Neonesidea arenalocus, Asaba & Asaba & Tsukagoshi, 2024

Asaba, Erika, Asaba, Reina & Tsukagoshi, Akira, 2024, Three new interstitial species of the genus Neonesidea (Bairdioidea: Podocopida: Ostracoda) from the infralittoral zone in Japan, Zootaxa 5397 (3), pp. 377-396 : 381-382

Neonesidea arenalocus sp. nov.

( Figs. 5 , 6 , 7A, B , 12C, D )

Neonesidea sp. I: Ito & Tsukagoshi 2022 , Fig. 8 and Tables 1‒3 .

Type series. All examined specimens collected at the upper infralittoral zone of coarse sand beach in Miho-Masaki Beach, Shizuoka City, Shizuoka Prefecture (35° 01′ 14″ N, 138° 31′ 15″ E; Loc. 1 in Fig. 1 ) on 18 June 2015. Holotype: adult male ( SUM-CO-2522 ), right valve length 0.89 mm, height 0.44 mm, left valve length 0.88 mm, height 0.48 mm, appendages mounted on glass slide and valves preserved in cardboard cell slide . Paratypes: 5 adult males ( SUM-CO-2517 , 2518 , 2521 , 2523 and 2524 ) and 3 adult females ( SUM-CO-2519 , 2520 and 2525 ).

Etymology. Latin arena (sand) and locus (space), owing to the habitat of this species.

Description. Carapace ( Figs. 5 and 12C, D ) small and thin, compressed laterally, streamlined subhexagonal in lateral view. Dorsal margin of right valve almost straight, making slightly steep slope with ventral margin. Biconvex-lens shape in dorsal view. Carapace epidermis semi-translucent. Surface throughout smooth with numerous sensilla of simple-type pore systems. Left valve larger and rounder than right valve, and overlapping right valve along dorsal and ventral margins. Anterior and posterior margins of right valve developing frills, posterior one serrated. Left valve without frill. Adductor muscle scars consisting of 8 elongated diagonally. Mandibular scar separated in two. Fulcral point just in front of top row of adductor muscle scars. Hingement weak and simple: right valve bearing simple bar with dorsal groove; left valve bearing groove with dorsal shelf. More than 10 auxiliary fine dentitions at centre of interior ventral margin in male left valve, but no complementary structure in right valve.

Eye. Naupliar eye. No eye spot on carapace.

Antennula ( Fig. 6A ). Seven articulated podomeres, approximate length ratio among them from proximal to distal 15: 8: 2: 3: 1: 2: 2. Three terminal podomeres with much longer setae than total length of antennule podomeres. First podomere with a few comb-like rows of setulae at antero-distal corner. Second podomere with 1 medium seta on posterior margin. Third podomere with 1 long apical seta on posterior distal end and 2 very short setae at antero-distal corner. Fourth podomere with 1 short apical seta at both anterior and posterior corners, respectively. Fifth podomere with 2 very long setae on both antero- and postero-distal ends. Sixth podomere with 2 and 3 very long setae on antero- and postero-distal ends, respectively. Seventh (terminal) podomere with 5 very long setae on distal end.

Antenna ( Fig. 6 Bm). Male with 5 articulated podomeres, approximate length ratio among them from proximal to distal 13: 9: 5: 18: 3. First podomere (protopodite) bearing 1 long and 1 medium-length setae on distal margin and assemblage (reduced exopodite) of 1 long and 2 short setae in distal end. Second podomere bearing 3 long setae on postero-proximal margin, and 1 long and 1 medium-length apical seta at postero-distal corner. Third podomere with 1 long and 1 medium-length setae at postero-distal corner. Fourth podomere with 1 short seta on middle of anterior margin, 1 medium-length setulous apical seta at postero-distal corner and 2 short apical setae on antero-distal margin, and assemblage of numerous short setulae along postero-distal margin. Fifth (terminal) podomere of male bearing 1 large terminally bifurcated claw with 1 tiny spine on posterior-distal margin, 1 short seta on antero-distal margin and 1 medium setulous seta on posterior-distal margin. Female antenna similar to that of male except fifth podomere ( Fig. 6 Bf) bearing 2 terminal claws, and 1 long and 1 medium-length seta on distal end.

