Palaemonella yalla Anker & Assayie 2023, sp. nov.
Creators: name: Anker, Arthur
name: Assayie, Aymere Awoke
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Palaemonidae
Palaemonella
Palaemonella yalla

description: Palaemonella yalla sp. nov.
(Figs. 1–3)
Type material. Holotype: ovigerous female, pocl 3.9 mm, cl 5.2 mm, FLMNH UF 71446, Saudi Arabia, Makkah Province, Thuwal, King Abdullah University of Science and Technology (KAUST), near King Abdullah Monument, 22°20’26.2”N / 39°05’15.1”E, shallow sandflat between small mangrove and deeper channel, some coral rubble and seagrass present, in burrow, suction (yabby) pump, depth 0.3–1 m, leg. A. Anker & A. Assayie, 29.12.2022 [fcn AA-22-437].
Additional material: ovigerous female, pocl 3.4 mm, cl 5.6 mm, FLMNH UF 71445, Oman, Masirah Island, Ghab, 20°15’06.6”N / 58°37’28.4”E, silty sandflat with numerous massive corals, sieving muddy water after flipping large coral rock, depth 0.2 m (at low tide), leg. A. Anker & J. Meiburg, 10.11.2022 [fcn BOMAN-13448].
Description. Medium-sized palaemonid shrimp with moderately slender, subcylindrical, not particularly compressed or flattened body. Carapace (Fig. 1A–C) smooth; orbit moderately shallow; inferior orbital angle strongly produced anteriorly; postorbital area with semicircular depression abruptly delimited posteriorly by unarmed, non-elevated ridge; supra-orbital tooth or tubercle absent; antennal tooth marginal, distally sharp, long, almost reaching distodorsal margin of basicerite; hepatic tooth well-developed, slightly smaller than antennal tooth and located distinctly below it; pterygostomial angle broadly rounded. Rostrum (Fig. 1A–C, P) well developed, almost straight, horizontal, about 0.7 times length of carapace; tip sharp, overreaching mid-length of scaphocerite and distal margin of second article of antennular peduncle; dorsal margin and continuing postrostral carina with eight large, equidistant, anteriorly directed, sharp teeth, five of them anterior to posterior orbital margin, one at about same level and two posterior to it in holotype (six anterior to posterior orbital margin and two posterior in non-type specimen), posterior-most tooth somewhat more separated from remaining teeth; ventral margin with two widely separated teeth both located in its distal half; lateral ridge fading at about mid-length of rostrum.
Pleon (Figs. 1D, 3) typical for genus; third pleonite not humped or posteriorly produced; pleura of first to fourth pleonites rounded; fifth pleonite posteroventrally subacutely produced; sixth pleonite 1.3 times as long as fifth pleonite (measured along mid-dorsal line), with sharply produced posterolateral angle and subacute posteroventral angle.
Telson (Fig. 1E, F) about twice as long as maximal width, tapering smoothly posteriorly; dorsal surface with two pairs of long, stout, submarginal spiniform setae, at about 0.4 and 0.7 times of telson length, respectively; posterior margin 0.3 times of proximal margin width, subtriangular, with central minute tooth, and three pairs of stout spiniform setae, as follows: short but stout lateral spiniform setae, stouter and much longer intermediate spiniform setae, and slenderer submedian spiniform setae, latter about half as long as intermediate ones and three times as long as lateral ones.
Eyestalks (Fig. 1A, B) with anterior margin convex, slightly wider than long (without cornea); cornea well developed and pigmented, as wide as eyestalk, hemispherical, with distinct accessory pigment spot (Nebenauge).
Antennule (Fig. 1A, B) not particularly modified; first article of antennular peduncle stoutest, longest and widest, with moderately developed, sharp distolateral tooth; statocyst visible dorsally, rounded; stylocerite slender, acute distally, its tip reaching mid-length of first article; ventromesial tooth small, acute; second and third articles subequal in length, together about 0.6 of dorsally visible portion of first article; flagella long, slender; dorsal (= lateral) flagellum biramous, fused portion composed of 11 subdivisions, free ramus well developed, slender, with five or so groups of aesthetascs.
