Ankerius aenigmaticus Ng, Rahayu & Shih, 2016, sp. nov.
Creators: name: Ng, Peter K. L.
name: Rahayu, Dwi Listyo
name: Shih, Hsi-Te
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Aphanodactylidae
Ankerius
Ankerius aenigmaticus

description: Ankerius aenigmaticus sp. nov.
(Figs. 1–4, 5 D)
Material examined. Holotype: female (7.2 × 7.0 mm) (UF) (BDJRS-3169, SAFA-041), 20.117°N, 40.2149°E, off Thuwal, Whale Shark reef, Red Sea, Saudi Arabia, in polychaete tube, 10 m, coll. A. Anker, P. Norby & J. Moore, 22 March 2013.
Comparative material. For Selwynia spp., Gandoa brevipes (H. Milne Edwards, 1853), Gustavus mecognathus Ahyong & Ng, 2009; see Ahyong & Ng (2009) and Ng & Rahayu (2016). Tetrias fischeri (A. Milne- Edwards, 1867): 3 males (ZRC 2010.0287), stn B6, Black Forest, Balicasag Island, Panglao, Bohol, Visayas, Philippines, coll. brushing of rocks, 4 June 2004.
Etymology. The name is derived from the Latin for enigmatic; alluding to the unusual features of the species.
Diagnosis. As in genus.
Description (female holotype). Carapace quadrate, approximately as long as wide; dorsal surface smooth, regions not defined except for shallow gastro-cardiac groove; finely pubescent but not obscuring surface or margins (Figs. 1, 2 A). Front entire, deflexed, medially emarginated in dorsal view, triangular in anterior view (Figs. 1, 2 A, B, 3A, B). Supraorbital tooth strongly deflexed, triangular from frontal view; separated from frontal margin by broad cleft (Figs. 2 B, 3A, B). Anterolateral margins prominently arcuate, entire, without teeth or cleft; lined with numerous plumose, short setae; anterolateral margins gradually confluent with posterolateral margins; posterolateral margins subparallel; posterior carapace margin gently convex (Figs. 1, 2 A). Orbit broad, transverse; supraorbital margin lined with very low, rounded granules, entire; eyes stout, completely filling orbit, mobile, cornea completely pigmented, ocular peduncle stout, unarmed; infraorbital margin with low inner tooth, outer part progressively lower, merging with carapace, not joining supraorbital margin (Figs. 2 B, 3A, B). Antennule folding obliquely, filling fossae; basal antennal article (article 2) lodged in orbital hiatus, mobile, slightly longer than wide; antennal article 3 subrectangular, as long as cylindrical antennal article 4, flagellum relatively long, not excluded from orbit (Figs. 2 B, 3A). Epistome broad, medially produced in triangular shaped, tip bidentate; lateral margins concave, entire; only outer edge of endostomial ridge present (Figs. 2 B, 3A, C).
Third maxilliped relatively slender, covering about half of buccal cavity when closed; ischium longer than merus, outer surface smooth, flat, proximomesial angle slightly produced to broadly rounded lobe, distomesial margin sloping; merus subquadrate, surface smooth with oblique shallow submedian sulcus, anterolateral angle broadly rounded; palp (dactylus, propodus, carpus) relatively long, tip of dactylus reaching middle of ischium, carpus longer than propodus, propodus shorter than dactylus; exopod slender, reaching distal quarter of merus, flagellum long (Figs. 3 D, 5D).
Left cheliped (P1) covered with short plumose setae; merus triangular in cross section, long plumose setae dorsally, outer anterior border (ventrolateral margin) with row of sharp, strong spines, plumose setae, inner anterior margin (ventromesial margin) smooth, with dense plumose setae, posterior border smooth; carpus short, surface unarmed but pubescent, long plumose setae on dorsodistal margin, inner angle rounded; lower margin, outer face of palm with rows of short sharp spines, more or less arranged longitudinally, denser spines on lower outer surface, rows of spines on upper outer surface, upper margin obscured by dense plumose setae; dactylus slightly longer than palm, row of spinules on dorsal margin, outer surface obscured by plumose setae, cutting edges serrated with denticles, fixed finger with rows of short spines partially obscured by plumose setae (Figs. 1, 2 A, 3F, G).
Ambulatory legs (P2–P5) relatively long, surface pubescent, upper, lower margins with scattered long plumose setae which does not obscure margins; P4 longest, P5 shortest; dactylus relatively elongated, longer than high, curved, tip of claw bifurcate; upper, lower margins with row of spines; propodus about 2.5 times length of dactylus, distal half or third of lower margin with row of short spines, distal margin with short spines that bracket dactylus, no distinct dacylo-propodal lock; carpus half-length of propodus, unarmed, without ridges; P2–P4 merus distinctly longer than propodus, P5 merus subqual in length to propodus, dorsal margin unarmed; inner, outer lower margins each with row of sharp, strong outwardly directed spines, that on outer margin stronger; basis-ischium with row of prominent short spines distally (Figs. 1, 2 A, 4).
Surface of thoracic sternum generally smooth; sternum relatively wide; sternites 1, 2 completely fused to form triangular plate; sternites 2/3 demarcated by low ridge; sternite 3, 4 separated by low ridge; sternites 4–8 complete (Fig. 2 C). Vulva rounded, operculum absent, situated close to sternite 4/5 suture (Fig. 2 C).
Female abdomen broad, ovate, covering most of thoracic sternum; 6 free somites plus telson; somite 1 markedly longitudinally narrow; somites 2–6 trapezoidal; telson broadly triangular with gently sinuous lateral margins (Fig. 3 E).
Color. Carapace yellow, tinged with orange; cheliped and ambulatory legs white with tinge of yellow on meri (Fig. 1).
Remarks. Little is known about the ecology of the species except that it was found associated with an unidentified tube-making polychaete worm (A. Anker, pers. comm.).
description: Published as part of Ng, Peter K. L., Rahayu, Dwi Listyo & Shih, Hsi-Te, 2016, Ankerius aenigmaticus, a new genus and new species of aphanodactylid crab symbiotic with polychaetes from the Red Sea coast of Saudi Arabia (Crustacea: Decapoda: Brachyura: Aphanodactylidae), pp. 271-278 in Zootaxa 4179 (2) on pages 273-277, DOI: 10.11646/zootaxa.4179.2.7, http://zenodo.org/record/163907