Madangella koumacensis Frolová & Ďuriš 2020, sp. n.
Creators: name: Frolová, Pavlína
name: Ďuriš, Zdeněk
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Madangella
Madangella koumacensis

description: Madangella koumacensis sp. n.
(Figs 1–5)
Type material. Holotype: ovigerous female MNHN-IU-2019-2713, Expedition Koumac2.3, Stn KD 503, New Caledonia, 20° 36.6’ S, 164° 15.9’ E, dredging, sandy-mud bottom, depth 8 m, 28 Oct. 2019.
Description. Small-sized palaemonid shrimp (Fig. 1) with body slender, subcylindrical, glabrous; specimen incomplete, second pereiopods lost. Rostrum (Figs 1, 2A, B) slightly upturned, short, with length about 0.6 of PoCL, reaching disto-dorsal margin of intermediate segment of antennular peduncle; rostral lamina moderately deep, strongly compressed, sides flat, without midrib; dorsal margin slightly convex, with 7 acute, anteriorly directed teeth, with interdental short setae, first rostral tooth more distant from epigastric tooth than from next tooth; ventral margin slightly sinuous, setose, with two distal teeth, first (proximal) tooth larger, second (subterminal) vestigial. Orbit feebly developed, postorbital ridge absent. Inferior orbital angle slightly produced in later view, obliquely truncate. Antennal, hepatic and epigastric teeth present, supraorbital tooth or tubercle lacking; antennal tooth marginal, reaching half of dorsal length of antennal basicerite, hepatic tooth as large as antennal one, situated posteriorly and slightly below latter.
Fourth thoracic sternite (Fig. 2C) with short finger-like median process, fifth sternite with transverse ridge formed by pair of triangular sub-median teeth with rounded apices and small U-shaped incision between them.
Pleonal segments (Fig. 1) smooth, with pleurae I-IV broadly rounded, and pleura V (Figs 1, 2D) posteroventrally produced to acute angle. Sixth segment (Figs 1, 2D) dorsal length subequal to telson length and about half length of PoCL, depth 0.6 of dorsal length; posterolateral angles subtriangular, produced; posteroventral angle sinuate, distoventrally produced into pointed apex (Fig. 2D); posterior dorsal margin simple, not produced in midpoint.
Telson (Figs 2E, F) subequal to sixth pleonal segment length and 3 times as long as maximal width; lateral margins feebly convex in anterior half, convergent posteriorly. Two pairs of submarginal dorsal spinules, small size, about 0.07 of telson length, situated at about 0.4 and 0.7 of telson length. Posterior margin about 0.5 of anterior width, subtriangular, with small rounded median point, with three pairs of marginal spiniform setae, lateral ones subequal to dorsal spines, intermediate pair longest, about 5 times longer than dorsal spines and about 0.3 of telson length, submedian pair setulose on sides, about 0.5 of intermediate spines length.
Antennula (Fig. 2A, G) with peduncle normally developed, exceeding tip of rostrum by distal segment. Proximal segment about 2 times longer than wide (at midlength); stylocerite stout, acute, directed anterolaterally, failing to reach middle of medial margin length; distolateral margin of proximal segment slightly convex with minute acute distolateral tooth distinctly subterminal, distal margin oblique medially from latter tooth, medial lobe obsolete. Distal two peduncular segments elongate, with combined length 0.6 of proximal segment length; intermediate segment about 1.7 times longer than wide, distal segment subequal but slenderer than previous segment. Upper flagellum biramous, with 10–12 proximal segments fused, fused part long and slender; shorter free ramus 2-segmented; with 6 groups of aesthetascs.
Antenna (Fig. 2H) with stout basicerite bearing short distolateral acute tooth. Carpocerite short, reaching to 0.3 of scaphocerite length. Scaphocerite elongate, extending well beyond antennular peduncle, about 3.5 times longer than wide and 0.8 of PoCL, lateral margin almost straight, with acute distolateral tooth slightly overreaching distal margin of lamina.
Eyes (Figs 1, 2A) well developed, large, not reaching end of proximal segment of antennular peduncle when extended anteriorly; cornea spherical, accessory pigment spot small, inconspicuous, situated dorsally on corneal margin. Eyestalk broad, shorter than cornea.
Mouthparts (Fig. 3) from left side dissected; paragnaths (Fig. 3A) with alae broadly rounded, anteromedially oblique, feebly subdivided laterally, alae separated by deeper U-shaped median notch.
