Arcotheres ocularius Komai & Kawai & Ng 2020, n. sp.
Creators: name: Komai, Tomoyuki
name: Kawai, Kei
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pinnotheridae
Arcotheres
Arcotheres ocularius

description: Arcotheres ocularius n. sp.
(Figs. 7–17)
Type material. Holotype: CBM-ZC 15952, ovigerous female (10.2× 11.8 mm), Kumi Village, Viti Leve, Fiji, 17°53.21’S, 178°36.07’E, intertidal, associated with Anadara sp. (Bivalvia: Arcidae), 16 August 2010, coll. K. Kawai.
Paratypes (all but CBM-ZC 15962 from same locality and host as holotype; females are all in post-hard stage V): ZRC 2019.1877, 1 female (8.2× 8.9 mm), 3 ovigerous females (8.4×9.6, 9.7×10.9, 11.9× 12.3 mm), 16 August 2010; CBM-ZC 15953, 2 females (5.0×5.5, 6.4× 6.9 mm), 17 ovigerous females (7.4×8.5–9.6× 13.4 mm); CBM-ZC 15954, 1 post-hard stage male (6.8× 6.2 mm), 16 August 2010; CBM-ZC 15956, 1 hard stage female, (5.2× 5.2 mm), 16 August 2010; CBM-ZC 15957, 1 hard stage male (5.0× 4.6 mm), 16 August 2010; CBM-ZC 15958, 2 pre-hard stage male (3.2×3.2, 3.4× 3.3 mm), 16 August 2020; CBM-ZC 15959, 1 post-hard stage male (5.8× 5.8 mm), 16 August 2010; ZRC 2020.0007, 1 post-hard stage male (5.4× 4.8 mm), 16 August 2020; CBM-ZC 15960, 1 ovigerous female (9.1× 10.7 mm), 6 September 2011; CBM-ZC 15961, 7 ovigerous females (7.2×8.6–9.5× 10.7 mm), August 2018; ZRC 2020.0008, 5 ovigerous females (8.0×9.4–9.3× 10.7 mm), August 2018; CBM-ZC 19562, 1 ovigerous female, Ucikumi, near Kumi Village, 22 February 2019.
Other material examined. Fiji. CBM-ZC 15955, 1 young female (post-hard stage; 4.0× 3.9 mm), same data as holotype; ZRC 2019.1878, 4 poorly preserved females (3.3×4.2–4.6×6.0 mm), same data as holotype.
Indonesia. ZRC 2019.1025, 1 female (8.4× 9.4 mm), Teluk Kodek, Lombok, intertidal, in Anadara antiquata (Linnaeus, 1758) (Arcidae), 12 November 2013, coll. S. Dwiono.
Description. Adult females (post-hard stages). Carapace (Figs. 7 A–D, 8A) subcircular, 1.1–1.3 times as wide as long; dorsal surface gently convex, smooth, glabrous; lateral surfaces also smooth, glabrous; front projecting anteriorly beyond orbits, entire, margin slightly convex; anterior quarter of anterolateral margin gently sloping posteriorly, forming slight angle with rest of slightly convex margin.
Eyes (Figs. 7C, D, 8A, B) small, visible in dorsal view, movable, completely filling orbit.
Antennular peduncles (Fig. 8B) folded obliquely into antennular fossae. Antenna (Fig. 8B) extending along lateral margin of front; article 2 subtriangular.
Maxilliped 3 (Fig. 8C, F, G) outer surface glabrous; propodus moderately stout, distinctly longer than carpus; dactylus short, digitiform, inserted submedially on flexor margin of propodus, tip just reaching propodal apex; ischiomerus completely fused, distinctly longer than wide, mesial margin angular at widest point. Exopod slender, about half length of ischiomerus (not illustrated).
Chelipeds (Figs. 7A, B, E, 9 A–E) moderately long, symmetrical. Dactylus about 0.6 times as long as palm, terminating in hooked, acute tip; upper margin rounded, gently convex; occlusal margin with 1 prominent, proximally directed, triangular tooth proximally and row of sparse short setae distal to occlusal tooth. Palm slightly widened distally, 1.9 times as long as high; outer surface glabrous; inner surface almost glabrous, but with longitudinal row of short setae adjacent to lower margin, extending onto fixed finger, becoming multiple rows. Fixed finger terminating in hooked, acute tip, bearing short longitudinal row of stiff setae on inner surface distally; occlusal margin with 2 small teeth flanking occlusal tooth on dactylus, margin between 2 teeth denticulate, margin distal to occlusal tooth slightly convex, laminar, bearing row of minute stiff setae. Carpus short, cup-shaped, glabrous on dorsal and outer surfaces; inner surface with sparse thin setae. Merus nearly straight slightly compressed laterally, slightly widened distally; outer and inner surfaces almost glabrous, former gently convex.
