Madangella altirostris

Frolová, Pavlína & Ďuriš, Zdeněk, 2018, Madangella altirostris, a new genus and species of palaemonid shrimps (Crustacea: Decapoda: Palaemonidae) from Papua New Guinea, Zootaxa 4438 (2), pp. 327-338: 330-336

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Madangella altirostris

sp. n.

Madangella altirostris  sp. n.

( Figs 1–5View FIGURE 1View FIGURE 2View FIGURE 3View FIGURE 4View FIGURE 5)

Type material. Holotype:1 ovigerous female MNHN-IU-2015-1581, Papua-Niugini Expedition, S. Nagada, Madang province, Papua New Guinea, stn PD55, 05° 09.3' S, 145° 47.4' E, 29 Nov. 2012, dredging, depth 4–5 m.GoogleMaps 

Description. Body subcylindrical, slender, non-hirsute ( Fig.1 View Figure ). Rostrum ( Fig. 2B View Figure ) slightly upturned, short, 0.6 of CL, almost reaching distal margin of basal antennular segment; rostral lamina deep, leaf-shaped, strongly compressed, flat, without midrib; dorsal margin distinctly convex, with 7 acute, evenly distributed and anteriorly directed teeth, with interdental setae, first rostral tooth about twice distance from epigastric tooth than from next tooth; ventral margin slightly convex, setose, with subapical vestigial tooth. Inferior orbital angle not produced, rounded. Antennal, hepatic and epigastric teeth present, supraorbital teeth or tubercles lacking; antennal tooth marginal, slender, overreaching half-length of basicerite, hepatic spine as large as antennal, situated posteriorly and slightly below level of antennal spine. Anterolateral angle of branchiostegite not produced.

Fourth thoracic sternum ( Fig. 2C View Figure ) with distinct acute finger-like median tooth. Fifth sternum with obsolete transverse carina.

Pleonal segments smooth. Third segment not posterodorsally produced; all pleura broadly rounded posteroventrally. Sixth segment ( Figs 1 View Figure , 2D View Figure ) elongate, slightly shorter than CL and twice as long as fifth segment dorsally, about 2.2 times longer than deep.

Telson ( Fig. 2D, E View Figure ) about 0.65 of CL and 0.7 of sixth pleonal segment length, about 3.3 times longer than broad anteriorly. Lateral margins convex anteriorly and convergent posteriorly, straight. Two pairs of submarginal dorsal spines minute, less than 0.05 of telson length, situated at about 0.5 and 0.75 of telson length. Posterior margin produced in submedian area, truncate, with 3 pairs of cuspidate setae; lateral setae slightly larger than dorsal spinules, intermediate setae long and wide, about 6 times longer than lateral setae and 0.25 of telson length, submedian setae with setules on sides, about 0.7 of intermediate setae length.

Antennular peduncle ( Fig. 2A View Figure ) normally developed, exceeding rostrum by 2 distal segments. Basal segment about 2.4 times longer than wide in midlength; stylocerite slender, acute, directed anterolaterally, reaching to about 0.6 of medial margin length, statolith rounded, distinct, about 0.5 of proximal basal segment width; distolateral margin of basal segment convex, slightly converging anteriorly, with small acute distolateral tooth not considerably exceeding more medial rounded distal lobe, medial margin almost straight, with distinct acute ventral tooth in midlength. Intermediate segment about 1.5 times longer than wide, dorsal length about 0.25 of basal segment length. Distal segment subequal and slightly slenderer than preceding segment. Upper flagellum (only right one preserved) very slender and long, biramous, with both rami fused proximally for 13 elongate segments with combined length exceeding CL; shorter free ramus consisting of one segment; about three groups of aesthetascs present; longer ramus (lost during examination) short, consisting of about 4 elongate segments. Lower flagellum filiform (broken basally, length unknown).

Antenna ( Fig. 2A, B View Figure ) with basicerite short, stout, with distoventral, anteriorly directed short acute tooth. Scaphocerite elongate, about 3.5 times longer than wide, and 0.9 of CL, lateral margin slightly convex, with distolateral tooth distinct, not overreaching distal margin of lamina. Carpocerite short, reaching proximal third of scaphocerite length.

Eyes ( Figs 1 View Figure , 2A View Figure ) well developed large, depressed (possibly due to preservation); cornea transversely elliptic, not reaching end basal antennular segment. Eyestalk broad and strongly depressed, length subequal to distal width and to corneal diameter in dorsal view, additional pigment spot absent.

Mouthparts ( Fig. 3 View Figure ), left side dissected. Mandible ( Fig. 3A, B View Figure ) without palp; molar process stout, expanding distally, apex truncate, with 4 large lobes; incisor process stout, tapering distally, with three blunt teeth, of which central shorter than others.

Maxillula ( Fig. 3C View Figure ) with bilobed palp, outer lobe tapering distally, inner lobe short, strongly curved inward; upper lacinia broad, dorsal margin convex, distal margin with about 7 spiniform setae; lower lacinia broad basally, tapering distally, dorsal margin concave and ventral margin convex, with about 15 slender terminal and subterminal setae.

Maxilla ( Fig. 3D View Figure ) with stout tapering palp, about 3 times longer than basal width, with single simple seta arising from middle of outer margin; basal endite well developed, deeply divided into two subequal lobes, each terminating with 10-11 long setae; coxal endite low, feebly produced but well demarcated; scaphognathite broad centrally and tapering distally, about 2.2 times longer than greatest width, with numerous plumose marginal setae.

