Tmethypocoelis simplex sp. nov.

Figs 2, 3, 4, 5, 6, 7, 8, 9, 17A, C

Material examined.

Holotype. Indonesia • 1 ♂ (7.7 × 4.4 mm); Tosale, Banawa District, Donggala, Central Sulawesi; 0°45'57.1"S, 119°40'58.4"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; MZB. Cru. 5573.

Paratypes. Indonesia • 12 ♂ (4.0 × 2.5 - 7.9 × 4.6) , 6 ♀ (5.8 × 3.6 - 6.5 × 4.0 mm); Towale River, Central Banawa District, Donggala, Central Sulawesi; 0°43'29.3"S, 119°40'43.9"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; MZB. Cru. 5182 • 15 ♂ (4.1 × 2.6 - 7.7 × 4.4 mm), 4 ♀ (3.8 × 2.6 - 6.1 × 3.9 mm); same data as for holotype; MZB. Cru. 5183 • 4 ♂ (4.7 × 3.0 - 5.3 × 3.3 mm), 4 ♀ (4.0 × 2.5 - 5.6 × 3.3 mm); Towale River, Central Banawa District, Donggala, Central Sulawesi; 0°43'29.3"S, 119°40'43.9"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; ZRC 2023.0055 • 4 ♂ (4.0 × 2.5 - 5.1 × 3.0 mm); Towale River, Central Banawa District, Donggala, Central Sulawesi; 0°43'29.3"S, 119°40'43.9"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; OMNH-Ar.12758-12761 • 4 ♀ (5.8 × 3.5 - 6.6 × 4.0 mm); Towale River, Central Banawa District, Donggala, Central Sulawesi; 0°43'29.3"S, 119°40'43.9"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; OMNH-Ar.12762-12765 • 6 ♂ (5.5 × 3.4 - 6.7 × 4.0 mm), 5 ♀ (5.0 × 3.1 - 5.8 × 3.5 mm); Towale River, Central Banawa District, Donggala, Central Sulawesi; 0°43'29.3"S, 119°40'43.9"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; RMNH.CRUS.D.58046 • 3 ♂ (6.5 × 3.7 mm - 7.5 × 4.3 mm); Tosale, Banawa District, Donggala, Central Sulawesi; 0°45'57.1"S, 119°40'58.4"E; 17 Sep. 2020; coll. DC. Murniati, D. Permatasari, Hairul, A. Padju; QM W29642 .

Comparative material.

Tmethypocoelis liki Murniati, Asakura, Nugroho, Hernawan & Dharmawan, 2022: Indonesia • paratypes 5 ♂ (5.3 × 3.1 mm - 5.5 × 3.2 mm); Liki Village, Sarmi District, Sarmi Municipality, Liki Island, Papua Province; 01°37'25.29"S, 138°44'26.54"E; 21 Nov. 2018; coll. DC. Murniati; MZB.Cru.5012 .

Diagnosis.

Carapace pentagonal, ca. 1.7 × as wide as long (Fig. 2A). Branchial regions sloping; protobranchial, mesobranchial and metabranchial regions well-defined. Sub-branchial region bulging, bearing regular setae and tubercles. Posterior margin slightly concave, ca. 0.53 distance between exorbital angles. Exorbital angle triangular, acute, directed forward (Fig. 4A). Second anterolateral tooth of carapace slightly acute, slightly shorter than exorbital angle. Male pleon ca. 2 × as long as wide (Fig. 4E). Male chelipeds long (Fig. 5); palm bulky, ca. 1.4 × as long as wide; fingers shorter than palm; pollex short, triangular, cutting margin gently convex over entire length, without differentiated tooth or lobe; dactylus cutting margin evenly dentate, one enlarged wide convex tooth over proximal half, upper margin with one median row of granules in simple row, narrower distally (Fig. 5O). G1 long, curved, conspicuously slender; apical portion forming two poorly defined lobes, with three conspicuously curved setae on outer margin becoming slightly longer distally, two or three long setae apically, and four short setae on inner margin (Fig. 8A-E).

Description.

