Alpheus schubarti, Anker, 2024

Anker, Arthur, 2024, Description of a new alpheid shrimp from the tropical western Atlantic (Decapoda: Caridea: Alpheus), Papéis Avulsos de Zoologia 64, pp. 1-12 : 2-7

publication ID	https://doi.org/ 10.11606/1807-0205/2024.64.022
persistent identifier	https://treatment.plazi.org/id/6C4187C4-FF87-B279-D3C1-F97FFAFAE860
treatment provided by	Felipe
scientific name	Alpheus schubarti
status	sp. nov.

Treatment

Alpheus schubarti sp. nov.

( Figs. 1 View Figure1 A-G, 2-5)

(?) Alpheus paracrinitus "spot″ – Williams et al., 2001: 377 (part.?) [not A. paracrinitus Miers, 1881 ].

(?) Alpheus paracrinitus – De Grave & Anker, 2017: 7 (part.?).

(?) Alpheus cf. rostratus – Almeida et al., 2012: 13, fig. 2E; Soledade & Almeida,2013:104,fig.6E [not A.rostratus Kim & Abele, 1988 ].

Type material: Holotype: male (cl 4.45 mm), MZUSP 45945 View Materials , Brazil, Alagoas, Maceió, Ponta Verde , fossilised coral platform with deep pools, partly exposed at low tide, depth: 0-2 m, in crevices of fossilised corals and coral rubble, leg. A. Anker & P.P.G. Pachelle, 01.08.2012 (photographic voucher AA-12-263) . Paratypes: 2 males (cl 4.55 mm, 4.50 mm), MZUSP 45946 View Materials , same collection data as for holotype (photographic vouchers AA-12-262, AA-12-264, respectively) ; 1 ovigerous female (cl 4.95 mm), MZUSP 45947 View Materials , Brazil, Alagoas, Maceió, Ponta Verde , fossilised coral platform with deep pools, partly exposed at low tide, depth: 0-2 m, in crevices of fossilised corals and coral rubble, leg. A. Anker & P.P.G. Pachelle, 02.08.2012 (photographic voucher AA-12-313) ; 1 male (cl 4.45 mm), MZUSP 45948 View Materials , Brazil, Alagoas, Maceió, Ponta Verde , fossilised coral platform with deep pools, partly exposed at low tide, depth: 0-2 m, in crevices of fossilised corals and coral rubble, leg. A. Anker & P.P.G. Pachelle, 31.07.2012 (photographic voucher AA-12-246) .

Description: Small-sized species of Alpheus (present material: cl 4.45-4.95 mm). Carapace glabrous. Rostrum short, subtriangular, about 1.4 times as long as wide at base, subacute distally, not reaching distal margin of first article of antennular peduncle, pointing straight forward in lateral view; rostral carina low, rounded, not extending past level of eyes ( Fig. 1A, B View Figure1 ). Orbital hoods rounded, slightly projecting anteriorly in dorsal view; frontal margin between rostrum and orbital hood shallowly concave; adrostral furrows distinct in anterior half of orbital hoods, relatively shallow ( Fig. 1A View Figure1 ). Rostro-orbital process present, low. Pterygostomial angle broadly rounded ( Fig. 1B View Figure1 ); cardiac notch well developed, deep. Telson broad, subrectangular, more noticeably tapering in distal third, about 1.8 times as long as maximal width; dorsal surface with two pairs of stout spiniform setae, both inserted at some distance from lateral margin, first pair at about telson mid-length, second pair at about 0.7 of telson length; posterior margin broadly rounded, with several small slender spiniform setae; posterolateral angles each with one pair of slender spiniform setae, mesial stouter and more than twice as long as lateral ( Fig. 1C View Figure1 ).

Eyes well developed, with large, normally pigmented corneas; ocellar beak (= bec ocellaire) protruding between eyes, visible in lateral view ( Fig. 1A, B View Figure1 ). Each epistomial sclerite with strong sharp process.

