Two new species of shrimp of the Indo-West Pacific genus Hamodactylus Holthuis , 1952 ( Crustacea : Decapoda : Palaemonidae )

Two new alcyonacean-associated species, Hamodactylus paraqabai sp. nov. from Papua New Guinea and the Great Barrier Reef and H. pseudaqabai sp. nov. from Indonesia and Malaysia, are described and illustrated. To evaluate the status of the new species and their relationship within the genus Hamodactylus Holthuis, 1952, we combined morphology and phylogenetic analyses based on the cytochrome c oxidase subunit I (COI) mitochondrial gene. Both new species are closely related, with their mutual genetic divergence reaching 3-4%. They are further most related to Hamodactylus aqabai Bruce & Svoboda, 1983, originally described from the Red Sea. Both new species are distinguished from all other congeners by the presence of multiple teeth distally on the cutting edges of the fingers of the first pereiopods, and, in the case of H. paraqabai sp. nov., by a full reduction of the fixed finger on the second pereiopod chela. In H. pseudaqabai sp. nov. the finger is greatly reduced to a small but distinct stub, and the telson bears only a single pair of dorsal spines, as in H. aqabai. A key for the identification of all six currently known species is proposed.

A series of specimens was recently obtained from material collected during research campaigns to Indonesia (1990), Malaysia (Semporna Marine Ecological Expedition, 2012), Australia (CReefs Lizard Island Expedition, the Great Barrier Reef, 2010) and Papua New Guinea (Papua Niugini Expedition, Madang, 2012).Those specimens, initially assigned to H. aqabai, were revealed to contain two new species, different from specimens of H. aqabai obtained by us from the northern Red Sea.The separation of those two new species is supported by morphological characters and molecular analyses.Both the new species are described and illustrated here, and their distinctions from H. aqabai and from other known congeners are discussed.

Material and methods
The following abbreviations are used in the methods and descriptions of taxa: The Netherlands UO = University of Ostrava, Czech Republic

Sample collection
The shrimps of the genus Hamodactylus were collected in the Indo-West Pacific region (Lizard Island, Australia, 2010;Sabah, Malaysia, 2010;Indonesia, 1990Indonesia, , 1994Indonesia, , 1996Indonesia, , 2010;;Madang Bay, Papua New Guinea, 2012) and in the Red Sea (Aqaba, Jordan, 2009) by hand net during scuba diving.Complete specimens were preserved in 80% ethanol for morphological studies and samples of tissues (abdominal muscle, pleopods or eggs) for molecular analysis in 96-99% ethanol.Voucher specimens are stored in the crustacean collections of RMNH, MTQ, MNHN and UO.
For the COI segments, PCR products were amplified using the universal primer pairs LCO 1490/HCO 2198 (Folmer et al. 1994).The thermal cycling profile conformed to the following parameters: 2.5 min at 94˚C for initial denaturing, followed by 40 cycles of 30 s at 90 ˚C, 1 min at 48 ˚C, 1 min at 72 ˚C, and a final extension step at 72 ˚C for 10 min.The PCR products were purified using GenElute PCR cleanup kit (Sigma, Aldrich, Germany).Sequencing reactions were performed using an ABI3730XL DNA Sequencer from Macrogen, Ins., Amsterdam.Partial segments of the COI mitochondrial gene (645 bp) were used for phylogenetic analysis and were deposited in GenBank (Table 1).

Phylogenetic analysis
Forward and reverse sequences were manipulated with Chromas v2.4.1, and multiple sequence alignment was conducted with MUSCLE (Edgar 2004) using the default settings within the software package MEGA6 (Tamura et al. 2013).Overall 12 specimens of the genus Hamodactylus were covered in the phylogenetic analyses; 6 of them were obtained from GenBank (Table 1).
The software jModelTest 2.1.6(Darriba et al. 2012) was used to evaluate the best-fitting substitution model using the Bayesian Information Criterion.Maximum likelihood (2,000 replications) was conducted in MEGA6 and the Bayesian analysis (SD of split frequencies < 0.05) using MrBayes v3.2.3 (Ronquist et al. 2012)  under the resultant Hasegawa-Kishino-Yano (HKY+I+G) model.The palaemonid shrimp Palaemonella rotumana (Borradaile, 1898) was used as outgroup.The number of base differences per site between COI gene sequences was calculated in MEGA6.

