 序列與細菌聚成一群。

14.Allopatric speciation: physical barrier separates populations, they evolve independently, become reproductively isolated. Sympatric speciation: speciation within the same geographic area, often via polyploidy in plants or sexual selection.

異域物種形成：物理屏障隔開族群，獨立演化，產生生殖隔離。同域物種形成：同一地理區域內形成新種，常見於植物多倍體化或性擇。

15.Reproductive isolation has two types. Prezygotic barriers prevent fertilization — habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation. Postzygotic barriers act after fertilization — reduced hybrid viability, reduced hybrid fertility (mules), hybrid breakdown.

生殖隔離有兩類。合子前隔離阻止受精——棲地、時間、行為、機械、配子隔離。合子後隔離在受精後作用——雜種活力下降、雜種不育（如騾）、雜種衰敗。