P2, P3 and P5 symmetrical, P4 longest, asymmetrical; relative length of meri P4>P3>P2>P5. P2 (Figs. 7, 9F, G) moderately long, slender, entirely glabrous; dactylus short, noticeably curved, terminating in acute tip, 0.5–0.6 times as long as propodus; propodus slightly narrowing distally, longer than carpus; merus somewhat compressed, almost straight. P3 (Figs. 7, 9H, I) generally similar to but slightly longer than P2; dactylus short, curved, about half-length of propodus. Longer P4 (Figs. 7, 9L, M)) about 1.2 times as long as shorter P4; dactylus slender, 0.9–1.0 times as long as propodus, approximately 10 times as long as wide, gently curved proximally, terminating in acute tip; surfaces almost glabrous except for subapical long seta on flexor margin; propodus slightly curved, more slender than those of P2 and P3; carpus curved at base; merus more slender than those of P2 and P3, glabrous; ischium-merus articulation oblique, ischium glabrous. Shorter P4 (Figs. 7, 9J, K) dactylus slightly arcuate, approximately 6 times as long as wide, 0.6–0.7 times as long as propodus, still longer than dactyli of P2 and P3, terminating in curved corneous claw; extensor surface with scattered minute setae; flexor margin with irregular rows of short, feather-like setae; propodus, carpus and merus generally similar to those of longer P4, but respective article shorter than corresponding article of longer side; ischium with sparse short setae on posterior surface. P5 (Figs. 7, 9N, O) propodus to merus shorter and slender than corresponding articles of P2 and P3; dactylus long (but shorter than that of longer P4), subequal in length to propodus, approximately 9 times as long as wide, slightly arcuate, gradually tapering to acute tip, extensor margin and upper surface with scattered short setae in distal half, flexor margin with numerous short setae becoming dense and longer distally, no comb-like rows of minute spiniform setae; propodus faintly curved, almost glabrous except for subterminal tuft of long setae on flexor margin; carpus glabrous, substantially curved; merus faintly sinuous, not narrowing proximally, glabrous; merus-ischium articulation straight.
Thoracic sternite very wide. Sternites 1–4 (Fig. 8D) fused, slightly narrowing anteriorly; narrow incision at base of maxilliped 3, suggesting boundary between sternites 3 and 4, still discernible; anteromedian margin faintly concave; anterolateral angles produced in rounded lobe; surface almost flat.
Pleon (Figs. 7, 8E) extremely wide, extending to buccal region, covering bases of ambulatory legs; telson very broad, partially recessed into distal margin of pleomere 6.
Female hard stage. Generally similar to male hard stage (see below) (Fig. 10A). P3 and P4 provided with natatory setae (Figs. 10, 11 C–E). P2 (Fig. 11B) dactylus with row of short setae on flexor margin. P3 (Fig. 11C) dactylus more stout than in hard stage male. Longer P4 (Fig. 11E) dactylus only with subapical setae on flexor margin, as in post-hard stage. Pleon (Fig. 10E) slightly wider than that of hard males; pleomeres 2–4 each with paired biramous pleopods; telson 1.3 times wider than long, roundly subhexagonal.
Male hard stage. Carapace (Figs. 12, 13A) well calcified, rounded, subcircular, 1.1 times as long as wide; dorsal surface convex, without demarcation of regions, with scattered minute pits laterally; front weakly projecting anteriorly beyond orbits, margin nearly straight with faint median notch in dorsal view; lateral angle of front produced into small triangular process directed downward, but not closing orbit (Fig. 11B).
Eyes (Fig. 13A, B) moderately small, clearly visible in dorsal view completely filling orbit.
Antennular peduncles (Fig. 13B) folded obliquely into antennular fossae. Antenna (Fig. 13B) extending along lateral margin of front; article 2 subtrapezoidal, narrowing distally.
Maxilliped 3 (Fig. 13C) generally similar to that of females, but inner margin of ischiomerus more strongly concave.
Chelipeds (Figs. 12, 14A, B) moderately large, symmetrical. Dactylus about 0.8 times as long as palm, strongly curved, terminating in hooked, acute tip; upper margin rounded; occlusal margin with 1 conspicuous triangular tooth proximal to midlength and with row of sparse short setae. Palm slightly widened distally, 1.3 times as long as high; outer surface almost glabrous, but with sparse minute pits; inner surface almost glabrous, but with longitudinal row of short to long setae adjacent to lower margin, extending onto fixed finger, becoming multiple rows. Fixed finger terminating in hooked, acute tip; occlusal margin with 2 or 3 small teeth proximal to midlength, flanking occlusal tooth on dactylus, and with row of minute setae distal to midlength. Carpus distinctly shorter than palm, somewhat inflated, with sparse minute pits. Merus slightly curved inwards, slightly compressed laterally; outer surface convex, glabrous, lower distal angle somewhat produced; inner surface with few short setae.