Antenna (Fig. 1A, B) typical for genus; basicerite moderately stout, with acute distolateral tooth; carpocerite subcylindrical, short, not reaching 0.3 of scaphocerite length; flagellum not thickened; scaphocerite extending well beyond end of antennular peduncle, about 3.5 times as long as maximal width; blade relatively narrow, with broadly rounded distal margin; lateral margin almost straight; distolateral tooth strong, distinctly exceeding distal margin of blade.
Epistome and labrum without specific features. Fourth thoracic sternite with strong, subacute, median process (not illustrated). Fifth thoracic sternite with two lateral lobes adjacent to second pereiopods, each with acute triangular submedian process. Sixth to eight thoracic sternites unarmed.
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Mouthparts typical for genus, as illustrated (Fig. 1G–N). Mandible (Fig. 1G) with small, biarticulated palp; incisor process with three stout teeth. Second maxilliped (Fig. 1K, L) with epipod bearing rudimentary podobranch consisting of single finger-like lamella. Third maxilliped (Fig. 1M, N) moderately stout, setose; coxa with large, rounded lateral plate (epipod); basis distinctly separated from endopod; antepenultimate article relatively stout, somewhat twisted and flattened laterally, widening distally, ventrolateral margin with row of small spiniform setae; penultimate article 0.7 length of antepenultimate article, about six times as long as wide; ultimate article 0.7 times as long as penultimate, strongly tapering distally, apex with stout spiniform seta; arthrobranch reduced to few lamellae.
First pereiopods (Fig. 2A, B) slender; coxa with ventral process; ischium about five times as long as wide; merus about 1.8 times as long as ischium, about eight times as long as wide; carpus 1.2 times as long as merus, widening distally; carpo-propodal brush well developed; chela slender, about 0.6 length of carpus; palm smooth, subcylindrical; fingers subequal in length, 1.2 times as long as palm, with spaced tufts of setae; fingertips curved, faintly crossing; finger cutting edges unarmed.
Second pereiopods (Figs. 2C–H, 3) equal in size and similar in shape and armature of chela, slender, elongate; coxa with ventral process; ischium almost five times as long as wide; merus 1.2 times as long as ischium, about 6.5 times as long as wide, distolateral margin produced as stout sharp tooth; carpus 1.2 times as long as merus, distally noticeably widening, except for shallow subdistal constriction, distal margin with three bluntly angular (one subacute) lobes; chela 1.6 times as long as carpus, feebly swollen; palm smooth, subcylindrical, about three times as long as high; fingers subequal in length, 0.9 times as long as palm, fingertips curved and crossing distally; cutting margins of pollex and dactylus each with two low, subtriangular teeth proximally fitting into gape between similar teeth on opposed margin.
Third pereiopod (Fig. 2I, J) very slender, elongate; ischium slightly curved posteriorly, more than eight times as long as wide; merus about 1.8 times as long as ischium, 13 times as long as wide, unarmed; carpus almost 0.7 length of merus, unarmed; propodus 1.6 times as long as carpus, subequal to merus in length, ventral margin with four widely spaced, short spiniform setae, in addition to distal pair of longer spiniform setae flanking base of dactylus; dactylus about 0.3 length of propodus, slender, gently curved, simple, dorsal margin slightly crenulate and with short row of setae. Fourth pereiopod (Fig. 2K) generally similar to third pereiopod, with comparatively longer propodus; dactylus about 0.3 length of propodus. Fifth pereiopod (Fig. 2L, M) longest and more slender than fourth pereiopod, with relatively longer ischium and propodus; propodus with five spiniform setae on ventral margin and longer spiniform seta at distomesial angle adjacent to base of dactylus; grooming brush short, composed of two rows of microserrulate setae distally on ventrolateral surface; dactylus barely reaching 0.3 length of propodus.
Female pleopods without noteworthy features; second pleopod (not figured) and remaining pleopods each with appendix interna; male characters currently unknown. Uropod (Fig. 1O) extending well beyond telson; protopod robust, lateral lobe distally produced as acute tooth; exopod with lateral margin faintly convex, terminating in small distolateral tooth; adjacent distolateral spiniform seta well developed, far exceeding distolateral tooth, not reaching distal margin of exopod; endopod subequal in length to exopod, more slender, ovate.
