Prismatopus peterngi, Manikandan & Megalaa & Valliappan & Nandini & Rani & Dakshinamurthi & Nagappan, 2022

Manikandan, K, Megalaa, N, Valliappan, Subramanian, Nandini, K, Rani, Lourdu V, Dakshinamurthi, Senthil & Nagappan, Nagappan, 2022, Crabs (Crustacea, Decapoda) from the Seas of East and Southeast Asia Collected by the RV Hakuhō Maru (KH- 72 - 1 Cruise) 3. Sahul Shelf, Bulletin of the National Museum of Nature and Science. Series A, Zoology 48 (2), pp. 35-83 : 57-59

Prismatopus peterngi sp. nov.

( Figs. 8B, 9D–F, 10C–D, 11F–G)

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Material examined. RV Hakuhō Maru KH-72-1 cruise, sta. 29, 1 Ə (holotype), ( CB 11.9 mm excluding branchial spines× PCL 17.8 mm) , NSMT-Cr 30728.

Description of holotype. Carapace 1.5 times as long as wide, weakly constricted behind hepatic regions ( Figs. 8B, 9D); surface sparsely adorned with curled setae. Pseudorostrum divergent anteriorly, with angle of 30°; pseudorostral horns weakly curved laterally, 0.3 times as long as PCL, weakly convex in lateral view. Frontal region with deep, broad, oval depression between 2 blunt longitudinal ridges. Supraorbital eave not markedly expanded; first preorbital lobes slender, directing downward, proximally with cluster of spinules, posterior margin with small spine somewhat ventrally, distal part spinulate; second preorbital lobes strongly curled dorsally, broadly C-shaped in frontal view, distal part armed with spinules; antorbital lobe narrow, lamellar, strongly curled dorsoanteriorly (broken on right side); intercalate lobe narrow, triangular, digitated on both margins (distal half broken on right side); postocular lobe distinctly longer than hepatic projections, posterior margin medially with 2 subequal round lobes. Eyestalk slender, cornea ventrally, as long as half length. Gastric region ( Figs. 8B, 9) weakly elevated, anteriorly with 2 distinct tubercles, longitudinally with 2 subequal knobbed spines, posterior slope obtusely ridged longitudinally toward cardiac region. Hepatic region ( Figs. 8B, 9) weakly inflated, not sloped anterolaterally, posterolater- ally with 2 distally knobbed, slender projections, ventral surface with row of 4 spines (mesialmost smallest). Branchial region ( Figs. 8B, 9) dorsolaterally with 2 long, knobbed spines, anterior dorsolateral margin bluntly defined, lined with granules, subsurface bearing incomplete row of 6 small tubercles, branchial submargin, posterior carapace margin unarmed. Cardiac region ( Figs. 8B, 9D–F) faintly elevated, mounted with 2 knobbed spines fused at base, which is higher than anterior gastric spines. Intestinal region ( Figs. 8B, 9) smooth, with long knobbed spine medially, short spine just above posterior carapace margin.

Basal antennal article ( Fig. 10C) narrow, lateral margin broadly concave; distolateral angle produced laterally into long, sharp, subtrigonal lobe, finger-like in frontal view; proximolateral angle produced into acute, ventrally erected, triangular tooth; distomesial angle produced ventrally into triangular lobe compressed, similar to but narrower than distolateral lobe (in frontal view); mesial margin ridged, bearing erected, triangular tooth, proximomesial lobe overlapped by round anterolateral angle of epistome. Distal 2 peduncular articles free; penultimate article as long as ultimate article; flagellum exceeding tip of pseudorostral horn.

Antennular peduncular first article generally smooth on external surface, medially with small spine. Inter-antennular septum large, acuminate, triangular, tip pointing slightly anteriorly.

Pterygostomian region weakly inflated, gener- ally smooth, bearing 4 papilliform tubercles.

