Chaetonotus machikanensis, Suzuki, Takahito G. & Furuya, Hidetaka, 2011

Suzuki, Takahito G. & Furuya, Hidetaka, 2011, Two new species of Chaetonotus (Gastrotricha, Chaetonotida, Chaetonotidae) from Japan, Zootaxa 3011, pp. 27-37 : 31-33

Chaetonotus machikanensis n. sp.

[New Japanese name: Machikane-itachimushi] ( Figs. 3 , 4 )

Type locality. Japan, Honshu, Osaka Prefecture, Toyonaka, Machikane Pond (34°80′N, 135°45′E).

Type specimens. Holotype (OUM-GA-00003) and paratype (OUM-GA-00004) deposited in Osaka University Museum ( OUM). Other specimens in the first author’s collection.

Etymology. After the type locality.

Diagnosis. A small-sized Chaetonotus of total length 95–124 μm including furca of 8.0–11.5 μm beginning at 87 U; PhIJ at 28 U; head slightly five-lobed, with cephalion and 2 pairs of sheaved sensory cilia. Eye-spots absent. Body enveloped by large scales, each with a long barbed spine, in 7 longitudinal alternating rows, with 15 in each. Three Y-shaped keeled scales located each side at base of furca. Ventral scales between two columns of ventral cilia, flattened and hexagonal shaped, in 2 or 3 longitudinal alternating rows. Two keeled scales present near the terminal plates. A pair of terminal plates, oval, keeled, and spined. Three small oval, keeled scales present each side of proximal part of furca.

Description. Based on an adult specimen, 99 μm in total length. Pharynx 28 μm in length from posterior edge of mouth to junction with intestine; pharyngeo-intestinal junction (PhIJ) at 28.5 U. Head slightly five-lobed. Diameter of mouth ring 6 μm and height 4 μm. Body size small, and tenpin-like shape, with distinct head, neck, trunk and caudal region. Widths of head / neck / trunk / caudal base are: 16.8 / 13.1 / 22.4 / 13.1 μm at 0 9 U / 28 U / 52 U / 84 U, respectively. Length of furca, 8 μm.

Sensory organs: Two pairs of 3- to 4- tufted cephalic sensory cilia, abut 13 μm length, on either side of head. Eye-spots and tactile bristles absent.

Cuticular armature: Body covered with alternating lines (7 longitudinal alternating rows, 15 in each) of spined, overlapping scales, except for cephalion and furca regions. Scales on neck region boomerang-shaped, width 5 μm, length 3.5 μm with well-developed barbed spine 6 μm long. Scales of trunk region arrowhead-shaped, width 9 μm, length 8 μm with well-developed barbed spine 19.5 μm long. Dorsal terminal plates with 3 Y-shaped keeled scales located each side at base of furca, width 2 μm, length 5 μm. Ventral scales hexagonal, flattened, width 1 μm, length 2.5 μm; 2 scales keeled near pair of terminal plates. Terminal plates 3 μm wide, 8 μm long, with spine 3 μm in length. Three minute scales present each side of proximal part of furca.

Ventral ciliation: Two almost parallel bands of cilia extend from posterior edge of mouth (06 U) along most of trunk region, ending at 83 U.

Digestive tract: Mouth opening 6 μm wide, and 4 μm deep. Pharynx swollen at anterior and posterior ends; anterior swelling more obvious (6.5 μm in wide) than posterior (6 μm wide); central portion fairly constant width (5.5 μm). Intestine is straight, slightly wider at anterior (9 μm), narrowing gradually over its width to 2 μm. Anus is ventral at 83 U.

Remarks. Chaetonotus machikanensis is similar to C. hystrix Metschnikoff , C. macrochaetus Zelinka , and C. persetosus Zelinka , in having arrowhead-shape dorsal scales each with a long denticular spine.

Chaetonotus hystrix has been reported from Africa, Europe, North America, and Northern Asia except China ( Schwank, 1990). Chaetonotus machikanensis is distinguished from C. hystrix in the furca length (8–11 μm vs. 14– 16 μm), the shape of ventral scales (flatten vs. keeled), and round-shaped scales at the base of furca: absent vs. present ( Metschnikoff, 1865).

Chaetonotus macrochaetus has been recorded from Africa, Europe, Northern Asia (excluding China) and North and South America ( Schwank, 1990). Chaetonotus machikanensis differs from C. macrochaetus in the shape of the ventral scales, which are flattened vs. keeled ( Zelinka, 1889).

Chaetonotus persetosus has been recorded in Europe and Northern Asia except China ( Schwank, 1990). Chaetonotus machikanensis differs from C. persetosus in body length (95–124 μm vs. 70–100 μm), the edge shape of dorsal trunk region scales (long barb vs. wide face with short barb), the shape of scales in the neck region (boomerang-shaped vs. arrowhead-shaped), and the line pattern of flattened ventral scales (2–3 scales per horizontal row vs. 5 scales per horizontal row). Further, C. machikanensis has 2 keeled scales immediately rostral to the terminal plates, but C. persetosus has 8 rostral scales, 6 of which are keeled, with 2 non-keeled scales immediately adjacent to the terminal plates. In addition, C. persetosus has 1 keeled scale between the terminal plates ( Zelinka, 1889).

Figures

FIGURE 3. Chaetonotus machikanensis n. sp., light (a) and scanning electron (b – d) microphotographs of holotype specimen. a, Coronal view. b, dorsal scale (neck). c, dorsal scale (trunk). d, ventral scales. Scale bars 10 μm in (a) and 2 μm in (b – d). Abbreviations: CE, cephalion; F, furca; INT, intestine; MR, mouth ring; PH, pharynx; SC, sensory cilium.

FIGURE 4. Chaetonotus machikanensis n. sp., line drawings of holotype specimen. a, Dorsal view; b, ventral view; c, dorsal scale (neck); d, dorsal scale (trunk). e, ventral scale; f, terminal plate and keeled ventral scale; g, dorsal terminal plate. Scale bars 5 μm. Abbreviations: CE, cephalion; DS, dorsal scale; DT, dorsal terminal plate; F, furca; KVS, keeled ventral scale; MR, mouth ring; SC, sensory cilium; TP, terminal plate; VC, ventral cilium; VS, ventral scale.