Dichaetura filispina, Suzuki, Takahito G., Maeda, Masako & Furuya, Hidetaka, 2013

Suzuki, Takahito G., Maeda, Masako & Furuya, Hidetaka, 2013, Two new Japanese species of Gastrotricha (Chaetonotida, Chaetonotidae, Lepidodermella and Dichaeturidae, Dichaetura), with Comments on the Diversity of Gastrotrichs in Rice Paddies, Zootaxa 3691 (2), pp. 229-239 : 233-236

Dichaetura filispina n. sp. Suzuki and Furuya

[New Japanese name: Ketoge-togeoitachimushi] ( Figs. 3 , 4 )

Type locality. Japan, Honshu, Shiga Prefecture, Otsu (35º07'54.72" N, 135º53'50.16” E). 21, June, 2011, Suzuki.

Type specimens. Holotype deposited in Lake Biwa Museum (LBM1360000014). All specimens were collected by T.G. Suzuki. Five paratypes in the first author’s collection (3 specimens, site 2, 26 June, 2011; 1 specimen site 2, 24, June, 2011; 1 specimen, site 3, 18 June, 2012)

Etymology. Species name from the Greek fili, thin, and Latin spina, spine, describing the characteristic its thin spines on the base of furca; noun in apposition,.

Diagnosis. A medium-sized gastrotrich of total length 168–185 μm including furca of 20–23 μm beginning at U89.8; PhIJ at U25.0. Head un-lobed, of simple rounded shape, without cephalion or hypostomion; one pair of sensory cilia; eye spots absent. Dorsal scales only caudally of basal constriction, each with a thin spine of length 11.0–15.9 μm. A thick caudal spine, length 7.2–11.0 μm, at base of furca. A small thick spine, length 5.0–6.2 μm, on median side of each limb of furca, about 39% of distance from furca base. Adhesive tube only in main furca, not in spine. No ventral scales in the area between the two columns of ventral cilia to terminal plates. Juvenile length about 125 μm. Basal constriction and spined furca are significant characteristics of this genus.

Description. Based on an adult specimen (holotype), 185.3 μm in total length. Body medium-sized, cylindrical shape with constriction at caudal region and no distinct neck region. Widths of head / neck / trunk / basal constriction /caudal base are 26.4 / 25.2 / 34.0 / 21.3 / 14.9 μm at U12.8 / U26.9 / U62.4 / U80.0 / U85.7, respectively. Length of distal furca 20.6 μm; spine on furca 8.1μm. Pharynx 45.0 μm in length, from posterior edge of mouth to junction with intestine; PhIJ at U25.0. Head of simple rounded shape, without cephalion or hypostomion.

Sensory organs: Three or more isolated cephalic sensory cilia on either side of head, length 10.0–15.2 μm. Eye-spots absent. Tactile bristles absent from both neck and caudal regions.

Cuticular armature: Scales only on dorsal region caudal of basal constriction, composed of 11 small round scales, each with a thin spine, arranged in 5 rows: 3 rows of 3 scales and a single scale anteriorly and posteriorly. Dorsal scales round, diameter 2 μm, spine length 11.1–15.9 μm. Ventral scales absent. Each limb of furca with a thick curved spine, length 6.2 μm, between which is a straight thick spine, length 9.8 μm.

Ventral ciliation: Densely packed field of cilia posterior of mouth ring (U4.8) splits into two parallel bands, one each side over most of trunk region, ending at U88. Each band widens then narrows again just posterior of head region, forming a characteristic triangular shape anteriorly.

Digestive tract: Mouth opening diameter 8.4 μm, 7.2 μm in depth. Pharynx is an irregular cylindrical shape (6.1–9.6 μm). Intestine straight, slightly wider anteriorly (11.1 μm) narrowing gradually over its length (to 4.7 μm width). Anus ventral, at U87.7.

Remarks. Dichaetura filispina n. sp. is similar to two species, D. capricornia and D. piscator , both from Europe (Metschnikoff 1865; Murray 1913). However, it is easily distinguished from these species in having independent sensory cilia and a branched furca, each limb of which has an adhesive tube. In this respect, D. filispina n. sp. can be distinguished from all other species (cf. Rudescu 1967; Schwank & Bartsch 1990). Metschnikoff (1865) described D. capricornia based on only one specimen, and subsequently Martin (1981) redescribed this species. Dichaetura filispina n. sp. is similar to D. capricornia in possessing spines on the inside of each limb of furca and in angle of furca. However, D. filispina n. sp. differs from D. capricornia in body length (168–185 µm vs. 102–150 µm), head sculpture (regular vs. three shallow lobes), the widest region of the body (trunk vs. head), and ventral scales (none vs. small spined scales).

Figures

FIGURE 3. Dichaetura filispina n. sp. light micrographs of the holotype. a, Coronal view; b, dorsal scale; c, furca spine and basal furca spine. Scale bars 5 μm. Abbreviations: BC, basal constriction; BFS, basal furca spine; DS, dorsal scale; F, furca; FS, furca spine; INT, intestine; MR, mouth ring; PH, pharynx; SC, sensory cilium.

FIGURE 4. Dichaetura filispina n. sp., line drawings of holotype. a, Dorsal view; b, ventral view. Scale bar 5 μm. Abbreviations: BC, basal constriction; BFS, basal furca spine; DS, dorsal scale; F, furca; FS, furca spine; INT, intestine; MR, mouth ring; PH, pharynx; SC, sensory cilium; VC, column of ventral cilia.