Alpheus alaincrosnieri Anker 2020, n. sp.
Creators: name: Anker, Arthur
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Alpheus
Alpheus alaincrosnieri

description: Alpheus alaincrosnieri n. sp.
Figs. 1–4
Alpheus acutocarinatus — Chace 1988: 15 (part., specimen from Masbate) [not A. acutocarinatus De Man 1909].
(?) Alpheus miyakei Miya 1974: 106; Bruce 1994: 23 (key); De Grave & Fransen 2011: 476 (listed as Nomen nudum).
Type material. Holotype: male, cl 7.6 mm, MNHN-IU-2011-2230, Papua New Guinea, off Sepik River, Campaign BIOPAPUA, R / V “Alis”, Sta. CP 3701, 03°57’S 144°41’E, depth 198–219 m, leg. S. Samadi & L. Corbari, 01.10.2010. Paratypes: 1 male, cl 6.5 mm, 2 females, cl 6.8, 7.2 mm (missing both P1 and major P1, respectively, both with bopyrid isopod parasites), MNHN-IU-2019-3168, same collection data as for holotype; male, cl 7.0 mm, MNHN-2011-3024, Papua New Guinea, off New Ireland, Campaign BIOPAPUA, R / V “Alis”, Sta. DW 3764, 04°39’S 153°03’E, depth 220 m, leg. S. Samadi & L. Corbari, 15.10.2010.
Additional material. 1 male, cl 7.4 mm (missing most legs, including both P1), MNHN-IU-2017-1947, Vanuatu, Espiritu Santo Island, inner Big Bay, Campaign BOA 1, R / V “Alis”, Sta. CP 2448, 15°06’60”S 166°50’80”E, depth 297–387 m, leg. S. Samadi / IRD et al., 10.09.2005; 1 ovigerous female, cl 8.5 mm, MNHN-IU-2010-1278, Madagascar, northwest coast, Mozambique Channel off Narinda (“Nazendry”) Bay, Campaign MIRIKY, Sta. CP 3293, 14°30’S 47°26’E, depth 268–408 m, leg. P. Bouchet et al., 14.07.2009.
Description. Medium-sized (present material: cl 6.5–8.5 mm) species of Alpheus brevirostris group. Carapace glabrous, neither setose nor pubescent. Rostrum well developed, slender, about twice as long as wide at base, subacute distally, reaching mid-length of first article of antennular peduncle, somewhat ascendant in lateral view; rostral carina strong, sharp, continuing on carapace well past orbital hoods, ending in conspicuous post-rostral tubercle in form of anteriorly elevated, gradually flattening tooth (Fig. 1a, b). Orbital hoods swollen, somewhat projecting anteriorly in lateral view; anterior margin of each orbital hood armed with small sharp tooth; frontal margin between rostrum and orbital hood shallowly concave; adrostral furrows rather shallow, distinct mainly in anterior portion of orbital hoods, between eyes (Fig. 1a, b). Pterygostomial angle protruding anteriorly as stout sharp tooth (Fig. 1b); cardiac notch well developed, deep. Eyes well developed, with large, normally pigmented corneas (Fig. 1a, b).
Telson narrow, subrectangular, tapering distally, about 2.7 times as long as maximal width, with lateral margins distinctly constricted at about telson mid-length; dorsal surface with two pairs of stout cuspidate setae both inserted at some distance from lateral margin, first pair at about 0.4 telson length, second pair at about 0.7 of telson length; posterior margin broadly rounded, with row of shorter slender setae above long plumose setae; posterolateral angles each with one pair of spiniform setae, mesial ones stouter and more than twice as long as lateral ones (Fig. 1c, d).
Antennular peduncle elongate, slender; stylocerite with basal part broad, swollen laterally, distal part slender, ending in sharp point, latter falling short of distal margin of first article; ventromesial carina with large tooth (not illustrated but visible in Fig. 1b); second article elongate, almost five times as long as wide; lateral antennular flagellum with secondary ramus fused to main ramus over most of its length, with numerous groups of aesthetascs distally, starting from about 14th subdivision (Fig. 1a, b, e). Antenna with basicerite very stout, its distoventral margin armed with very large, anteriorly projecting, sharp tooth; scaphocerite well developed, with straight lateral margin, moderately broad blade and strong distolateral tooth, latter reaching far beyond distal margin of blade, but not reaching end of antennular peduncle; carpocerite reaching slightly beyond scaphocerite, also not reaching end of antennular peduncle (Fig. 1a, b).
