Alpheus vanuatu, Anker, 2020

Anker, Arthur, 2020, On two new deep-water snapping shrimps from the Indo-West Pacific (Decapoda Alpheidae: Alpheus), Zootaxa 4845 (3), pp. 393-409 : 401-407

Alpheus vanuatu n. sp.

Figs. 5–8

Type material. Holotype: male, cl 6.0 mm, MNHN-IU-2017-1953, Vanuatu, Espiritu Santo Island , inner Big Bay, Campaign BOA 1, R / V “Alis”, Sta. CP 2445, 15°08’0”S 166°53’3”E, depth 231–285 m, leg. S. Samadi / IRD et al., 10.09.2005 . Paratypes: 1 female, cl 4.8 mm, MNHN-IU-2019-3169, same collection data as for holotype ; 1 male, cl 4.2 mm, MNHN-IU-2017-1952, Vanuatu, Espiritu Santo Island , inner Big Bay, Campaign BOA 1, R / V “Alis”, Sta. CP 2444, 15°07’80”S 166°53’70”E, depth 250–331 m, leg. S. Samadi / IRD et al., 10.09.2005 ; 4 males, cl 3.5, 3.5, 4.0, 4.5 mm, 2 females, cl 3.6, 3.8 mm, 1 ovigerous female, cl 4.0 mm, MNHN-IU-2017-1955, same collection data as for previous paratype.

Description. Small to medium-sized (present material: cl 3.5–6.0 mm) species of Alpheus . Carapace glabrous, neither setose nor pubescent. Rostrum well developed, moderately slender, about twice as long as wide at base, subacute distally, reaching mid-length of first article of antennular peduncle, slightly descendant in lateral view; rostral carina strong, rounded, continuing and noticeably widening and flattening between orbital hoods, abruptly delimited from adrostral furrows, not extending past orbital hoods, disappearing posterior to level of eyes ( Fig. 5a, b ). Orbital hoods swollen, slightly projecting anteriorly in lateral view, with rounded anterior margin; frontal margin between rostrum and orbital hood very shallowly concave; adrostral furrows shallow, distinct mainly in anterior portion of orbital hoods, between eyes ( Fig. 5a, b ). Pterygostomial angle broadly rounded ( Fig. 5b ); cardiac notch well developed, deep. Eyes well developed, with large, normally pigmented corneas ( Fig. 5a, b ).

Telson broad, subrectangular, tapering distally, about 2.0–2.2 times as long as maximal width, with lateral margins slightly concave posterior to telson mid-length; dorsal surface typically with two pairs of stout cuspidate setae both inserted far from lateral margin, first pair at about telson mid-length, second pair at about 0.7–0.8 of telson length, rarely with several cuspidate missing (as in one paratype); posterior margin broadly rounded; posterolateral angles each with one pair of slender spiniform setae, mesial ones much stouter and almost three times as long as lateral ones ( Fig. 5 c–e).

Antennular peduncle moderately stout; stylocerite with basal part moderately broad, slightly swollen laterally, distal part slender, ending in sharp point, latter slightly exceeding distal margin of first article; ventromesial carina with large, anteriorly directed tooth; second article about twice 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 eighth subdivision ( Fig. 5a, b, f ). Antenna with basicerite stout, its distoventral margin armed with anteriorly projecting, slender, sharp tooth; scaphocerite well developed, with straight to faintly concave lateral margin, broad blade and very strong distolateral tooth, latter reaching far beyond distal margin of blade, also typically reaching or slightly overreaching end of antennular peduncle (distolateral tooth of left scaphocerite curved and shorter, slightly abnormal, in illustrated specimen); carpocerite reaching well beyond scaphocerite and end of antennular peduncle ( Fig. 1a, b ).

Mouthparts typical for genus in external observation. Mandible with incisor process bearing about 10 teeth. Third maxilliped relatively stout, moderately setose; coxa with subacutely 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 short, distally widening, at most twice as long as maximal width; ultimate article unarmed distally, with numerous rows of shorter serrulate setae and much longer stiff setae, especially on and near apex ( Fig. 5g ).

