Salmoneus tiburon Anker 2019, sp. nov.
Creators: name: Anker, Arthur
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Salmoneus
Salmoneus tiburon

description: Salmoneus tiburon sp. nov.
Figs. 1–4
Type material. Holotype: non-ovigerous specimen (cl 8.8 mm), MZUSP 34070, Panama, Las Perlas Archipelago, small rocky islet off north-eastern coast of Isla Saboga, rock-sand bottom, depth at low tide: 0.5 m, strong current passage, deep under large rock on sand and small coral fragments, leg. A. Anker, 21.04.2015. Paratype: post-ovigerous specimen (cl 8.2 mm, major cheliped regenerating, dissected), OUMNH. ZC. 2015-08-0035, Panama, Las Perlas Archipelago, Isla Bartolomé off Isla Contadora, extreme low tide, under large rock on coarse sand-rubble sediment, close to large burrow entrance, leg. A. Anker, 31.03.2006 [fcn 06-349].
Description. Medium-sized (cl 8.4–8.8 mm) alpheid shrimp with stout, non-compressed body. Carapace, pleon and telson sparsely setose, with minute pits (Fig. 1a). Rostrum well developed, moderately long, subtriangular, as long as wide at base, acute distally, reaching or slightly overreaching mid-length of second article of antennular peduncle, lateral margins slightly concave; ventral rostral carina unarmed; dorsal rostral carina feebly developed, not reaching level of eyes (Fig. 1a, b, k). Orbital teeth well developed, sharp distally, pointing slightly mesially in dorsal view, up-turned by almost 45° and noticeably directed anterodorsally in lateral view (Fig. 1a, b, k). Pterygostomial region broadly rounded; anterolateral suture present (Fig. 1b); cardiac notch well developed. Each epistomial sclerite with acute process.
Pleon with first to fourth pleura broadly rounded to slightly angular; fifth pleuron with posteroventral angle produced into sharp point; sixth pleonite without articulated flap, posterior margin produced into long sharp tooth flanking telson; preanal plate also sharply produced posteriorly (Fig. 1c, d, e). Telson moderately slender, subrectangular, tapering distally, about 2.7 as long as maximum (proximal) width; dorsal surface with two pairs of stout cuspidate setae both inserted at some distance from lateral margin, first pair just anterior to telson mid-length, second pair between 0.7 and 0.8 of telson length; posterior margin with deep V-shaped notch; posterolateral angles each with one pair of spiniform setae, mesial stouter and about 1.7 times longer than lateral (Fig. 1e, f).
Eyes completely concealed in dorsal view, mostly concealed or partly exposed in lateral view; cornea somewhat reduced, pigmentation restricted to lateral portion of eyestalk; anteromesial margin of eyestalk rounded, without tubercle (Fig. 1a, b, k).
Antennular peduncle very stout; stylocerite long, slender, with sharp tip reaching beyond distal margin of second article; ventromesial carina with small, anteriorly directed tooth; second article square-shaped in dorsal view, as long as wide; lateral antennular flagellum with very short fused portion, consisting of only one or two subdivisions, and well-developed secondary ramus, latter with numerous groups of aesthetascs; mesial antennular flagellum very stout (Fig. 1a, b, g). Antenna with basicerite stout, distoventral margin with subacute lobe dorsal to robust sharp tooth; scaphocerite ovoid in general shape, not reaching end of antennular peduncle, with slightly convex lateral margin and very broad blade, latter slightly overreaching stout sharp distolateral tooth; carpocerite very short, cylindrical, hardly reaching mid-length of scaphocerite (Fig. 1a, b, h).
Mouthparts not dissected, typical for genus in external observation. Third maxilliped moderately slender, pediform; coxa with subrectangular lateral plate; antepenultimate article slightly flattened ventrolaterally; penultimate article about 2.5 times as long as wide; ultimate article with numerous rows of short serrulate setae and longer simple setae, tip with blunt corneous point and two short stout spiniform setae; arthrobranch hyper-developed, with two lobes each with numerous lamellae (Fig. 2a, b).