Colour pattern. Body largely translucent with pale yellow tinge; carapace with scattered, small, reddish spots; pleon with similar reddish spots, some arranged in diffuse transverse bands along posterior margin of each pleonite; eyestalks with pale reddish bands dorsally, cornea golden; antennules with some pale reddish spots; second pereiopods semi-hyaline with pale orange tinge; remaining appendages largely translucent and colourless, sometimes with yellowish tinge; eggs green (Fig. 3).
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Etymology. The name of the new species derives from the common and popular Arabic word yallah (with the subtly pronounced terminal “h” omitted for consonance), meaning “let’s go”, “hurry up” or “alright”, and used in many situations depending on the context (such as yallah! – “let’s go! (for fieldwork)” and yallah! – “alright, let’s go!”); used as a noun in apposition.
Distribution. Presently known only from two localities in the north-western Indian Ocean, viz. the Saudi Arabian coast of the Red Sea near Thuwal (type locality) and Masirah Island, eastern Oman.
Ecology. The type locality of Palaemonella yalla sp. nov. in Saudi Arabia is the same as that of P. jamila (see Anker & Benzoni 2023). Both species were collected from burrows of unknown hosts on a shallow (less than 1 m), near-shore sandflat with patchy seagrass and fragmented coral rubble, not far from mangrove stands (Fig. 4A). The Omani specimen was collected on a silty sandflat dominated by living, mostly massive corals, near large rocky outcrops (Fig. 4B). More precisely, this specimen was found by sieving murky water after turning over a massive coral standing at a depth of 20 cm at incoming tide; however, it cannot be excluded that the shrimp was dwelling inside some kind of burrow excavated by a larger animal (such as a pair of snapping shrimps or a ghost-shrimp) under the coral.
Remarks. Palaemonella yalla sp. nov. is morphologically and probably also phylogenetically closest to P. okunoi Komai & Yamada, 2015, which is presently known only from the Ryukyu Islands, Japan (Komai & Yamada 2015). The two species share many morphological features, including the presence of a moderate, unarmed postorbital ridge, and also have very similar colour patterns (cf. Fig. 4; Komai & Yamada 2015: fig. 1). The most obvious and reliable morphological feature to separate them is the presence in P. yalla sp. nov. vs. absence in P. okunoi of a stout sharp tooth on the distoventral margin of the merus of the second pereiopod (cf. Fig. 2C, D; Komai & Yamada 2015: fig. 5). Further differences are the presence in P. yalla sp. nov. of an apical spiniform seta on the ultimate article of the third maxilliped, which seems to be absent in P. okunoi; the number of articles in the mandibular palp, i.e., two in P. yalla sp. nov. vs. one in P. okunoi; and the proportions of the dactylus of the third pereiopod, which is relatively longer (0.4 length of propodus) and more slender (almost eight times as long as wide at base) in the new species (vs. 0.25 length of propodus and less than six times as long as wide in P. okunoi) (cf. Figs. 1G, M, 2I, J; Komai & Yamada 2015: 354, figs. 3D, 4A, F, G, note: palp missing in fig. 3E, F). Noteworthy, P. okunoi was collected at depths of 5–30 m, among coral rubble, whereas P. yalla sp. nov. was collected in shallower water (0.2–1 m).