Mouthparts generally typical for genus in external observation. Mandible with incisor process bearing nine teeth. First maxilliped with well-developed caridean lobe and endopod subdivided into two articles (Fig. 1f). Second maxilliped with third article of endopod armed with small sharp tooth on mesial (ventral) margin (Fig. 1g, h). Third maxilliped slender, elongate, very setose; coxa with bluntly projecting lateral plate; antepenultimate article flattened ventrolaterally, with distinct ridge running parallel to dorsal margin on lateral surface, mesial margin slightly rugose; penultimate article relatively long, about 3.5 times as long as wide proximally, distoventral surface noticeably bulging distally, strongly convex, furnished with very long stiff setae; ultimate article unarmed distally, with numerous rows of shorter serrulate setae and much longer stiff setae, some of more apically situated setae extremely elongate, much longer than ultimate article; arthrobranch moderately developed (Fig. 1i).
Major cheliped not sexually dimorphic, slightly weaker in smaller females. Male major cheliped more robust, but only slightly longer than minor cheliped; ischium short, stout, ventrolateral surface with small granules, ventromesial margin with at least two elevations each carrying slender spiniform seta; merus elongate, trigonal in cross-section, about four times as long as wide at base, patchily covered by small granules, distodorsal margin blunt, without distal or subdistal tooth, ventromesial margin rugose, armed with two or three slender spiniform setae in proximal third, with stout sharp distal tooth; carpus subcylindrical, short, distally widening, cup-shaped in larger individuals, with more or less protruding blunt distodorsal process; chela extremely elongate, slender; palm strongly compressed, subrectangular in cross-section, length / height ratio ranging from about 4.2 in smaller individuals to over 5.0 in larger individuals, ventral margin broadly concave distally, forming shallow sinus, without deep constriction, dorsal margin without transverse groove or notch subdistally, large sections of palmar surface covered by small granules; fingers unequal in length, with dactylus noticeably shorter than pollex, about 0.25–0.3 times (dactylus) to 0.3–0.35 times (pollex) length of palm, not twisted or significantly deviating from chela axis, largely gaping proximally when closed; dactylus distally rounded, plunger highly reduced, continuous with dactylar cutting edge anteriorly, abruptly delimited posteriorly; adhesive disks small; distodorsal surface of merus, ventral and dorsal margins of palm, and ventral margin of pollex fringed with long setae, those of pollex projecting forward, often forming conspicuous tuft of several parallel setae (Fig. 2 a–f).
Minor cheliped sexually dimorphic, balaeniceps in males, simple in females (Fig. 3). Male minor cheliped with ischium short, stout, its ventromesial margin rugose, with at least two slender spiniform setae; merus elongate, trigonal in cross-section, about 4.5 times as long as wide at base, patchily covered by small granules, some organised in row on ventral surface, especially in larger individuals, distodorsal margin blunt, without distal or subdistal tooth, ventromesial margin rugose, armed with four or so slender spiniform setae in proximal third, with stout sharp distal tooth; carpus subcylindrical, short, distally widening, cup-shaped in larger individuals, with protruding blunt distodorsal process, dorsal and ventral surfaces more or less rugose or covered with small granules; palm compressed, subrectangular in cross-section, without grooves or notches, length / height ratio ranging from about 5.5 in smaller individuals to over 6.5 in larger individuals, surface slightly rugose in smaller individuals, covered with small granules in addition to rugosities in larger individuals; fingers about 0.6–0.7 length of palm, not twisted, slightly gaping when closed, subequal in length, strongly crossing distally; dactylus more or less flattened dorsoventrally and with margins slightly broadened, strongly bent distally, with two balaeniceps ridges, one on mesial side and one on lateral side, each furnished with densely inserted, thickened, plumose setae; both balaeniceps ridges extending from about half-length of dactylus to point of its curvature; pollex more gradually curving distally, without balaeniceps setae on either side; proximal surface of both dactylus and pollex covered with small granules; adhesive disks reduced; dorsal margin of palm, and ventral margin of pollex fringed with long setae, those of pollex projecting forward, often as conspicuous tuft of several parallel setae (Fig. 3 a–d). Female minor cheliped more slender than male minor cheliped; carpus longer, vase-shaped, with rugosities or granules and elongate setae; chela with fingers about 0.8 length of palm, slightly gaping; dactylus not expanded, simple, without balaeniceps setae; ventral and dorsal margins of palm, ventral margin of pollex and dorsal margin of dactylus fringed with long setae (Fig. 3e).
