Anchistrocheles hayatotanakai, Ito & Tsukagoshi, 2022

Ito, Misumi & Tsukagoshi, Akira, 2022, Two species of the genus Anchistrocheles (Bairdioidea: Ostracoda: Crustacea) from Japan and their developmental characteristics for adaptation to interstitial environments, Zootaxa 5194 (1), pp. 71-91 : 73-78

Anchistrocheles hayatotanakai sp. nov.

( Figs. 2 , 3A, B , 4 , 5A, B )

Type series. All examined specimens collected at intertidal coarse sand beach in Miho-Uchihana, Shizuoka City , Shizuoka Prefecture (35°00′54″N, 138°31′51″E; Fig. 1A ) on 5 October 2017. Holotype: adult male (SUM-CO- 2481), carapace length 0.80 mm, height 0.39 mm, appendages mounted on glass slide and valves preserved in cardboard cell slide. Paratypes: 6 adult males ( SUM CO-2482–2484 , 2486 , 2487 and 2490) and 3 adult females (SUM-CO-2485, 2488 and 2489) .

Etymology. Named after Dr Hayato Tanaka (Kasai Aquarium, Tokyo, Japan), in recognition of his significant contribution to our knowledge on interstitial ostracod species.

Description. Carapace ( Figs. 2 and 3A, B ) streamlined sub-reniform in lateral view, surface extremely smooth, thin, and translucent. Outline convex in dorsal view. Marginal infold, with wide vestibule and about 40 short radial (marginal) pore canals, well developed along antero-ventral and postero-ventral margins. Left valve slightly larger than right valve and overlapping on both anterior and posterior ends of hingement. Surface covered with around 100 simple type normal (lateral) pore systems. Central muscle scars consisting of 4 adductor scars, 2 small elongated mandibular scars, 1 small elongated frontal scar, 1 limb scar in both valves. Hingement very simple: right valve bearing small blunt brim-like teeth at anterior and posterior ends; left valve bearing anterior and posterior elongated sockets with dorsal weak shelf.

Eye. Absent.

Antennule ( Fig. 4A ). Seven articulated podomeres and coxa, length ratio among them from proximal to distal 31: 24: 6: 7: 4: 2: 1. First podomere with numerous setulae along anterior and anterior distal margins. Second podomere with 1 long stout seta at posterior distal corner. Third podomere with 1 medium length seta at postero-distal corner and row of setulae on anterior distal margin. Fourth podomere with 1 medium length apical seta at antero-distal corner. Fifth podomere with 1 long and 1 very long setae on both antero- and postero-distal ends, respectively. Sixth podomere with 2 very long setae on antero- and postero-distal ends, respectively. Seventh (terminal) podomere with 5 very long distal setae longer than twice of total length of all seven podomeres.

Antenna ( Fig. 4B ). Coxa and five articulated podomeres, length ratio among them from proximal to distal 9: 16: 9: 7: 13: 4. Coxa with 1 long and 1 medium length setae at postero-distal corner. First podomere (basis) bearing reduced exopodite consisting of 1 long setulous, 1 medium length, and 1 very short setae on antero-distal end, and 1 long setulous seta on postero-distal end. Second podomere with 2 medium length setae at middle of posterior margin and 1 long seta on postero-distal end. Third podomere with 1 very short seta on posterior proximal margin, and 1 medium length and very1 short setae at posterior distal corner. Fourth podomere with 2 short setae on middle of anterior margin, 1 short seta on postero-proximal margin and 1 medium length stout setulous seta at posterior distal corner. Fifth (terminal) podomere with 1 long claw-like seta and 2 medium length setae on ledge on middle of posterior margin, and 1 very long stout terminal claw and 1 short seta on anterior distal end.

