Laomenes albonigrus, Bruce, A. J., 2014

Bruce, A. J., 2014, Laomenes albonigrus sp. nov., (Crustacea: Decapoda; Pontoniinae) from Ashmore Reef, Western Australia, Zootaxa 3846 (3), pp. 439-446 : 440-445

Laomenes albonigrus sp. nov.

( Figs 1–4 )

Material examined. 1 ♀, holotype, Ashmore Reef, Western Australia, north side, lagoon middle entrance, 12° 11' 40.128"S 123° 3' 0.54"E, 7 m, 1 October 2013, coll. M. Ekins, WAM C55074.

Diagnosis. A typical species of the genus Laomenes Clark, 1915 , of the amboinensis species group, characterised by its hemispherical cornea without a distal papilla, second pereiopods strongly unequal, dissimilar, and the third ambulatory dactyl with shorter erect accessory tooth and propod with longer distoventral spines and seven ventral spines, dorsal telson spines of normal length, projecting over lateral telson margin.

Description. Medium-sized shrimp with slender subcylindrical anterior body shape.

Rostrum ( Fig. 1 B) deep, compressed, acute, reaching to end of antennular peduncle, with five well developed acute, anteroverted subequal dorsal teeth on distal half, proximal half convex, unarmed, interdental spaces sparsely setose proximally, ventral margin convex, with two acute teeth distally, lateral carinae distinct posteriorly, confluent with supraorbital teeth.

Carapace ( Fig. 1 A) about twice as long as deep in lateral view, compressed, with large supraorbital teeth, without epigastric tooth, well developed rounded inferior orbital angle, orbit well developed, deep, antennal tooth and hepatic tooth subequal ( Fig. 1 C, 3A), antennal tooth slightly exceeding carapace margin, anterolateral angle anteriorly produced, rounded.

Abdomen slender, pleura small, rounded, third segment not posterodorsally produced, sixth segment 1.6 times longer than fifth, 0.78 of telson length, with posterolateral angle and posteroventral angle similar, acute.

Telson ( Fig. 1 J) 0.6 of CL, 2.6 times longer than anterior width, tapering posteriorly, lateral margins straight, posterior margin broadly rounded ( Fig. 3 J), without median point, with two pairs of similar marginal dorsal spines at 0.46 and 0.73 of telson length, about 0.06 of telson length, overhanging lateral telson margin, lateral posterior spines as dorsal spines, intermediate spines 0.25 of telson length, robust, submedian spines slender, non-setulose, 0.5 of intermediate spine length.

Antennule ( Fig. 1 D) with peduncle slightly exceeding rostrum, proximal segment 1.5 times longer than broad, medial margin straight, setose, with large ventral tooth ( Fig. 3 B) at near half length, anterolateral region strongly produced, with distolateral tooth exceeding intermediate segment, with well developed lobe medially ( Fig. 3 C), slightly angular distally, sparsely setose, stylocerite acute, reaching half proximal segment length, intermediate and distal segments of subequal length, 0.5 of proximal segment length, flagella damaged.

Antenna ( Fig. 1 E) with robust basicerite with stout distolateral tooth, carpocerite subcylindrical, twice as long as wide, reaching to half scaphocerite length, merocerite and ischiocerite normal, scaphocerite exceeding antennular peduncle, 2.4 times longer than broad, lateral margin straight, with acute distolateral tooth at 0.8 of length, lamella distally rounded, well exceeding lateral tooth.

Eye ( Fig. 1 F) with globular cornea, slightly oblique, without terminal papilla, diameter about 0.22 of CL, well pigmented, with posterolateral pigment spot, reaching to level of second rostral tooth, stalk stout, subcylindrical, 1.5 times longer than broad. Ophthalmic somite unarmed, with low median carina anteriorly, median black pigment spot posteriorly.

Epistome with well developed acute convergent submedian processes ( Fig. 3 D).

Mandible with molar process robust, subcylindrical, with two large ventral teeth ( Fig. 3 E); incisor process ( Fig. 3 F) distally expanded, oblique distally with large feebly bilobed medial tooth and eight smaller similar simple acute teeth. Other mouthparts not examined.

Thoracic sternites narrow, fifth with transverse carina with well marked median notch posterior to second pereiopod attachments, posterior segments unarmed.

First pereiopod ( Fig. 1 G) exceeding scaphocerite by chela; chela ( Fig. 1 H) slender, about 0.33 of CL, feebly bowed, palm oval in section, about 2.5 times longer than deep, with several short rows of cleaning setae proximally, fingers slender, tapering to fine simple hooked tips, about 0.75 of palm length, cutting edges entire; carpus 1.6 times chela length, 7.5 times longer than distal width, tapering proximally, with few cleaning setae distoventrally; merus 1.45 times chela length, 8.0 times longer than central depth, ischium and basis normal; coxa with strong setose lobe ventrally.

