Notes on a Bifurcation of the Main Axis of the Oligochaete Enchytraeus fragmentosus Bell, 1959

Gabe, Philip R.; Gotthold, Mary Louise; Fatt, Helene V.

doi:10.2307/3224827

Cited by 2 publications

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Section: (A) Lateral Bifurcationmentioning

confidence: 99%

“…Within these simple reports with limited information, we identified 36 cases of lateral bifurcation at the posterior end (Fig. 2; Terhivuo & Valovirta, 1974; Thompson Lowne, 1872; Bülow, 1883; Bell, 1885; Hors, 1886; Bell, 1887; Schmidt, 1889; Marsh, 1890; Andrews, 1891; Collin, 1891; Friend, 1892; Horst, 1892; Service, 1894; St‐Joseph, 1894; Korschelt, 1897; Morgan, 1897; Michel, 1898; Hunt, 1915; Hyman, 1916; Langhammer, 1928; Gabe et al ., 1968; Erséus, 1997; Tovar‐Hernández et al ., 2009; Dualan & Williams, 2011; Capa et al ., 2014; Georgieva et al ., 2016; J. Marticorena, personal communication; K. Mortimer‐Jones & T. Darbyshire, personal communication; N. Kojuro, personal communication; T. van Haaren, personal communication), and 12 at the anterior end (Fig. 3; Langerhans, 1881; Friend, 1892; Hyman, 1916; von Haffner, 1928; Stock, 1965; Gibson & Harvey, 2000; Dualan & Williams, 2011; David & Williams, 2012; Blake & Magalhães, 2019; B. Pernet, personal communication; C. Ruta, personal communication) (Table 1).…”

Section: Bifurcated Annelidsmentioning

confidence: 99%

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Monsters reveal patterns: bifurcated annelids and their implications for the study of development and evolution

2021

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During recent decades, the study of anatomical anomalies has been of great relevance for research on development and its evolution. Yet most animal groups have never been studied under this perspective. In annelids, one of the most common and remarkable anomalies is anteroposterior axis bifurcation, that is animals that have two or more heads and/or tails. Bifurcated annelids were first described in the 18th century and have been occasionally reported since then. However, these animals have rarely been considered other than curiosities, one‐off anomalies, or monsters, and a condensed but comprehensive analysis of this phenomenon is lacking. Such an analysis of the existing knowledge is necessary for addressing the different patterns of annelid bifurcation, as well as to understand possible developmental mechanisms behind them and their evolution. In this review we summarize reports of annelid bifurcation published during the last 275 years and the wide variety of anatomies they present. Our survey reveals bifurcation as a widespread phenomenon found all over the annelid tree. Moreover, it also shows that bifurcations can be classified into different types according to anatomy (lateral versus dorsoventral) or developmental origin (embryonic versus postembryonic, the latter occurring in relation to regeneration, reproduction, or growth). Regarding embryos, three different types of bifurcation can be found: conjoined twins (in clitellates); Janus embryos (two posterior ends with a single head which shows duplicated structures); and duplicitas cruciata embryos (with anterior and posterior bifurcation with a 90° rotation). In adults, we show that while lateral bifurcation can result in well‐integrated phenotypes, dorsoventral bifurcation cannot since it requires the discontinuity of at least some internal organs. The relevance of this distinction is highlighted in the case of the Ribbon Clade, a group of syllid annelids in which some species reproduce by collateral and successive gemmiparity (which involves dorsoventral bifurcation), while others grow by branching laterally. Although most known cases of bifurcation came from accidental findings in the wild or were unintentionally produced, experimental studies resulting in the induction of bifurcation of both embryos and adults are also reviewed. In embryos, these experimental studies show how mechanical or chemical disruption of the zygote can result in bifurcation. In adults, the ventral nervous system and the digestive tract seem to play a role in the induction of bifurcation. Based on the reviewed evidence, we argue that the long‐forgotten study of annelid developmental anomalies should be incorporated into the growing field of annelid EvoDevo and examined with modern techniques and perspectives.

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Section: (A) Lateral Bifurcationmentioning

confidence: 99%

Section: Bifurcated Annelidsmentioning

confidence: 99%

Monsters reveal patterns: bifurcated annelids and their implications for the study of development and evolution

2021

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Donn�es morphologiques et anatomiques sur quelques cas de d�doublement chez les Nereidae: Interpr�tation morphog�n�tique

Boilly

Boilly-Marer

Combaz

1975

Wilhelm Roux' Archiv

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The authors describe 12 cases of duplication (6 without bifurcation of the body et 6 with bifurcation of the body) in the caudal part of three species of Nereids (Nereis pelagica L.,Nereis diversicolor O.F.M.,Perinereis cultrifera G.)Duplication without bifurcation of the body concerns the dorsal blood vessel alone (1 case) or segmentary structures i.e. parapodia, nerve cord, nephridia and longitudinal ventral muscles (5 cases). The bifurcation of the body arises either in the forntal plane (1 case) without alteration of segmentary organogenesis of the supernumerary tail, or in the sagittal plane on the dorsal (4 cases) or ventral (1 case) face with modification of the segmentary organogenesis; the dorsal bifurcation have no parapodia, nerve cord, nephridia and longitudinal ventral muscles while the ventral bifurcation possesses twice this lot of structures.The comparative morphological and anatomical study of these abnormal Annelids leads us to consider:The bifurcation of the body as resulting from only junction between ventral or dorsal body wall and the intestine;The alterations of segmentary organogenesis as a consequence either of the duplication or the absence of the nerve cord, the number of pairs of structures like parapodia, nephridia and longitudinal ventral muscles corresponding to the number of nerve cords present in the segment.

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Notes on a Bifurcation of the Main Axis of the Oligochaete Enchytraeus fragmentosus Bell, 1959

Cited by 2 publications

References 0 publications

Monsters reveal patterns: bifurcated annelids and their implications for the study of development and evolution

Monsters reveal patterns: bifurcated annelids and their implications for the study of development and evolution

Donn�es morphologiques et anatomiques sur quelques cas de d�doublement chez les Nereidae: Interpr�tation morphog�n�tique

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