Major cheliped feebly sexually dimorphic, weaker in females. Male major cheliped much more robust and longer than minor cheliped; ischium short, stout, smooth, unarmed; merus moderately stout, subtrigonal in crosssection, less than three times as long as wide at base, smooth, distodorsal margin bluntly protruding, without strong tooth, ventromesial margin smooth proximally, faintly rugose distally, with very stout sharp subdistal tooth; carpus very short, cup-shaped, smooth; chela slightly elongate; palm not noticeably compressed, subcylindrical in crosssection, length / height ratio more or less equal to 2.0, without grooves, notches, smooth (no granules), ventral margin faintly concave distally, forming shallow sinus, dorsal margin somewhat convex near mid-length; fingers subequal in length, about half-length of palm, slightly twisted laterally, gaping proximally when closed in lateral view; dactylus distally rounded, plunger somewhat reduced, continuous with dactylar cutting edge anteriorly, abruptly delimited posteriorly; adhesive disks large ( Fig. 6 a–f).

Minor cheliped sexually dimorphic, balaeniceps in males, simple in females ( Fig. 7 ). Male minor cheliped with ischium short, smooth; merus moderately slender, subtrigonal in cross-section, about four times as long as wide at base, smooth, distodorsal margin blunt, ventromesial margin smooth over most of its length, with stout sharp subdistal tooth; carpus short, cup-shaped, smooth; palm slender, subcylindrical in cross-section, smooth, without grooves or notches, length / height ratio about 2.5; fingers about 0.9 length of palm, slightly twisted, gaping when closed, subequal in length, strongly crossing distally; dactylus strongly flattened ventrodorsally, with lateral and mesial margins expanded, strongly curved 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 0.4 to 0.7 of dactylar length; mesial and lateral sides of pollex each with row of balaeniceps setae on proximal half; adhesive disks modestly developed ( Fig. 7a, b ). Female minor cheliped smaller and more slender than male minor cheliped; chela with fingers slightly longer than palm, not gaping when closed; dactylus not expanded, simple, without balaeniceps setae ( Fig. 7c, d ).

Second pereiopod slender; ischium and merus subequal in length; carpus with five subdivisions, first longest, ratio of carpal subdivisions approximately equal to 3.5/2/1/1/1.6; chela longer than distal-most carpal subdivision ( Fig. 8a ). Third pereiopod moderately slender; ischium with stout cuspidate seta on ventrolateral surface; merus about 6.5 times as long as maximal width, unarmed distoventrally; carpus about half-length of merus, slightly slenderer than merus, unarmed; propodus much longer than carpus, with numerous (some elongate) stiff setae, ventral margin with five or six smaller or larger spiniform setae, in addition to one pair of longer slender spiniform setae near propodo-dactylar articulation; dactylus slightly more than half-length of propodus, faintly curving distally, subconical, noticeably flattened ventrally ( Fig. 8b, c ). Fourth pereiopod generally similar to third, somewhat slenderer. Fifth pereiopod much slenderer than third pereiopod; ischium longer than in third pereiopod, unarmed; merus slender, almost seven times as long as wide; carpus slenderer than merus, about 0.8 length of merus; propodus much longer than carpus, distal ventrolateral surface with rows of serrulate setae forming cleaning brush, ventromesial margin with about six slender spiniform setae, including longest one near propodo-dactylar articulation; dactylus similar to that of third and fourth pereiopods ( Fig. 8d, e ).

Male second pleopod with appendix masculina shorter than appendix interna, with long stiff setae on apex and along margins ( Fig. 5h ). Uropod with both mesial and lateral lobes of protopod ending in sharp tooth; exopod broad, broadly rounded distally, with stout triangular distolateral tooth; diaeresis sinuous for most part, with two rounded lobes in its lateral section, one of them adjacent to slender distolateral spiniform seta, latter not reaching level of distal margin of exopod; endopod much narrower than exopod, ovate; neither exopod nor endopod with spiniform setae on their distal margins ( Fig. 5i ).

Colour pattern unknown.

Etymology. This interesting new species is named after the country of the type locality, the Republic of Vanuatu; used as a noun in apposition.

Distribution. West Pacific: presently known only from Vanuatu (Espiritu Santo Island), at depths of 231– 331 m.

Remarks. Alpheus vanuatu n. sp. appears to be morphologically closest to the pantropical A. paracrinitus Miers, 1881 species complex, which contains species found mostly in waters shallower than 50 m (A. Anker, unpublished data). The assignment of A. paracrinitus and related taxa to the A. diadema Dana, 1852 group dates back to Coutière (1905) and was followed by most subsequent workers (e.g. Miya 1974; Banner & Banner 1982; Chace 1988; Kim & Abele 1988). However, the A. diadema group sensu Banner and Banner (1982) is rather vaguely defined and contains morphologically diverse taxa, including several species that are obviously not closely related to the remaining species traditionally assigned to this group. Therefore, the present author does not recognise the A. paracrinitus complex as part of the A. diadema group. In fact, it seems most reasonable to treat this morphologically well-defined species complex as a separate species group of Alpheus , hereafter the A. paracrinitus species group.