Chelipeds very asymmetrical in shape and dissimilar in size, carried flexed when not in use. Major cheliped relatively stout; ischium short, stout, with one robust cuspidate seta on ventrolateral surface; merus stout, about 3.5 times as long as maximum width, not widening distally, smooth, distodorsal and distomesial margins unarmed, ventral surface depressed distally; carpus very short, cup-shaped, with strong subacute ventrolateral process on distal margin; chela elongate, with palm slightly longer than fingers, smooth, somewhat compressed; fingers not gaping when closed, subequal, strongly crossing distally, not noticeably twisted, with serrated cutting edges; cutting edge of dactylus with 10 teeth increasing in size from most proximal to subdistal, most-distal tooth smaller than subdistal tooth, fifth to ninth teeth (from proximal to distal) broader and with two additional blunt teeth or bumps, reminiscent of shark teeth; cutting edge of pollex with 11 teeth intercalating with dactylar teeth, most teeth triangular, sixth to tenth teeth (from proximal to distal) broader, but not in form of shark tooth (Fig. 3 a–d). Minor cheliped significantly smaller than major cheliped; ischium rather slender, with one cuspidate seta on ventrolateral surface; merus subequal to ischium in length, slightly swollen, not widening distally, smooth, unarmed; carpus about 0.8 length of merus, cylindrical, widening distally; chela about as long as carpus, simple, with palm slightly longer than fingers, smooth; fingers slightly gaping when closed, subequal, crossing distally, cutting edges unarmed (Fig. 3e, f).
Second pereiopod slender; ischium with one small cuspidate seta on proximal ventrolateral surface; merus slightly longer than ischium; carpus with five subdivisions, first equal to sum of others, with ratio approximately equal to 4.0/1.0/0.8/1.0/1.7; chela longer than distal-most carpal subdivision, simple (Fig. 2c). Third pereiopod moderately slender; ischium with one small but stout cuspidate seta on ventrolateral surface; merus about six times as long as wide, unarmed; carpus about 0.6 times length of merus, noticeably more slender, unarmed distoventrally; propodus slightly longer than carpus, with three widely spaced, appressed spiniform setae on ventral margin, in addition to one pair of longer spiniform setae near dactylar base; dactylus (broken on right third pereiopod in illustrated specimen) about 0.4 length of propodus, rather stout, conical, simple, smoothly curving distally (Fig. 2d). Fourth pereiopod generally similar to third, slightly more slender (Fig. 2e, f). Fifth pereiopod as slender as fourth pereiopod; ischium unarmed; merus about five times as long as wide, unarmed; carpus noticeably longer and more slender than merus, unarmed; propodus with six spaced spiniform setae on ventromesial margin and one pair of longer spiniform setae adjacent to dactylar base (not visible in lateral view), as well as numerous rows of progressively longer serrulate setae forming dense cleaning brush on distal half of ventrolateral surface; dactylus slightly less than 0.4 length of propodus, similar to that of third and fourth pereiopods (Fig. 2g, h).
Second pleopod with appendix masculina slightly longer than appendix interna, furnished with numerous stiff setae, as illustrated (Fig. 1i). Uropod with lateral lobe of protopod ending in sharp tooth; exopod broadly ovoid, with strong distolateral tooth; diaeresis strongly sinuous, with subtriangular blunt tooth adjacent to stout spiniform seta; endopod as long as exopod, ovoid, without specific features (Fig. 1j).
Gill formula typical for genus.
Colouration. Semitransparent creamy whitish, with pale yellow tinge; bright yellow-orange ovaries visible through semi-translucent carapace (Fig. 4).
Type locality. Las Perlas Archipelago, Panama.
Distribution. Eastern Pacific: presently known only from the type locality in Panama.
Ecology. Intertidal and shallow subtidal (less than 1 m at extreme low tide); sand-rock flats, typically with coarse sand and abundance of coral rubble and rocks; possibly associated with burrows of stomatopods (see below).
Etymology. The new species name (tiburón = Spanish for shark) refers to the peculiar dentition on the cutting edge of the major chela dactylus, with the largest teeth resembling shark teeth; used as a noun in apposition.