Second pereiopods well developed, unequal, dissimilar. Major second pereiopod ( Fig. 2 A) robust, chela ( Fig. 2 B) about 1.2 of CL, palm smooth, glabrous, 0.85 of CL, oval in section, 2.6 times longer than central depth, tapering proximally and distally, fingers ( Fig. 2 C) about 0.3 of palm length, incurved; dactyl robust, medially subspatulate, 3.0 times longer than proximal depth, strongly curved, acute, cutting edge distally entire, without distinct cutting edge, central third laminar with larger distal tooth, three smaller proximal teeth, proximal third with flatted plaque, sparsely setose, with strongly hooked tip occluding into deep preterminal notch on fixed finger; fixed finger 3.5 times longer than central depth, raised, curved, carinate, with broad low distal tooth, separated by deep notch from feebly curved tip, proximal cutting edge with three low subacute teeth; carpus short, 0.2 of palm length, distally excavate, distal width subequal to length, unarmed; merus 0.45 of palm length, 3.5 times longer than central depth, straight, tapering proximally, with large acute distoventral tooth, ventral margin unarmed; ischium 0.25 of palm length, 2.4 times longer than distal width, tapering proximally, ventral margin unarmed; basis and coxa normal. Minor second pereiopod ( Fig. 2 D) slender, chela ( Fig. 2 E) about 0.72 of major palm length, about 0.76 of CL, palm smooth, glabrous, 0.45 of CL, oval in section, 2.7 times longer than central depth, subcylindrical, dactyl ( Fig. 2 F) 0.7 of palm length, feebly curved, tip hooked, cutting edge feebly concave with three small acute teeth on central third; fixed finger ( Fig. 2 F) straight, 4.0 times longer than proximal depth with stout strongly hooked tip separated by deep notch from distal cutting edge, cutting edge proximally blunt with two small acute teeth, distal third with larger proximal tooth, distal cutting edge sharp; carpus and proximal segments as in major chela but smaller.

Ambulatory pereiopods slender, third pereiopod ( Fig. 1 I) with dactyl ( Fig. 3 H) short, compressed, about 0.2 of propod length, unguis distinct from corpus, dorsal margin about 2.5 times distal propod depth, unguial portion about 0.6 of dorsal margin length, ventral margin of corpus straight with small slender straight erect acute distal accessory tooth, about 0.5 of unguis length, proximal margin straight, unarmed; propod ( Fig. 3 G) slender, about 0.27 of CL, 4.5 times longer than wide, with pair of subequal similar simple slender distoventral spines, longer spine 0.45 of propod width, with seven well spaced small spines along ventral margin, several long simple distolateral setae; proximal segments without special features.

Pleopods of normal format. Second pleopod ( Fig. 3 I) with endopod subequal to exopod length, 5.0 times longer than wide, with appendix interna 0.4 of exopod length attached at 0.3 of medial margin length.

Uropods with rami exceeding telson, protopod posterolaterally unarmed non-setose; exopod 3.3 times longer than broad, lateral margin straight, non-setose, posterolateral angles with small acute tooth with large fossa medially ( Fig. 3 K), both distolateral spines lost; endopod 0.9 of exopod length.

Measurements (mms). Holotype female, rostrum and carapace, 4.3; postorbital carapace, 3.7; total body length (approx.), 11.0; major second pereiopod chela, 4.8; minor second pereiopod chela, 3.0. Etymology. Named after the black and white colouration of the live animal. From albus (Latin), white, and nigrus (Latin), black.

Host. Oxycomanthus bennetti Müller, 1841 (Crinoidacea) , det. L. Marsh.

Colouration. (From colour photograph, Fig 4 ). Generally black and white. Body and appendages white except for proximal halves of antennae, antero-dorsal carapace, ventral branchiostegite, most of first to fourth abdominal segments except posterior part of each pleuron, antero-ventral half of fifth segment, second pereiopods with distal carpus and proximal chela, bases of third to fifth pereiopods and pleopods. Second pereiopod chelae with golden tinge.

Systematic position. Marin, Chan and Okuno (2012) noted that the only species of Laomenes that had a cornea lacking a terminal papilla was L. gymnophthalmus .

