無脊椎共筆4.15
海洋無脊椎動物 4.15
Xenoturbellids( fig 4.70a )
1 Hermaphrodite, flatwormilike animals that occur on soft marine
sediments in northwestern Europe.
2 許多特點類似扁蟲,但是有些細微的構造和後口動物相似
3 曾被認為是paedomophic deuterstome larva,最近根據胚胎發生學認為
他的關係和bivalve molluscs較接近,且是經過dedifferentiation的
metamorphosed trochophore larva.
Buddenbrockids( fig 4.70b )
1 沒有腸和神經系統,有點類似旋轉蟲( rhombozoan )或直游蟲( orthonectidans )
2 possesses longitudinal tracts of muscle fibers and outer
layer of cells are no ciliated
3 運動方式像線蟲
Lobatocerebrids
1 hermaphrodite interstitial worm
2 occur on soft marine sediments in North Atlantic and Red Sea
3 表面上非常像free living扁蟲,但是在體壁的構造、腸和雄性的生殖
系統都較類似環節動物
4 Two contrasting views:
(i) It is a paedomorphic larva of some larger, possibly polychaete annelid, worm.
(ii) It is an early acoelomate offshoot of the line that ultimately gave rise to the schizocoelomate worms.
Orthonectidans直游蟲
1 Bilaterally symmetrical,in the sexual phase at least.
2 Parasite unattached within the tissue of marine turbellarian,
annelids, nemertines, mollusks and echinoderms
3 Helical symmetry
4 Two phase,sexual and asexual. The sexes is separate in sexual
phase and dimorphic.
5 身體結構是一層輪狀排列的體細胞圍繞住一團配子,體細胞下層有環肌和縱肌
6 精子由雄性個體釋出進入雌體,在慈體內授精後會形成ciliated larva（實際上是一層具有纖毛的細胞包圍著一層germinal cells）在雌體內發育
7 The germinal cells are considered to be mesodermal in origin.
8 當larva釋出侵入寄主後,會除去具有纖毛的細胞而留下germinal cells
繼續增殖形成multinucleate plasmodium,這些plasmodium可以形無性分
裂形成另外的plasmodium
9 A single plasmodium producing either those of a single sex or
both males and females, and these sexual phases then leave the
host and complete the life history.
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凌雲吾志 宇宙翔行 勁風展翼 鷹揚千里
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