Mandible ( Fig. 6C ) consisting of 5 podomeres, approximate length ratio among them from proximal to distal 30: 7: 4: 6: 4. First podomere (coxa) bearing masticatory part of 4 stout denticles, several very short thin setae on distal end, and one short simple seta on anterior margin. First podomere of palp (basis) with 1 medium-length seta and 1 short seta on antero-distal corner and middle of distal end, respectively. Branchial plate (reduced exopodite) consisting of 1 very long stout setulous, 1 long and 1 medium-long setulous setae on dorso-proximal margin. Second podomere of palp (1st podomere of endopodite) with 2 setae on anterior-distal end, 1 seta on middle of distal end, and 2 long setae on middle of dorsal margin. Third podomere (2nd podomere of endopodite) of palp with 4 setae on ledge of dorso-median margin and 3 setae on anterio-distal end. Fourth (terminal) podomere bearing 2 short setae on middle of dorsal margin, 1 stout spatula-like seta with setulae along distal margin, and 3 setae on distal end.

Maxillula ( Fig. 6D 1 , D 2 ). Thin branchial plate (exopodite) with 25 plumose setae and 6 long reflexed setae. Basal podomere bearing 1 palp (endopodite) and 3 masticatory endites. Palp with 1 medium-length seta on middle of ventral margin, 3 medium-length setae on ledge of antero-distal margin, 1 simple and 1 spatula-like stout seta with numerous marginal setulae on distal margin. First (dorsal-most) endite bearing 2 brush-like stout seta with setulae along distal margin, and 2 short setae on antero-distal corner. Second endite with 3 short and 1 spatula-like seta on distal end. Third endite with 8 short setae on distal end and 1 short seta on middle of ventral margin.

Fifth limb ( Fig. 6E ) consisting of 5 articulated podomeres, length ratio among them from proximal to distal 18: 9: 6: 11: 1. First podomere with branchial plate (bearing 15 plumose setae and 2 reflexed setae on middle of ventral margin), 1 seta on anterior margin at three-fourths from proximal end, 2 setae on ledge on anterior margin at four-fifths from proximal end, and 2 long and 3 medium setae on distal end. Second podomere with 1 long and 1 medium apical seta at anterior distal corner. Third podomere with 1 medium-length apical seta at anterior distal corner. Fourth podomere with 1 short apical seta at anterior distal corner. Fifth podomere with 1 very short seta and 1 long, stout terminal claw on distal end.

Brush-shaped organ (in male) ( Fig. 6H ), consisting of asymmetrical paired branches. Longer and shorter branches with longer and shorter distal setae, respectively.

Sixth limb ( Fig. 6F ). Consisting of 5 articulated podomeres, approximate length ratio among them from proximal to distal 18: 11: 6: 13: 2. First podomere with 1 medium-length seta on anterior margin at one-third and two-thirds from proximal end, respectively, 2 medium-length setae on posterior margin at four-fifths from proximal end, and 2 short setae on distal end. Second podomere with 2 medium-length setae on antero-distal end. Third podomere with 1 medium-length apical seta at antero-distal corner. Fourth podomere with 1 short apical seta at antero-distal corner. Fifth podomere with 1 very short apical seta at antero-distal corner and 1 long terminal claw on distal end.

Seventh limb ( Fig. 6G ). Consisting of 5 articulated podomeres, approximate length ratio among them from proximal to distal 14: 10: 6: 15: 2. First podomere with 1 medium-length seta on anterior margin at one-third and two-thirds from proximal end, respectively, 2 medium-length setae on posterior margin at two-thirds from proximal end, 1 medium-length seta at anterior distal corner and on distal end, respectively. Second podomere with 2 apical setae at antero-distal corner. Third podomere with 1 medium-length apical seta at antero-distal corner. Fourth podomere with 1 short apical seta at antero-distal corner. Fifth podomere with 1 very short apical seta at antero-distal corner, and 1 very long terminal claw on distal end.

Furca ( Fig. 7A, B ) bearing 7 setae. Terminal-most 2nd seta (2) longest. Terminal-most 6th (6) and 7th (7) setae much shorter than others.

Caudal process ( Fig. 7A, B ). One simple seta, approximately 40–50 µm long.

Male copulatory organ ( Fig. 7A ). Basal capsule elliptical and consisting of some lobes. Distal lobe forming pliers-like shapes. Copulatory duct very long, curving around more than halfway of outline of basal capsule.

Female genital lobe ( Fig 7B ). Semicircular with doubly coiled spiral tube inside.

