Alpheus dingabadi, Anker, 2023

Anker, Arthur, 2023, A conspicuously coloured new species of the Alpheus macrocheles group from the central Indian Ocean (Decapoda: Alpheidae), Zootaxa 5271 (1), pp. 155-162 : 156-160

publication ID	https://doi.org/ 10.11646/zootaxa.5271.1.6
publication LSID	lsid:zoobank.org:pub:9B44C9EC-D177-4B5C-9D0D-AC8F264C5DCE
DOI	https://doi.org/10.5281/zenodo.7864451
persistent identifier	https://treatment.plazi.org/id/03881556-C46D-FFC8-FF01-00D970784B31
treatment provided by	Plazi
scientific name	Alpheus dingabadi
status	sp. nov.

Treatment

Alpheus dingabadi sp. nov.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Type material. Holotype: male (cl 5.4 mm), FLMNH UF 39660 , Maldives, Faafu Atoll , 1.6 km east of Magoodhoo Island, Dhign Reef, 3.0803 72.9827 [3°04’49.1” N 72°58’57.7”E], high impact forereef, 10–30 m, leg. J. Moore, 13 May 2014 [MALD-282]. GoogleMaps

Description. Carapace glabrous, with short, scattered setae ( Fig. 1A, B View FIGURE 1 ). Rostrum short, narrow, about twice as long as wide at base, slightly descendent in lateral view, acute distally, barely reaching mid-length of first article of antennular peduncle, posteriorly continued by well-developed, narrow, blunt rostral carina, latter abruptly flattening between eyes ( Fig. 1A, B View FIGURE 1 ). Orbital hoods swollen, somewhat projecting anteriorly in lateral view, with small, acute teeth, latter not reaching beyond tip of rostrum, directed anteriorly or slightly anteromesially; frontal margin between rostrum and orbital hood slightly flattened, almost straight ( Fig. 1A, B View FIGURE 1 ). Pterygostomial angle broadly rounded ( Fig. 1B View FIGURE 1 ); cardiac notch deep.

Telson very broad, strongly tapering distally, about 1.7 times as long as maximal width; lateral margins slightly convex, more noticeably converging in posterior half; dorsal surface with two pairs of very stout spiniform setae inserted far from lateral margin, first pair at 0.4 of telson length, second pair between 0.6 and 0.7 of telson length; posterior margin broadly rounded; posterolateral angles each with one pair of spiniform setae, mesial ones between double and triple length of lateral ones ( Fig. 1C View FIGURE 1 ).

Eyes completely concealed in lateral view, partly concealed in frontal view; cornea large, well-pigmented ( Figs. 1A, B View FIGURE 1 , 3 View FIGURE 3 ).

Antennular peduncle moderately elongate; stylocerite narrow, feebly swollen, acuminate distally, tip not reaching distal margin of first article; ventromesial carina with strong, anteriorly directed tooth; second article about 2.5 times as long as wide; lateral antennular flagellum with secondary ramus fused to main ramus over most of its length, free portion represented by small stump; numerous groups of aesthetascs present from about 19th subdivision of flagellum to distal end of free portion ( Fig. 1A, B, D–F View FIGURE 1 ). Antenna with basicerite very stout, much higher than long, armed with prominent, sharp tooth on distoventral margin; scaphocerite relatively small, with reduced blade and broadly concave lateral margin; distolateral tooth very strong, slightly overreaching distal margin of second article of antennular peduncle and distinctly reaching beyond mid-length of carpocerite; carpocerite very stout, subcylindrical, tapering distally, reaching or slightly overreaching distal end of antennular peduncle; flagellum moderately stout, furnished with long setae ( Fig. 1A, B, D View FIGURE 1 ).

Mouthparts typical for genus.Third maxilliped moderately slender, elongate, setose; coxa with bluntly projecting lateral plate; antepenultimate article flattened ventrolaterally, slightly twisted, with blunt ridge running parallel to dorsal margin on lateral surface, about four times as long as maximal width, with somewhat rugose ventral margin; penultimate article distally widening, about 2.8 times as long as distal width, with long setae on ventral margin; ultimate article 1.7 times as long as penultimate article, distally tapering, densely furnished with transverse rows of serrulate setae on dorsomesial and mesial surfaces and variously long, slender setae; exopod well developed, overreaching distal margin of antepenultimate article; arthrobranch well developed ( Fig. 1G View FIGURE 1 ).

