Eupontonia nudirostris Marin, 2014, sp. nov.
Creators: name: Marin, Ivan
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Eupontonia
Eupontonia nudirostris

description: Eupontonia nudirostris sp. nov.
(Figs. 1–4, 5 a, b)
Material examined.— Holotype, non-ovigerous female (pcl. 8.8 mm, tl. 30 mm)—Pacific Ocean, South China Sea, Vietnam, Nhatrang Bay, south-east of Tre Island, Dam Bay, 12°12′19.53″ N 109°18′ 11.12″E, mangrove littoral, 0.5 m depth, muddy sand bottom, burrow of thalassematid spoon worm Listriolobus sp., by yabby-pumping, collected by I. Marin & S. Sinelnikov, 6 April 2014 (ZMMU).
Description.—Medium-sized pontoniine shrimp with cylindrical body and long slender appendages (Fig. 1). Carapace swollen, smooth, with reduced antennal tooth represented by blunt triangular protuberance, without hepatic or supraorbital teeth (Fig. 2 a, b). Rostrum compressed, unarmed dorsally and ventrally, distally blunt and turned downward, reaching to distal antennular segment (Fig. 2 a–c), without dorsal or medial carinae. Orbit well developed, unarmed; inferior orbital angle bluntly produced distally. Pterygostomial angle produced, bluntly rounded distally (Fig. 2 a, b).
Abdominal somites smooth; pleura of abdominal somites I–IV rounded, pleura of abdominal somite V pointed (Fig. 1). Fourth thoracic sternite with spine-like median process directed anteroventrally; fifth sternite with pair of acute submedian teeth separated by U-shaped notch (Fig. 2 d). Telson (Fig. 2 e, f) relatively stout, about 1.5 times as long as proximal wide, narrowing distally, with 2 pairs of dorsal submarginal spines, which situate at 0.45 and 0.75 of telson length (Fig. 2 f), distal margin armed with 3 pairs of spines (Fig. 2 g), medial pair about 10–12 times longer than wide, about 4 times longer than lateral spines and twice longer than central spines.
Eyes well developed, large; eyestalk smooth, cylindrical, stout, about twice wider than long; cornea well developed, subovate (Fig. 2 a, c).
Antennula (Fig. 2 h, i) well developed; basal segment stout, about 1.5 times longer than wide, with stylocerite well developed, overreaching the medial part of the segment, with distolateral angle sharply produced slightly overreaching distal margin of the segment, ventromesial tooth small, situated at distal part of the segment; intermediate segment stout, shorter than wide; distal segment stout, as long as wide, equal to previous segment; proximal part of upper antennular flagellum with 5–7 separate segments, shorter ramus with more than 5–6 segments; about 7–9 groups of aesthetascs present.
Antenna (Fig. 2 j) well developed, basicerite about 1.5 times longer than wide, smooth, with blunt reduced distoventral tooth; scaphocerite wide, about 1.5 times longer than maximal width, overreaching the distal margin of antennular peduncle (Fig. 2 c), with distolateral tooth well developed, acute, small, not overreaching to the distal margin of the blade.
Mouthparts characteristic for the genus and previously described species (Fig 3). Mandibles with well developed processes, with small but well-marked 2-segmented palp (Fig. 3 b). Upper lacinia of maxillula with strong stout sharp setae, resembling teeth (Fig. 3 c, d). Maxilliped III (Fig. 3 h) with well developed exopod, earshaped epipod and small podobranch, with relatively slender unarmed segments; ischiomeral segment about 5 times longer than wide; antepenultimate segment about 4.5 times longer than wide; penultimate segment tapering distally, about 3.5 times longer than wide.
Pereiopod I (Fig. 4 a) with relatively slender unarmed segments, without specific features; coxal segment about as long as wide, with distoventral lobe; basis as long as wide; ischium about 1.5 times longer than wide; merus slender, about 5.5 times as long as wide; carpus about 5.5 times as long as wide, equal to merus; palm (Fig. 4 b) about twice as long as wide, cylindrical, about 0.75 length of fingers; fingers simple and slender, about 4 times as long as proximal width, tapering distally, pincer-like, with straight smooth cutting margins and simple tips (Fig. 4 b).
Pereiopods II similar in shape and size (Fig. 1), with robust and smooth segments; coxal segment (Fig. 4 c) as long as wide, with small distoventral lobe; basis as long as wide; ischium about 3–4 times longer than wide; merus robust, about 4.5–5 times longer than wide, with straight lateral margins; carpus slender, flaring distally, with distal margin triangular in shape, slightly overlapping carpo-propodal articulation (Fig. 4 e); palm (Fig. 4 d) smooth, cylindrical, convex in medial part, about 3 times as long as wide, slightly narrowing medially; fingers relatively slender, about half palm length, about 3 times as long as proximal width; fixed finger (pollex) compressed, about 4 times longer than wide, with 2 small teeth situated in proximal third of the length, with simple sharp curved tip; movable finger (dactylus) slender, compressed, about 4 times longer than wide, with single small tooth situated in proximal third of the cutting margin, opposite to position of teeth on pollex, with simple curved tip.