Dimension. See Table 1 .

Occurrence. Known only from type locality.

Remarks. The carapace size of interstitial Neonesidea species is smaller than the epiphytic Neonesidea species, and the length of the adult instar of the former is approximately corresponding to the A-1 instar of the latter. The slope of the hingeline of the right valve is steep in the interstitial species, but in the epiphytic species, it is very small and almost parallel to the ventral margin. Most of the appendage morphology of Neonesidea arenalocus sp. nov. is similar to that of the other two new interstitial species, N. alyamanai sp. nov. and N. alwakasaensis sp. nov. However, N. arenalocus sp. nov. can be distinguished from the other two new species by its pliers-like distal lobe in the male copulatory organ and the twice-coiled inside tube in the female copulatory organ. A species-specific tiny spine on the posterior distal margin of the terminal claw of the male antenna is present. This new species was the interstitial Neonesidea sp. I examined for carapace dimensions in Ito & Tsukagoshi (2022).

Figures

FIGURE 1. Map showing the sampling localities of Neonesidea species. Miho-Masaki Beach (Loc. 1), Motojima (Loc. 2), and Tai Beach (Loc. 3).

FIGURE 2. Sampling in Miho-Masaki Beach (Loc. 1 in Fig. 1). A, detailed location of Miho-Masaki Beach (Loc. 1). B, sampling scheme in Loc. 1, sediment materials were collected at eight points at 0.5 m intervals. C, individual number / 500 ml of Neonesidea arenalocus sp. nov. (grey bars at the back) and other ostracod species (black bars at the foreground). Materials were collected on 18 June 2015.

FIGURE 5. Carapace morphology of Neonesidea arenalocus sp. nov. A and B, male left and right valves, respectively (SUMCO-2517, paratype). C and D, internal view of male left and right valves, respectively (SUM-CO-2518, paratype). E and F, external view of female left and right valves, respectively (SUM-CO-2519, paratype). G and H, internal view of female left and right valves, respectively (SUM-CO-2520, paratype). I, dorsal view of male carapace (SUM-CO-2521, paratype). J, centre of internal ventral margin of male left valve (SUM-CO-2518, paratype). K, central muscle scars on female right valve (SUM-CO-2520, paratype). Scale: 200 μm for A–I, 50 μm for J, K.

FIGURE 6. Appendages of Neonesidea arenalocus sp. nov. A, antennule; Bf, antenna of female; Bm, antenna of male, C, mandibula; D1/D2, maxillula; E, 5th limb; F, 6th limb; G, 7th limb; H, brush-shaped organ. A and C, male holotype, SUM-CO-2522; Bf, female paratype, SUM-CO-2525; Bm, H and D2, male paratype, SUM-CO-2523; D1, E, F and G, male paratype, SUM-CO-2524. Scale:100 μm.

FIGURE 7. Copulatory organs, furcae, and caudal process of Neonesidea arenalocus sp. nov. (A, male holotype, SUM-CO2522; B, female paratype, SUM-CO-2525), Neonesidea alyamanai sp. nov. (C, male holotype, SUM-CO-2532; D, female paratype, SUM-CO-2535), and Neonesidea alwakasaensis sp. nov. (E, male holotype, SUM-CO-2542; F, female paratype, SUM-CO-2544). CD, copulatory duct; CP, caudal process; DL, distal lobe. Setae on furcae are numbered (1–7) from distal to proximal. Scale: 100 μm.

FIGURE 8. Carapace morphology of Neonesidea alyamanai sp. nov. A and B, male left and right valves, respectively (SUMCO-2526, paratype). C and D, internal view of male left and right valves, respectively (SUM-CO-2527, paratype). E and F, external view of female left and right valves, respectively (SUM-CO-2528, paratype). G and H, internal view of female left and right valves, respectively (SUM-CO-2529, paratype). I, dorsal view of male carapace (SUM-CO-2530, paratype). J, centre of internal ventral margin of male left valve (SUM-CO-2527, paratype). K, internal posterior-ventral margin of female left valve (SUM-CO-2529, paratype). Scale: 200 μm for A–I, 50 μm for J, K.

FIGURE 12. Carapace images by the X-ray micro CT scan in epiphytic Neonesidea sp. (A, B) and interstitial N. arenalocus sp. nov. (C, D). A and C, right lateral views; B and D, transversal views from anterior.