Major cheliped robust; ischium short, stout, with two movable spinules on ventromesial margin; merus stout, trigonal in cross-section, slightly more than twice as long as maximal width of lateral surface; distodorsal margin terminating in blunt tooth; ventromesial margin straight, terminating in blunt distoventral lobe, armed with row of movable spinules; carpus very short, wider than long, cup-shaped; chela of basic macrocheles - type, not particularly elongate, rather stout, swollen, with numerous setae along dorsal and ventral margins and denser setal cover on most of mesial surface, especially on distal portion of palm and fingers; palm somewhat compressed, distally narrowing, slightly less than twice as long as maximal height (in lateral view of chela); distal area of lateral surface with strong longitudinal crest between two deep depressions, terminating in large acute tooth; dorsomesial margin with deep transverse groove extending somewhat to mesial surface, ending in large, blunt crest overhanging base of dactylus in mesial view; dorsomesial surface posterior to transverse groove and mesial to shallow dorsal groove crenulate; fingers, especially dactylus, noticeably deviating from main chela axis; pollex short, ending bluntly; dactylus exceeding pollex, distally strongly curved, rounded; plunger short, stout, distally truncate, well demarcated from anterior cutting edge of dactylus; adhesive disks very large and conspicuous ( Fig. 2A–F View FIGURE 2 ).

Minor cheliped relatively robust; ischium short, stout, with several movable spinules on ventromesial margin; merus slenderer than that of major cheliped, trigonal in cross-section, about 2.3 times as long as maximal width of lateral surface; distodorsal margin terminating in blunt tooth; ventromesial margin straight, terminating in blunt distoventral tooth, armed with row of movable spinules; carpus short, cup-shaped; chela swollen, stout, with numerous setae along dorsal and ventral margins and denser setal cover on mesial surface of palm and fingers; palm somewhat compressed, about 1.6 times as long as maximal height (in lateral view of chela); lateral surface without sculpture, terminating distally in small blunt tooth; dorsomesial margin with shallow longitudinal sulcus distally, delimiting very large, triangular, distally subacute, anteriorly protruding crest, latter extending well beyond base of dactylus; dorsomesial surface posterior to this crest somewhat crenulate; ventral surface between palm and fingers with broad, deep sinus; fingers slightly deviating from main chela axis, subequal in length, with blade-like cutting edges and fingertips curved and crossing distally; dactylus not expanded dorsally, not lamellar, without ridges, with strongly curved tip; adhesive disks small ( Fig. 2G–I View FIGURE 2 ).

Second pereiopod moderately slender; ischium and merus subequal in length; carpus with five subarticles, first longest, ratio of carpal subarticles approximately equal to 4.5: 2: 1.3: 1: 2; chela slender, about as long as first carpal subarticle ( Fig. 1H View FIGURE 1 ). Third pereiopod robust; ischium with large spiniform seta on ventrolateral surface; merus about 3.7 times as long as maximal width, with prominent, acute, distoventral tooth; carpus about 0.6 times length of merus, much slenderer than merus, with small, subacute, distoventral tooth; propodus noticeably slenderer than carpus, about 1.7 times length of carpus, with row of about 10 small spiniform setae on ventral margin and one pair of spiniform setae on distoventral margin adjacent to base of dactylus; dactylus 0.35 times length of propodus, rather stout, strongly curved, distinctly biunguiculate, with secondary unguis shorter and slightly divergent from axis of main unguis ( Fig. 1I, J View FIGURE 1 ). Fourth pereiopod generally similar to third pereiopod, slenderer; ischium more elongate, with large spiniform seta on ventrolateral surface; carpus slenderer than that of third pereiopod, otherwise similar; merus about 4.1 times as long as maximal width, with prominent, subacute, distoventral tooth, latter distinctly smaller than tooth of merus of third pereiopod; propodus with eight small spiniform setae on ventral margin and one pair of spiniform setae on distoventral margin adjacent to base of dactylus; dactylus similar to that of third pereiopod ( Fig. 1K View FIGURE 1 ). Fifth pereiopod not noticeably slenderer than fourth pereiopod; ischium elongate, unarmed; merus about 4.2 times as long as wide; carpus slenderer than merus, about same length as merus, unarmed; propodus subequal to carpus in length, with propodal grooming brush composed of four rows of serrulate setae on distal fourth of ventrolateral surface, ventral margin with two spiniform setae both situated in distal fourth of article, distoventral margin with pair of slender spiniform setae adjacent to base of dactylus; dactylus similar to that of third and fourth pereiopods ( Fig. 1L, M View FIGURE 1 ).

Second pleopod with appendix masculina almost double length of appendix interna, reaching beyond distal margin of endopod, densely furnished with slender spiniform setae ( Fig. 1N, O View FIGURE 1 ). Uropod with mesial and lateral lobes of protopod each distally produced as blunt or acute tooth, respectively; exopod with straight lateral margin ending in blunt distolateral tooth; adjacent spiniform seta very stout, reaching far beyond distal margin of exopod; distal margin armed with row of small spiniform setae; diaeresis sinuous, with subtriangular tooth near distolateral spiniform seta; endopod slightly narrower than exopod, oval-shaped; distal margin with row of spiniform setae increasing in size towards distolateral margin ( Fig. 1P View FIGURE 1 ).