Pereiopod III (Fig. 4 g) relatively slender, with smooth unarmed segments; coxal segment as long as wide, unarmed; basis as long as wide; ischium robust, about 3 times longer than wide; merus slender, about 6 times as long as wide; carpus about 5 times longer than wide, about half length of propodus and merus; propodus relatively stout, about 8.5 times as long as wide, with smooth unarmed parallel margins, without 3 ventral simple spines (Fig. 4 g) and a pair of simple distoventral spines (Fig. 4 h); dactylus (Fig. 4 h) simple, with basal part about 3 times as long as proximal width, with simple slender and curved unguis. Pereiopod IV similar to pereiopod III (Fig. 4 i). Pereiopod V (Fig. 4 j) with similar to pereiopods III and IV, distoventral part of propodus with numerous rows of small grooming setae.
Pleopods normal, without specific features; pleopod II with appendix interna (Fig.2 k). Uropods relatively stout, exceeding telson (Fig. 2 e, f); distolateral margin of uropodal exopod (Fig. 2 f) with sharply produced distolateral margin and small movable distolateral spine.
Coloration. —Generally body and appendages generally transparent, covered with tiny orange-red bars and bands; cornea black, eyestalk transparent; pereiopods II (chelipeds) covered with particularly broad orange-red band along all segments (Fig. 5 a, b).
Host. —The species was found in association with the thalassematid spoon worm Listriolobus sp. (Echiura, Thalassematidae) (Fig. 5 c). The other shrimp collected in the same echiurian hole was a male specimen of Alpheus sp. (Crustacea: Decapoda: Alpheidae), probably a new specialized echurian-associated species (Anker & Marin, in prep.). All animals were collected with the help of yabby-pump.
Distribution. —The species is presently known exclusively from its type locality, Dam Bay of Tre Island, Nhatrang Bay, Vietnam.
Discussion. —The new species can be easily differentiated from congeners by the unarmed rostrum and the reduced antennal tooth on the carapace (see Fig. 2 a, b). Such morphological features differ greatly from the other three species and likely present an adaptation to the symbiotic lifestyle in the cramped confines of the burrow of a thalassematid spoon worm, the host of the species. The rostrum of Eupontonia nudirostris sp. nov. resembles that of other echiurian-associates, namely the alpheid shrimp genus Athanopsis Coutière, 1897 (Crustacea: Decapoda: Alpheidae) (Berggren, 1991; Anker & Ahyong, 2007; Marin et al, 2014) and highly-specialized bivalve-associated pontoniine shrimps, such as some Anchistus spp., Conchodytes spp., Neoanchistus cardiodytes Bruce, 1975, Bruceonia ardea (Bruce, 1981) and Pinnotherotonia rumphiusi Marin & Paulay, 2010 living inside the narrow mantle cavity space of bivalve shells (Bruce, 1972; 1975, 1981; 1989; Marin & Paulay, 2010; Anker et al, 2010; Britayev & Marin, 2011) or some ascidian-associated species living inside their hosts (see Fransen, 2002). From representatives of the genera Exoclimenella, Palaemonella and Vir the species can be separated by the absence of a hepatic tooth on the carapace (characteristic for the genus Palaemonella), stripes on eyestalk (characteristic for all species of the genus Vir) and the simple chela of the first pereiopod (vs. spatulated in Exoclimenella). The new species undoubtedly belongs to the genus Eupontonia, as demonstrated by the presence of a 2-segmented mandibular palp and the sharp processes on the fourth and fifth thoracic sternites (see diagnosis in Bruce, 1971 and Komai & Minemizu, 2014).
Revised key to species of Eupontonia Bruce, 1971
1. Dorsal and ventral margin of rostrum armed with well-developed teeth........................................... 2 – Rostrum unarmed.................................................................... E. nudirostris sp. nov. 1. Carapace with supraorbital tooth................................................................ E. noctalbata – Carapace without supraorbital tooth...................................................................... 2 2. Posteriormost tooth of dorsal rostral series distinctly postrostral; pereiopod II with carpus distinctly longer than palm, unarmed
........................................................................................... E. gracilipes – Posteriormost tooth of dorsal rostral series not postrostral; pereiopod II with carpus distinctly shorter than carpus, armed with
small distomesial tooth............................................................................ E. oahu
description: Published as part of Marin, Ivan, 2014, The first record of an association between a pontoniine shrimp (Crustacea: Decapoda: Palaemonidae: Pontoniinae) and a thalassematid spoon worm (Echiura: Thalassematidae), with the description of a new shrimp species, pp. 557-566 in Zootaxa 3847 (4) on pages 558-564, DOI: 10.11646/zootaxa.3847.4.5, http://zenodo.org/record/226009