Chiridota impatiens, Yamana & Tanaka, 2017

Yamana, Yusuke & Tanaka, Hayato, 2017, A new species of Chiridota (Echinodermata: Holothuroidea: Apodida: Chiridotidae) from Japan, and First record of C. rigida from Japan, Zootaxa 4341 (2), pp. 243-257 : 250-254

Chiridota impatiens sp. nov.

Figures 3 , 4

Material examined. Holotype: WMNH-INV- 2016-56 (length 66.5 mm, width 4.1 mm). Paratype: WMNH-INV- 2016-57 (length 58.8 mm, width 5.7 mm).

Description. Body medium, cylindrical, length of holotype: 66.5 mm ( Table 1). Body colour, faint reddish brown or ochre yellow in preserved specimens ( Fig. 3A ), red or reddish brown in living specimens ( Fig. 3B ). Mouth anterior; anus posterior. Oral disc slightly inclined toward ventral side. Numerous verrucous surfaces present in inter-radius of anterior body skin, sparse posterior, high hemisphere form (preserved and living specimens). Colour of verrucous surfaces (preserved and living specimens) same as adjacent body skin in paratype specimen, but darker in holotype specimen.

Wheel-papillae, dense in dorsal, sparse in ventral, conical shape, diameter approximately 0.3–0.7 mm at basal part, restricted in inter-radius, colour white (preserved and living specimens). Contents of wheel-papillae forming a cord-shaped structure (preserved and living specimens), it can be emitted from the surface with breaking skin of papillae if it is stimulated in living state (possibly released by animal itself) ( Figs 3C, D ). All wheel papillae having a ‘cord’, width approximately 0.1–0.2 mm (preserved specimens), length approximately 2–5 mm (preserved specimens), having approximately 7–12 disorganized rows of wheel ossicles arrangement. Wheel ossicles in basal part of ‘cord’ larger than that in distal part. Each wheel ossicle connect with a short bunch cord to a long main line. Main line of ‘cord’, semitransparent, flexible, width approximately 0.03–0.06 mm (preserved specimens).

Polian vesicle 4–5 ( Table 1), one long and others short. Stone canal single ( Fig. 3E ), short, with funnel-shaped madreporite, opening just behind the calcareous ring. Only immature reproductive tubules observed. Intestine straight, with no loop. One narrow line of ciliated funnels situated in anterior to middle body cavity, in inter-radius of left lateral side. Ciliated funnels present separately, not gathering to make a stalked cluster.

Twelve tentacles, non-retractile, each with 4–7 pairs of digits (frequently unpaired digit present), distal pair largest ( Fig. 3G , Table 1), largest number of digits counted at ventral tentacles in two specimens. Sensory cups of 0–5 clusters presented in basal part of tentacles, facing to oral side, 3–12 cups gathering to make a cluster ( Fig. 3F, H ). Colour of tentacles paler than body skin (preserved and living specimens).

Calcareous ring composed of five radial and seven inter-radial plates, in which two inter-radial plates continuously presented in dorsal lateral side ( Fig. 4A ). Both radial and inter-radial plates with posterior depression, plates on ventral side larger than that on dorsal side. In both two specimens, radial plates with recognizable anterior notch, however, lacking perforation (even in medioventral).

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Tentacles containing flattened rod ossicles and curved rod ossicles ( Fig. 4B , Table 3). Flattened rod ossicles, elongated peanut shape, flat surface, without spine. Curved rod ossicles, crescent shape, sometimes with spines pointing outwards distally, and also rarely having low number of branches on middle part. Flattened rod ossicles, length 18–41 µm (means of 30 and 31 µm in different specimens), width 4–14 µm (means 7 and 8 µm) (Table 3). Curved rod ossicles, length 13–39 µm (means 22 and 26 µm), width 3–7 µm (means 4 and 4 µm) (Table 3).