Etymology
The specific name paraqabai is a noun composed of the prefix para-(from Greek: besides) and the adjective -aqabai, a species name used for H. aqabai, a closely similar species from the Red Sea.
Carapace smooth.Rostrum (Fig. 2A) well developed, exceeding intermediate segment of antennular peduncle (Fig. 2B); lamina deep, lateral carina situated slightly above straight, setose, toothless ventral margin; dorsal margin convex, elevated, strongly compressed, with six subequal teeth, of which first situated above level of posterior orbital margin.Supra-orbital and epigastric spines absent.Orbit obsolescent, inferior orbital angle acutely produced in lateral view.Antennal spine small and slender, marginal, situated closely below inferior orbital angle.Hepatic spine larger and more robust than antennal, situated just behind level of posterior orbital margin and well below level of antennal spine.Antero-lateral angle moderately produced, rounded.
Abdominal segments smooth (Fig. 1).First segment pleuron highly produced anteriorly, third segment not produced posterodorsally, sixth segment twice as long as deep.Pleura all broadly rounded.Posteroventral angle of sixth segment feebly produced, postero-lateral angle feebly acute.
Telson 0.8 of length of sixth abdominal segment and 3.2 times as long as maximum width (Fig. 2C).Lateral margins convex in anterior half, posteriorly converging.Two pairs of very small marginal dorsal spines, about 0.05 of telson length, present at 0.55 and 0.8 of telson length.Posterior margin (Fig. 2D) rounded, about half of anterior width, with three pairs of spines; lateral spines short but distinctly twice as long as dorsal spines.Intermediate spines largest, about 0.2 of telson length and 1.5 times length of more slender, setulose, submedian spines.
Antennular peduncle (Fig. 2B) normal, exceeding tip of rostrum by distal segment.Basal segment broad, 2 times as long as wide, with stylocerite slender, acute, reaching almost to middle of segment; lateral border convex, anterolateral margin slightly acutely produced mesially, with 2 acute distolateral teeth (Fig. 2E); medioventral margin with tooth in front of statocyst level.Intermediate and distal segments short, together equal to 0.3 of proximal segment length.Upper flagellum biramous, with first 7 segments fused, shorter free ramus 3-segmented and longer ramus consisting of about 10 slender segments.About 6 groups of aesthetascs present.Lower flagellum consisting of about 11-13 slender segments.
Antenna (Fig. 2B) with robust basicerite without lateral tooth.Carpocerite slender, short, reaching almost to middle of scaphocerite.Scaphocerite large, extending well beyond antennular peduncle, about 2.5 times as long as broad, with greatest width in midlength, distomedially angulated; lateral border almost straight, with acute distal tooth; lamina extending far beyond distolateral tooth.
First pereiopod (Fig. 3A-D) slender, reaching to end of scaphocerite.Chela with palm subcylindrical, slightly bowed and compressed, about 4 times as long as wide.Fingers about 0.75 of palm length; cutting edges gaping distally, bearing series of 5 small blunt teeth at distal third on dactylus, and 3 such European Journal of Taxonomy 188: 1-26 ( 2016) teeth on fixed finger; very thin denticulate lamella present laterally along latter series of teeth on both fingers, tip of fingers slender, hooked.Cleaning setae present proximally on palm and on disto-ventral end of carpus, latter being subequal to chela length and 6.5 times as long as wide distally.Merus about 1.3 times as long as carpus and almost twice length of ischium.Basis and coxa normal.
Second pereiopods (Fig. 3E-F) greatly reduced, small, reaching almost to end of carpocerite, subequal and similar, resembling ambulatory pereiopod.Chela without any trace of fixed finger; dactylus resembles that of walking legs.Unguis distinct, occupying distal 0.25 of dactylus length, corpus slender, 4.2 times as long as basal width, slightly curved, without accessory spines or teeth, long setae arising from distal and subdistal part of corpus.Propodus subcylindrical, unarmed, about 6.5 times as long as wide and 2 times length of dactylus; dactylus unarmed.Carpus, merus and ischium unarmed, lengths in ratio of 1.2, 1.0 and 1.6 times length of propodus.Basis and coxa normal.
Ambulatory pereiopods slender, distinctly longer and more robust than second pereiopods.Third pereiopod (Fig. 3G) exceeds tip of scaphocerite by dactylus.Dactylus (Fig. 3H) slender, uniformly tapering, unarmed and with a distinct unguis on distal 0.45 of length, total length about 5 times width near base.Propodus about 12 times as long as wide, 3 times length of dactyl, and devoid of spines.Carpus, merus and ischium 0.5, 0.8 and 0.5 of propodus length, unarmed.Fourth and fifth pereiopods similar, dactylus of fifth pereiopod (Fig. 3I) slightly more slender and straighter than that of third leg.Uropods (Fig. 2C) slender, extending well beyond tip of telson.Protopodite unarmed laterally.Exopod about 3 times as long as wide, extending well beyond endopod, with lateral border almost straight, entire, terminating in small mobile spine (Fig. 2F).Endopod 3.3 times as long as wide.
Second maxilliped (Fig. 4G) with small dactylar segment, about 1.6 times as long as wide, convex medially, bearing row of stout, serrulate spines.Propodal segment large, twice as long as dactylar segment, twice as long as wide, with subrectangular distomedial angle.Medial margin broadly convex, with row of coarsely serrulate setae.Carpus short.Merus partly fused to ischium, ischium partly fused to basis, basis without exopod; combined segment stout, about twice as long as wide.Coxa produced medially, with small, suboval epipod laterally.
Third maxilliped (Fig. 4H) with broad antepenultimate segment, about 4 times as long as wide.Basis completely fused with ischiomerus, junction indicated medially by small knob; median margin sparsely provided with serrulate setae over proximal two thirds.Penultimate segment slender, about 3 times as long as wide, 0.33 of length of antepenultimate segment and with 2 slender, serrulate setae on medial border.Terminal segment 3 times as long as wide, slightly shorter than penultimate segment, with groups of serrulate setae medially and slender terminal setae.Exopod absent.Coxa not produced medially, with broadly rounded lateral lobe and small reduced arthrobranch laterally.