The A. paracrinitus group can be defined by the following combination of morphological characters: (1) rostrum present, often small; (2) rostral carina, if present, not flattened and abruptly delimited from adrostral furrows, rostro-orbital region, including orbital hoods, without teeth; (3) third maxilliped with antepenultimate article often projecting distodorsally; (4) cheliped merus more or less slender, ventromesial margin with strong distal or subdistal tooth; (5) major chela subcylindrical, smooth, without grooves or notches; (6) minor cheliped simple or balaeniceps in males, simple in females; (7) third pereiopod merus lacking distoventral tooth and spiniform setae on ventral margin; and (8) third pereiopod dactylus typically simple, not strongly spatulate or biunguiculate. The following species can be presently assigned to the A. paracrinitus group: A. paracrinitus Miers, 1881 (currently regarded as pantropical species, but probably restricted to the East and West Atlantic, A. Anker, unpublished data); A. rostratus Kim & Abele, 1988 (East Pacific); A. alpheopsides Coutière, 1905 ; A. paralpheopsides Coutière, 1905 ; A. tenuipes De Man, 1910 ; A. labis Banner & Banner, 1982 ; A. mitis Dana, 1852 , and A. vanuatu n. sp. (all from the Indo-West Pacific). Two junior synonyms of A. paracrinitus will need to be resurrected, in addition to descriptions of possibly two cryptic or pseudocryptic species in the A. paracrinitus complex sensu stricto. The taxonomic identity of A. mitis remains problematic ( Banner & Banner 1983), although the species seems to be distinguishable from both A. paracrinitus sensu Miers (1881) and A. paracrinitus sensu Banner & Banner (1982) . The recent record of A. mitis from Iran ( Ashrafi et al. 2020) has to be treated with caution. Thus, the A. paracrinitus group, when fully revised, may include at least 12 species (A. Anker, under study). Apart from A. vanuatu n. sp., all the species of the A. paracrinitus group are distributed in shallow waters, although the habitat and depth of the single known specimen of A. labis are unknown ( Banner & Banner 1982).

Alpheus vanuatu n. sp. can be easily separated from all of the species listed above by the strongly balaeniceps male major chela, with the dactylus strongly flattened and expanded laterally and mesially ( Fig. 7a, b ) (cf. Coutière 1905; De Man 1911; Banner & Banner 1982; Kim & Abele 1988). The only species of the A. paracrinitus group, in which the minor cheliped is feebly balaeniceps, is A. paracrinitus sensu Banner & Banner (1982 : fig. 36d). However, this taxon (currently under study) differs from A. vanuatu n. sp. in several other morphological features (see below). The new species also differs from A. paracrinitus sensu Miers (1881) and sensu Banner & Banner (1982), as well as A. alpheopsides , A. paralpheopsides , A. rostratus , A. labis , A. mitis by the presence of a strong, posteriorly extending rostral carina, which is not distinct in the other species (cf. Coutière 1905; Banner & Banner 1982; Kim & Abele 1988). In A. tenuipes , a rostral carina is present, but is less developed and not extending beyond the level of eyes (cf. De Man 1911).