P2, P3 and P5 symmetrical, P4 longest, asymmetrical; natatory setae present on propodi and carpi of P3 and P4 (Figs. 10, 12 D–F). P2 (Figs. 12, 14C) generally glabrous except for row of sparse short setae on flexor margin of propodus; dactylus curved, half-length of propodus; carpus curved proximally; merus almost straight, slightly widened distally. P3 (Figs. 12, 14D) dactylus slender than that of P2, about 0.6 times as long as propodus, extensor margin with row of short setae; propodus with low of long natatory setae on upper surface adjacent to extensor margin and flexor margin, respectively; carpus upper surface with oblique low of long natatory setae. P4 (Figs. 12A, 14E, F) longer dactylus 1.3 times as long as shorter dactylus, slightly arcuate, gradually tapering distally to acute tip, extensor margin glabrous, flexor margin with row of sparse setae (distalmost subterminal seta elongate); shorter dactylus with low of long setae on extensor margin and sparse short setae on flexor margin; propodus with long natatory setae on upper surface adjacent to extensor margin and on flexor margin; carpus with oblique row of natatory setae on upper surface; merus nearly straight, glabrous. P5 (Figs. 12, 14G) shortest; dactylus slightly arcuate, 0.8 times as long as propodus, approximately 8 times as long as wide; extensor margin with rows of short setae at least on distal half, flexor margin with sparse longer setae; propodus almost glabrous except for sparse long setae on lower margin; carpus glabrous, gently curved; merus subcylindrical, straight, with row of moderately long setae on upper margin; ischium slightly wider than merus, about half-length of merus.
Thoracic sternum (Fig. 13 D–G) broad. Sternites 1–4 fused, slightly narrowing anteriorly; narrow incision at base of maxilliped 3, suggesting boundary between sternites 3 and 4, still discernible; broad anteromedian concavity well delimited; anterolateral angles produced in rounded lobe; surface almost flat. Exposed parts of sternites 5–7 nearly smooth, each posteriorly with small but conspicuous, rounded episternites. Sternite 8 clearly visible in lateral part; lateral margin almost entire. Sterno-pleonal cavity (Fig. 13F) deep, defined by clearly delimited margin, widened anteriorly (corresponding to telson), reaching anteriorly to level of anterior ends of cheliped coxae; press button on sternite 5 relatively large, rounded; sternite 6 with pair of large, rounded protuberance accommodating lateral margin of G1.
Pleon (Fig. 13H) moderately narrow, tapering distally to pleomere 6; lateral margins of pleomeres 3 generally rounded, those of sternite 4 slightly concave. Pleomeres 1 and 2 subequal in width, longitudinally very short. Pleomere 3 widely subtrapezoidal. Pleomeres 4–6 all subtrapezoidal. Telson subhexagonal, 3.6 times wider than long, maximal width greater than distal width of pleomere 6; distal margin nearly straight, lateral margin angular.
G1 (Fig. 13I, J) noticeably arcuate outward and slightly twisted, dorsoventrally compressed, gradually tapering to subacutely pointed apex, reaching to anterolateral end of sterno-pleonal cavity; ventral surface with irregular rows of setae extending to lateral margin. G2 (Fig. 13K) biramous; endopod narrowing distal to midlength; exopod well developed, flattened, evenly tapering to rounded apex, slightly longer than endopod. Pleopods 3–5 absent.
Male post-hard stage. Carapace (Fig. 15A) well chitinised but less calcified than in hard stage, rounded, subcircular, 1.1 times as long as wide; dorsal surface convex, without demarcation of regions, glabrous (no minute pits); front weakly projecting anteriorly beyond orbits, margin broadly rounded; lateral angle of front produced into small triangular process directed downward, but not closing orbit.
Eyes (Fig. 15A) small, clearly visible in dorsal view, completely filling orbit.
Antennular peduncles folded obliquely into antennular fossae. Antenna extending along lateral margin of front; article 2 subtrapezoidal, narrowing distally.
Maxilliped 3 (Fig. 16A) similar to that of adult females.