Other specimens
Females similar to holotype.Dorsal rostrum teeth varying from 4 (smaller specimen, PoCL 1.2 mm, damaged, lost) to 5, lamina shallower in smallest specimens, first pereiopod fingers with 3-4 distal cutting teeth.Single male specimen available (Fig. 5) comparatively smaller and more slender than adult females; rostrum (Fig. 5A) more shallow, bearing 4 dorsal teeth; first male pleopod (Fig. 5B-C) with endopod almost half length of exopod, enlarged distally, with apex rounded, with 3 short simple setae proximally on medial border and 2 short setae more distally on lateral border; second pleopod (Fig. 5D-E) with endopod slightly shorter than exopod, with appendix masculina about as long as appendix interna, with two unequal distal serrulate setae and one simple seta subdistally on lateral margin.
Colouration (Fig. 10B-C) Males largely transparent, with diffuse yellow and white speckles, more dense on cephalothorax.Adult females more heavily coloured.Body generally transparent, faintly speckled with yellow and white colour, with yellow dots on base of the rostrum and on eyestalks, yellow colour more condensed to transverse bands on sides of each basis of antennae, two bands on carapace, and one wide band on each of 1 st to 5 th abdominal segments, all interspaced by faint white dots.Whitish path transversely on the tailfan articulations to the last abdominal segment.Anterior rostrum, antennal flagella, pereiopods, the HORKÁ I. et al., Two new species of Hamodactylus (Palaemonidae) sixth abdominal segment, and tailfan, predominantly transparent.One female from Papua New Guinea reddish coloured instead of yellow.

