Ostracolethe fruhstorfferi Simroth, 1901

Ostracolethe fruhstorfferi Simroth, 1901 View in CoL

Figs 2 View Figure 2 , 3 A, B View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8

Ostracolethe fruhstorfferi View in CoL : Simroth 1901, p. 64.

Myotesta fruhstorferi View in CoL : Collinge 1901, p. 118.

Myotesta fruhstorferi View in CoL : Fischer 1904, Dautzenberg, p. 8.

Ostracolethe fruhstorfferi View in CoL : Fischer 1904, Dautzenberg, p. 9.

Ostracolethe fruhstorfferi View in CoL : Schileyko 2003, p. 1340.

Ostracolethe fruhstorfferi View in CoL : Schileyko 2011, p. 37.

Material examined.

Vietnam • 1 adult; Lào Cai Province, Sa Pa district, Ngu Chi Son village, tropical forest near village ; 22.4283°N, 103.7495°E; 1505 m alt.; 22 Oct. 2023; Chi Toan Le leg.; on leaves of a tree; IBER-BAS 40616 GoogleMaps ; • 1 subadult; Vinh Phuc Province, Tam Dao town, Tam Dao National Park, tropical forest near the town ; 21.4672°N, 105.6440°E; 1005 m alt.; 17 Oct. 2023; I. Dedov, N. Simov, R. Bekchiev, M. Langurov leg.; under tree bark of decaying trunks; IBER-BAS 40604 GoogleMaps .

Description.

The body is relatively wider and shorter than Ostracolethe penevi Dedov & Vu , sp. nov. The visceral hump is large and elevated, but this elevation is better visible in fixed animals (Fig. 2 A, C View Figure 2 ). The preserved body dimensions (N = 1, adult specimen) are: body length 24 mm, body width 5.2 mm, visceral hump length 11.9 mm, visceral hump width 5.2 mm, length of free mantle flap 5.2 mm, sole length 21.2 mm, sole width 2.6 mm, width of lateral zones of sole 0.75–0.85 mm, central zone of sole 0.85–0.95 mm, length of the genital pore 0.5 mm, width of the genital pore 0.6 mm (Fig. 2 A – D View Figure 2 ).

The primary color of the body is pinkish-ocher-brownish (Fig. 3 A, B View Figure 3 ), although variable (see Discussion). On the neck, three well-defined, blackish-gray- stripes are visible (one on the top and two laterally, best visible in fixed specimens). The tentacles are pale grayish, which are more intensely colored near the ommatophores and visible in active live animals. On the pinkish-ocher-brownish visceral hump, numerous yellowish spots are visible and grouped in larger stains and zones of irregular shapes. The posterior of the body has similar colors; yellowish pigment is grouped on the edge of the Y-shaped dorsal groove behind the visceral hump. The sole of living specimens is generally pale, but with lateral zones more pinkish in color, while the central zone is milky whitish. The differences in coloration between central and lateral zones is still visible in preserved specimens. The body cavity is not enlarged in the posterior part of the foot, but this part is not as muscular as in Ostracolethe sp. nov. and Laocaia simovi ( Dedov et al. 2019) . The caudal horn is not very prominent.

Shell is fingernail-like (3.2 × 2.3 mm), and sparse growth lines are visible on the upper surface. The rudimentary shell is fully covered by the mantle (Fig. 4 A – C View Figure 4 ).

Reproductive system (Fig. 5 A – E View Figure 5 ). The penis is relatively short and thinner in the area towards the atrium. The penis retractor muscle is apically attached to the bulbiform posterior end of the penis. The epiphallus is relatively short, with two caeca, one shorter and another longer, located opposite each other (Fig. 5 D, E View Figure 5 ). The vas deferens is short and entering epiphallus laterally. The vagina is thick and short. The bursa copulatrix is not well visible and is not visible in the drawing by Schileyko (2003: fig. 1752); it is most probably closely adjacent to the spermoviduct duct, as in O. penevi sp. nov. The albumen is gland small.

Remarks.

According to Simroth (1901) (in Collinge 1902, p. 14) “ the vas deferens has, before it passes into the penis, 3 short, thick flagella ”. In fact, the “ three tubercles ” visible on the side of the body integuments (Fig. 5 B View Figure 5 ) represent the structure described above, which is better visible on the side of the viscera (Fig. 5 D, E View Figure 5 ).

The “ disc ” structure reported by Collinge (1902) is present (Fig. 6 A – F View Figure 6 ). The “ discs ” are not flat but rather have a torus-toroid shape (doughnut-like) readily visible in Figure 6 D View Figure 6 . The tori are attached to a veil of the base of connective tissue at one of its flat parts. The structure consists of 35–40 tori of varying sizes (diameter 77.88–379.26 µm) (Fig. 6 A – F View Figure 6 ). When viewed at high magnification under a stereomicroscope, the “ torus ” appears to be formed by a network of symmetrically interwoven fibers (Fig. 6 A-C, E, F View Figure 6 ).

Habitat.

Ostracolethe fruhstorfferi inhabits tropical and degraded tropical forests, where it lives on leaves or branches in the crowns of trees (Fig. 7 B, C View Figure 7 ).

Biology.

Color change to blend in with the environment, which is a new phenomenon of metachrosis among terrestrial gastropods, was observed in specimens from Tam Dao National Reserve ( IBER-BAS 40604). When a specimen was photographed on a stone surface it looked whitish transparent, and only melanin kept the pattern of coloration (Fig. 8 A View Figure 8 ). The very same specimen photographed on tree bark became more colorful, and pinkish, ocher, brownish, and yellowish colors appeared (Fig. 8 B View Figure 8 ).

Distribution.

North Vietnam ( Schileyko 2003).