Chelipeds (Fig. 15A, 16B) rather small, symmetrical. Dactylus 0.6 times as long as palm, strongly curved, terminating in hooked, acute tip; upper margin rounded; occlusal margin with 1 conspicuous tooth proximal to midlength and with row of sparse short setae. Palm slightly widened distally, 1.6 times as long as high; outer surface glabrous; inner surface almost glabrous, but with longitudinal row of short setae adjacent to lower margin, extending onto fixed finger, becoming multiple rows. Fixed finger terminating in hooked, acute tip; occlusal margin with 2 small teeth proximal to midlength, flanking occlusal tooth on dactylus, and with row of short setae distal to proximal teeth. Carpus distinctly shorter than palm, widened distally, glabrous. Merus slightly curved inwards, slightly compressed laterally; outer surface convex, glabrous, lower distal angle somewhat produced.
Ambulatory legs (Fig. 15A) relatively shorter and slender compared with those of hard stage males, P3 longest; no natatory setae on every pereopod; P2, P3 and P5 symmetrical, P4 with asymmetrical dactyli. P2 (Figs. 15A, 16D) entirely glabrous; dactylus curved, half-length of propodus; carpus curved proximally; merus almost straight, slightly widened distally. P3 (Figs. 15A, 16E) generally similar to P2 except for length; dactylus about 0.6 times as long as propodus; carpus lower surface with scattered short setae, otherwise glabrous. P4 (Figs. 15A, 16F, G) with left dactylus slightly longer than right dactylus (left 1.1 times as long as right), 0.9 times as long as propodus, extensor margin glabrous, flexor margin with 2 long subterminal setae followed by row of sparse short setae; shorter right dactylus 0.7 times as long as propodus, flexor margin with 1 long subterminal seta followed by fewer short setae; propodus to merus glabrous; carpus longest among ambulatory legs; merus nearly straight. P5 (Figs. 15A, 16H) shortest; dactylus slightly arcuate, subequal in length to propodus, approximately 9 times as long as wide; extensor margin with irregular rows of short setae on distal half, lower margin with row of setae becoming longer distally; propodus almost glabrous except for sparse short setae on lower margin; carpus glabrous, gently curved; merus subcylindrical, straight, also glabrous; ischium slightly wider than merus, about half-length of merus.
Thoracic sternum broad. Sternites 1–4 (Fig. 153B) fused, narrowing anteriorly; narrow incision at base of maxilliped 3, suggesting boundary between sternites 3 and 4, still discernible; broad anteromedian concavity well delimited; anterolateral angles produced in rounded lobe; surface almost flat. Exposed parts of sternites 5–7 (Fig. 15C) nearly smooth, each posteriorly with small but conspicuous, rounded episternites. Sternite 8 (Fig. 15D) clearly visible in lateral part, lateral margin deeply notched. Sterno-pleonal cavity (Fig. 15E) deep, defined by sharply delimited margin, widened anteriorly (corresponding to telson), reaching anteriorly to level of anterior ends of cheliped coxae; pleon locking apparatus consisting of 2 press buttons on either side on sternite 5 inside of cavity; sternite 6 with trace of low elevation on either side.
Pleon (Fig. 15F) moderately narrow, tapering distally to pleomere 6. Pleomeres 1 and 2 subequal in width, longitudinally short. Pleomere 3 widely subtrapezoidal; lateral margins convex. Pleomeres 4–6 all subtrapezoidal; lateral margins of pleomere 4 concave. Telson (Fig. 15F) pentagonal, 1.8 times wider than long, maximal width greater than distal width of pleomere 6, distal margin slightly produced medially.
G1 (Fig. 15G, H) noticeably arcuate outward and slightly twisted, dorsoventrally compressed, gradually tapering to bluntly pointed apex; ventral surface with irregular rows of short setae adjacent to lateral margin. G2 (Fig. 15I) endopod abruptly tapering at midlength to blunt apex, about 0.2 length of G1; exopod well developed, slender, flattened, evenly tapering to blunt apex, slightly longer than endopod. Pleopods 3–5 absent.
Variation. Carapace shape is not a stable character; even in the series of specimens of A. ocularius examined, the carapace of ovigerous females varies from broadly ovate (Fig. 7A) to almost circular (Fig. 7B, C).
Colour in life. Entirely whitish; female ovary, visible through integument, orange; cornea of eye red (Fig. 17).
Distribution. Fiji and Indonesia (Lombok); intertidal; exclusively associated with of Anadara spp. (unidentified).
