Anchistrocheles yamaguchii Yajima, 1987

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 : 78-81

Anchistrocheles yamaguchii Yajima, 1987

( Figs. 3C, D , 5C, D , 6 , 7 , 11 )

Anchistrocheles yamaguchii Yajima, 1987: 62 , Figs 5–3 , 4 , 11-3a, b , 4a, b .

Description. Carapace ( Figs. 3C, D , 6 ) characters almost corresponding to Anchistrocheles hayatotanakai sp. nov. Outline in dorsal view flat around middle. Surface covered with around 120 simple type pore systems.

Eye. Absent.

Antennule ( Fig. 7A ). Seven articulated podomeres, length ratio among them from proximal to distal 27: 23: 5: 9: 5: 3: 2. Chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Antenna ( Fig.7B ).Number and length ratio of podomeres and chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Mandibula ( Fig. 7C ). Number and length ratio of podomeres and chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Maxillula ( Fig. 7D ). Palp with 2 medium length setae on ventral margin of three-fourths from proximal end. Other chaetotaxy almost corresponding to A. hayatotanakai sp. nov.

Fifth limb in male ( Fig. 7E 1 ). Consisting of 4 articulated podomeres, length ratio among them from proximal to distal 9: 7: 5: 1. Second podomere with 2 long setae at middle of anterior margin. Third podomere with 1 short setulous seta on anterior distal end. Other chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Fifth limb in female ( Fig. 7E 2 ). Second podomere with 2 equal-length long setae on antero-distal corner. Number and length ratio of podomeres and other chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Sixth limb ( Fig. 7F ). First podomere with 1 very short and 1 medium length setae on anterior margin, 2 short setae on distal margin. Number and length ratio of podomeres and other chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Seventh limb ( Fig. 7G ). First podomere with 1 very short and 1 long setae on anterior margin, 2 short setae on distal margin. Number and length ratio of podomeres and other chaetotaxy almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Brush-shaped organ (in male) ( Fig. 7H ). Consisting of symmetrical paired lobes without seta. Located between 6th legs.

Male copulatory organ ( Fig. 5C ). Basal capsule semicircular with beak-like shape in distal part. Two clasping apparatus: proximal one (CA1) short and claw-like shape; distal one (CA2) almost straight. Copulatory duct arched.

Female copulatory organ ( Fig. 5D ). Outline blunt sub-triangular. Inside tube coiled 4 times, proximal part with appearance of twisted, wrung-out cloth.

Furca ( Fig. 5C, D ). Almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Caudal process ( Fig. 5C, D ). Almost corresponding to Anchistrocheles hayatotanakai sp. nov.

Dimensions. See Table 1B .

Occurrence. Type locality and at coarse sand beach at Arai-hama , Miura City, Kanagawa Pref., east-central Japan (Loc. 3 in Fig. 1C ) .

Remarks. Anchistrocheles yamaguchii is similar to Anchistrocheles hayatotanakai sp. nov. (see Remarks section of the latter). There is an equal number of clasping apparatus in the copulatory organs of both species, and there is no significant difference in the external shape of the distal lobe. The differences between the two species are relatively minor, suggesting that they are closely related, mainly based on the similarity of their other appendages. Many cytherocopine species have setulae on the male brush-shaped organs, but the organs in A. yamaguchii have no setulae. Other Anchistrocheles species have a convex carapace outline in dorsal view, but the outline of A. yamaguchii is flat in the middle. The carapace size of the holotype of A. yamaguchii is 0.743 mm in length and 0.376 mm in height ( Yajima 1987). These values were smaller than those of the specimens examined in this study ( Table 1B ). Previous studies have reported that carapace size depends on water temperature. For example, a study by Kamiya (1988b) showed seasonal changes in carapace size in Loxoconcha japonica Ishizaki, 1968 by monthly sampling. The maximum difference was between March (largest) and August (smallest), which was approximately 20%. The difference between the holotype of A. yamaguchii and the specimens illustrated in this study was within this range. Malz & Ikeya (1982) pointed out that the smaller fossil Pleistocene species Cythere simplex Hu, 1977 from Taiwan was a junior synonym of the larger extant species Cythere omotenipponica Hanai, 1959 from Japan. The carapace size of ostracods is difficult to diagnose.

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.

FIGURE 6. Carapace morphology of Anchistrocheles yamaguchii Yajima, 1987. A and B, external view of male right and left valves, respectively (SUM-CO-2495). C and D, internal view of male left and right valves, respectively (SUM-CO-2496). E and F, external view of female right and left valves, respectively (SUM-CO-2497). G and H, internal view of female left and right valves, respectively (SUM-CO-2498). I, dorsal view of male carapace (SUM-CO-2499). J, central muscle scars on female right valve (SUM-CO-2498). Scale 1: 200 µm for A–I. Scale 2: 20 µm for J.

FIGURE 7. Appendages of Anchistrocheles yamaguchii Yajima, 1987. 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–C and E1, male, SUM-CO-2491; D, F and G, male, SUM-CO-2493; E2, female, SUM-CO-2494. Scale: 100 µm.

FIGURE 11. Anatomical location of brush-shaped organ in Anchistrocheles yamaguchii Yajima, 1987. A, anatomical location among appendages. B, high magnification. Male, SUM-CO-2500. L5, fifth limb; L6, sixth limb; L7, seventh limb. Scale: ca. 35µm for A, ca. 10µm for B.