Body wall containing curved rod, flattened rod, however wheel ossicles only in wheel papillae ( Figs 4C, D , Table 3). Flattened rod ossicles, mostly present along longitudinal muscle and along mesentery, elongated peanut shape, flat surface, without spine. Curved rod ossicles, mostly present in body wall, crescent shape, sometimes distally with spines on circumference, and also rarely having low number of branches on middle part. Both flattened rod and curved rod dense in body anterior, rare in posterior. Flattened rod ossicles, length 18–47 µm (means 32 and 34 µm) and width 3–13 µm (means 6 and 9 µm) in anterior ventral side, length 22–31 µm (means 24 and 35 µm) and width 7–13 µm (means 9 and 12 µm) in anterior dorsal side (Table 3). Curved rod ossicles, length 15–75 µm (means 34 and 41 µm) and width 3–11 µm (means 5 and 6 µm) in anterior ventral side, length 17–74 µm (means 35 and 40 µm) and width 3–10 µm (means 6 and 6 µm) in anterior dorsal side (Table 3).

Wheel ossicles round form with six spokes (rarely 4–8 spokes present). Inner margin of rim mostly parallel to outer margin. Teeth of inner margin of rim sharp, however, large sized wheel ossicles (that present in basal part of ‘cord’) frequently incomplete, lacking teeth and having under-grown rim and spoke. In anterior dorsal side, complete form of wheel ossicles, diameter 39–94 µm (means 58 and 75 µm), with 8–15 teeth per radiant (means 11 and 13), and spoke width composing 15–31% of diameter (means 20 and 22%) ( Fig. 4C , Table 3). In posterior dorsal side, complete form of wheel ossicles, diameter 37–96 µm (means 62 and 76 µm), with 8–16 teeth per radiant (means 11 and 13), and spoke width composing 16–31% of diameter (means 21 and 21%) ( Fig. 4C , Table 3).

Distribution. So far known only from the type locality, in sandy-gravel sediment (depth of approximately 10– 30 cm from surface) just upper the tide pool surface in the south part of calm beach, Sesoko Island, Okinawa, southern Japan.

Ecology. At the type locality, the new species co-occurred with Taeniogyrus roseus ( Ohshima, 1914) . The density of T. roseus was very high, collected approximately 20 or more individuals per 1 m 2, however the new species was very rare, collected only two individuals from the area of 5 m 2 or more.

Etymology. The specific name impatiens is derived from a Latin word meaning “impatient”, the property of wheel-papillae of this species.

DNA barcode sequence. The 819bp sequence of the mitochondrial CO1 gene was obtained from a holotype specimen (WMNH-INV- 2016-56, GenBank accession number LC 271194 ). Base frequency was A=15.0%, C=17.5%, G=26.9%, T=40.7%.

Figures

FIGURE 3. A, preserved specimen; and B, living specimen of Chiridota impatiens sp. nov., lateral view, dorsal upper (holotype, WMNH-INV- 2016 - 56). C, wheel-papilla with emitted content of it; D, content of wheel-papilla; and E, stone canal of C. impatiens sp. nov. (holotype, WMNH-INV- 2016 - 56). F, oral side; and G, outer side of left lateral tentacles; with H (enclosed area with solid line in F), a cluster of sensory cups of C. impatiens sp. nov., dorsal upper (holotype, WMNH-INV- 2016 - 56). Abbreviations: ad, anterior dorsal; av, anterior ventral; ca, calcareous ring; ma, madreporite; pd, posterior dorsal; pv, posterior ventral; st, stone canal; te, tentacle.

FIGURE 4. A, SEM image of calcareous ring of right side of Chiridota impatiens sp. nov. (holotype, WMNH-INV- 2016 - 56), viewed from right side, dorsal upper. B – D, SEM images of ossicles (paratype, WMNH-INV- 2016 - 57). B, ossicles from a tentacle of lateral side; C, ossicles from wheel papillae of anterior dorsal; D, ossicles from wall of anterior dorsal. Abbreviations: cr, curved rod ossicles; fr, flattened rod ossicles; ip, inter-radial plate; rp, radial plate; wh, wheel ossicles; wh', internal side of wheel ossicles.