Antennular peduncle rather stout; stylocerite slightly swollen laterally, ending in sharp point, latter reaching, but not exceeding distal margin of first article;ventromesial carina with subtriangular, anteriorly directed tooth; second article about 1.4 times as long as wide; lateral antennular flagellum with secondary ramus fused to main ramus over most of its length, distally recognisable as short stump, with at least seven groups of aesthetascs ( Fig. 1A, B, D View Figure1 ). Antenna with basicerite moderately stout, armed with sharp tooth on distoventral margin; scaphocerite well developed, lateral margin almost straight, blade moderately broad, distolateral tooth strong, reaching well beyond distal margin of blade, reaching or slightly overreaching end of antennular peduncle; carpocerite reaching slightly beyond both scaphocerite and end of antennular peduncle ( Fig. 1A, B View Figure1 ).

Mouthparts not dissected, typical for genus in external observation. Third maxilliped relatively stout proximally, slender distally; coxa with subacutely projecting lateral plate; antepenultimate article somewhat broadened, flattened ventrolaterally, distodorsal margin bluntly projecting; penultimate article relatively short, about 2.3 times as long as maximal width, with long setae on dorsal margin; ultimate article tapering distally, with numerous rows of serrulate setae on ventromesial surface and long stiff setae, especially on dorsal surface; exopod noticeably thickened, somewhat hinged, reaching beyond distal margin of antepenultimate article ( Fig. 1E View Figure1 ).

Major cheliped not markedly sexually dimorphic (except for larger size in males), much more robust than minor cheliped; ischium short, stout, smooth; merus stout, about 2.2 times as long as distal width, smooth, distodorsal margin ending bluntly, ventromesial margin smooth, with sharp distal tooth; carpus short, much wider than long, cup-shaped; chela moderately elongate, not particularly swollen; palm not noticeably compressed, subcylindrical in cross-section, smooth, without grooves, notches or sinuses, length / height ratio around 2.0; fingers subequal in length (dactylus sometimes slightly longer), 0.5-0.6 length of palm; dactylus distally rounded or with curved apex, plunger prominent, moderately stout, with distal bulge; adhesive disks rather small ( Fig. 2 View Figure 2 A-D). Minor cheliped not markedly sexually dimorphic; ischium short, smooth; merus moderately slender, slightly convex dorsally, about 3.5 times as long as wide,smooth, distodorsal margin blunt, ventromesial margin smooth, with small sharp distal tooth; carpus longer than that of major cheliped, cup-shaped; chela moderately slender, not particularly swollen;palm subcylindrical in cross-section,smooth,without grooves or notches,length / height ratio subequal to 2.5; fingers slightly longer than palm, not gaping and distally crossing when closed, extremely setose, especially on mesial surface, without balaeniceps ridges and setae in both sexes ( Fig. 2 View Figure 2 E-G).

Second pereiopod slender; ischium and merus subequal in length; carpus with five subarticles, first by far longest, ratio of carpal subdivisions: 3.0/1.7/1/1/1.6; chela longer than distal-most carpal subarticle ( Fig. 3A View Figure 3 ). Third pereiopod slender; ischium with stout spiniform seta on ventrolateral surface; merus about 6.2 times as long as maximal width, unarmed distoventrally; carpus about half-length of merus, noticeably more slender than merus; propodus much longer than carpus, more setose, ventral margin with six slender spiniform setae, in addition to pair of longer spiniform setae near propodo-dactylar articulation; dactylus slightly less than half-length of propodus, faintly curving distally, subconical ( Fig. 3B View Figure 3 ). Fourth pereiopod generally similar to third, somewhat more slender ( Fig. 3C View Figure 3 ). Fifth pereiopod more slender than fourth pereiopod; ischium armed with spiniform seta on ventrolateral surface; merus almost seven times as long as wide; carpus slightly more slender than merus, about 0.7 length of merus; propodus somewhat longer than carpus, distal half with at least eight rows of microserrulate setae on ventrolateral surface (grooming brush), ventromesial margin with four slender spiniform setae, in addition to one longer spiniform seta near propodo-dactylar articulation; dactylus similar to that of third and fourth pereiopods, about half as long as propodus ( Fig. 3D View Figure 3 ).