Mandible (Fig. 3B, C) without palp; stout molar process distally truncate, with four large lobes, stout incisor process tapering distally, with three blunt teeth. Maxillula (Fig. 3D) with bilobed palp, outer lobe depressed, rounded distally; lower lobe short, strongly curved inward, with small apical seta; upper lacinia moderately broad, dorsal margin obtusely angulate, with about 9 stout serrulate terminal setae; lower lacinia tapering distally, dorsal margin sinuate and ventral margin convex, with about 8 stout serrulate terminal and few slender subterminal setae. Maxilla (Fig. 3E) with stout palp, tapering distally, without setae; basal endite slender, deeply bilobed, distal lobe slightly larger than proximal lobe, with about 13 and 10 slender distal setae, respectively; coxal margin feebly produced; scaphognathite strongly narrowed distally, moderately broad proximally, about 2.5 times longer than central width, with numerous plumose marginal setae. First maxilliped (Fig. 3F) with palp tapering distally, with single pappose preterminal seta; basal endite large, broad, anterolateral convex, with slender marginal and sub-marginal setae along distal and medial margins; coxal endite distinct, separated from basal endite by deep notch, with several slender setae; exopod well-developed, tapering distally, flagellum with 4 terminal setae, with small elongate caridean lobe proximolaterally; epipod large, feebly bilobed, subtriangular. Second maxilliped (Fig. 3G) as usual for family, endopod with dactylar segment about 3 times longer than wide, with numerous robust serrate setae along medial margin; propodal segment broadly rounded anteriorly, with numerous serrate setae; carpus short, with distodorsal pre-terminal seta, merus normal, ischium and basis fused, with suture feebly demarcated; exopod well-developed, with flagellum bearing 4 terminal setae; coxa strongly produced medially, subquadrate, with few setae; epipod simple, 1.5 times longer than greatest width. Third maxilliped (Fig. 3H) slender and long, overreaching distal end of antennal carpocerite; ultimate segment tapering distally, about 6 times longer than broad basally, 0.7 times length of penultimate segment, with numerous serrate setae, penultimate segment about 0.7 of antepenultimate segment (ischiomerus), about 5 times longer than proximal width, with several long medial setae; ischiomerus fused with basis, with sutures feebly demarcated, about 6 times longer than proximal width, medial margin with setae, distal half of lateral margin with 8 spinules and few small setae; basis short, about 0.15 of ischiomeral length; exopod with flagellum reaching distal end of ischiomerus, with 4 long terminal setae; coxa with rounded lateral lobe, medially produced into subtriangular lobe; single reduced finger-like arthrobranch present.
First pereiopod (Fig. 4 A-C) slender, exceeding end of scaphocerite by chela and distal quarter of carpus; chela about 0.4 of PoCL; palm about 3.5 times longer than deep, with about 6 rows of short cleaning setae proximomedially; fingers as long as palm, with simple cutting edges and small acute hooked tips; carpus slender, 1.5 times chela length, about 9 times longer than distal width, tapering proximally; merus subequal to carpus length, about 12 times longer than central width, unarmed; ischium 0.6 of merus length, and slightly deeper; basis with series of submarginal setae along ventral margin; coxa with subquadrate distoventral setose lobe.
Both second pereiopods lacking from holotype.
Ambulatory pereiopods (Fig. 4 D-I) slender; third pereiopod exceeding scaphocerite by dactylus and propodus; dactylus long and slender, simple, feebly curved, about 0.6 of propodus length, 15 times longer than basal depth; propodus about 22 times longer than wide in midlength, sparsely setose dorsally; carpus about 0.6 times propodus length; merus 2.0 times longer than carpus, 20 times longer than wide, unarmed; ischium 0.5 of merus length and slightly deeper than latter; basis and coxa without special features. Fourth (Fig. 4 F–G) and fifth pereiopods (Fig. 4 H–I) similar to third pereiopod.
Uropod (Fig. 2E, I) with protopod unarmed; exopod with lateral margin almost straight, terminating in small acute tooth reaching level of distal end of telson, with larger, curved mobile spine more medially, diaeresis deeply sinuate, distal end of exopod broadly rounded, semicircular; endopod broadest proximally, tapering distally, exceeding distal end of telson.
Branchial formula:
Measurements. PoCL, 3.1 mm; rostrum length, 2.0 mm. Sixth pleomere dorsal length, 1.6 mm; depth, 1.0 mm. Total length of body (from tip of rostrum to posterior end of telson), 14 mm. Telson length, 1.7 mm. First pereiopod segments length (fingers – palm – carpus – merus – ischium): 0.7 – 0.6 – 1.7 – 1.6 – 1.0 mm; third pereiopod (dactylus to ischium): 1.2 – 2.2 – 1.4 – 2.5 – 1.4 mm.
Etymology. The species name is derived from Koumac, the regional centre in the North Province of New Caledonia.
