Krumbachia virginiana ( Kepner & Carter, 1931 ) Ruebush, 1938

Houben, Albrecht M., Monnens, Marlies, Proesmans, Willem & Artois, Tom J., 2022, Limnoterrestrial ‘ Typhloplanidae’ (Rhabdocoela, Platyhelminthes), with the description of four new species and a new genus, European Journal of Taxonomy 798, pp. 70-102 : 92-93

Krumbachia virginiana ( Kepner & Carter, 1931) Ruebush, 1938

Fig. 8D–E

Olisthanella virginiana Kepner & Carter, 1931 .

Olisthanella virginiana – Senn 1935: 47–50. — Vandel 1937: 526. — Birstein 1991: 108.

Material examined

CANADA • 6 specs, studied alive, one of which horizontally sectioned and the rest of which sagittally sectioned; Ontario, Dundas Valley Conservation Area ; 43°14′20″ N, 79°59′17″ W; 6 May 2009; Niels Van Steenkiste leg.; submersed roots in a puddle of mud in a forest; XIV.2.43–XIV.2.48; HU .

Description

Specimens are very dark and around 3 mm long. The body is constricted at ±30% and has a rounded anterior and posterior end ( Fig. 8D ). At ±65% the body is at its widest. Rostrally, rhabdite glands ( Fig. 8D : ar) are present and arranged in two groups. Dermal rhabdites are lacking. Protonephridiopores ( Fig. 8D : pp) are positioned just behind the pharynx ( Fig. 8D : ph), which is situated just before the body middle (±45%).

The gonopore ( Fig. 8E : gp) is situated at ±50% of the body and connected to a genital atrium ( Fig. 8E : ga). The genital atrium is surrounded by an inner circular and outer longitudinal muscle layer and lined with a high, nucleated epithelium that is somewhat ruffled. Moreover, some fine-grained eosinophilic glands ( Fig. 8E : gl1) are situated posterior to the atrium and open anteriorly into the genital atrium.

The large, elongated, paired testes ( Fig. 8D : t) lie anterior to the pharynx and ventral to the paired vitellaria ( Fig. 8D : vi). The paired vasa deferentia ( Fig. 8E : vde) fuse just before entering the copulatory bulbus ( Fig. 8D : co). Two layers of spiral muscles and a third, weaker, outer longitudinal muscle layer surround the 240–320 µm long, slightly bent copulatory organ (see Fig. 8E ). This organ bears an intracapsular seminal vesicle ( Fig. 8E : vs) and a 215–250 µm long, slightly bent, ejaculatory duct ( Fig. 8E : de) with a thick, sclerotised layer (5–6 µm). The entire ejaculatory duct is surrounded by a loose matrix ( Fig. 8E : mx) and at the proximal end, it shows a constriction. Large, coarse-grained, extracapsular basophilic glands ( Fig. 8D–E : gg) are associated with the copulatory organ. A 200–260µm long bursa ( Fig. 8D– E : bu) is situated next to the copulatory organ. This bursa is a muscular, elongated sack with a clear constriction at 20% of its length from the proximal tip (see Fig. 8E ), dividing it into a proximal and distal part. Both parts are lined with a very thin epithelium, which is lacking at some places. The proximal part is surrounded by two weak layers of diagonal muscles. In the distal part, these muscles divide into a strong outer circular and weaker inner longitudinal layer. This entire structure is surrounded by a matrix ( Fig. 8E : mx) and an additional strong layer of longitudinal muscles.

The vitellaria ( Fig. 8D : vi) extend from the region of the rhabdite glands to the almost posterior end. The vitelloducts ( Fig. 8E : vd) fuse just before opening into the female duct ( Fig. 8E : fd). At this place, the female duct also receives the oviduct ( Fig. 8E : od), a large globular seminal receptacle ( Fig. 8D–E : rs) and large, coarse-grained basophilic glands ( Fig. 8E : gl2), which are situated around the receptacle. The oviduct and vitelloducts are surrounded by weak, circular muscles.