Third maxilliped surface set with microscopic setae. Mesial two-thirds of ischium distinctly depressed, separated from lateral part by blunt, longitudinal ridge, anteromesial lobe rounded, produced anteriorly, firmly fitted in bluntly rimmed, posteromesial concavity of merus (when closed). Merus dilated distolaterally, proximolat- eral lobe depressed. Carpus short, entire, external surface depressed, lateral margin sharply defined, rounded. Propodus rectangular, extensor margin sharply defined. Dactylus finger-like, slighter shorter than propodus.

Both chelipeds subequal in length, but right merus somewhat deformed by sessile organism. Ischium not markedly inflated, armed proximally with small tubercle, distally with lamellar lobe. Merus trigonal, dorsally armed with 5-dentate carina, ventrally with 3 triangular teeth; medial knob at articulation with carpus compressed into claw-shaped lobe, distomesial knob bearing small triangular tooth subproximally. Carpus not markedly inflated, outer margin compressed into irregularly dentate carina next to large, triangu- lar, subproximal tooth, dorsal surface with 3 lamellar teeth, inner margin sharp, irregularly dentate, with small medial spine, ventral surface bearing small median tubercle. Propodus slender, reflecting morphometrical immaturity, upper margin narrowly ridged in proximal half, bearing 2 or 3 low teeth, lower margin obtusely defined. Fingers narrowly gaping in proximal half, finely toothed on both cutting margins; dactylus marked with broad, low, rectangular tooth.

Ambulatory legs (P2–5) slightly decreasing in length posteriorly, extensor, flexor surfaces bear- ing rows of strongly curled setae, long, simple setae. Basis-ischium unarmed. Merus cylindrical, extensor, flexor margins unarmed, distolateral knob at articulation with carpus prominent, elongated into knobbed spine. Carpus subconical, elongate. Propodus cylindrical, extensor surface bearing small proximal spine, flexor surface bearing 2 or 3 low tubercles each bearing simple seta apically. Dactylus slender, gently curved in distal half, extensor margin arranged with row of long setae.

Thoracic sternites 5–8 loosely set by round tubercles, with distinct sutures. Sterno-pleonal cavity sharply rimmed, continuous with both mesial tubercles of sternite 4, but not lateral tubercles.

Pleon ( Fig. 10D) with 6 somites and telson; distal 5 somites1.8 times longer than proximal width, distal 6 somites medially elevated, anterior end protuberant in somites 2–6, produced into subacute tubercle in somites 3–5. Somite 1 short, narrow, anterolateral lobe spinulate, slightly upturned. Somite 2 divergent anteriorly, lateral margin straight. Somite 3 subrhomboid, with strong protuberance on both lateral parts, lateral margin arcuate. Somite 4 rhomboid, lateral margins mostly convergent, subparallel only proximally. Somite 5 rectangular, lateral margin almost straight. Somite 6 rectangular, lateral margin weakly convex on midlength. Telson subtri- angular, weakly sinuate.

G1 shaft ( Fig. 11F) bent laterally, distal 1/6 teardrop-shaped, tip acuminate, lateral margin lined with stiff setae in distal 1/3; subapical flap grooved, twisted toward pleonal side. G2 shaft short, slightly curved, with small, conical apical process ( Fig. 11G).

Etymology. This species is dedicated to our friend and colleague, Prof. Peter K. L. Ng of the Lee Kong Chian Natural History Museum, Faculty of Science, National University of Singapore, whose contribution to crab taxonomy is beyond description.

Remarks. Davie (2002) listed six species of Prismatopus from Australia, and Poore et al. (2008) recorded Prismatopus sp. with a color photograph from Western Australia, 100 m in depth. The new species described herein, P. peterngi , is the eighth species of the genus from Australian waters, and thirteenth of the known species of Prismatopus .

The present new species represented only by a morphologically immature male is the closest to P. albanyensis Ward, 1933 , but can be distinguished by the following characters. The orbital eave bears an additional preorbital spine anterior to the preorbital spine; the preorbital spines are relatively long and curved dorsally more strongly than in P. albanyenesis . This new species has a long intestinal spine, but P. albanyensis does not. Moreover, distal part of the G1 shaft is weakly bent laterally in P. peterngi , but almost straight in P. albanyensis .

Distribution. Known only from the type locality, SW of Bathurst Island on the Sahul Shelf, 49–52 m depth.