Carapace (Fig. 2A, B) pentagonal, weakly convex along mid-dorsal line, weakly convex laterally, ca. 1.7 × as wide as long. Dorsal surface smooth, lateral portion with granules, regions semi-defined; epigastric lobe poorly defined. Cervical grooves well-marked. Cardiac region with slight central depression. Branchial regions sloping; protobranchial, mesobranchial and metabranchial regions well-defined. Sub-branchial region bulging, bearing regular setae and tubercles. Carapace widest between exorbital angles. Intestinal and branchial borders poorly defined. Lateral margin of carapace recurved, with row of tubercles and short stout setae. Posterior margin weakly concave, ca. 0.53 distance between exorbital angles; fine ridge parallel to posterior margin forming broad rim. Front with lateral border moderately converging, width at base ca. 0.24 × distance between exorbital angles, ca. 0.21 at anterior margin; frontal angle rounded; anterior margin with small central blunt prominence (Fig. 3B). Exorbital angle triangular, acute, directed forward; anterior margin with microscopic tubercles, lateral margin glabrous; one short tubercular ridge parallel to supraorbital margin; posteriorly followed by broad U-shaped sinus. Second anterolateral tooth slightly acute, slightly shorter than exorbital angle. Posterolateral facet well-defined by crest originating anteriorly from base of exorbital angle (Fig. 4A). Supraorbital margin sinuous, sloping backward, microscopically tubercular. Infraorbital margin with medial notch; pterygostome with inwardly directed oblique channel; inner portion consisting of two granular ridges separated by shallow channel; upper ridge granular, with one row of setae; lower ridge granular, granules larger than those of upper ridge, without setation; outer portion granular, concave, ending in broad notch below exorbital angle (Fig. 4B).

Eyestalks long, not reaching exorbital angle, medial and distal diameters of similar width; projecting ocular style as long as cornea, tipped with setae; medial slope giving twisted appearance; cornea slightly bulging (Figs 2, 3B, 4C).

Third maxillipeds slightly vaulted, not completely covering buccal cavern. Ischium subquadrate; upper-mesial angle with wide triangular lobe; anterolateral angle narrow and triangular; mesial and lower margins with dense setae; lateral margin with setation medially; outer surface with oblique row of dense long setae, scattered granules distributed unevenly (Fig. 4D). Merus slightly larger than ischium; lateral margin convex, narrower distally, covered with short setae; mesial margin straight, with long setae; outer surface covered with scattered short setae (Fig. 4D). Carpus trihedral in cross section, mesial margin with dense long setae (Fig. 4D). Propodus short, margins tubercular and covered with dense setae (Fig. 4D). Dactylus slender, long, twice as long as propodus, margins tubercular, with long dense setae (Fig. 4D).

Male pleon (Fig. 4E) ca. 2 × longer than wide; noticeably constricted at base of pleonite 5 (Pl5). Pl1 trapezoidal, narrow, ca. 9.5 × wider than long; anterior margin ca. 0.7 × as long as posterior margin; ca. 1.3 × wider than Pl2. Pl2 ca. 7.5 × as wide as long. Pl3 ca. 3.0 × wider than long, anterior margin nearly straight, posterior margin convex. Pl4 ca. 2.9 × as wide as long, widest proximally, narrowing distally, distolateral angle pointed. Pl5 ca. 1.4 × wider than long (widest distally), markedly constricted at base. Pl6 ca. 1.4 × as wide as long; widest sub-distally; 1.1 × longer than Pl5; lateral margins subparallel, slightly concave. Male telson rounded, ca. 1.4 × wider than long (Fig. 4E).

Female pleon conspicuously broad (Fig. 4F). Pl1 shortest; Pl2 distinctly longer, as wide as Pl1; Pl3 trapezoidal, longer than Pl2; Pl4 rectangular, slightly longer than Pl3, lateral margins convex; Pl5 longer than Pl4; Pl6 distinctly longest. Female telson triangular (Fig. 4F).

Male chelipeds stout, long, equal. Merus cross-section triangular; standing higher than exorbital angle (Fig. 3C); lower margin covered with granules extending entire length, granulation branched sub-medially into two rows (Fig. 5A); upper margin narrower proximally, wider distally, with irregular rows of granules on distal half, proximal portion smooth (Fig. 5K); outer margin with a single row of granules extending whole length, granulation branched proximally (Fig. 5L); upper surface slightly convex, with ovate tympanum, microscopic granules outside tympanum, granulation mainly on distal portion, scattered setae (Fig. 5I); lower surface smooth, flattened, without tympanum (Fig. 5J); outer surface slightly convex, wider than upper surface, tympanum smaller than on upper surface, granules outside tympanum distributed evenly (Fig. 5B). Carpus shorter than merus, elongate, ca. 1.5 × as long as wide; upper and lower margins tubercular (Fig. 5C, D); outer surface rectangular, convex, microscopic granules only (Fig. 5E); inner surface shiny, with one oblique row of granules (Fig. 5F). Palm bulky, ca. 1.4 × wider than long; upper margin with one row of granules, distinct groove extending below granular rows forming clear granular string (Fig. 5G); lower margin granular, granulation branched into two rows medial to distal portion (Fig. 5H); inner surface irregularly granular, upper granulation extending over median portion, curved to sharply cut upper margin of outer surface and base of fingers, lower granulation extending near lower margin from proximal portion to base of pollex (Fig. 5M); outer surface distinctly granular over upper half to base of pollex, lower half smooth (Fig. 5N). Fingers shorter than palm, broadly gaping at base; curved inwards, expanded distally forming spooned-tip; cutting margins evenly serrated; inner margin at tip of both fingers with short row of stout setae. Pollex short, triangular, cutting margin evenly dentate; long flat enlarged dentate tooth over most of length, ca. 0.4 × as wide as palm; inner surface smooth (Fig. 5M); outer surface granular proximally parallel to cutting margin (Fig. 5N); lower margin granular nearly whole length (Fig. 5H). Dactylus ca. 0.6 × as wide as palm; cutting margin evenly dentate; one enlarged wide convex tooth over proximal half; inner surface granular from proximal to median portion near cutting margin, one clutch of granules proximally near upper margin (Fig. 5M); outer surface with 1 row of granules medially, densest on proximal portion of surface, granulation extending nearly entire length, irregular granulation near cutting margin, a single row of spaced tubercles medially, parallel to upper margin (Fig. 5N); upper margin with median row of granules, narrower distally matching shape of upper margin (Fig. 5O).