Remarks. Arcotheres ocularius n. sp. is most similar to A. arcophilus and a group of four nominal species closely allied to A. palaensis. This group includes A. rhombifer (Bürger, 1895), A. guinotae Campos, 2001, and two species currently in Pinnotheres but clearly also referable to Arcotheres, A. onychodactylus (Tesch, 1918) comb. nov. and A. paralatissimus (Dai & Song, 1986) comb. nov. (PKLN & S.T. Ahyong, unpublished data). All differ from A. ocularius in the same features as discussed for A. palaensis, below. In addition, Japanese specimens identified as “ Arcotheres alcocki ” by Takeda & Konishi (1988) actually represent A. palaensis after re-examination of the material (NSMT-Cr 9363). Additional specimens of this taxon from Japan were also obtained for comparisons (see Material and methods).
In A. ocularius n. sp., the carapace is distinctly more strongly chitinised and calcified, with the cuticle stiff and relatively rigid (versus cuticle distinctly less chitinised and softer, even in fresh specimens of A. palaensis); eyes are clearly visible in the dorsal view in A. ocularius n. sp. (Fig. 7 A–C, 8A) (versus eyes are not visible or occasionally, only the edge of the eye is visible in A. palaensis; Ahyong & Ng 2007: fig. 9A; PKLN & S.T. Ahyong, unpublished data); the maxilliped 3 dactylus reaches to or extends beyond the tip of the propodus in A. ocularius n. sp. (Fig. 8C, F, G, 16A) (versus the maxilliped 3 dactylus is always shorter, never reaching the tip of the propodus in A. palaensis; cf. Ahyong & Ng 2007: fig. 9C); the female P4 merus and propodus are proportionately longer in A. ocularius n. sp. (Fig. 9L) (versus proportionately shorter in A. palaensis; Ahyong & Ng 2007: fig. 9A); the male telson is subpentagonal or subhexagonal in A. ocularius n. sp. (Figs. 13H, 15F) (versus semicircular in A. palaensis; cf. Takeda & Konishi 1988: fig. 3C, as P. alcocki); and the G1 has the tip subtruncate (Figs. 13I, J, 15G, H) (versus the tip of the G1 has an elongated slender projection in A. palaensis; cf. Takeda & Konishi 1988: fig. 3D, E, as P. alcocki). Arcotheres ocularius n. sp. and A. palaensis are both associated with Anadara spp., but A. palaensis is also reliably known from Barbatia species (also Arcidae) (Takeda & Konishi 1988; Campos 2001; Watanabe & Henmi 2008; Watanabe 2013; PKLN & S.T. Ahyong, unpublished data). Schmitt et al. (1973) also listed Mactra (Mactridae) and Placuna (Placunidae) as host bivalves for A. palaensis but these records are probably incorrect and the pinnotherid species was probably misidentified. For Placuna from Singapore, at least, Ng (2018) showed that the species present is A. placunicola Ng, 2018.
Compared to A. arcophilus, in which the eyes are also distinctly visible in the dorsal view, in A. ocularius n. sp. the maxilliped 3 dactylus reaches to or extends beyond the tip of the propodus (Figs. 8C, F, G, 16A) (versus never reaching the tip of the propodus in A. arcophilus; cf. Ahyong & Ng 2007: fig. 2C), the female P4 merus is proportionately longer in A. ocularius n. sp. (Fig. 9L) (versus proportionately shorter in A. arcophilus; cf. Ahyong & Ng 2007: fig. 2A), the male telson is subpentagonal or subhexagonal in A. ocularius n. sp. (Figs. 13H, 15F) (versus semicircular in A. arcophilus; Ahyong & Ng 2007: fig. 2E), and the G1 is C-shaped with the tip subtruncate in A. ocularius n. sp. (Figs. 13I, J, 15G, H) (versus G1 more slender and elongate, being only broadly arcuate with the tip possessing an elongate projection in A. arcophilus; PKLN & S.T. Ahyong, unpublished data).
In an ongoing genetic study of Asian pinnotherids, the Fijian and present Lombok specimens cluster closely with each other, distinct from what is here defined as A. palaensis s. str. on the basis of the 16S mitochondrial gene (Tsang Ling-Ming, pers. comm.). Lombok actually has both species, with another Lombok female specimen (ZRC 2018.762) clustering with A. palaensis s. str. instead.
Etymology. The specific epithet “ ocularius ” (= optic) refers to the dorsally visible eyes in the new species.
description: Published as part of Komai, Tomoyuki, Kawai, Kei & Ng, Peter K. L., 2020, On the identity of the poorly known pea crab, Pinnothera obesa Dana, 1852, and description of a new species of Arcotheres Manning, 1993 from the Southwest Pacific (Decapoda: Brachyura: Pinnotheridae), pp. 221-247 in Zootaxa 4822 (2) on pages 232-244, DOI: 10.11646/zootaxa.4822.2.5, http://zenodo.org/record/4401461