Male second pleopod with appendix masculina slightly longer than appendix interna, with long stiff setae on apical part ( Fig. 1F View Figure1 ). Uropod with both mesial and lateral lobes of protopod ending in sharp tooth; exopod broad, with stout triangular distolateral tooth and slender distolateral spiniform seta,diaeresis sinuous,with two broadly rounded lobes in its lateral section; endopod noticeably narrower and shorter than exopod, ovate, distal margin armed with small spiniform setae ( Fig. 1G View Figure1 ).

Colour pattern: Background translucent whitish; posterior half of carapace with two broad, transverse, dark brown bands, not extending to branchiostegial margin, one short brown band or patch on each flank at about one-fourth of carapace length, and one narrow brown band along each anterolateral margin; rostral area with greenish brown patch; pleon with six transverse, dark brown bands, forming incomplete rings; third band with two widely separated black spots dorsally; sixth band broadest, with irregularly shaped, whitish window; telson whitish anteriorly (except for two brown patches near anterior margin), mostly brown in posterior twothirds; antennules and antennae whitish with some olive brown patches or marbling, flagella pale yellowish or colourless; cheliped merus and carpus largely whitish with some brown patches; mesial face of major chela marbled with white, pale yellow and brown, distal half of palm with broad, obliquely transverse, white band, followed more distally by narrower brown band; base of pollex with smaller, oblique white band, rest of pollex orange-brown, calcified portion pale pinkish; dactylus brown grey proximally, calcified portion pale pinkish; second to fifth pereiopods largely translucent; uropods whitish with brown patches; ovigerous females with yolk yellow eggs ( Figs. 4 View Figure 4 , 5 View Figure 5 ).

Etymology: The new species is named after the author′s late friend and colleague, Christoph D. Schubart (1966-2023), for his significant contributions to decapod systematics.

Distribution: Presently known with certainty only from the type locality in Alagoas, Brazil (present study); possibly also present in Bahia (Almeida et al., 2012; Soledade & Almeida, 2013; both as A. cf. rostratus). The Panamanian material, including A. paracrinitus "spot″ in Williams et al., (2001) and A. paracrinitus in De Grave & Anker (2017, in part), as well as material personally collected in Panama and Costa Rica between 2005 and 2019, most likely represents A. schubarti sp. nov., at least judging from the nearly identical colour pattern; however, its identity needs to be confirmed by morphological and molecular analyses (Pachelle et al., in prep.).

Ecology: All type specimens of A. schubarti sp. nov., were extracted from crevices in fossilised coral rocks or large pieces of coral rubble, from the low tide mark to about 2 m.

Remarks: Within the A.paracrinitus complex, A. schubarti sp. nov., is most closely related to A.rostratus, from which it is distinguishable by (1) the rostrum subtriangular, about 1.5 times as long as wide at base vs. almost twice as long as wide at base in A. rostratus; (2) the distolateral tooth of the scaphocerite not as strongly developed as in A. rostratus, more precisely, reaching only slightly beyond the end of the antennular peduncle vs. reaching far beyond it in A. rostratus; and (3) the antepenultimate article of the third maxilliped being more expanded, and with a more prominent distodorsal projection than in A. rostratus (cf., Fig. 1A, E, H, I View Figure1 ; see also Kim & Abele, 1988: fig. 21a, b). The two species also differ in the colour pattern of the major and minor chelae. In A. schubarti sp. nov., the distal half of the major chela palm has a broad, white, oblique somewhat irregularly shaped band, crossing the full width of the palm ( Figs. 4 View Figure 4 , 5 View Figure 5 ). In contrast, in A. rostratus, the distal half of the major chela palm is largely brown, except for a small white patch continuing onto the pollex ( Fig. 6 View Figure 6 ). The same colour difference between the two species can be observed on the minor chela (cf., Fig View Figure 4 View Figure 5 View Figure 6 . 4-6).

