Alpheus thompsoni, Anker, 2022

Anker, Arthur, 2022, Description of two new species of goby-associated snapping shrimps from the tropical western Pacific (Decapoda: Alpheidae: Alpheus), Zootaxa 5092 (3), pp. 273-290 : 274-280

Alpheus thompsoni sp. nov.

( Figs. 1–3 , 8A, B )

(?) Alpheus ochrostriatus — Karplus et al. 1981: 6, fig. 2F (black-and-white photograph); Debelius 2001: 150 (part.?), 2 colour photographs; Randall et al. 2003: 512, fig. 8 (colour photograph); Poupin 2010: 33; Karplus & Thompson 2011: 591, fig. 4.4.10-B (black-and-white photograph) [nomen nudum].

(?) Alpheus “ ochrostriatus ” — Anker 2000: 3, fig. 2; Jaafar & Randall 2009: 29, pl. 2A (colour photograph); Kuiter & Debelius 2009: 151, 3 colour photographs (as Alpheus sp. ‘ ochrostriata ’) [nomen nudum].

(?) Alpheus sp. 4 — Minemizu 2013: 102, colour photograph.

Type material. Holotype: ov. female (cl 13.3 mm), MNHN-IU-2013-16813, Papua New Guinea, Madang, sta. PR242, 5°10.2’S, 145°50.4’E, depth 4–24 m, leg. A. Anker et al., 12.12.2012 [fcn PR242-PZD-660D].

Description. Carapace sparsely setose, not pubescent, pitted ( Fig. 1A, B ). Rostrum well developed, slender, about twice as long as wide at base, subacute distally, reaching distal third of first article of antennular peduncle, somewhat descendent in lateral view; rostral carina well marked, rounded dorsally, gently sloping into shallow adrostral furrows, continuing well beyond base of orbital hoods, gradually flattening, not reaching mid-length of carapace ( Fig. 1A, B ). Orbital hoods swollen, somewhat projecting anteriorly in lateral view, unarmed; frontal margin between rostrum and orbital hood shallowly concave ( Fig. 1A, B ). Pterygostomial angle rounded; cardiac notch well developed, deep ( Figs. 1B , 3B ).

Telson moderately broad, subrectangular, gently tapering distally, about 2.5 times as long as maximal width, with lateral margins somewhat constricted and tapering at about 0.7 times telson length; dorsal surface with two pairs of stout cuspidate setae both inserted far from lateral margin, first pair at about 0.4 telson length, second pair at about 0.7 times telson length; posterior margin broadly rounded, with row of slender spiniform setae above plumose setae; posterolateral angles each with one pair of spiniform setae, mesial ones stouter and almost three times as long as lateral ones ( Fig. 1C ).

Eyes well developed, with large, normally pigmented corneas ( Figs. 1A, B , 3 ). Antennular peduncle moderately elongate and stout; stylocerite slightly swollen laterally, distal part more slender, ending in sharp point, latter slightly overreaching distal margin of first article; ventromesial carina with large, subacute tooth; second article about 2.7 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 13th subdivision ( Fig. 1A, B, D ). Antenna with basicerite fairly stout, its distoventral margin armed with large, anteriorly projecting, sharp tooth; scaphocerite with broad blade reaching slightly beyond stout, subacute distolateral tooth, lateral margin very shallowly concave; scaphocerite reaching slightly beyond end of antennular peduncle and far beyond carpocerite ( Fig. 1A, B ).

Mouthparts not dissected, generally typical for genus in external observation. Third maxilliped relatively slender, elongate; coxa with bluntly projecting lateral plate; antepenultimate article flattened ventrolaterally, with distinct ridge running parallel to dorsal margin on lateral surface and rugose mesial margin, about 5.3 times as long as high; penultimate article short, cup-shaped, bulging ventrally, its distoventral margin with tuft of very long setae; ultimate article densely furnished with rows of very long, stiff setae, apical setae longest; arthrobranch well developed ( Fig. 1E ).

