Morphology and phylogenetic implications of oesophageal modifications in the Limnodriloidinae (Oligochaeta, Tubificidae)

Abstract

Two features have been considered apomorphic for the subfamily Limnodriloidinae (Tubi®cidae): the lobed prostate glands, which are broadly attached to prostatic pads inside the atrial ampullae, and thè modi®ed oesophagus' in segment IX. The homology of the modi®ed oesophagus may be questioned, as it is not of the same kind in all taxa. In Limnodriloides, Smithsonidrilus, and Tectidrilus, there is a pair of diverticula, whereas in Thalassodrilides, Parakaketio, and Doliodrilus, the oesophagus is dilated to form a barrel-shaped portion. In a few species of Limnodriloides lacking diverticula, a short part of the corresponding oesophagus is swollen. A scrutiny of these features shows that they are morphologically different in several aspects: the thickness and the structure of the epithelium, the granulation, the shape of the cells and the length of the modi®cations. Moreover, a regular, semi-embedded blood plexus always occurs around the barrel-shaped portion but rarely around the diverticula (if present, plexus irregular), and never around the swollen part of the oesophagus. These different types of modi®cations fail the similarity test and thus should be regarded as independently evolved structures and coded as different characters in a parsimony analysis. Species from other subfamilies within the Tubi®cidae were also morphologically investigated, and modi®cations of the alimentary canal were found in a few of them: Ainudrilus lutulentus, Heronidrilus bihamis, H. fastigatus (all Rhyacodrilinae) and Clitellio arenarius (Tubi®cinae). The modi®cation in segment VIII of Heronidrilus spp. resembles the barrel-shaped portion in, for example, Thalassodrilides, and should primarily be coded as the same character in a congruence test of homology.

The development of the genital ducts in Limnodriloidinae (Tubificidae, Clitellata)

“…Two features have been considered as apomorphies for Limnodriloidinae: (1) the lobed prostate glands, which are broadly attached to prostatic pads inside the atrial ampullae, and (2) the`modi®ed oesophagus' in segment IX. The homology of the latter, however, was recently questioned as the modi®cation of the oesophagus is not uniform in all taxa (Gustavsson & Erse Âus, 1999b) but appears to be in one of three forms. In Limnodriloides, Smithsonidrilus and Tectidrilus, there are a pair of anteriorly directed oesophageal diverticula, whereas in Thalassodrilides, Parakaketio and Doliodrilus, the oesophagus is dilated to form a barrel-shaped portion.…”

“…In Limnodriloides, Smithsonidrilus and Tectidrilus, there are a pair of anteriorly directed oesophageal diverticula, whereas in Thalassodrilides, Parakaketio and Doliodrilus, the oesophagus is dilated to form a barrel-shaped portion. In a few species of Limnodriloides lacking diverticula, a short part of the oesophagus is swollen and the cells in that part of the gut epithelium are granulated (Erse Âus, 1982b;Gustavsson & Erse Âus, 1999b).…”

A phylogenetic analysis of Tubificinae and Limnodriloidinae (Annelida, Clitellata, Tubificidae) using sperm and somatic characters

“…The presence of paired oesophageal diverticula in segment IX (character 39) is a state common to all Limnodriloidinae analysed here except the Thalassodrilides + Doliodrilus clade. The presence of a barrel‐shaped, dilated portion of the oesophagus (Gustavsson & Erséus 1999) is the only autapomorphy for the Thalassodrilides + Doliodrilus group (character 38), while the presence of a well‐developed and strongly muscular atrial duct sac unites T. gurwitschi and T. ineri (character 52).…”

A New Species of the Subterranean Genus Krenedrilus Dumnicka (Oligochaeta, Tubificidae) from the Deep Bottom of an Oligotrophic Caldera Lake in Japan

“…Oesophageal modifications occur in three subfamilies in the Tubificidae (Limnodriloidinae, Rhyacodrilinae, and Tubificinae) as well as in some naidids and enchytraeids, but complex structures such as diverticulate and barrel-shaped modifications are limited to Limnodriloidinae, and there invariably restricted to segment IX (Gustavsson and Erséus, 1999). Gustavsson and Erséus (1999) concluded that different types of oesophageal modifications could evolve independently even in the subfamily Limnodriloidinae. Thick-walled modifications found in Rhyacodrilinae and Tubificinae could also evolve independently.…”

“…Similar modifications were found in different segments of K. papillatus and K. ibericus (Giani et al ., 1990), but not in K. sergei (Giani et al ., 1990) and K. realis (Martínez-Ansemil and Collado, 1996). Oesophageal modifications occur in three subfamilies in the Tubificidae (Limnodriloidinae, Rhyacodrilinae, and Tubificinae) as well as in some naidids and enchytraeids, but complex structures such as diverticulate and barrel-shaped modifications are limited to Limnodriloidinae, and there invariably restricted to segment IX (Gustavsson and Erséus, 1999). Gustavsson and Erséus (1999) concluded that different types of oesophageal modifications could evolve independently even in the subfamily Limnodriloidinae.…”