Colour pattern. Body background whitish, almost opaque; carapace and pleon covered with bright red chromatophores disposed as following: carapace with large semicircular area of red chromatophores on gastric and postrostral regions, extending ventrally as oblique band on each side, and U-shaped posterior band consisting of two obliquely running bands, one on each side, joining each other along posterior margin; rostral area red; pleon with narrow transverse bands of red chromatophores, one per pleonite, joining each other on lateral surface of pleura; eyes with bluish-grey cornea; antennular peduncles mostly red; antennal peduncle mostly whitish to pale orange, with some red dots on basicerite and distal part of carpocerite; antennular and antennal flagella pale orange; third maxillipeds mainly red distally; major and minor chelipeds with merus mostly white with few scattered chromatophores, carpus pale orange-red, and mesial surface of chela decorated with large, irregularly shaped, redorange blotches and deep-red spots between whitish patches; second to fifth pereiopods largely colourless, except for reddish tinge on second pereiopod carpus; pleopods also colourless; telson and uropods with some reddish chromatophores (exact pattern not clearly seen in the only photograph available) ( Fig. 3 View FIGURE 3 ).

Etymology. The specific epithet is a combination of two Maldivian (Dhivehi) words, din’gaa (shrimp) and badi (gun) ( Abdulla & O’Shea 2005), with one letter omitted for euphony, and obviously referring to the fact that A. dingabadi sp. nov. is a pistol shrimp. The name is used as a noun in apposition.

Common name proposed. Dingabadi snapping shrimp.

Distribution. Central Indian Ocean: presently known only from the type locality in the Maldives.

Ecology. The holotype was collected on an exposed forereef, between 10 and 30 m, most likely by breaking up coral rubble.

Remarks. The combination of seven diagnostic characters of Alpheus dingabadi sp. nov., as following: (1) frontal margin of carapace with distinctly carinate rostrum and small, acute orbital teeth ( Fig. 1A View FIGURE 1 ); (2) antennal scaphocerite short, with reduced blade and distolateral tooth not reaching distal fourth of carpocerite, reaching only slightly beyond distal margin of second article of antennular peduncle ( Fig. 1A, B, D View FIGURE 1 ); (3) major chela swollen, not elongate, with two deep grooves and distally sharp crest between them on lateral surface, deep transverse groove proximally delimiting large blunt crest on dorsomesial surface, and area posterior to transverse groove conspicuously crenulate ( Fig. 2A–C View FIGURE 2 ); (4) minor chela swollen, deeply concave ventrally between pollex and palm, and with dorsomesially margin of palm ending in prominent tooth ( Fig. 2G, H View FIGURE 2 ); (5) both major and minor chelae densely setose, especially on mesial surfaces ( Fig. 2C, G View FIGURE 2 ); (6) third pereiopod with relatively stout merus, distoventrally armed with strong, sharp tooth, and with strongly biunguiculate dactylus ( Fig. 1I, J View FIGURE 1 ); and (7) second pleopod with appendix masculina reaching far beyond appendix interna and overreaching distal margin of endopod ( Fig. 1N, O View FIGURE 1 ), separates the new species from all other members of the A. macrocheles group, including the morphologically closest species, A. collumianus (species complex) and A. deuteropus .

The elongation of the appendix masculina in A. dingabadi sp. nov. appears to be unique within the A. macrocheles group. The degree of setation of the major and minor chelae, as seen in A. dingabadi sp. nov. is also uncommon, although a dense cover of very thin, almost fluffy setae is also present on the chelae of A. deuteropus (cf. Miya 1974: pl. 15, fig. C; Banner & Banner 1982: fig. 8d, g). The two species also share a similar frontal margin of the carapace and the presence of a prominent crest on the distomesial margin of the minor chela palm (cf. Banner & Banner 1982: fig. 8a, g). On the other hand, the well-known colour pattern of A. deuteropus , with its uniform dark brownred or grey-blue body and conspicuously red-and-white banded antennular and antennal flagella (e.g., Dehghani et al. 2019: fig. 2A, B), is very different from that of A. dingabadi sp. nov. Similarly, none of the species of the A. collumianus complex (A. Anker, pers. obs.) has a colour pattern that approaches that of A. dingabadi sp. nov. In addition, they appear to be morphologically more distinct from the new species than A. deuteropus (cf. Banner 1956; Miya 1974; Banner & Banner 1982).