在19世紀(jì)中葉,，法國(guó)博物學(xué)家Jean Louis Armand de Quatrefages de Bréau將蠕蟲(chóng)分為孑孓——爬行和游泳是它們的核心內(nèi)容,，例如海洋巖蟲(chóng)（左圖），和更為定棲,、典型的在隧道中居住的非孑孓類——例如蚯蚓（右圖）。
然而，早期的遺傳學(xué)研究卻對(duì)此種分類方法產(chǎn)生了質(zhì)疑,。
例如，這些研究表明,，孑孓彼此之間的相互關(guān)系并非那么密切,；相反,，它們身體的相似性只是其適應(yīng)類似生活方式以及環(huán)境的結(jié)果。
如今,，更為全面的遺傳學(xué)證據(jù)表明,，de Bréau終究是正確的。
通過(guò)對(duì)來(lái)自34種環(huán)節(jié)蠕蟲(chóng)的231種基因進(jìn)行的分析,，德國(guó)奧斯納布呂克大學(xué)的生物學(xué)家Torsten H. Struck和同事發(fā)現(xiàn),，孑孓和非孑孓類確實(shí)代表了兩種不同的進(jìn)化種群。
此外,，研究小組發(fā)現(xiàn),，這兩個(gè)種群之間的分離發(fā)生在蠕蟲(chóng)進(jìn)化的很早期階段；然而確切時(shí)間尚未搞清,，這是因?yàn)槿湎x(chóng)柔軟的身體很難在化石中完好地保存下來(lái),。
為了在周圍走動(dòng)和覓食，孑孓保存了它們的剛毛附屬物,，然而非孑孓類則喪失了這些附屬物,，這是因?yàn)樗鼈冊(cè)谶M(jìn)化后能夠待在自己的洞穴中以沉積物和浮游生物為食。
研究人員在最近出版的《自然》雜志上報(bào)告了這一研究成果,。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09864
Phylogenomic analyses unravel annelid evolution
Torsten H. Struck,1 Christiane Paul,2 Natascha Hill,3 Stefanie Hartmann,3 Christoph H?sel,1 Michael Kube,4 Bernhard Lieb,5 Achim Meyer,5 Ralph Tiedemann,2 Günter Purschke1 & Christoph Bleidorn2, 6
Annelida, the ringed worms, is a highly diverse animal phylum that includes more than 15,000 described species and constitutes the dominant benthic macrofauna from the intertidal zone down to the deep sea. A robust annelid phylogeny would shape our understanding of animal body-plan evolution and shed light on the bilaterian ground pattern. Traditionally, Annelida has been split into two major groups: Clitellata (earthworms and leeches) and polychaetes (bristle worms), but recent evidence suggests that other taxa that were once considered to be separate phyla (Sipuncula, Echiura and Siboglinidae (also known as Pogonophora)) should be included in Annelida1, 2, 3, 4. However, the deep-level evolutionary relationships of Annelida are still poorly understood, and a robust reconstruction of annelid evolutionary history is needed. Here we show that phylogenomic analyses of 34 annelid taxa, using 47,953 amino acid positions, recovered a well-supported phylogeny with strong support for major splits. Our results recover chaetopterids, myzostomids and sipunculids in the basal part of the tree, although the position of Myzostomida remains uncertain owing to its long branch. The remaining taxa are split into two clades: Errantia (which includes the model annelid Platynereis), and Sedentaria (which includes Clitellata). Ancestral character trait reconstructions indicate that these clades show adaptation to either an errant or a sedentary lifestyle, with alteration of accompanying morphological traits such as peristaltic movement, parapodia and sensory perception. Finally, life history characters in Annelida seem to be phylogenetically informative.