Other species that are morphologically similar to P. yalla sp. nov. are: P. hachijo Okuno, 1999; P. rotumana (Borradaile, 1898); P. pottsi (Borradaile, 1915); P. lata Kemp, 1922; P. tenuipes Dana, 1852; and P. foresti Bruce, 2002 (Dana 1852; Borradaile 1915; Kemp 1922; Okuno 1999; Bruce 2002a). The new species can be distinguished from P. hachijo by the biarticulate mandibular palp (vs. unarticulated in P. hachijo); the ultimate article of the third maxilliped apically armed with a stout spiniform seta (vs. with slender setae in P. hachijo); the proximal tooth on the pollex of the second pereiopod being subtriangular (vs. distally serrated in P. hachijo); and the dorsal surface of the telson with much larger spiniform setae, which are also more distant from the lateral margin than in P. hachijo, where they are submarginal (cf. Okuno 1999: figs. 1–3). The new species can be easily separated from the common and widespread P. rotumana by the absence of a small tubercle at the dorsal end of the postrostral ridge (typically present in P. rotumana); the much longer and slenderer second pereiopods (cf. Bruce 1982: fig. 1); and the absence of reddish brown or pale orange transverse bands on each of the second pereiopod fingers, which are typical for P. rotumana (cf. Anker & De Grave 2016: fig. 96). Furthermore, P. yalla sp. nov. differs from P. pottsi by the much shorter rostrum and distinctly more slender second to fifth pereiopods (cf. Bruce 1970), and from P. lata by the much longer fused portion of the lateral antennular flagellum (11 subdivisions in the new species vs. only five in P. lata), the distally armed merus of the second pereiopod (vs. unarmed in P. lata), and the much slenderer third to fifth pereiopods (cf. Kemp 1922). In addition, P. pottsi is an obligate associate of crinoids, and both P. pottsi and P. lata have different colour patterns (cf. Ďuriš 2017; Anker & De Grave 2016: figs. 94, 95). The new species is easily distinguishable from P. tenuipes and P. foresti by the rostral configuration, and from P. tenuipes also by the more ventral and more posterior position of the hepatic tooth (cf. Li 2000: fig. 117; Bruce 2002a: fig. 1B). The remaining species of the genus present more numerous differences with the new species (e.g., Holthuis 1973; Bruce 1975, 1991, 2002b, 2008; Li & Bruce 2006; Marin 2008; Hayashi, 2009; Fransen et al. 2022, 2023; Anker & Benzoni 2023). At least nine of them have different colour patterns, including all species associated with scleractinian corals, up to recently assigned to the genus Vir Holthuis, 1952, which is now considered to be a synonym of Palaemonella (Holthuis 1973; Marin 2008; Kuiter & Debelius 2009; Anker & De Grave 2019; Frolová et al. 2022; Fransen et al. 2022, 2023; Anker & Benzoni 2023), whereas some are deep-water forms (Bruce 1991, 2008; Li & Bruce 2006) or inhabitants of land-locked lava pools (Holthuis 1973).
The identity of Palaemonella sp. sensu Bruce (2003) from Hong Kong, originally reported as Periclimenes digitalis Kemp, 1922 by Bruce (1979, 1982), remains unknown. The illustrations of a single male specimen (pocl 3.2 mm) provided by Bruce (1982: figs. 4, 5) suggest that this form may be very close, if not identical with P. yalla sp. nov., despite their wide geographic separation. However, two morphological differences between the holotype of P. yalla sp. nov. and Palaemonella sp. sensu Bruce (2003) prevent the inclusion of the Hong Kong record under the synonymy of the new species. These are the presence of only one tooth on the ventral margin of the rostrum in the male from Hong Kong vs. two in P. yalla sp. nov. (cf. Fig. 1B, P; Bruce 1982: fig. 4A), and the presence of four spiniform setae on the antepenultimate article of the third maxilliped vs. seven in P. yalla sp. nov. (cf. Fig. 1M, N; Bruce 1982: fig. 5E). For the time being, it seems most reasonable to leave Palaemonella sp. sensu Bruce (2003) as a presumably undescribed species with affinities to P. yalla sp. nov., P. okunoi and P. hachijo.
Palaemonella yalla sp. nov. is the fifth species within the family Palaemonidae associated, at least facultatively, with larger burrowing animals (Marin 2008; Kuiter & Debelius 2009; Okuno 2017; Anker & De Grave 2019; Anker & Benzoni 2023). However, the elusive burrowing host or hosts of the new species remain to be determined, as is the consistency of this association.
description: Published as part of Anker, Arthur & Assayie, Aymere Awoke, 2023, A further new species of Palaemonella Dana, 1852 from the coasts of the Arabian Peninsula (Malacostraca: Decapoda: Palaemonidae), pp. 427-436 in Zootaxa 5369 (3) on pages 428-434, DOI: 10.11646/zootaxa.5369.3.6, http://zenodo.org/record/10151690