In addition to the strong balaeniceps condition of the male minor chela and well-developed rostral carina, A. vanuatu n. sp. differs specifically from each of the above-mentioned species, e.g. from A. paracrinitus sensu Banner & Banner (1982) by the major cheliped merus with the tooth on the ventromesial margin in subdistal position (vs. more proximal, closer to merus mid-length in A. paracrinitus of Banner & Banner 1982); from A. paracrinitus sensu Miers (1881) , Crosnier & Forest (1966) and Kim & Abele (1988) by the longer stylocerite, exceeding the distal margin of the first article of the antennular peduncle (vs. not reaching it in A. paracrinitus ) and the third maxilliped not protruding distodorsally (cf. Crosnier & Forest 1966; Kim & Abele 1988); from the form described as A. paracrinitus bengalensis Coutière, 1905 by the longer stylocerite, as well as the proportions of the major chela and telson; from A. alpheopsides by the relatively longer second article of the antennular peduncle, the stronger distolateral tooth of the scaphocerite and the much narrower telson; from A. paralpheopsides by the shape of the rostro-orbital margin, especially by the margin between the rostrum and orbital hood not as deeply incised as in A. paralpheopsides , and by the second pereiopod carpus with the first subdivision much longer than the second (vs. the two being subequal in A. paralpheopsides ) (cf. Coutière 1905); from A. rostratus by the longer stylocerite, exceeding the distal margin of the first article of the antennular peduncle (vs. not reaching it in A. rostratus ), the distomesial margin of the major chela palm protruding forward, forming almost a right angle, the major cheliped merus with the tooth on the ventromesial margin in subdistal position (vs. distal in A. rostratus ), and the third pereiopod dactylus noticeably longer and slenderer (cf. Kim & Abele 1988); from A. labis by the distolateral tooth of the scaphocerite by far overreaching the distal margin of the blade (vs. not reaching it in A. labis ), the non-expanded antepenultimate article of the third maxilliped (noticeably expanded in A. labis ), the major chela with a much higher palm length / dactylus length ratio (i.e. with the relatively longer dactylus in the new species), and the major cheliped merus without spiniform setae on the ventromesial margin; from A. mitis sensu Banner & Banner (1982 , but see Banner & Banner 1983: p. 55) by the longer stylocerite, exceeding the distal margin of the first article of the antennular peduncle (vs. not reaching it in A. mitis ) and the major cheliped merus less stout and with the tooth on the ventromesial margin clearly in subdistal position (vs. more distal in A. mitis ) (cf. Banner & Banner 1982); and from A. tenuipes by the major cheliped merus much stouter and without spiniform setae along the ventromesial margin (cf. De Man 1911).

Based on the comparisons above, A. vanuatu n. sp. does not seem to be very closely related to any of the species of the A. paracrinitus group, the morphologically closest taxa being A. tenuipes and A. labis , and possibly A. paracrinitus sensu Banner & Banner (1982) .

Figures

FIGURE 1. Alpheus alaincrosnieri n. sp.: a—frontal region, dorsal; b—same, lateral; c—telson, dorsal; d—same, posterior margin, dorsal (setae omitted); e—lateral flagellum of antennule, lateral; f—first maxilliped, lateral; g, h—second maxilliped, lateral; i—third maxilliped, lateral; j—appendix masculina and appendix interna of male second pleopod, anterior (lateral); k—uropod, dorsal. Drawn from: paratype male, cl 7.0 mm, MNHN-2011-3024, off New Ireland, Papua New Guinea [a–g, i–k]; non-type ovigerous female, cl 8.5 mm, MNHN-IU-2010-1278, from Mozambique Channel off Madagascar [h].

FIGURE 5. Alpheus vanuatu n. sp.: a—frontal region, dorsal; b—same, lateral; c—telson with abnormal number of cuspidate setae, dorsal; d—same, posterior margin, dorsal (setae omitted); e—telson with normal number of cuspidate setae, dorsal; g—third maxilliped, lateral; h—appendix masculina and appendix interna of male second pleopod, anterior (lateral); i—uropod, dorsal. Drawn from paratype male, cl 4.5 mm, MNHN-IU-2017-1955 [a–d, f–i]; paratype female, cl 3.6 mm, MNHN-IU-2017- 1955 [e], both from Espiritu Santo, Vanuatu.

FIGURE 6. Alpheus vanuatu n. sp.: a—right (major) cheliped, lateral; b—same, carpus and chela, mesial; c—same, lateral; d—same, distal part of palm and fingers open, lateral; e—same, distal part of merus, mesial; f—dactylus, lateral. Drawn from paratype male, cl 4.5 mm, MNHN-IU-2017-1955, from Espiritu Santo, Vanuatu.

FIGURE 7. Alpheus vanuatu n. sp.: a—left (minor) male cheliped, lateral; b—same, chela, lateral; c—right (minor) female cheliped, lateral; d—same, chela, lateral. Drawn from paratype male, cl 4.5 mm, MNHN-IU-2017-1955 [a, b]; paratype female, cl 3.6 mm, MNHN-IU-2017-1955 [c, d], both from Espiritu Santo, Vanuatu.

FIGURE 8. Alpheus vanuatu n. sp.: a—second pereiopod, lateral; b—third pereiopod, lateral; c—same distal part of propodus and dactylus, lateral (slender setae omitted); d—fifth pereiopod, lateral; e—same, propodus and dactylus, mesial. Drawn from paratype male, cl 4.5 mm, MNHN-IU-2017-1955, from Espiritu Santo, Vanuatu.