First maxilliped ( Fig. 3E View Figure ) with slender pointed palp bearing series of plumose setae along distal 0.7 of inner margin and few distally on outer margin, about 7 times longer than wide at midlength; basal endite large, rounded anteriorly, with slender marginal and submarginal setae along distal and medial margins; coxal endite low, feebly produced, separated by deep notch from basal endite, with several slender setae; exopod well-developed, flagellum with 4 plumose terminal setae and single subterminal seta; caridean lobe well-developed, tapering distally, with 14 simple marginal plumose setae; epipod large, broadly subtriangular and faintly bilobed.

Second maxilliped ( Fig. 3F View Figure ) of usual form, endopod with dactylar segment about 3 times longer than wide, with numerous long spiniform setae medially and distally; propodal segment with anterior margin broadly rounded, with slender marginal setae; carpus short, normal; merus and ischium fused, with suture feebly demarcated; exopod with well-developed flagellum bearing 4 terminal setae; coxa strongly produced medially, with few simple setae; epipod simple, slightly longer than broad, without podobranch.

Third maxilliped ( Fig. 3G View Figure ) slender, not reaching distal end of carpocerite; ultimate segment tapering distally, 0.7 times length of penultimate segment, with numerous serrate setae; penultimate segment about 0.6 of ischiomerus and about 4 times longer than proximal width, with several long medial setae; antepenultimate segment (ischiomerus) completely distinct from basis, about 5 times longer than proximal width, medial margin with scattered setae, distal half of lateral margin with 4 spines and several small simple setae; basis short, about 0.15 of ischiomeral length; exopod with flagellum well developed, slightly overreaching distal end of ischiomerus, with 4 long terminal setae; coxa with produced rounded lateral lobe, without arthrobranch.

First pereiopod ( Fig. 4A–C View Figure ; only left leg preserved; right one lost) slender, exceeding end of scaphocerite by length of fingers; chela about 0.32 of CL; fingers simple, tips slightly hooked; palm as long as fingers and about 1.8 times longer than deep, with about 5 rows of short cleaning setae proximomedially; carpus slender, slightly swollen distally, about 8 times longer than distal width, about 16 times width in midlength, and 1.5 times length of chela, with several long setae distoventrally posterior to palmar brush setae; merus 0.85 of carpus length, about 10 times longer than wide, unarmed; ischium 0.65 of merus length, slightly wider than merus; basis without special structures; coxa with simple distoventral seta.

Second pereiopods ( Fig. 4D–F View Figure ) slender, subequal and similar, exceeding end of scaphocerite by distal half of carpus and chela; chela slender, similar to first pereiopod chela but about 1.4 times longer, 0.45 of CL; fingers straight and slender, subequal to palm length, tips slightly hooked, fixed finger with subapical tooth, both fingers with entire thin cutting edges and several stout submarginal setae; palm slightly compressed, 2.5 times longer than deep; carpus long and sender, slightly swollen distally, 1.8 times length of chela, about 30 times longer than wide in midlength; merus 0.8 of carpus length, about 20 times longer than wide in midlength, unarmed; ischium as deep as merus and 0.6 of merus length; basis and coxa without special structures.

Third and fifth pereiopods detached, lacking. Fourth pereiopod (only right leg present; Fig. 4G, H View Figure ) slender, exceeding scaphocerite by distal third of propodus; dactylus long and slender, feebly curved, simple, about 0.33 of CL and 15 times longer than basal depth, unguis feebly demarcated; propodus slender, about 2 times length of dactylus, about 22 times longer than wide in midlength, sparsely setose dorsally and with pair of minute distoventral spines only, latter subequal or smaller than proximal depth of dactylus; carpus about 0.6 times propodus length; merus 1.7 times longer than carpus, 17 times longer than wide, unarmed; ischium 0.5 of merus length and slightly stouter than latter; basis and coxa without special structures.

Uropod ( Fig. 2D View Figure ) with protopod unarmed; branches exceeding distal end of telson; exopod with lateral margin almost straight, non-setose ventrally, lateral margin terminating in small acute tooth and larger spine medially, diaeresis not indicated; endopod tapering distally, slightly shorter than exopod.

Measurements [mm]. CL, 1.6; rostrum length, 1.1. Sixth pleomere dorsal length, 1.6; depth, 0.7. Telson length, 1.1. Pereiopods segment lengths (fingers – palm – carpus – merus – ischium): first pereiopod, 0.35 – 0.25 – 0.9 – 0.75 – 0.5; second pereiopod, 0.4 – 0.5 – 1.6 – 1.25 – 0.8; fourth pereiopod (dactylus to ischium), 0.7 – 1.2 – 0.7 – 1.3 – 0.7. Eggs, length 0.48 (early stage, without eye spots).

Etymology. The species name is a combination of ‘ altum ’ (Latin—deep, high) and ‘rostrum’, referring to the unusual shape of the latter.

Host. Unknown. Based on the slender simple ambulatory dactyli, a free-living habit at soft bottoms can be inferred.

Habitat. The specimen was collected by dredging in shallow water inside a small narrow bay, in depths of 4– 5 m.

Distribution. Known only from Madang province, Papua New Guinea, the Bismarck Sea (this report).

Remarks. See the systematic position of the new genus.

GenBank. For accession numbers, see Tab. 1.