Mandibula ( Fig. 4C ). Consisting of 5 podomeres, length ratio among them from proximal to distal 47: 12: 4: 6: 5. First podomere (coxa) with masticatory part of several denticles and several very short thin setae on distal end. One short simple seta on anterior distal margin and numerous minute process on anterior ventral area. First podomere of palp (basis) with 1 setulous seta on anterior margin at one-third from distal end, 1 seta on distal end, and branchial plate (reduced exopodite) consisting of 1 very long and 2 medium-long plumose setae on dorsal margin. Second podomere of palp (1 st podomere of endopodite) with 1 setulous and 1 simple setae on distal end. Third podomere of palp with 1 long simple and 2 medium length setulous setae around middle of dorsal margin, and 1 short setulous and 1 medium length simple setae on anterior distal end. Fourth (terminal) podomere with 2 short setae on middle of dorsal margin, 2 brush-like terminal claws and 1 short seta on distal end.

Maxillula ( Fig. 4D ). Thin branchial plate (exopodite) bearing 25 plumose setae and 7 long reflexed setae. Basal podomere bearing 1 palp (endopodite) and 3 masticatory endites. Palp with 2 short setae on ventral margin at threefourths from proximal end, 5 medium length setae and 1 spatulate seta bearing fine setulae along distal end. First (dorsal most) endite with 2 short setae, 1 claw-like and 1 spatulate setae on distal end. Second endite with 3 short setae, 1 claw-like and 1 spatulate setae on distal end. Third endite with 1 short seta at middle of ventral margin, short claw-like and 7 short simple setae on distal end.

Fifth limb in male ( Fig. 4E 1 ). Consisting of 4 articulated podomeres, length ratio among them from proximal to distal 8: 8: 5: 1. First podomere with branchial plate bearing 9 plumose setae and 5 reflexed setae on ventro-distal margin, 1 very short and 1 long setae on anterior margin, and 2 long setae on antero-distal corner. Second podomere with 1 long and 1 medium length setae at middle of anterior margin. Third podomere with 1 very short setulous seta on anterior distal end. Fourth podomere with 1 very short thin seta and 1 long stout terminal claw on distal end.

Fifth limb in female ( Fig. 4E 2 ). Consisting of 5 articulated podomeres, length ratio among them from proximal to distal 40: 23: 7: 23: 4. First podomere with branchial plate bearing 9 plumose setae and 5 reflexed setae on ventro-distal margin, 1 very short and 1 long setae on anterior margin, 2 long setae on anterior-distal corner. Second podomere with 2 unequal-length long setae on antero-distal corner. Third podomere without setae. Fourth podomere with 1 short setulous seta on antero-distal corner. Fifth podomere with 1 very short thin seta and 1 long stout terminal claw on distal end.

Sixth limb ( Fig. 4F ). Consisting of 5 articulated podomeres, length ratio among them from proximal to distal 19: 14: 6: 12: 2. First podomere with 1 very short and 1 medium length setae on anterior margin, 1 short and 1 medium length setae on distal margin. Second podomere with 1 long setulous seta at anterior-distal corner. Third podomere without seta. Fourth podomere with 1 short setulous seta at anterior-distal corner. Fifth podomere with 1 very thin and short seta and 1 long curved terminal claw on distal end.

Seventh limb ( Fig. 4G ). Consisting of 5 articulated podomeres, length ratio among them from proximal to distal 20: 15: 6: 11: 2. First podomere with 1 very short and 1 long setae on anterior margin, 1 short and 1 medium setae on distal margin. Second podomere with 1 long setae at anterior-distal corner. Third podomere without seta. Fourth podomere with 1 short setulous seta at anterior-distal corner. Fifth podomere with 1 very thin short seta and 1 long curved terminal claw on distal end.

Brush-shaped organ (in male) ( Fig. 4H ). Consisting of paired symmetrical lobes, each bearing about 10 to 12 long thin setae.

Male copulatory organ ( Fig. 5A ). Basal capsule semicircular with beak-like shape in distal part. Two clasping apparatus: proximal one (CA1) with branched tip; distal one (CA2) curved. Copulatory duct arched.

Female copulatory organ ( Fig. 5B ). Outline blunt sub-triangular. Inside tube coiled 2 times and straight at proximal parts.