Laomenes albonigrus may be distinguished from L. gymnophthalmus as indicated below ( L. gymnophthalmus characters in parentheses):

Rostral dentition 5/2 (vs 5/1, with additional minute preterminal denticle), antennal and hepatic teeth subequal (v s hepatic tooth larger than antennal), second pereiopods unequal, minor chela half length of major chela (vs subequal), distoventral merus acutely produced (vs bluntly produced), major chela with fingers 0.33 of palm length, strongly dentate, (vs about 0.66 of palm length, feebly dentate), minor chela fingers 0.7 of palm length (vs about 0.66 of palm length, feebly dentate), third pereiopod dactylar unguis about 0.7 of corpus length (vs 0.59), accessory tooth 0.1 of unguis length (vs 0.18), ventral corpus straight (vs sinuous), propod with pair of long slender distoventral spines (vs short spines), ventral margin with 7 small spines along whole length (vs 2 distal spinules), telson with two pairs of well developed dorsal spines, 0.06 of telson length, projecting over lateral margin of telson (vs minute dorsal spines, 0.015 of telson length, not projecting over margin.

Remarks. Marin (2009) divided the then known species of Laomenes into three species groups centered on L. amboinensis , L. jackhintoni and L. ceratophthalmus . The taxonomically important characters in these groups are presence or absence of ventral rostral teeth, hemispherical or papillate cornea, relative development of third pereiopod dactylar accessory tooth, presence or absence of distolateral spines on third pereiopod propod, presence or absence of tooth on uropodal exopod.

The L. amboinensis group is distinguished by the presence of ventral rostral teeth, cornea hemispherical or papillate, distoventral spines on third pereiopod propod, and a fixed tooth on distolateral margin of uropodal exopod. Included species are L. amboinensis ( De Man, 1888) , L. cornutus ( Borradaile, 1915) , L. clarki Marin, 2009 , L. pardus Marin, 2009 , L, holthuisi , Marin & Okuni, 2010, L. pestrushka Marin, Chan & Okuno, 2012 , and L. gyrophthalmus Marin, Chan & Okuno, 2012 .

The L. jackhintoni group is characterized by the absence of ventral rostral teeth, extremely elongated apical corneal papilla, third pereiopod propod without distoventral spines, with large accessory tooth on dactyl, and a fixed tooth on exopod of uropod. Included species are Laomenes jackhintoni ( Bruce, 2006) and L. tigris Marin, 2009 .

The L. ceratophthalmus group is characterized by the absence of ventral rostral teeth, cornea papillate, distoventral spines on propod and accessory tooth on dactyl of third pereiopod small, tiny marginal dorsal spines on telson and the absence of a fixed distolateral tooth on uropodal exopod. Included species are Laomenes ceratophthalmus ( Borradaile1915) and L. nudirostris ( Bruce, 1968) .

Laomenes albonigrus belongs to the L. amboinensis species group as it has ventral rostral teeth, a robust antennal tooth, a hemispherical cornea, epistomal horns well developed, acute, second pereiopods unequal, major fingers less than half palm length, very strongly dentate, minor feebly dentate, third pereiopod dactyl with small anteroverted accessory tooth, third pereiopod propod with setiform distoventral spines, uropodal exopod with distolateral tooth, dorsal telson spines normal. As noted by Marin et al (2012) L. gyrophthalmus it is the only species in this group, and in the genus Laomenes , that has a globular cornea lacking any vestige of a distal papilla. Laomenes albonigrus is a second species with this character and is closely similar morphologically. The species of the amboinensis species group may be distinguished by the following key.

Figures

FIGURE 1. Laomenes albonigrus sp. nov., female holotype, Ashmore Reef, WAM C 55074. A, anterior carapace and appendages. B, rostrum. C, carapace, antennal region. D, antennule. E, antenna. F, eye, lateral. G, first pereiopod. H, same, chela. I, third pereiopod. J, telson.

FIGURE 2. Laomenes albonigrus sp. nov., female holotype, Ashmore Reef, WAM C 55074. A, major second pereiopod. B, same, chela. C, same, fingers. D, minor second pereiopod. E, same, chela. F, same, fingers.

FIGURE 3. Laomenes albonigrus sp. nov., female holotype, Ashmore Reef, WAM C 55074. A, antennal and hepatic teeth, dorsal. B, proximal segment of antennular peduncle and epistomal horn, medial. C, proximal antennular segment, distolateral angle. D, epistome. E, mandible, molar process. F, same, incisor process. G, third pereiopod, propod and dactyl. H, same, distal propod and dactyl. I, second pleopod. J, posterior telson spines. K, uropod, posterolateral exopod.

FIGURE 4. Laomenes albonigrus sp. nov., female holotype, Ashmore Reef, WAM C 55074. Photograph, Andrew Hosie.