The real identity of A. paracrinitus presently remains unknown, due to the superficial description of Miers (1881) and the poor condition of the type specimens. The presence of at least two genetically distinct lineages (Williams et al., 2001) and two junior synonyms (A. ascensionis, A. togatus) in the Atlantic Ocean further complicates this issue. Herein the author tentatively follows Crosnier & Forest (1966), who, after having examined several specimens from Cape Verde and a specimen from Ghana reported by Holthuis (1951), did not find any significant differences with the type specimens of Miers (1881) from Senegal. Alpheus schubarti sp. nov., can be separated from A. paracrinitus sensu Crosni- er & Forest (1966) by (1) the more prominent rostrum; (2) the dactylus of the major chela close to half-length of the palm vs. slightly more than 0.3 times as long as the palm in A. paracrinitus; and (3) the propodus of the third pereiopod armed with six spiniform setae vs. four in A. paracrinitus (cf., Figs. 1A View Figure1 , 2B, C View Figure 2 , 3 B View Figure 3 ; Crosnier & Forest, 1966: fig. 15).

At the author′s request, Paul F. Clark (pers. comm., June 2024) briefly examined Miers′ (1881) type specimens of A. paracrinitus (NHM 1881.24) and confirmed that the the smaller, more damaged specimen has three longer setae and one smaller seta on the left side of the rostral area, but no setae on the right side, whereas the larger specimen has three setae on the right side of the rostrum and no setae on the left side. The absence of setae on one side is most probably due to their fragility, i.e., they may have simply broken off. This important observation adds an important diagnostic character for A. paracrinitus sensu Miers (1881), i.e., the presence of erect setae on the rostrum or rostro-orbital area. These setae were neither described nor illustrated by Crosnier & Forest, 1966) for the Cape Verdean material, although in their illustration of the frontal area (idem: fig. 15a), all setae have been omitted. Thus, A. schubarti sp. nov., can be additionally separated from A. paracrinitus by the absence of erect setae on or near the rostrum.

Furthermore, A. schubarti sp. nov., can be easily separated from the species herein tentatively identified as A. cf. paracrinitus from Alagoas and Atol das Rocas, Brazil (see comparative material), by (1) the longer and more prominent rostrum, with a more developed rostral carina; (2) the more distinct adrostral furrows, which are very shallow in A. cf. paracrinitus; and (3) the absence of erect setae on the rostrum and sometimes also on the orbital hoods;these setae are present in all four herein examined specimens of A. cf. paracrinitus (see also below). In addition, the colour pattern of A. schubarti sp. nov., markedly differs from that of A. cf. paracrinitus from Maceió by the presence of two dark (often black) spots on the third pleonite, as well as by the bands on the pleon being noticeably broader (cf., Figs. View Figure 4 4, 5 View Figure 5 , 7 View Figure 7 ). Whether the Brazilian A. cf. paracrinitus and the eastern Atlantic A. paracrinitus sensu Miers (1881) represent the same species remains to be shown.

The western Atlantic taxon described as A. togatus by Armstrong (1940, as Crangon togatus) was placed in the synonymy of A. paracrinitus by Crosnier & Forest (1966). However, A. togatus differs from A. paracrinitus sensu Crosnier & Forest (1966) in the more numerous spiniform setae on the third pereiopod propodus, more precisely seven vs. four (cf., Armstrong, 1940: fig. 1C; Crosnier & Forest, 1966: fig. 15f). Miers (1881) did not describe in detail the walking legs of A. paracrinitus, most of which are missing in the type specimens. In all other morphological characteristics, A. togatus is identical to A. paracrinitus in Crosnier & Forest (1966). Whatever its taxonomic status might be, A. schubarti sp. nov., can still be separated from A. togatus by (1) the more prominent rostrum (1.4 times as long as wide in the new species vs. as long as wide in A. togatus); (2) the presence of a blunt rostral carina, which was not shown by Armstrong (1940: fig. 1A), whilst the rostrum was described as "not continued back on the carapace as a carina″ in A. togatus; and (3) the minor chela fingers being about 1.2 times as long as palm vs. almost 1.5 times as long as palm in A. togatus (cf., Figs. 1A View Figure1 , 2F View Figure 2 , G; Armstrong 1940: fig. 1).