Distribution
Up to date known from the Madang Lagoon, Papua New Guinea, and the Great Barrier Reef, Australia.
Carapace smooth.Rostrum well developed, almost reaching distal margin of antennular peduncle (Fig. 7A-C), lamina deep, lateral carina situated near to slightly convex, setose, toothless ventral margin; dorsal margin convex, elevated, strongly compressed, with 6 subequal teeth, with first one situated above level of posterior margin of orbit.Supra-orbital and epigastric spines absent.Antennal spine small and slender, marginal, situated closely below inferior orbital angle.Hepatic spine larger and more robust than antennal spine, situated just behind level of posterior orbital margin and well below level of antennal spine.Orbit obsolescent, inferior orbital angle well developed, acutely produced in lateral view.Antero-lateral angle of carapace moderately produced.
Abdominal segments smooth (Fig. 6), with all pleurae broadly rounded posteroventrally.First segment pleuron highly produced anteriorly, third segment not produced posterodorsally, fifth segment dorsal length about half length of sixth segment; latter twice as long as deep, with posteroventral angle feebly produced and postero-lateral angle subtriangular, pointed.
Telson (Fig. 7D-E) 0.8 times as long as sixth abdominal segment and 3.2 times as long as maximum width; lateral margins converge posteriorly, feebly over anterior half and more strongly over posterior half.One pair of very small marginal dorsal spines present at about 0.42 of telson length.Posterior margin feebly angular, about one third of anterior width, with three pairs of spines.Lateral spines short, but distinctly longer than dorsal spines.Intermediate spines well developed, 0.15 of telson length and 1.5 times length of more slender submedian spines, which are finely plumose.
Antennular peduncle (Fig. 7C) exceeding tip of rostrum by 1/3 length of distal segment.Proximal segment broad, 1.6 times as long as wide.Stylocerite slender and acute, reaching almost to middle of segment.Lateral border feebly convex and anterolateral margin slightly produced, bearing 4 acute teeth and numerous setae.Medial ventral margin with tooth at about third of length.Statocyst normally developed and contains a granular statolith.Intermediate and distal segments short, together equal to 0.34 of proximal segment length.Upper flagellum biramous, with first three segments of each ramus fused.Shorter free ramus indistinctly segmented and longer ramus consists of about 9 slender segments, five groups of aesthetascs present, lower flagellum slightly longer than upper flagellum, with about 13 segments.
Antenna (Fig. 7C) with robust basicerite, without lateral tooth.Ischiocerite and merocerite normal.Carpocerite slender, reaching to middle of scaphocerite.Scaphocerite large and broad, lamella extends well beyond antennular peduncle.Lateral border almost straight and ends in an acute distal tooth.Lamella extends far beyond tooth, feebly angulated distomedially, about 2.2 times as long as broad, with greatest width at about one third of its length.
Second maxilliped (Fig. 8F) with small triangular dactylar segment, about 1.6 times as long as wide, convex medially, bearing row of stout, biserrulate spines.Propodal segment large, twice as long as dactylar segment, twice as long as wide, with subrectangular distomedial angle; medial margin almost straight, with row of coarsely serrulate setae.Carpus short.Merus partly fused to ischium; ischium partly fused to basis; basis without exopod.Coxa not produced medially, with small, suboval epipod laterally.
Third maxilliped (Fig. 8G) with broad antepenultimate segment, about three times as long as proximal width.Basis completely fused with ischiomerus, junction indicated medially by small knob.Median margin sparsely provided with simple setae over proximal two thirds.A row of five long setulose setae present distally, submarginally.Penultimate segment slender, 2.9 times as long as wide, 0.36 of length of antepenultimate segment and with few slender, setulose setae distally on medial border.Terminal segment five times as long as wide, 1.1 times length of penultimate segment, with few groups of short, serrulate setae medially and slender, simple terminal setae.Exopod absent.Coxa feebly produced medially, with rounded epipod laterally.Multilamellar arthrobranch present laterally.
First pereiopod (Fig. 9A-B) slender, reaching to end of scaphocerite.Chela with palm subcylindrical, slightly bowed and compressed, about 2.3 times as long as wide.Fingers short, 0.33 of palm length, feebly subspatulate.Cutting edges gape proximally, very thin denticulate lamella laterally in distal third, with series of 4 blunt teeth medially.Tip of dactylus with distinct unguis, smaller spine present laterally.Cleaning setae present proximally on palm and on distoventral end of carpus, latter 1.2 times as long as chela, 5.0 times as long as wide and moderately wider distally.Merus about 1.2 times as long as carpus and twice length of ischium.Basis normal.Coxa with very small, medial setose process.
Second pereiopods (Fig. 9C-D) greatly reduced, equal and similar, extending slightly beyond carpocerite with fingers.Chela with strongly reduced fixed finger, about third length of corpus of dactylus, distally acute, with several long setae.Dactylus resembles that of an ambulatory pereiopod.Unguis distinct and corpus without accessory spines or teeth.Setae arise from anterior, distoventral and extreme distolateral aspects of corpus, which is about 2.3 times as long as wide and 2.3 times as long as unguis.Propodus subcylindrical, about 5.4 times as long as wide centrally and 2.3 times length of dactylus.Propodus without spines.Carpus, merus and ischium unarmed, lengths in ratio of 0.9, 1.6 and 1.1 times length of propodus.Basis and coxa normal.
Ambulatory pereiopods slender, distinctly more robust than second pereiopods.Third pereiopod (Fig. 9E-F) not exceeding scaphocerite.Dactylus slender, uniformly tapering, unarmed and with indistinct unguis.Total length about five times width near base.Propodus about twelve times as long as wide, 4.0 times length of dactylus, devoid of spines except for blunt, short ventrodistal spine, with series of plumose setae dorsolaterally.Carpus, merus and ischium 0.43, 0.92 and 0.45 of propodus length, unarmed.Fourth and fifth pereiopods similar to third.
Uropods (Fig. 7D) slender and extend well beyond tip of telson (Fig. 7E).Protopodite unarmed laterally.Exopod about 3.6 times as long as wide, extends well beyond endopod, which is 3.6 times as long as wide; with lateral border almost straight, entire, terminating in small mobile spine (Fig. 7D).
About 30 eggs of ca.0.5 mm in length present under abdomen.

