Endothyrella Zilch, 1960

Pall-Gergely, Barna, Budha, Prem B., Naggs, Fred, Backeljau, Thierry & Asami, Takahiro, 2015, Review of the genus Endothyrella Zilch, 1960 with description of five new species (Gastropoda, Pulmonata, Plectopylidae), ZooKeys 529, pp. 1-70 : 9-11

Taxon classification Animalia Pulmonata Plectopylidae

Genus Endothyrella Zilch, 1960

Endothyrella 1899c Endothyra (section of the genus Plectopylis ) Gude: Science Gossip, 6: 148., non Endothyra Phillips, 1845 (Foraminifera).

Endothyrella 1960 Plectopylis (Endothyrella) , - Zilch: Handbuch der Paläozoologie, 6 (2).

Endothyrella 1999 Endothyrella , - Schileyko: Treatise on Recent Terrestrial Pulmonate Molluscs, Part 4.(...): 2: 460.

Type species.

Helix plectostoma Benson, 1836, by original designation.

Diagnosis.

Shell sinistral or dextral; protoconch usually finely, regularly ribbed (see also discussion and Figures 6 A–F); periostracal folds usually present on the body whorl; they are arranged in 3-7 lines; folds hair-like in most species, resulting from the rolling of flat folds; folds flat (not rolled) in some species only (see Figures 8D, 20 A–F); dorsal sculpture strong, usually reticulated (both radial and spiral lines present, see Figure 8A); umbilicus wide to narrow; body whorl rounded in some species but rather bluntly shouldered (keeled) in others; apertural fold always absent; main plica usually absent (present in a few species only); low plica (if present) runs close to and parallel with the lower suture, it is usually very short (present only under the lamella), but in some species it reaches the callus; parietal wall with a single lamella with denticles posteriorly (probably homologous with the posterior lamella); two lamellae were reported in one species ( Endothyrella aborensis ) only; palatal plicae complicated in most species with many small denticles at their posterior ends; in many species they are at least party divided in the middle.

Genitalia (see Figures 18, 21, 22 B–F, 25, 26): The left ommatophoral retractor passes between penis and vagina (in sinistral species). Penis internally with hollows (small pocket-like structures) having calcareous granules inside; penial papilla absent; epiphallus may be longer than penis and enters penis laterally; epiphallus with longitudinal folds internally; small penial caecum usually present at the penis-epiphallus boundary; retractor muscle inserts on the caecum and attaches to the diaphragm; diverticulum (if present) and gametolytic sac are of the same size.

Radula (see Figures 19 A–F): Central tooth larger than the ectocones of the first laterals; marginals tricuspid (= ectocones are divided) or even quadricuspid (both the endocones and ectocones are divided); the incision between the ectocones and endocones usually deep ( Endothyrella fultoni has rhomboid marginals which are unique in the whole family).

Differential diagnosis.

All known species of the genera Sinicola , Gudeodiscus , Halongella and Sicradiscus are dextral. Regardless of the coiling direction, most Endothyrella species differ from Sinicola by the presence of usually hair-like periostracal folds standing in multiple lines. Deciduous periostracal folds in Sinicola are present only along the keel and the folds are always flat. Most Sinicola species (especially the large species) have a sharp keel, whereas Endothyrella species usually have a rounded or slightly keeled, shouldered body whorl. The palatal plicae of Sinicola are usually simple, horizontal, straight and parallel, but in Endothyrella they are often oblique to vertical, divided and ornamented with minute denticles at their posterior ends. In Sinicola the posterior lamella is present on the parietal wall, with two horizontal plicae anteriorly above and below, whereas in most Endothyrella species (probably except for Endothyrella aborensis ) the anterior lamella is present and the posterior is missing or reduced to one or two short vertical plicae.

Some Gudeodiscus and Halongella species possess low, radial periostracal folds (e.g. Páll-Gergely et al. 2015, fig. 10 e–f), similar to those of Endothyrella nepalica sp. n. (see there). The radial folds have serrated edges in Gudeodiscus phlyarius (Mabille, 1887). The tiny tips of the serrated folds seem to occur in a spiralling pattern (see Páll-Gergely and Hunyadi 2013, fig. 113 and Páll-Gergely et al. 2015, fig. 10 c–d). All of these periostracal features of Gudeodiscus and Halongella are, however, easily distinguishable from the long, hair-like folds of the genus Endothyrella .

Some Gudeodiscus species possess a fold in the aperture, which is always missing in Endothyrella . The palatal plicae in Gudeodiscus are usually depressed Z- or L-shaped and posterior small denticles are very rare (except for one denticle above the posterior end of the last plica), whereas the palatal plicae of Endothyrella are frequently divided in the middle and posterior small denticles are usually present. In Endothyrella the anterior lamella is present, and often the upper horizontal plica is missing, whereas in Gudeodiscus both lamellae, or only the posterior one, are visible and the upper horizontal plica (above the lamella) is almost always present. Additionally, Gudeodiscus species have a rounded body whorl, while in many Endothyrella species the body whorl is angled or shouldered. Our limited knowledge on the anatomy of Endothyrella species shows that the entire inner penial wall of Endothyrella is covered by pits, whereas in Gudeodiscus these pocket-like structures are restricted to the a certain (usually apical) portion of the penis.

Sicradiscus is similar to Endothyrella in possessing a weak or reduced posterior lamella. Long periostracal folds standing in more than one row have also been found in one Sicradiscus species, namely in juveniles of Sicradiscus transitus Páll-Gergely, 2013. This species, however, has hairs standing in two spiral lines on the body whorl, whereas in Endothyrella the hairs are arranged in 3-7 spiral lines. This trait seems to be absent in adult Sicradiscus transitus shells and all other species of Sicradiscus , but is common in fully grown Endothyrella shells (i.e. most species possess them). The two genera (i.e. Endothyrella and Sicradiscus ) differ in the short, straight palatal plicae, which are usually connected in Sicradiscus vs. longer, more complex palatal plicae sometimes having additional denticles in Endothyrella . In both genera divided plicae may occur, but in the case of Sicradiscus the posterior fourth and fifth plicae seem to be always connected, whereas in Endothyrella all plicae are free. Moreover, western Sicradiscus species ( feheri Páll-Gergely, 2013, invius [Heude, 1885], mansuyi [Gude, 1908b], securus [Heude, 1885] and transitus ) differ from Endothyrella by the presence of a strong apertural fold.

Plectopylis and Endoplon species have a granulated or smooth protoconch, whereas it is usually finely ribbed in Endothyrella . Moreover, Plectopylis and Endoplon usually have a strong apertural fold which is often connected to a long main plica. In contrast, although some Endothyrella species have a main plica, they all lack an apertural fold. See also under Chersaecia and Table 3.

Content.

aborensis , affinis , angulata sp. n., babbagei , bedfordi , blanda , brahma , dolakhaensis sp. n., fultoni , inexpectata sp. n., macromphalus (syn.: gregorsoni ), minor , miriensis , nepalica sp. n., oakesi , oglei , pinacis , plectostoma , robustistriata sp. n., serica (syn: munipurensis ), sowerbyi , tricarinata , williamsoni . See also Tables 4 and 5.

Distribution.

The distribution of this genus is restricted to Nepal, northeastern India and the province Sichuan in China. One species ( Endothyrella plectostoma ) was reported from Myanmar (Figure 3).