Arachnochium mirabile ( Kemp, 1917 ) Kemp, 1917

Wowor, Daisy & Ng, Peter K. L., 2010, On two new genera of Asian prawns previously assigned to Macrobrachium (Crustacea: Decapoda: Caridea: Palaemonidae) *, Zootaxa 2372, pp. 37-52 : 39-44

Arachnochium mirabile ( Kemp, 1917) comb. nov.

( Figs. 1–3 )

Palaemon mirabilis Kemp, 1917: 227 , Pl. 10.

Macrobrachium mirabilis . — Suvatti 1937: 49.

Macrobrachium mirabile . — Holthuis 1950: 174. — Chace & Bruce 1993: 34. — Ng 1994: 75, Fig. 3 . — Naiyanetr 1998: 32; 2007: 37. — Dang & Ho 2001: 35. — Wowor & Choy 2001: 287. — Cai et al. 2004: 591 .

Material examined. INDIA: 9 females, syntypes, ( ZMA De 102.809), Hughly River, Sibpur near Calcutta, India. THAILAND: 3 ov. females ( USNM 65500), Bang Pakong River, leg. H. M. Smith, 14.II.1924; 2 females ( USNM 65573), Chao Phraya River at Pak Nam, leg. H. M. Smith, 21.VII.1925; 1 ov. female ( USNM 65498), Mae Nam at Pak Nam, leg. H. M. Smith, 5.VII.1923; 2 ov. females ( USNM 65533), Bangkok, leg. H. M. Smith, 12.IX.1923; 1 male (cl 10.25) ( USNM 65534), Head of Gulf of Siam, leg. H. M. Smith, 11VI.1923; 1 female, 6 ov. females ( USNM 65499), Mae Nam at Bakret, leg. H. M. Smith, 29.VI.1923; 2 ov. females ( USNM 65535), Chao Phraya River at Pak Nam, leg. H. M. Smith, 10.VIII.1923. BORNEO: 6 males (cl 6.5– 8.4), 9 females (cl 5.4–11.1), 1 ov. female (cl 11.9) ( ZRC 2009.0747), Sg. Baram at Marudi, Sarawak, leg. D. Wowor, 13.IX.1998; 1 female (cl 7.2) ( MZB Cru 2587), Sg. Sambas at Sambas, W. Kalimantan, leg. D. Wowor, V.1998; 2 males (cl 7.0–7.8), 3 females (cl 5.4–9.2) ( MZB Cru 2588), Sg. Sambas at Sambas, W.

Kalimantan, leg. A. Tjiu & D. Wowor, 31.V.1998; 2 females (cl 7.6–11.8), 3 ov. females (cl 10.7–13.8) ( ZRC 2009.0748), Sintete, Sambas Regency, leg. D. Wowor, 2.VI.1998; 2 ov. females (cl 13.0–13.7) ( ZRC 2009.0749), Sambas, W. Kalimantan, leg. H. H. Tan, 18.IV.1998; 16 males (cl 6.3-9.4), 28 females (cl 6.2- 12.6) ( MZB Cru 2604), purchased at Palangka Raya wet market which were caught from Sg. Rungan, C. Kalimantan, coll. D. Wowor, 19.VIII.2009; 1 female (cl 13.2) ( MZB Cru 1435), Sg. Pela at Semayang Lake, E. Kalimantan, leg. D. I. Hartoto & Syawal, 12.VI.1997; 27 males (cl 6.7–12.5), 16 females (cl 9.6–16.0), 49 ov. females (cl 8.3–16.3) ( MZB Cru 2589), Samarinda, Mahakam River basin, E. Kalimantan, leg. D. Wowor, 7.XI.1999; 8 males (cl 7.3–10.2), 4 females (cl 10.0–10.8), 8 ov. females (cl 9.5–14.1) ( ZRC 2009.0763), Samarinda, Mahakam River basin, E. Kalimantan, leg. D. Wowor, 7.XI.1999; 3 females (cl 11.6–12.4) ( MZB Cru 2590), Labanan camp, Labanan Concession, Bulungan Regency, E. Kalimantan, leg. R. Stuebing, 9.IV.2001; 1 female (cl 7.9) ( ZRC 1995.520), Sg. Sebuku, Pambeliangan, E. Kalimantan, leg. M. Kottelat, 12.II.1993; 8 males (cl 5.2–12.7), 3 females (cl 6.1–7.9) ( ZRC 1995.519), Sg. Sebuku, Pambeliangan, E. Kalimantan, leg. M. Kottelat, 16.II.1993; 1 male (cl 3.2), 6 females (cl 3.3–7.2) ( ZRC 1995.463), tidal creek near Semunad, E. Kalimantan, leg. M. Kottelat, 10.II.1993; 2 males (cl 6.0–6.3), 37 females (cl 4.3–12.1) ( ZRC 1995.469), Sg. Tulit at Semunad, E. Kalimantan, leg. M. Kottelat, 10.II.1993.