Male allotype
First pleopod (Fig. 7F) with endopod almost half length of exopod, broadly lobate with two long plumose setae lateroproximally and five short simple setae medioproximally.Second pleopod (Fig. 7G) with endopod slightly shorter than exopod, with appendix masculina about as long as appendix interna, with two distal serrulate setae and two simple setae along lateral margin.

Colouration
Adult females (Fig. 10D) with semi-translucent body covered by distinct transverse bands -two on carapace and one on each of 1 st to 6 th abdominal segment; first carapacial band running dorsally from base of rostrum obliquely to sides, forming wide "V-shaped" figure on anterior dorsum; first abdominal band diffused dorsally, but compact on sides, widening ventrally; 2 nd segment with additional large spot anteriorly on sides; 6 th abdominal segment transparent except for narrow brown band posteriorly; transparent interspaces of body irregularly speckled brown.Tail fan transparent but with widely-spaced dark punctuation, with irregular, partly diffused, anterior brown portion.Eyes and bases of antennae brown, distal antennular peduncle brown speckled.Pereiopods and antennal flagella semi-translucent, whitish.

Host
Associated with soft corals of the family Nephtheidae (Octocorallia: Alcyonacea).

Distribution
Known from northeastern and southwestern Sulawesi and Ambon in Indonesia and from Sabah, Malaysia.