Remarks. The two most diagnostic morphological features of Salmoneus tiburon sp. nov. are the obliquely upwards directed extra-corneal teeth (Fig. 1b) and the peculiar shark-tooth-type dentition on the cutting edges of the major cheliped dactylus (Fig. 3d). These two features combined separate S. tiburon sp. nov. from all other species currently assigned to the genus Salmoneus, including all species currently recorded from the eastern Pacific (see above). Furthermore, Salmoneus tiburon sp. nov. is distinguished from them by its comparatively large size, with both type specimens exceeding 8.0 mm in carapace length, and is indeed one of the largest species in the genus. Only a few other species of Salmoneus may reach a carapace length of about 6 mm (for instance, S. serratidigitus, see below).
The presence of a strong ventrolateral process on the distal margin of the major cheliped carpus is shared by S. tiburon sp. nov., S. caboverdensis Dworschak, Anker & Abed-Navandi, 2000 from the eastern Atlantic, and S. teres Manning & Chace, 1990 from the central Atlantic [the western Atlantic material reported as S. teres in Anker (2010) will be re-assigned to a closely related species (Anker, in prep.)]. However, in S. caboverdensis, both chelipeds are strongly enlarged and armed with teeth on their cutting edges (cf. Dworschak et al. 2000: figs. 29–31). The two species also differ in the relative length of the spiniform setae on the posterior margin of the telson, with the mesial ones being longer than the lateral ones in S. tiburon sp. nov. vs. the lateral ones being longer than the mesial in S. caboverdensis (cf. Dworschak et al. 2000: fig. 41). In S. tiburon sp. nov., the ischia of the major cheliped and the third and fourth pereiopods are armed with stout spiniform setae; these articles are unarmed in S. teres (cf. Manning & Chace 1990: fig. 10n, q, r). The stylocerite of the new species reaches well beyond the distal margin of the second article of the antennular peduncle versus not reaching this margin in S. teres (cf. Manning & Chace 1990: fig. 10b, f). In addition, both S. caboverdensis (holotype: cl 6.0 mm) and S. teres (holotype: cl 2.8 mm) are much smaller than S. tiburon sp. nov. (holotype and paratype: cl 8.8 mm and 8.2 mm, respectively).
Two incompletely known Indo-West Pacific species, viz. S. hilarulus (De Man, 1910) and S. tafaongae Banner & Banner, 1966, differ from S. tiburon sp. nov. by numerous morphological characters, such as, for S. hilarulus, the very different proportions of the third pereiopod, especially the dactylus, and the general shape of the rostrum and orbital teeth, and for S. tafaongae, the much longer rostrum, distally armed with a small ventral tooth, and the length-width ratio of the second article of the antennular peduncle (cf. De Man 1911: fig. 10, 10g; Banner & Banner 1966). The new species is not closely related to any of the other four eastern Pacific species of the genus, differing from them by a number of morphological characters and much larger size (see key below).
Noteworthy, the first specimen (paratype) of S. tiburon sp. nov. was found at low tide in a shallow pool under a large piece of coral rubble, together with several agile white clams (Bivalvia: Galeommatidae) aggregating close to a deep hole bordered by smaller pieces of rubble, possibly indicating an entrance to the burrow of an unknown animal. A medium-sized colourful stomatopod, Tetrasquilla mccullochae (Schmitt, 1940) (Tetrasquillidae) was found under the same piece of rubble (specimen deposited under FLMNH UF 19476). The second specimen (holotype) was found dwelling deep under a very large rock, with traces of oblique or horizontal galleries, but also without a host. These field observations and the rarity of S. tiburon sp. nov. suggest that this species may be indeed associated with galleries of some larger burrowing animals, possibly T. mccullochae and/or other stomatopods.
description: Published as part of Anker, Arthur, 2019, The eastern Pacific species of Salmoneus Holthuis, 1955, with description of a remarkable new species from Las Perlas Archipelago, Panama (Malacostraca: Decapoda: Alpheidae), pp. 125-140 in Zootaxa 4651 (1) on pages 126-132, DOI: 10.11646/zootaxa.4651.1.8, http://zenodo.org/record/3359237