Description. The description is mainly based on an ovigerous female (cl 14.7) from Samarinda, E. Kalimantan (MZB Cru 2589), since the syntypes examined are small and not complete. Rostrum short, 0.53 of cl (0.48–0.55 in other specimens) with tip reaching mid or distal end of third segment of antennular peduncle, basal crest well developed, very high; deep, maximum depth distinctly more than maximum dorsoventral diameter of cornea; lateral carina well developed, continuing almost to tip; dorsal carina distinctly convex with tip directed anteriorly, teeth more closely spaced above orbit, armed with 16 teeth (14–17 in other specimens, mode 16), 4 teeth completely postorbital (4 or 5 in other specimens, mode 4), postorbital teeth on anterior 0.24 of carapace (0.21–0.24 in other specimens); ventral carina with 1 teeth (1–2 in other specimens, mode 1), first tooth located at about distal half ( Fig. 1 A). Ocular cornea well developed, 0.16 of cl (0.18–0.23 in other specimens). Carapace glabrous, inferior orbital margin feebly produced, slightly angular, appearing truncated, postantennular carapace margin straight ( Fig. 1 B). Antennal spine sharp, slender, continuing posteriorly as a ridge, situated below lower orbital angle; hepatic spine smaller, situated behind and below antennal spine; branchiostegal suture running from hepatic spine to carapace margin. Ocular beak well developed, expanded lateral tip folded vertically to anterior direction. Epistome completely bilobed, each lobe with 1 tuft of long soft setae, lobes with rounded margin ( Fig. 1 C). Scaphocerite slender, 0.65 CL (0.68–0.75 in other specimens), length 2.57 times maximum width (2.67–3.04 in other specimens), lateral margin straight, distolateral tooth failing to reach end of lamella, anterior margin strongly produced forward at inner margin. Third maxilliped with distal half of ultimate segment extending beyond antennal peduncle; ultimate shorter than penultimate segment, 0.69 times as long as penultimate (0.65–0.71 in other specimens); exopod shorter than ischiomerus ( Fig. 3 G).

First pereiopods slender, exceeding scaphocerite by half or entire fingers, shorter than second pereiopods; fingers about as long as palm; carpus 1.76 times chela length (1.76–1.83 in other specimens), 1.05 times merus length (1.00– 1.06 in other specimens); few scattered short stiff setae present on fingers, inner margin of ischium and basal segments ( Fig. 2 A).

Second pereiopods similar in shape, equal in size, very slender; chela extending beyond distal end of scaphocerite. Whole leg glabrous except few stiff short setae on distal half of fingers, about 1.6 as wide as first pereiopod. Chela 0.58 of cl (0.63–0.74 in other specimens), length 7.08 times width (9.38–10.67 in other specimens), outer and inner margins more or less straight, fingers curving inwards, upper and lower margins rounded; palm greater than maximum merus width, subcylindrical, width 1.08 times depth (1.07–1.16 in other specimens); fingers 1.18 times palm length (1.24–1.35 in other female specimens, 1.48–1.67 in male specimens), touching along cutting edges, oblique carina present along cutting edge of pollex; dactylus and pollex without tooth; fingers uncinate at tip; carpus slightly tapered, 1.45 times palm length (1.41–1.61 in other female specimens, 1.21-1.37 in male specimens), length 5.65 times distal width (5.35–6.25 in other female specimens, 4.14–5.14 in male specimens), 0.66 times chela length (0.63–0.68 in other female specimens, 0.48–0.51 in male specimens), 0.90 times merus length (0.86–0.94 in other female specimens, 0.69–0.73 in male specimens); merus not inflated, 1.09 times ischium length (1.02–1.17 in other specimens); ischium slightly tapered ( Figs. 2 B, G–H).