Female chelipeds small, of typical dotillid type (Figs 2B, 6). Merus with ovate tympanum on upper and lower surfaces. Fingers longer than palm, spooned-tip (Fig. 6). Pollex outer surface with one tubercular ridge parallel to lower margin; lower margin entire; cutting margin with very low denticles. Dactylus cutting margin without denticles.

Pereiopods slender, elongate, P2-P5 similar; smooth ovate tympanum on anterior and posterior surfaces of meri. Tympani on posterior surfaces becoming progressively smaller from P2-P5. Dactyli nearly straight, pointed, shorter than propodi.

P2 (Fig. 7A, B) shorter than P3; merus ca. 2.84 × longer than wide; anterior surface with scattered granules mainly near upper margin; posterior surface with sparse granules mainly near distal portion of tympanum; upper margin serrated, sparse long setae; lower margin smooth, sparse setae. Carpus subequal in length to propodus, surfaces smooth; margins smooth, sparse setae. Propodus with anterior and posterior surfaces bearing scattered granules; margins with sparse long setae.

P3 (Fig. 7C, D) longest; merus ca. 2.67 × longer than wide; anterior surface with scattered granules, denser near upper margin; posterior surface with sparse granules denser distal to tympanum; upper margin serrated, sparse long setae; lower margin smooth, sparse setae. Carpus shorter than propodus, surfaces smooth; margins smooth, sparse setae. Propodus with anterior surface bearing sparse granules; posterior surface with sparse setae and granules; margins with sparse long setae.

P4 (Fig. 7E, F) merus ca. 2.78 × longer than wide; anterior surface with scattered granules denser near upper margin; posterior surface sparsely granulate, denser towards upper margin; upper margin serrated, sparse long setae; lower margin smooth, sparse setae. Carpus shorter than propodus, surfaces smooth; margins smooth, sparse setae. Propodus with anterior surface with sparse setae and granules; posterior surface with granules; margins with sparse long setae.

P5 (Fig. 7G, H) shortest; merus ca. 2.71 × longer than wide; anterior surface with scattered granules, denser near upper margin; posterior surface sparsely granulate, denser toward upper margin; upper margin serrated, sparse long setae; lower margin smooth, sparse setae. Carpus shorter than propodus, surfaces smooth; margins smooth, sparse setae. Propodus with anterior and posterior surfaces smooth; margins with sparse long setae.

Reproductive organs. G1 (Fig. 8A-E) long, curved, very slender; sub-proximal bulge (Fig. 8A, B); apical portion forming two poorly defined lobes, with three conspicuous curved setae on outer margin becoming slightly longer distally, two or three long setae apically, and four short setae on inner margin (Fig. 8C-E). Vulva (Fig. 8F) rounded, projecting.

Gastric mill (Fig. 17A, C). Median tooth plate simple, without defined ridges. Urocardiac ossicle relatively broad throughout length. Propyloric ossicle semi-circular, relatively flat and broad; posterior margin curved; anterior margin with one pointed lobe medially; lateral margins slightly truncated, evenly convex (Fig. 17A). Lateral zygocardiac tooth plate with nine slender teeth, four anterior teeth largest (Fig. 17C).

Habitat.

Tmethypocoelis simplex sp. nov. lives in estuarine conditions on both sandy and muddy substrata (Fig. 9). At Towale Village, it inhabits sandy substrates alongside other ocypodoids, Austruca annulipes (H. Milne Edwards, 1837) and Scopimera intermedia Balss, 1934, but also in muddier areas where it co-occurs with Tubuca dussumieri (H. Milne Edwards, 1852). At Tosale Village, it was typically collected on sandy substrates. While not collected, it was also observed along a small muddy canal near local residences. It was recorded approximately 1 km further upstream beyond the estuary in non-tidal area.

Etymology.

The name simplex refers to the simple form of the cheliped dactylus that lacks a conspicuous outer subdistal dorsal projection, a character that is characteristic of other described species.

Remarks.

Differences to distinguish and separate the species from T. celebensis sp. nov. and other congeners are given under “Remarks” for T. celebensis sp. nov.