Chartocinus rarus Ng & Rahayu 2022, n. gen., n. sp.
Creators: name: Ng, Peter K. L.
name: Rahayu, Dwi Listyo
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Hymenosomatidae
Chartocinus
Chartocinus rarus

description: Chartocinus rarus n. gen., n. sp.
(Figs. 1, 2)
Material examined. Holotype: male (2.9 x 3.1 mm) (MZB Cru 5342), station EM330, sandy mud substrate, Kamora estuary, 4°48’48’’S 136°38’56’’S, Papua, Indonesia, coll. trawl from survey, 7 November 2003.
Description of male holotype. Carapace longitudinally subovate, slightly longer than wide, width to length ratio 1.07; carapace distinctly dorsoventraly flattened; dorsal surface almost flat, surrounded by almost distinct continuous rim except behind rostrum; regions not discernible, without any visible grooves, H-shaped gastric groove shallow, joining cervical groove, no visible grooves on posterior part (Figs. 1A, 2A). Carapace rim and margin of rostrum lined with dense short, hooked setae that partially obscure surface (Fig. 1A). Rostrum unilobate, subtriangular, short, horizontal, no lateral lobes present; joining entire concave supraorbital margin (Figs. 1A, 2A). Lateral margin of carapace (including branchiostegal surface) smooth, unarmed; anterolateral margin unarmed; posterolateral margin with 3 low, wide lobes above P3 and P4 coxae (Figs. 1A, 2A). Posterior carapace margin gently convex (Figs. 1A, 2A).
Orbits clearly visible in dorsal view; eyes well developed, mobile, with prominent peduncle, visible dorsally, cornea rounded, fully pigmented (Figs. 1A, 2A). Antennular fossa shallow, surface gently concave, separated by narrow triangular septum without spine or tooth; basal antennular article quadrate, not swollen, free, positioned at base of fossa, second and third articles elongated, unable to fold into fossa (Fig. 2B). Antenna with short flagellum, positioned between base of ocular peduncle and outer margin of antennular fossa; first article (osmoregulatory opening) present as round pore on each side of epistome; basal article fused with epistome (Fig. 2B). Epistome distinct, broad, not projecting anteriorly, almost vertical from lateral view; posterior margin with gently sinuous lateral margins, with 2 low, subtruncate median lobes; not projecting anteriorly, not visible from dorsal view, area between lobes low, weakly triangular, sloping inwards to endostome (Fig. 2B). Suborbital tooth low, indistinct, not visible from dorsal view (Fig. 2B).
Third maxilliped short, subquadrate; operculiform, with most of median part of buccal cavity covered when closed; merus short, subtrapezoidal, longer than ischium, anteroexternal angle distinct, produced; ischium with mesial margin gently convex, without visible sulcus; palp as long as merus, carpus and dactylus subequal in length, carpus rounded; exopod relatively stout, reaching to distal margin of merus, with distinct flagellum (Fig. 2C).
Chelipeds symmetrical, slender, relatively short; margins lined with dense short hooked setae which partially obscure surfaces; basis and ischium separate, short, unarmed; merus long, subcylindrical, margins unarmed; carpus gently curved, unarmed; chela with smooth rounded palm, outer surface gently convex, covered with long dense plumose setae which partially obscures surface and margins; fingers as long as palm, setose on outer surfaces; cutting edge of dactylus with prominent submedian tooth, cutting edge of propodus 2 low teeth and numerous denticles, tips gently curved (Figs. 1, 2F).
Ambulatory legs slender, long, P2 longest; margins lined with dense short, hooked setae along margins that do not obscure surface; all meri with dorso-distal angle unarmed; carpus gently curved, unarmed; propodus subrectangular, elongated, unarmed; dactylus gently falciform with gently curving sharp tip, flexor margin unarmed; lengths of dactyli P4>P5>P3>P2 (Figs. 1, 2G–J).
Thoracic sternum wide, almost flat (Figs. 1B, 2D); sternites 1 and 2 fused, no suture visible but demarcated by a fold, with sternite 1 gently bent inwards towards mandibles; sternite 2 separated from sternite 3 by distinct groove; sternites 3–8 fused, without trace of sutures or depressions, sternite 4 strongly displaced posteriorly; sternopleonal cavity short, deep, reaching to imaginary line joining anterior edge of P4 coxae (Fig. 2D); margins of sternopleonal cavity with rim, low knob on subdistal edge forming sternal part of pleonal locking mechanism; pterygostome gently produced as low convexity, joining anterolateral extension of sternite 4, separating Milne Edwards openings from base of chelipeds; Milne Edwards openings relatively broad, ovate, margins lined with dense setae.
Pleon-pleotelson short, triangular; somite 1 longitudinally narrow, laterally broad, subrectangular, reaching to base of P5, somite 1 visible from dorsal view, lateral margins gently convex; somite 2 as wide as somite 1, longitudinally wide, mobile; somites 3–6 fused but still demarcated by shallow but visible sutures, especially laterally, forming trapezoidal plate; pleotelson free, almost semicircular elongated, lateral margins gently distinctly convex, with depression on each side of ventral surface forming socket of pleonal locking mechanism (Fig. 2E).
G1 short, stout, distal half tapering to slender sharp tip, directed towards median part of sternum; outer margin distinctly convex; inner margin appears bilobed, with deep median cleft, each lobe with strongly convex margin; groove for G2 submarginal; subdistal surface with row of long setae (Fig. 2K, L). G2 short, half length of G1; tip subspatuliform tip; base elongate (Fig. 2M).
Females. Not known.
Etymology. From the Latin noun (rarus) for rare and delicate.
Remarks. The only known specimen was trawled from soft substrates on estuary of Kamora, Timika, in Indonesian Papua, in shallow waters. No other data is available. Five other species of hymenosomatids are known around Timika— Amarinus pristes Rahayu & Ng, 2004, Neorhynchoplax aspinifera (Lucas, 1980), N. elongata Rahayu & Ng, 2004, Lucascinus bedfordi (Montgomery, 1931) and Elamenopsis gracilipes Rahayu & Ng, 2019 (Rahayu & Ng, 2004, 2019). All of them, including A. pristes, occur in intertidal mangrove habitats.
description: Published as part of Ng, Peter K. L. & Rahayu, Dwi Listyo, 2022, A new genus and new species of Hymenosomatidae (Crustacea: Brachyura) from Indonesian Papua, pp. 480-486 in Zootaxa 5092 (4) on pages 482-485, DOI: 10.11646/zootaxa.5092.4.7, http://zenodo.org/record/5886538