Third pereiopods with entire dactylus or distal one-seventh of propodus extending beyond distal end of scaphocerite, shorter than second pereiopods, but longer than first pereiopods; few scattered very short stiff setae present on propodus and ischium, otherwise glabrous; dactylus slender, curved, fringed with dorsolateral setae, ventral carina obsolete; 6 ventral spines distributed along length of propodus ( Figs. 2 C–D).

Fourth pereiopods with distal half or three-quarters of propodus extending beyond distal end of scaphocerite, longer than second pereiopods; few scattered very short stiff setae present on propodus and ischium, otherwise glabrous; 5 ventral spines distributed along length of propodus ( Fig. 2 E).

Fifth pereiopods with distal four-fifths or whole propodus extending beyond distal end of scaphocerite; few scattered very short stiff setae present on propodus, merus and ischium, otherwise glabrous; 8 ventral spines distributed along length of propodus ( Fig. 2 F).

T4 with large blunt tip triangular median process, with moderate posterior submedian plate ( Fig. 1 E); T5 without transverse plate ( Fig. 1 F); T8 of male without anterolateral lobes, with low, wide median process ( Fig. 1 G). Abdomen smooth, glabrous, fifth segment with bilobed posterolateral margin ( Fig. 1 L). First 2 male abdominal sternites with small triangular median process of similar form and size; third abdominal sternite without median process ( Fig. 1 H). Inter-uropodal sclerite not developed, preanal carina absent. Telson elongated and slender, glabrous, 5.20 times median width (4.93–5.17 in other specimens), lateral margin straight, convergent, 2 pairs of dorsal spines present, posterior subventral margin straight with long pointed median point, median projection overreached by inner pair of posterior spines, with 1 pair of long plumose subventral setae, longer than inner pair of spines ( Figs. 1 J, K). Uropods with acute distolateral tooth, mobile mesial spine distinctly longer than distolateral tooth ( Fig. 1 I); exopod 3.80 times longer than wide (3.50–4.00 in other specimens). Developed eggs small, maximum size 0.6 × 0.4 mm, ovoid, numerous.

Habitat. Brackish and fresh water bodies subject to tidal influence.

Remarks. Arachnochium mirabile comb. nov., was described and illustrated in detail by Kemp (1917), based on specimens collected from the Rangoon and Moulmein Rivers in Myanmar (= Burma) and various localities in the Gangetic delta in India. During the present study only the syntypes from Sibpur, near Calcutta, India, were available. These consist of young females with some legs missing; therefore, a lectotype has not been designated from this syntypic series. Instead, the present description is based on newly collected material. The high basal crest and short rostrum, slender, glabrous and relatively short second pereiopod, and long fifth pereiopod easily distinguish it from all Macrobrachium species (see Remarks for Arachnochium nov. gen).

Distribution. Gangetic Delta in west India, Myanmar, Thailand, southern Vietnam and Borneo.

Figures

FIGURE 1. Arachnochium mirabile (Kemp, 1917) comb. nov.: A, lateral view of carapace; B, postantennular carapace margin; C, epistome; D, paragnaths; E, T 4; F, T 4 and T 5; G, T 8; H, first 3 abdominal sternites; I, mobile mesial spine of exopod of uropod; J, telson; K, same, tip; L, lateral view of last 3 abdominal somites. A – B, J – L, ov. female (cl 10.7, MZB Cru 2589); C, E, G – I, female (cl 8.8, MZB Cru 2589); D, F, female (cl 11.0, ZRC 2009.0747). Scales: L = 5.0 mm; A – B, D, F = 2.0 mm; C, E, G – K = 1.0 mm.

FIGURE 2. Arachnochium mirabile (Kemp, 1917) comb. nov.: A, first pereiopod; B, second pereiopod; C, third pereiopod; D, same, dactylus; E, fourth pereiopod; F, fifth pereiopod; G, female second pereiopod; H, male second pereiopod. A – F, ov. female (cl 14.7, MZB Cru 2589); G, female (cl 16.0, MZB Cru 2589); H, male (cl 12.0, MZB Cru 2589). Scales: G = 5.0 mm; A – C, E – F, H = 2.0 mm; D = 1.0 mm.

FIGURE 3. Arachnochium mirabile (Kemp, 1917) comb. nov.: A, mandible; B, maxillula; C, same, palp; D, maxilla; E, first maxilliped; F, second maxilliped; G, third maxilliped; H, first pleopod; I, second pleopod. A – G, female (cl 11.0, ZRC 2009.0747); H – I, male (cl 11.0, MZB Cru 2589). Scale: A – I = 1.0 mm.