Hamodactylus pseudaqabai Horká, Fransen & Ďuriš, 2016, sp. nov.

Hamodactylus pseudaqabai sp. nov.

urn:lsid:zoobank.org:act: 5306FF2F-64E9-47A5-8554-393952257DEF

Figs 6–9, 10D

Hamodactylus aqabai – Fransen 2012: 102. — Fransen & Rauch 2013: 287 (Tab. 1), 288 (comparative material).

non H. aqabai – Bruce & Svoboda 1983: 26, figs 10–14.

Etymology

The specific name pseudaqabai is a noun combined from the prefix pseudo - (Greek: false) and the suffix - aqabai, the species name used for H. aqabai, a very similar species from the Red Sea.

Material examined

Holotype

INDONESIA: ovigerous ♀ (PoCL 2.0 mm), North Sulawesi, Lembeh Strait, Kelapadua, 1°26.1' N 125°12.6' E, stn LEM.12, depth 4 m, on nephtheid Alcyonacea, 4 Feb. 2012, coll. C.H.J.M. Fransen (GenBank acc. nr. KT598272) (RMNH. CRUS.D.57195).

Allotype

INDONESIA: 1 ♂ (PoCL 1.4 mm), same data as holotype (RMNH. CRUS.D.57007).

Paratypes

INDONESIA: 2 ovigerous ♀♀ (PoCL 1.7 and 1.8 mm), 1 non ovigerous ♀ (PoCL 1.6 mm), 7 ♂♂ (PoCL 0.9–1.1 mm), 7 juveniles (PoCL 0.7–0.9 mm), Moluccas, Ambon, W side of Pombo Island, stn RBE.16, depth 10 m, diving, from nephtheid Alcyonacea (host preserved), 15–17 Nov. 1990, coll. C.H.J.M. Fransen (RMNH. CRUS.D.48243); 1 ♂ (PoCL 1.7 mm), SW Sulawesi, Spermonde Archipelago, S side, depth 10 m, scuba diving, on purple Nephthea, 26 Sep. 1994, leg. C.H.J.M. Fransen (RMNH. CRUS.D.46369); 1 non ovigerous ♀ (PoCL 1.4 mm), Moluccas, Ambon, Outer bay, N coast W of Sahuru, Stn MAL.03, 03°40' S 128°09' E, depth 10 m, diving, on Nephthea sp., 5 Nov. 1996, leg. C.H.J.M. Fransen (RMNH. CRUS.D.47481).

MALAYSIA: 1 ovigerous ♀ (PoCL 2.2 mm), Ligitan reef N2, Semporna area, Sabah, stn SEM.09b, 04º15.0' N 118º37.9' E, depth 10 m, on nephtheid Alcyonacea, 1 Dec. 2010, coll. Nina Ho (GenBank acc. nr. KC633175) (RMNH. CRUS.D.53969).

Description of holotype (ovigerous ♀)

Small sized shrimp with slender pereiopods (Fig. 6).

Carapace smooth. Rostrum well developed, almost reaching distal margin of antennular peduncle (Fig. 7 A–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. 7 D–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

CRUS.D.57195), habitus, lateral view. Scale bar = 1 mm. 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.

Eyes (Fig. 7C) well developed. Cornea globular, obliquely set on proximally swollen stalks, with distinct accessory pigment spot posteriorly.

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

ventral mm.

view. G. Right third maxilliped, ventral view. Scale bars: A, C-G = 1 mm; B = 0.25 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.

Fourth thoracic sternite unarmed.

Mouthparts (Fig. 8; dissected from Malayan ovigerous female paratype). Mandible (Fig. 8 A–B) rather feeble, with cylindrical molar process (Fig. 8B) bearing a few brushes of setae distally. Incisor process of normal size, with four teeth distally, of which lateral most enlarged. Mandible without palp.

Maxillula (Fig. 8C) with slender, feebly bilobed palp, lower lobe bearing small seta distally. Upper lacinia rather short and stout, with single row of robust simple spines and few spinose setae distally. Lower lacinia slender, with several slender serrulate setae distally.

Maxilla (Fig. 8D) with tapering, non-setose palp. Basal endite simple, short, stout and blunt, with simple seta distally. Coxal endite obsolete, medial region slightly convex. Scaphognathite normal, posterior lobe lost in dissection. Marginal plumose setae well developed.

First maxilliped (Fig. 8E) with, slender, tapering, non-setose palp. Basal region broad and round, not distinctly separated from coxal region. Median margin sparsely provided with slender, setulose setae.

Y. Chan (B), A.F. Berberian (C), C.H.J.M. Fransen (D).

Caridean lobe distinct, with coarsely setulose, plumose marginal setae. Flagellum of exopod greatly reduced, devoid of setae. Epipod small, rounded.

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. 9 A–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. 9 C–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. 9 E–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.

Pleopods well developed. Marginal plumose setae of exopod and endopod coarsely serrulate.

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.

Measurements (mm)

PoCL of ovigerous females 1.7–2.0; of non-ovigerous female 1.6; of males 0.9–1.7.

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 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).