Introduction

Mimobdella Blanchard, 1897 was originally erected under Herpobdellidae, which is a junior synonym of Erpobdellidae, for macrophagous leeches in Asia without the type species designation (Blanchard 1897). The genus was diagnosed by mid-body somite novem-annulate or septannulate. However, its internal diagnostic characters were not described. Later, Soós (1966) designated Mimobdella japonica Blanchard, 1897 as the type species of the genus, and also included Mimobdella in Erpobdellidae. In Sawyer (1986), however, the genus was placed in the subfamily Gastrostomobdellinae along with Gastrostomobdella Moore, 1929, and Orobdella Oka, 1895. Gastrostomobdellinae was originally established as the family Gastrostomobdellidae for the two genera, Gastrostomobdella and Orobdella by Richardson (1971). The subfamily belonged to Cylicobdellidae under Hirudiniformes in Sawyer (1986), but has been recently classified as the family under Erpobdelliformes based on the molecular phylogenetic study (Oceguera-Figueroa et al. 2011). Erpobdellidae, Gastrostomobdellidae and Salifidae belong to Erpobdelliformes in their study.

The family Gastrostomobdellidae is characterized by an agnath, euthylaematous pharynx, gastropore and gastroporal duct, whereas Erpobdellidae is characterized by an agnath and strepsilaematous pharynx, and Salifidae is characterized by three myognaths, pharyngeal stylets, and strepsilaematous pharynx (Richardson 1971, Sawyer 1986). It is already clear that leeches of the genera Gastrostomobdella and Orobdella have the gastrostomobdellid internal characters (Moore 1929, 1935, 1946, Nakano 2010, 2011, Richardson 1971, 1975). However, it is uncertain whether the genus Mimobdella belongs to Gastrostomobdellidae, since the internal morphology of the three Mimobdella species remains unknown. Therefore, it is urgently needed to reveal the internal anatomy of the type species, Mimobdella japonica, and clarify the taxonomic position of the genus.

In the original publication about Mimobdella japonica, Blanchard (1897) mentioned two specimens without the type designation. One was collected from Japan by Siebold, and was deposited in the National Museum of Natural History Naturalis (Musée de Leyde in his paper). The other one was collected from Nikko, Japan, and was deposited in the Museum für Naturkunde (Musée de Berlin) (Neuhaus pers. com.). The position of the gonopores of the former is different from that of the latter. However, Blanchard gave the diagnosis of Mimobdella japonica based only on the specimen deposited in the Naturalis (Blanchard 1897: 94). Therefore, the specimen stored in the Naturalis is the holotype for Mimobdella japonica fixed by monotypy according to Article 73.1.2 of the Code (International Commisson on Zoological Nomenclature 1999).

After its original description was published, this species was redescribed based on other specimens collected from various places in Japan (Oka 1910a, b, 1917, 1923). Oka (1923) noted that Mimobdella japonica possesses a strepsilaematous pharynx without stylets in the oral cavity. However, the position of the female gonopore in Oka’s description (Oka 1923: fig. 1) differs from that in the original description (Blanchard 1897: pl. 6, fig. 16). Thus, there is a possibility that the description of Mimobdella japonica in Oka (1923) was based on misidentified specimens. However, his description of Mimobdella japonica was followed in Yang (1996) without any comment on this taxonomic problem. The type series of Mimobdella japonica thus should be reexamined.

In this paper, the systematic position of the genus Mimobdella is determined according to an evaluation of the internal morphology of its type species, Mimobdella japonica. The holotype of Mimobdella japonica is redescribed herein.

Material and methods

I examined one specimen of Mimobdella japonica: RMNH.VER.650, holotype, deposited in the National Museum of Natural History Naturalis (RMNH). Two measurements were taken: body length (BL) from the anterior margin of the oral sucker to the posterior margin of the caudal sucker, and maximum body width (BW). Examination, dissection, and drawing of the specimens were accomplished under a stereoscopic microscope with a drawing tube (Leica M125). Numbering conventions are based on Moore (1927): body somites are denoted by Roman numerals and annuli in each somite are given alphanumeric designations.

Taxonomy

Erpobdelliformes Sawyer, 1986

Salifidae Johansson, 1910

Discussion

According to the possession of a strepsilaematous pharynx and three myognaths with stylets by the holotype of Mimobdella japonica, the genus Mimobdella is placed under the family Salifidae, not Gastrostomobdellidae with euthylaematous and agnathous pharynx, or Erpobdellidae with strepsilaematous and agnathous pharynx. The genus Mimobdella differs from the other salifid genera in the following combination of characters: 1) mid-body somite novem-annulate; 2) testisacs multiple; and 3) accessory copulatory pit and gastropore absent. In addition to those characteristics, Mimobdella japonica possesses rudimentary post-crop caeca in pairs. In the family Salifidae, two leeches of the genus Barbronia Johansson, 1918, have been known as possessors of post-crop caeca: Barbronia arcana (Richardson, 1970); and Barbronia assiuti Hussein and El-Shimy, 1982 (El-Shimy 1996, Hussein and El-Shimy 1982, Richardson 1970). However, the other Barbronia species does not bear a crop caecum (Sawyer 1986). On account of the Barbronia case, it is uncertain whether post-crop caeca could be treated as a diagnostic character of the genus Mimobdella.

The type locality of Mimobdella japonica is noted only as Japan on its label and could not be defined further. However, characteristics of two salifid specimens collected from Amamioshima Island, the Ryukyu Archipelago, Japan, are coincident with those of the holotype of Mimobdella japonica (Nakano pers. obs.). The other large salifid leeches collected from various places in Japan are not identified as Mimobdella japonica (Nakano pers. obs.). Therefore, there is a possibility that Amamioshima Island is the type locality of this species. However, field surveys are insufficient to determine the island as the type locality.

In accordance with clarifying the taxonomic position of the genus Mimobdella, taxonomic relationships between Mimobdella and Odontobdella Oka, 1923, should be reconsidered. The genus Odontobdella belongs to Salifidae according to the description of its type species, Odontobdella blanchardi (Oka, 1910) in Oka (1923) (Sawyer 1986). In his paper, Oka noted that Odontobdella blanchardi could be distinguished from Mimobdella japonica by the presence of pharyngeal stylets although both Mimobdella japonica and Odontobdella blanchardi possess novem-annulate mid-body somites. He concluded that Mimobdella and Odontobdella, should be treated as distinct genera. His conclusion has been followed in the major taoxonomic works (Sawyer 1986, Soós 1966, Yang 1996). However, the taxonomic status of Odontobdella should be reconfirmed, since Mimobdella japonica possesses pharyngeal stylets. In addition, Odontobdella blanchardi collected from Japan have post-crop caeca, as does Mimobdella japonica (Nakano pers. obs.), in contrast to several descriptions of Odontobdella species (Lai and Chen 2010, Moore 1930, Nesemann 1995, Oka 1923, Yang 1996). Therefore, the type series and topotypes of Odontobdella blanchardi should be reexamined to clarify the taxonomic status of the species and genus. There is a possibility that Odontobdella will be considered to be a junior synonym of Mimobdella. Further faunal surveys and examination of salifid leeches from East Asia will be needed to clarify the type locality of Mimobdella japonica and reveal the taxonomic relationships between Mimobdella and Odontobdella.