Discussion

See the general discussion on the genus Krumbachia .

Remarks

The bursa is filled mainly with some type of secretion. The seminal receptacle contains sperm and secretion.

Previously known distribution

A swamp, small stream, and pond near the University of Virginia, Virginia, USA ( Kepner & Carter 1931; Ruebush 1938).

General discussion on Krumbachia

The genus Krumbachia is the most species-rich genus within ‘Protoplanellinae’ ( Van Steenkiste et al. 2010). Members of this genus can measure from 0.3 mm in the smallest species (i.e., K. minuta Ruebush, 1938 ) to over 3 mm in the largest one (i.e., K. paludicola Schwank, 1979 and K. virginiana ( Kepner & Carter, 1931) Ruebush, 1938 ). The diagnostic features are: lack of dermal rhabdites and presence of adenal rhabdites, presence of a sclerotised ejaculatory duct, and a pharynx with a median to posterior position. However, in practice, this genus is a conglomeration of animals roughly matching the diagnostic features (e.g., K. guttulata Schwank, 1980 possesses dermal rhabdites) and there are many similarities between the genera Krumbachia and Olisthanella Voigt, 1892 (see Ruebush 1938 for an elaborate discussion).

Krumbachia subterranea and K. virginiana possess the diagnostic features of the genus Krumbachia . Moreover, both are quite large species, lack eyes (but see further), have testes positioned rostral to the pharynx, and possess a strongly muscular bursa. There are only two other species that correspond to this description: K. paludicola and K. styriaca Reisinger, 1924 .

Krumbachia virginiana strongly resembles K. paludicola because it has a bipartite bursa with strong muscles around its distal part. Krumbachia virginiana differs from K. paludicola in having a joint vas deferens, lacking a blindside branch on the ejaculatory duct, and lacking a large sphincter between the genital atrium and male copulatory system. In the original description, Kepner & Carter (1931) mention the fact that the dark colouration in their specimens of K. virginiana disappears when the animals are starved for a weak, except for two tiny black spots that, according to them, may be eyes. As we did not starve the animals, this could not be confirmed. Krumbachia paludicola has a wide European distribution, whereas K. virginiana has a Nearctic distribution.

In his extensive redescription of K. virginiana, Ruebush (1935) mentions intraspecific variability in several features, leading to the description of a new variety: K. virginiana var. glandulosa . The identification of this variety is based on the position of the pharynx, subtle differences in the construction of the adenal rhabdite tracks, and the lack of a seminal receptacle in K. virginiana var. glandulosa . The latter character is considered a doubtful one by Ruebush (1935), as this may depend on the condition of the animal. The specimens studied by us show all characteristics of the nominal K. virginiana .

Krumbachia subterranea is morphologically similar to K. styriaca , and its description was based mainly on three differences (see Reisinger 1933). First, K. styriaca has a thin, sclerotised bursa with many bends and knicks, while it is a flattened, broad sack in K. subterranea . Second, the female duct in K. styriaca possesses a pronounced bend at the point where the female glands occur, while no such bend occurs in K. subterranea . Furthermore, the transition between the female duct and bursal stalk is very smooth in the latter species. Third, the vitellaria have small branches in K. subterranea , while they are very smooth in K. styriaca . These branches are not that pronounced in our specimens, and also do not seem strongly developed in the specimens studied by Schwank (1981: fig. 5).

Figures

Fig. 8. Two species of Krumbachia Reisinger, 1924. A–C. Krumbachia subterranea Reisinger, 1933. A. Internal organisation of a live specimen. B. Organisation of the genital system of a live specimen. C. Reconstruction of reproductive organs based on sagittal sections of the neotype (neotype no. 823). D–E. Krumbachia virginiana (Kepner & Carter, 1931) Ruebush, 1938. D. Internal organisation of a live specimen. E. Reconstruction of reproductive organs based on sagittal sections.