Furca ( Fig. 5A, B ). Bearing 1 very short seta at middle of ventral margin and 2 setulous setae at distal part, distal most one slightly longer than second most one.

Caudal process ( Fig. 5A, B ). One simple seta.

Dimensions. See Table 1A .

Occurrence. Miho-Uchihana, Shizuoka City, Shizuoka Prefecture (type locality, Loc. 2 in Fig. 1B ) and Motojima, Tanabe City, Wakayama Pref., Japan (Loc. 1 in Fig. 1A ) .

Remarks. Anchistrocheles hayatotanakai sp. nov. and A. yamaguchii Yajima, 1987 are similar except for the soft-parts characters: the male and female copulatory organs, furcae, and brush-shaped organs. In the new species the proximal clasping apparatus is branched at the tip, but that of A. yamaguchii has a sharp tip. The inner tube of the female copulatory organ is coiled two times in A. hayatotanakai sp. nov., but four times in A. yamaguchii . The middle seta on the furca is as long as the width of the furca in A. hayatotanakai sp. nov., but is shorter than that in A. yamaguchii . Furthermore, the distal most seta of the furca is slightly longer than the second distal most seta in A. hayatotanakai sp. nov., but both setae are of similar lengths in A. yamaguchii .

Yajima (1987) reported two Anchistrocheles species, A. yamaguchii and A. hondai , as new species from the Pleistocene Atsumi Formation in central Japan. However, the latter species could belong to the genus Orlovibairdia because of the numerous pits on the carapace surface and remarkable spines along the anterior and postero-ventral margins. Although there is no information on copulatory organs in the type specimen of A. yamaguchii , because they are fossil, the new species described herein can be distinguished from A. yamaguchii by the wider marginal infoldment and more convex carapace outline in dorsal view.

Figures

FIGURE 1. Map showing the sampling locations of Anchistrocheles species. Motojima (A, Loc. 1), Miho-Uchihama (B, Loc. 2), and Arai-Hama (C, Loc. 3).

FIGURE 2. Carapace morphology of Anchistrocheles hayatotanakai sp. nov. A and B, male right and left valves, respectively (SUM-CO-2486, paratype). C and D, internal view of male left and right valves, respectively (SUM-CO-2487, paratype). E and F, external view of female right and left valves, respectively (SUM-CO-2488, paratype). G and H, internal view of female left and right valves, respectively (SUM-CO-2489, paratype). I, dorsal view of male carapace (SUM-CO-2490, paratype). J, central muscle scars on male right valve (SUM-CO-2487, paratype). Scale 1: 200 µm for A–I. Scale 2: 20 µm for J.

FIGURE 3. Internal lateral view of the male carapace in two Anchistrocheles species. A and B, left and right valves of Anchistrocheles hayatotanakai sp. nov. (male paratype, SUM CO-2482), respectively. C and D, left and right valves of Anchistrocheles yamaguchii Yajima, 1987 (male, SUM-CO-2492), respectively. Scale: 100 µm.

FIGURE 4. Appendages of Anchistrocheles hayatotanakai sp. nov. A, antennule; B, antenna; C, mandibula; D, maxillula; E, 5th limb (E1, male; E2, female); F, 6th limb; G, 7th limb. H, brush-shaped organ. A, B, D, E1, F, and G, male holotype, SUM- CO-2481; C, male paratype, SUM-CO-2483; E2, female paratype, SUM-CO-2485; H, male paratype, SUM-CO-2484. Scale: 100 µm.

FIGURE 5. Copulatory organs, furcae, and caudal process of Anchistrocheles hayatotanakai sp. nov. (A, male holotype, SUM- CO-2481; B, female paratype, SUM-CO-2485) and Anchistrocheles yamaguchii Yajima, 1987 (C, male SUM-CO-2491; D, female SUM-CO-2494). CA1, clasping apparatus 1; CA2, clasping apparatus 2; CD, copulatory duct; CP, caudal process; DP, distal part of capsule. Scale: 100 µm.