Lepidodasys tsushimaensis, Lee & Chang, 2011

Lee, Jimin & Chang, Cheon Young, 2011, Two new species of the genus Lepidodasys (Gastrotricha, Lepidodasyidae) from Tsushima Island, Japan, Journal of Natural History 45 (13 - 14), pp. 855-867 : 861-866

Lepidodasys tsushimaensis sp. nov.

( Figures 4 , 5 )

Type locality

Miuda Beach , Tsushima Island, Japan (34 ◦ 40 ′ 20 ′′ N, 129 ◦ 29 ′ 06 ′′ E) .

Type specimens

Holotype ( DBG1501 ) and 11 paratypes ( DBG1502–12 ), mounted in glycerine on H-S slides, 1 October 2009, leg. J.M. Lee and C.Y. Chang. Another two paratypes (NHM reg. nos. NHMUK 2010.3 , 2010.4 ), mounted in glycerine, collection data same as in the holotype.

Additional material examined

Six specimens with the same collection data were mounted on an aluminium stub for scanning electronic microscopy.

Diagnosis

Lepidodasys with strap-shaped, slender body, at least 650 µm long; body with almost parallel sides, narrowing to caudum; cuticular armature with numerous small wholegrain-shaped scales without keels, arranged in alternating rows; a pair of longitudinal ventral ciliary bands at U03–U88; three to five TbA per side, slightly forming an arc; six to nine TbD distributed along median line in intestinal region, 7–11 TbVL per side, restricted to pharyngeal region, TbL numbered up to 9–14 per side in intestinal region, 11–14 TbP along posterior margin of caudum; paired testes with different lengths; copulatory organ nearly pyriform.

Description of the holotype

Body ( Figures 4A, B , 5A ). Conspicuously slender and elongated, Lt 730 µm long, 35 µm in maximum width (05U) at U54; gently vaulted dorsally and flattened ventrally; body sides parallel to each other, then a little narrowing ahead of caudum; pharynx relatively short, 117 µm long, PhJIn at U16, pharyngeal pores not seen. Widths of mouth opening / PhJIn / trunk / caudal portion 15 / 32 / 34 / 21 µm at U04 / U16 / U53 / U97, respectively.

Sensory hairs (ca. 2–3 µm long). Several implanted around mouth opening; numerous long hairs (ca. 11–14 µm long) arrayed in two longitudinal rows per side rather asymmetrically on dorso- and ventrolateral surfaces throughout nearly whole body length (U03–U97).

Cuticular armature. Body ornamented with small, smooth wholegrain-shaped scales, each lacking a keel ( Figure 5B ); dorsal scales (ca. 2.5 × 6 µm) slightly larger than ventral ones (ca. 1.8 × 4 µm) between ciliary bands; dorsal surface armed with about 14–16 columns of scales in mid-trunk region; ventral scales between ciliary bands forming three to five columns in anterior intestinal region; all columns arranged somewhat in parallel.

Ventral ciliation. Locomotor ciliation consists of a pair of narrow columns of numerous fine cilia from just behind anterior adhesive tubes (U03) to near seminal receptacle at U88 ( Figure 4B ).

Adhesive tubes. Four TbA per side (ca. 6–7 µm long), forming a gentle arc behind oral opening at U02 ( Figure 4D ); nine TbD (ca. 12 µm long) arrayed in single row along median line, more or less evenly distributed in intestinal region from U35 to U83 ( Figure 4A ); eight or nine TbVL per side (ca. 8–10 µm long) restricted to pharyngeal region at U4–U17, somewhat evenly spread, last tube located just behind PhJIn at U17 ( Figure 4B ); 10–14 TbL (ca. 10–14 µm long) per side, asymmetrically arrayed in intestinal region at U25–U93 ( Figure 4A ); 12 TbP (ca. 7–8 µm long) forming an arc along posterior margin of narrow caudum, inserted a little ventrally ( Figures 4E , 5E ).

Reproductive apparatus. Paired testes of slightly different lengths, reaching to middle of the intestinal region, at U54 and U57, respectively, not coiled, with anterior ends dilated. Vasa deferentia extending posteriorly to front of the seminal receptacle (U83), coming closer to each other at U80–U82, then divergent again posteriorly ( Figure 4E ). Seminal receptacle with vague boundary, located ahead of copulatory organ at U85–U88, containing several coiled spermatozoa ( Figure 4E ). Copulatory organ nearly pyriform with narrow posterior end (11 × 32 µm), located at U90–U95 ( Figure 4E ). Eggs not observed.