Remarks
There is some variation in morphological characters related with the size of the specimens examined.The smallest specimens have only 2 teeth on the dorsal side of the rostrum, whereas the largest specimens can have 6 teeth.The number of teeth along the distolateral margin of the first segment of the antennular peduncle also varies with size to some extent; the smallest specimen only has one tooth, while the larger ones can have 4 teeth.The number of fused segments of the upper antennular flagellum increases with size, up to about 5 segments.It was noted that in the larger males, the number of series of aesthetascs on the upper antennular flagellum was much higher than in juveniles and females, reaching about 11.Also the number of segments of the longer free ramus of the upper antennular flagellum was much larger, as is its length.The same holds for the lower antennular flagellum.
In the small specimens, the distal denticulate lamina with the blunt teeth medially on the cutting edge of the chela of the first pereiopod is absent.Pleopods are longer in males than in females.
Most examined specimens of the type series are consistent in the presence of only one pair of the dorsal telson spines, while the distal pair, clearly present in most congeners, is missing in all specimens of H. pseudaqabai sp.nov.In the larger specimens the remaining pair of small spines is situated in the middle of the telson (Figs 6, 7D).In the smaller specimens of RMNH.CRUS.D.48243 this pair of spines is also missing and the telson is thus fully devoid of the dorsal spines.

Molecular analysis
The obtained phylogenetic tree resolved by Maximum Likelihood based on COI sequence data (Fig. 11A) indicates, with high basal support of both the ML and BI methods, two genetic lineages among described species of the genus Hamodactylus.The first one is composed of H. boschmai together HORKÁ I. et al., Two new species of Hamodactylus (Palaemonidae) with H. macrophthalmus (their mutual division is well supported basally by the BI method) and the second one contains all the remaining species.In the second clade, H. noumeae occupies the basal position, subsequently followed by H. aqabai.The latter species is a sister taxon to the terminal couple of new species, H. paraqabai sp.nov.and H. pseudaqabai sp.nov.The genetic divergence of H. aqabai in relation to the pair of new species reaches 14-15%.While the genetic distance between those new species is comparatively low (3-4%), their subdivision is well supported basally.
The median-joining network (Fig. 11B) reveals two well separated groups of nodes for haplotypes respective to the two new species (colour circles) described in this paper, and hypothesised haplotypes (small black circles).The links connecting the nodes indicate the number of character differences.The shortest interspecific link from one species to another represents 15 mutation events for the COI gene.The intraspecific haplotype network covers 7 mutation events for two analysed H. pseudaqabai sp.nov., but up to 11 mutations between 4 specimens of H. paraqabai sp.nov.; just one mutation is indicated for the Australian specimens of H. paraqabai sp.nov., but 10 mutations for their two conspecifics from Papua New Guinea (or 1-7, if the hypothesised haplotypes are included).