Second pereiopod very slender, especially in larger individuals; ischium and merus subequal in length; carpus with five subdivisions, first longest, ratio of carpal subdivisions approximately equal to 3.0/2.2/1/0.9/1.2; chela longer than distal-most carpal subdivision (Fig. 4a, b). Third pereiopod generally slender; ischium with stout cuspidate seta on ventrolateral surface; merus slender, about 10.5 times as long as maximal width, unarmed distoventrally; carpus about 0.6 length of merus, much slenderer than merus, unarmed; propodus noticeably longer than carpus, with numerous long stiff setae, ventral margin without spiniform setae; dactylus about half-length of propodus, gradually curving distally, spatulate, broadened, flattened ventrally, with distinct longitudinal keel (Fig. 4 c–e). Fourth pereiopod generally similar to third, but slenderer; ischium longer than in third pereiopod, with stout cuspidate seta on ventrolateral surface; merus about 11.4 times as long as maximal width; propodus and dactylus as in third pereiopod (Fig. 4f, g). Fifth pereiopod much slenderer than third pereiopod and slightly slenderer than fourth pereiopod; ischium longer than in third and fourth pereiopods, unarmed; merus about 10.3 times as long as wide; carpus slenderer than merus, about 0.8 length of merus; propodus longer than carpus, with numerous long stiff setae, ventral margin without spiniform setae, distal ventrolateral surface with rows of serrulate setae forming cleaning brush; dactylus similar to that of third and fourth pereiopods (Fig. 4h, i).
Male second pleopod with appendix masculina slightly longer than appendix interna, with long stiff setae on apex and along margins (Fig. 1j). Uropod with both mesial and lateral lobes of protopod ending bluntly; exopod fairly broad, somewhat truncate distally, with short triangular distolateral tooth; diaeresis straight for most part, except for blunt lobe adjacent to slender distolateral spiniform seta, latter reaching level of distal margin of exopod; endopod much narrower than exopod; neither exopod nor endopod with spiniform setae on their distal margins (Fig. 1k).
Colour pattern presently unknown.
Etymology. This spectacular deep-water species is named after Dr. Alain Crosnier (formerly at ORSTOM / MNHN), in recognition of his invaluable contribution to taxonomy of various groups of Decapoda, including the presently most complete monograph of the Alpheidae of the tropical eastern Atlantic (Crosnier & Forest 1966).
Distribution. Indo-West Pacific: Papua New Guinea (off Sepik River, New Ireland), Vanuatu (Espiritu Santo Island) and Madagascar (off Narinda Bay), at depths of 198– 408 m.
Remarks. Alpheus alaincrosnieri n. sp. clearly belongs to the A. brevirostris group based on the overall shape of the chelipeds. However, this new species is unique within the A. brevirostris group by the presenting two small, but well-developed, acute orbital teeth, projecting from the anterior margin of each orbital hood (Fig. 1a, b). In addition, the pterygostomial angle of A. alaincrosnieri n. sp. is strongly projecting anteriorly in form of a stout sharp tooth (Fig. 1b), a feature not commonly seen in the genus Alpheus. Within the A. brevirostris group, only A. kagoshimanus Hayashi & Nagata, 2000 has a pterygostomial tooth, which, however, is much smaller than in the present new species.All other species of the A. brevirostris group characterised by the significantly elongated chelipeds, viz. A. macroskeles Alcock & Anderson, 1894, A. talismani Coutière, 1898, A. acutocarinatus De Man, 1909, A. notabilis Stebbing, 1915, A. explorator Boone, 1935, A. migrans Lewinsohn & Holthuis, 1978, A. nonalter Kensley, 1969, and A. longipalma Komai & Ohtomi, 2018, can be easily separated from A. alaincrosnieri n. sp. both by the rounded orbital hoods and rounded to slightly angular pterygostomial angle.
