Hepatogaster Čejka, 1910

Rota, Emilia, Martinsson, Svante & Erséus, Christer, 2018, Two new bioluminescent Henlea from Siberia and lack of molecular support for Hepatogaster (Annelida, Clitellata, Enchytraeidae), Organisms Diversity & Evolution (New York, N. Y.) 18 (3), pp. 291-312 : 292-293

On Hepatogaster Čejka, 1910

Both our two new species fit the diagnosis of Hepatogaster Čejka, 1910 , a taxon considered by Welch (1920) and Stephenson (1930) subordinate to the genus Henlea , but that Černosvitov (1937) maintained in a distinct position within the Henleinae. The species included in Hepatogaster by Černosvitov (1937) indeed satisfy the original uncommon criteria established by Čejka (1910): (1) oesophageal appendages extending into VI and VII, (2) “gastrointestinal glands”, forming a quadruple multitubular structure surrounding gut in VIII, (3) spermathecae opening into the oesophagus in the very back of V (in VI from an external view), (4) a gradual dilatation of the oesophagus to form the intestine. What principally differentiates the named (sub) group from the other Henlea species also possessing oesophageal diverticula in VIII and dorsal vessel originating in IX ( H. ventriculosa , H. jutlandica Nielsen and Christensen 1959 ), is the multitubular substructure (as opposed to a largely hollowed cavity) of the pouches closely surrounding the gut in VIII.

Figure 2 shows how Michaelsen (1886) illustrated through histological cross-sections the different structures of the gut diverticula in Enchytraeus leptodera Vejdovský 1879 (= Henlea nasuta auct.) and E. ventriculosus d’ Udekem (= H. ventriculosa ). In E. leptodera , two lateral pouches protrude from the intestine and project freely forward into the bodycavity ( Fig. 2a ). In E. ventriculosus , four pockets closely adhere to the intestine ( Fig. 2b ). In both cases, the lumen of the pockets is constricted by the multiple, irregular folds of the walls, so that a considerable enlargement of the inner surface takes place. Later, Michaelsen (1889) illustrated the structure of the gut diverticula in the types of Archienchytraeus nasutus Eisen, 1878 , where two short, wide pockets are attached laterally to the posterior end of the oesophagus, and extend forward without fusing with it. The walls of the pockets are “often and irregularly folded, and so strongly that the central cavity of the pockets almost completely recedes against the folds and their interstices” ( Michaelsen 1889; Fig. 2c ). Welch (1920), Stephenson (1922, 1930) and Černosvitov (1931, 1937) speculated about an ontogenetic and phylogenetic transition between the different degrees of folding of the diverticula walls, from being fairly even and smooth (as seen in H. ventriculosa ) to variously folded (as seen in H. nasuta ) to the fusion between the adjacent folds to form the tubuliferous condition of Hepatogaster . In fact, Černosvitov (1931, 1937) placed Hg. sibiricus Čejka, 1910 outside Hepatogaster because of its incomplete replacement of folds by tubules.

The status of Hepatogaster was briefly commented upon in morphocladistic terms by Tynen et al. (1991). In this paper we will attempt to verify if this old name deserves taxonomic status, or not, on a molecular basis.

Figures

Fig. 2 Histological cross sections of the gut diverticula in Enchytraeus leptodera Vejdovský (a) and Enchytraeus ventriculosus d’Udekem (b), and in Archienchytraeus nasutus Eisen (c), as shown by Michaelsen (1886) and Michaelsen (1889), respectively