Colouration. Unknown; only faded traces of live colour composed of irregular reddish spots and yellowish dots over the carapace and pleon are evident in a post mortem photo (Fig. 5).
Host. Unknown. Based on the slender simple ambulatory dactyli, potentially free-living.
Habitat. The specimen was collected by dredging in shallow water between shore and a large reef platform inside a lagoon near Koumac, at a depth of 8 m.
Molecular analysis. The sequences of two mitochondrial genes were obtained for the species, namely 16S rRNA (561 bp) and COI (672 bp). The molecular comparison of both known species in the genus reveals their genetic divergences 17.6 % of 16S and 21.2 % of COI, supporting separate species recognition.
GenBank accession numbers. MT816395 (COI) and MT819437 (16S).
Remarks. The new species, Madangella koumacensis sp. n. clearly belongs to the previously monotypic genus Madangella sharing with the type species, M. altirostris, the following main diagnostic characters: (1) a short, slightly upturned rostrum, (2) epigastric tooth present, (3) well-developed antennal and hepatic teeth, (4) postorbital ridge and supraorbital tooth absent, (5) outer antennular flagellum with fused part slender, long, composed of over 10 elongate segments, and (6) ambulatory legs, and in particular the dactyli, long and slender. The mouthparts, including the mandible without the palp, are closely similar to those described and illustrated by Frolová & Ďuriš (2018).
Madangella koumacensis sp. n. can be easily distinguished from M. altirostris through the following characters: (1) rostrum reaching the distal margin of the intermediate segment of the antennal peduncle, tapering distally, and with 2 subterminal ventral teeth (vs rostrum reaching distal margin of the basal antennular segment, broadly convex dorsally, with a single distoventral tooth in M. altirostris); (2) basal antennular segment with the distolateral margin oblique, and both distolateral tooth and lobe strongly reduced (vs distolateral tooth and rounded lobe small but well developed, subequal); (3) first pereiopod carpus and merus being subequal (vs carpus being distinctly longer); (4) ambulatory legs with distal stiff setae on the propodus, on both sides of the dactylar base (vs feebly setose distally on the propodus); (5) fifth pleomere being acutely produced posteroventrally (vs broadly rounded); (7) telson being stouter, less than 3 times longer than wide anteriorly (vs more elongate, 3.5 times longer than wide).
As mentioned in the Introduction, the genus Madangella belongs to a complex of palaemonid genera (the ‘CP’, or ‘Pon-1’, complex, sensu Horká et al., 2016 and Chow et al., 2020, resp.) separated from the main diversity of symbiotic shrimps of the previous subfamily Pontoniinae. Most species of its current genera (e.g. Cuapetes, Exoclimenella Bruce, 1995, Harpilius, and Periclimenella Bruce, 1995) previously were placed in the polyphyletic genus Periclimenes Costa, 1844 which still contains numerous species of yet unresolved taxonomic position. From those species, the present new species might be closely allied to, inter alia, Periclimenes leptopus Kemp, 1922 from the Andaman Islands, or P. exederens Bruce, 1969 from the South China Sea, due to their shared general morphology, especially the length and armature of the rostrum and the slender ambulatory pereiopods with elongate simple dactyli. Periclimenes exederens is, however, easily distinguished from the new species by the hepatic tooth situated closer to the anterior margin of the carapace, the rounded pleurae of the fifth pleomere, and the longer fingers of the first pereiopods (see Bruce, 1969). Both species, P. exederens and P. leptopus, have the ambulatory dactyli failing to reach the median length of the propodus whilst in the present new species the dactyli are distinctly longer.
Periclimenes leptopus seems to be morphologically closest to the present new species. However, its antennula has the basal segment with a produced lobe and a small lateral tooth distolaterally (Kemp, 1922), while the present new species has the basal segment obliquely truncated distolaterally and without a lobe, whilst possessing only a minute subdistal tooth. The new species also has a larger number of fused segments in the upper antennular flagellum. The affiliation of P. leptopus to the ‘Pon-I complex’ of genera cannot be confirmed due to the lack of the key character of the complex, the median tooth on the fourth thoracic sternite (mentioned by Kemp, 1922 for some other taxa). A re-examination of syntypes, if extant, might help to clarify this question. Based on the observed morphological differences and lack of a sternal tooth in these related species, we suggest M. koumacensis sp. n. to be a distinct species.
description: Published as part of Frolová, Pavlína & Ďuriš, Zdeněk, 2020, Madangella koumacensis, a new species of palaemonid shrimps (Decapoda Palaemonidae) from New Caledonia, pp. 253-263 in Zootaxa 4845 (2) on pages 255-261, DOI: 10.11646/zootaxa.4845.2.6, http://zenodo.org/record/4406586