Alpheus alaincrosnieri n. sp. can be separated from each of these species by at least one additional, taxonomically significant character, for instance, from A. kagoshimanus by the much stronger distolateral tooth of the scaphocerite, distinctly overreaching the distal margin of the blade (cf. Hayashi & Nagata 2000); from A. kagoshimanus, A. notabilis and A. migrans (and possibly from most if not all other species) by the presence of a sharp tooth on the third article of the endopod of the second maxilliped (cf. Lewinsohn & Holthuis 1978; Hayashi & Nagata 2000); from A. macroskeles, A. talismani and A. longipalma by the cheliped merus without subdistal dorsal tooth (cf. Alcock & Anderson 1894; Coutière 1898; Alcock 1901; Crosnier & Forest 1966; Komai & Ohtomi 2018); from A. macroskeles and A. talismani by the minor chela strongly balaeniceps in males (cf. Alcock & Anderson 1894; Coutière 1898; Alcock 1901; Crosnier & Forest 1966); from A. macroskeles by the better developed cornea of eyes (cf. Alcock & Anderson 1894; Alcock 1901; Komai & Ohtomi 2018); from A. talismani by the presence of an elevated rostral carina armed with a post-rostral tubercle (cf. Coutière 1898; Crosnier & Forest 1966); from A. acutocarinatus by the third pereiopod ischium armed with a stout cuspidate seta (cf. De Man 1911); from A. acutocarinatus and A. migrans by the absence of small tubercle on the mid-dorsal line of the posterior region of the carapace and the second pereiopod with the first carpal subdivision longer than the second (cf. De Man 1911; Lewinsohn & Holthuis 1978); from A. notabilis by the broader and less constricted telson and the scaphocerite with a straight (not noticeably concave, as in A. notabilis) lateral margin (cf. Stebbing 1915); from both A. explorator and A. nonalter by the major chela palm without a deep constriction near the base of the pollex (Boone 1935; Kensley 1969; Chace 1988; Komai 2011); from A. explorator by the position of the ventromesial tooth on the cheliped merus (distal in the new species vs. clearly subdistal in A. explorator) (Boone 1935; A. Anker, in prep.); and from A. migrans by the much longer penultimate article of the third maxilliped and the lower, more reduced plunger of the major chela (cf. Lewinsohn & Holthuis 1978; Dworschak & Pervesler 2002). It must be noted that A. notabilis, described by Stebbing (1915) on the basis of a heavily damaged specimen missing its major cheliped, with somewhat diagrammatic and possibly not very accurate illustrations, has not been reported since the original description (Banner & Banner 1983).
Chace (1988) listed a mutilated ovigerous female (cl 8.3 mm) collected at a depth of 245 m near Masbate, Philippines, in the remarks under A. acutocarinatus. However, the author’s notes show that he was well aware that it did not belong to that species. Based on Chace’s (1988) observations, the specimen from Masbate had “the remnant of what must have been a larger mesial gastric tooth [= post-rostral tubercle], by a small spine on the frontal margin either side of the rostrum [= orbital teeth], and by a rather distinct branchiostegal spine [= pterygostomial tooth]”, which are the most diagnostic features of the carapace of A. alaincrosnieri n. sp. Therefore, Chace’s (1988) specimen is here tentatively referred to the new species, extending its distribution to the Philippines.
Miya (1974), while providing short diagnoses of the seven species groups of Alpheus, mentioned under the A. brevirostris group “ A. miyakei sp. nov. which will be described in Part III”. However, Part III of Miya’s monograph of the Alpheidae of Japan was never published and Miya’s name is therefore a Nomen nudum (De Grave & Fransen 2011). It remains unknown from which locality (or localities) Miya’s material came from and if it was collected in shallow or in deep water. The only character mentioned by Miya (1974) for A. miyakei was the presence of orbital teeth, which was used by Bruce (1994) in the first couplet of his key to the A. brevirostris group. Miya’s invalid name is here tentatively listed in the synonymy of A. alaincrosnieri n. sp., although its true identity may never be uncovered.
description: Published as part of Anker, Arthur, 2020, On two new deep-water snapping shrimps from the Indo-West Pacific (Decapoda Alpheidae: Alpheus), pp. 393-409 in Zootaxa 4845 (3) on pages 394-396, DOI: 10.11646/zootaxa.4845.3.5, http://zenodo.org/record/4406729