Discussion
The genus Hamodactylus currently contains six species, including the two new ones described here.The genus is unique among symbiotic palaemonid shrimps in the strong reduction in size of the second pereiopods, up to a small and slender appendage similar to an ambulatory leg, while those are generally well developed, larger and more robust, sometimes highly modified, in other symbiotic palaemonids.Other remarkable characters are more or less widely distributed among often unrelated genera.The European Journal of Taxonomy 188: 1-26 (2016) present).In addition to these characters, the adult female of H. paraqabai sp.nov.has the posterior dorsum of the carapace slightly swollen, while a female of H. pseudaqabai sp.nov. is distinctly gibbous in that place.The first gonopod of the male of H. paraqabai sp.nov.has the endopod elongate, slightly enlarged distally, but the endopod in H. pseudaqabai sp.nov. is broadly ovoid distally.
Actually, the known species of Hamodactylus differ also geographically: H. boschmai and H. noumeae are widely distributed throughout the Indo-West Pacific area, while H. aqabai is the westernmost species, known only from the northern Red Sea; H. macrophthalmus and H. pseudaqabai sp.nov.occupy the central IWP region, being known from Indonesia and Malaysia; and H. paraqabai sp.nov.occurs in seas around Papua New Guinea and northeastern Australia.
Based on the present molecular analyses of known Hamodactylus species, both new species are closely related and have separated from a common ancestor quite recently, which, together with their geographical proximity, is confirmed by the synapomorphic state of the multidentate distal cutting edge on the fingers of the first pereiopod.The distal denticulate lamina on those fingers is a character shared with their closest sister taxon from the Red Sea, H. aqabai.From the present pair of new species, H. pseudaqabai sp.nov. is more similar to H. aqabai, sharing with it the level of reduction of the second pereiopod chela (to a small but distinct stub, vs full reduction in H. paraqabai sp.nov.) and the reduction of the dorsal telson spines to a single proximal pair.
Hamodactylus noumeae, as the basal member of the 'aqabai' lineage, possesses laterally compressed dactyli on the walking legs, and has the fingers of the first pereiopod chelae bearing a long denticulate lamina occupying almost the whole length of the otherwise unarmed cutting edges.Those characters might be regarded as plesiomorphic, being shared with H. boschmai, a member of the second genetic lineage of Hamodactylus.
Hamodactylus boschmai and H. macrophthalmus are remarkably different from the quite uniformly built members of the above mentioned 'aqabai' clade.Hamodactylus boschmai possesses supraorbital teeth on the carapace, as well as strongly hooked dactyli overhanging the half-reduced fixed finger on the second pereiopod chela.The latter leg is not noticeably reduced in size.This also confirms the basal position of this species in the actual two-member clade.Hamodactylus macrophthalmus shares with H. boschmai the elongate lamina on the first pereiopod fingers; the pectination of H. macrophthalmus is, however, feebly developed (Fransen & Rauch 2013: fig. 4A).Based on a comparison of the COI sequences, the latter species is genetically most advanced resulting, among others, into the unique eye elongation and the strongly shortened rostrum, and by the modification of the second pereiopods chelae into the 'atyid-like' shape as noted above.The level of size reduction of the second pereiopod as well as the elongate, slender walking dactyli, are comparable with those of the 'aqabai' clade members (excluding H. noumeae with regards to the later character, see above).The size and shape reduction of the second pereiopods is, however, most advanced in the three terminal members of the 'aqabai' clade, i.e., H. aqabai, H. pseudaqabai sp.nov., and H. paraqabai sp.nov.Both the new species are evidently derivates of the most modern cleavage within the known species of the genus resulting in comparatively low molecular divergence on the low end of the commonly used 3-5% p-distance approach for delimiting species.Nevertheless, their morphological distinctions, particularly in the key morphological characters (below), are in good conformity with the basally well supported molecular divergence of these two species in the present molecular (BI) analysis.
The haplotype network analysis provides more details on the molecular divergence between the new species, confirming together with that their closer phylogenetic relationship, and into their intraspecific haplotype variability.While the COI sequences of the two Australian specimens analysed are almost identical, their conspecific specimens from Papua New Guinea show a wider molecular divergence.

European Journal of Taxonomy 188: 1-26 (2016)
The number of specimens analysed is, however, too low to provide a more adequate insight into the haplotype variability covered by those two species.
Thanks to the discovery of the two new species, the number of species in the genus Hamodactylus increased by 50%, now comprising six species.A key for their identification is proposed here.

Fig. 11 .
Fig. 11.Results of molecular analyses of Hamodactylus spp. A. Phylogenetic tree resolved by Maximum Likelihood based on COI sequence data with the HKY+I+G substitution model (bootstrap values are expressed as percentages in the order ML/BI; GenBank accession numbers are provided for all specimens; newly described species are in bold).B. Median-joining haplotype network showing phylogenetic relationships among haplotypes of the COI gene of two new species of Hamodactylus (yellow colour denotes haplotypes sampled in Madang Lagoon, Papua New Guinea; green in Lizard Island, Australia; blue in Sabah, Malaysia; red in Sulawesi, Indonesia); small black circles represent missing (hypothesised) haplotypes to connect existing sequences within the network with maximum parsimony.

Table 1 .
Species used in the molecular analysis, with details on sampling locations, GenBank accession numbers (COI) and voucher identification numbers of specimens examined.AU = Australia; IN = Indonesia; JO = Jordan; MA = Malaysia; PNG = Papua New Guinea; * = sequences obtained from GenBank.