Measurements and variability

In total, 14 type specimens including three sub-adults were examined. The three subadult specimens were 475, 573 and 625 µm long and 31, 33 and 32 µm in maximum width, respectively. All three were similar in appearance to adults, except for having a smaller number of adhesive tubes, e.g. one or two TbA, one to six TbVL, 4–11 TbL per side asymmetrically, three or four TbD and six to ten TbP.

Eleven adults mounted in glycerine ranged from 651 to 932 µm long (mean 804 µm, SD 83), and from 31 to 45 µm (04U–06U) in maximum width.

TbL located typically in the intestinal region. However, in one paratype, a TbL was situated in the head region (at U01) on one side only.

Etymology

The specific name tsushimaensis refers to the type locality of the new species, Tsushima Island , Japan .

Remarks

Among the four congeneric species sharing the parallel pattern of scales, in contrast to the herring-bone orientation, L. tsushimaensis sp. nov. is closely allied with L. arcolepis Clausen from the Faroe Bank in the North Sea in having similar body appearance and round caudum with TbP. However, L. tsushimaensis sp. nov. is clearly distinguished from L. arcolepis by the smooth scales without keel, TbD arranged in a single row along the median line of the intestinal region and TbVL restricted in the pharyngeal region.

Lepidodasys castoroides is similar to L. tsushimaensis sp. nov. in having smooth scales oriented in the parallel pattern, but it differs by the paired TbD (against a single row along median line in L. tsushimaensis sp. nov.), TbVL distributed in the intestinal region (against restricted in the pharyngeal region in L. tsushimaensis sp. nov.), and barrel-shaped copulatory organ (against pyriform in L. tsushimaensis sp. nov.). Furthermore, L. castoroides has a constricted body at the end of the trunk, like a “beaver tail”, with a flattened caudum ( Clausen 2004).

Lepidodasys platyurus , originally described as bearing two longitudinal keels ( Remane 1927), was presumed to have a keel by Clausen (2004), as in the case of L. martini . In any case, L. platyurus is discernible from L. tsushimaensis sp. nov. with smooth scales. Moreover, L. platyurus is distinguished from the new species by semicircular caudum with 20 TbP (against narrow and round caudum with 11–14 TbP in L. tsushimaensis sp. nov.) and the absence of TbD (against those arranged in a column on the median line of trunk in L. tsushimaensis sp. nov.).

Lepidodasys unicarenatus was insufficiently described with one photograph of dorsal scales with a keel on the head (see Balsamo et al. 1994; fig. 2A). Later, it was reported additionally from the Mediterranean ( Todaro et al. 2001, 2003, 2008) but important characters of the species have not been clarified. Nonetheless, L. tsushimaensis sp. nov. appearently differs from this species by smooth scales without keel (versus scales each with a keel, as indicated in the specific name, unicarenatus ).

The two new species from Japan are evidently discernible from each other in the shape and arrangement of scales. Furthermore, they are distinguished by the body length: width ratio and the arrangements of TbA, TbVL and TbP.

A key to the seven species currently recognized in the genus Lepidodasys Remane is presented as follows.

A key to the species of genus Lepidodasys Remane

1. Cuticular armature with herring-bone pattern of dorsal scales............. 2 Cuticular armature with parallel fashion of scales......................... 3

2. With six to ten TbD................................... L. laeviacus sp. nov. Without TbD.................................................. L. martini

3. Scales with keel(s)....................................................... 4 Scales smooth without keel.............................................. 6

4. Caudum swollen.............................................. L. platyurus Caudum narrowing gradually............................................ 5

5. Body very long (about 1 mm in length)......................... L. arcolepis Body a little short (about 0.5 mm in length)................. L. unicarenatus

6. With six to nine TbD; TbVL restricted to the pharyngeal region.............................................................. L. tsushimaensis sp. nov. Without TbD; TbVL distributed in the trunk region.......... L. castoroides

Figures

Figure 4. Lepidodasys tsushimaensis sp. nov. (A) Habitus, dorsal; (B) habitus, ventral; (C) dorsal scales in the pharyngeal region; (D) arrangement of TbA, TbVL and ventral scales between ciliary bands in the pharyngeal region; (E) reproductive organs, ventral. Scale bars: A, B, 100 µm; C–E, 50 µm.

Figure 5. Lepidodasys tsushimaensis sp. nov. Scanning electron micrographs: (A) habitus, dorsal; (B) dorsal scales in the trunk region; (C) ventral scales between ciliary bands in the intestinal region; (D) head and anterior pharyngeal region, ventral; (E) caudum with TbP, dorsal. Scale bars: A, 100 µm; C–E, 10 µm; B, 5 µm.