Major cheliped (female) moderately robust; ischium short, stout, smooth; merus moderately stout, somewhat elongate, trigonal in cross-section, at most four times as long as maximal width, distodorsal margin ending bluntly, ventromesial margin somewhat rugose, with weak, blunt, distal tooth, without spiniform setae; carpus short, distally widening, cup-shaped; chela not particularly elongate, fringed with long setae along dorsal and ventral surfaces; palm strongly compressed, subrectangular in cross-section, length / maximal height ratio about 1.9; surfaces relatively smooth, not markedly granulated; dorsal margin with well-marked transverse groove subdistally, without marked longitudinal ridges; ventral margin almost straight; lateral surface with distinct depression distally, near base of pollex; fingers slightly unequal in length, with dactylus shorter than pollex, about half-length of palm, not twisted or significantly deviating from chela axis; dactylus distally rounded, with plunger greatly reduced, poorly demarcated from anterior cutting edge, latter feebly bulging; adhesive disks very small ( Fig. 2A–D ).

Minor cheliped (female) with ischium short, smooth; merus slightly stouter than that of major cheliped, trigonal in cross-section, about 3.5 times as long as maximal width, distodorsal angle blunt, ventromesial margin slightly rugose distally, without pronounced distal tooth, armed with one spiniform seta; carpus somewhat more slender and longer than that of major cheliped, distally widening, cup-shaped; chela not elongate, not swollen, fringed with long setae along dorsal and ventral surfaces; palm compressed, subrectangular in cross-section, length / maximal height ratio about 2.0; surfaces smooth, not granulated; dorsal margin without groove; ventral margin straight; fingers slightly unequal in length, with dactylus shorter than pollex, about 1.2 times length of palm, not twisted, slightly gaping when closed, without balaeniceps crests and setae; adhesive disks greatly reduced ( Fig. 2E–G ).

Second pereiopod slender; ischium and merus subequal in length; carpus with five subarticles, first and second subequal, ratio of carpal subarticles approximately equal to 2.3/2.2/1.0/0.9/1.5; chela longer than distal-most carpal subarticle ( Fig. 1F ). Third pereiopod moderately stout; ischium with small spiniform seta on ventrolateral surface; merus about 4.5 times as long as maximal width, ventromesial margin unarmed distally; carpus about half-length of merus, much more slender than merus, unarmed; propodus noticeably longer than carpus, moderately setose, with seven or so spiniform setae along ventral margin, including distal pair adjacent to dactylar base; dactylus about half-length of propodus, gradually curving distally, subspatulate, moderately broadened, flattened ventrally, with distinct longitudinal keel separating ventral and dorsal surfaces, latter with several tufts of setae ( Fig. 1G, H ). Fourth pereiopod generally similar to third pereiopod, somewhat slenderer. Fifth pereiopod much slenderer than third and fourth pereiopods; ischium with small spiniform seta on ventrolateral surface; merus about nine times as long as wide; carpus slightly more slender than merus, about 0.9 length of merus; propodus subequal to carpus, with rows of serrulate setae forming cleaning brush on distal third of ventrolateral surface, and about 10 spiniform setae along ventromesial margin, including distal pair adjacent to dactylar base ( Fig. 1I, J ).

Uropod with mesial and lateral lobes of protopod each ending in sharp distal tooth; exopod broad, somewhat truncate distally, with short triangular distolateral tooth; diaeresis straight for most part, except for blunt lobe adjacent to slender spiniform seta, latter not reaching level of distal margin of exopod; endopod much narrower than exopod, with row of spiniform setae on distal margin ( Fig. 1K ).

Colour pattern. General background colour pale pink; carapace and pleon with broad, parallel-running, longitudinal bands each composed of narrower, ochre-red to brick-red lines and streaks, many anastomosing, forming net-like pattern; carapace flanks with broader, more diffuse and more obliquely running bands; posterior end of carapace and first pleonite with very conspicuous, transverse, white, dorsal “saddle”; fourth and fifth pleonites with smaller dorsal “saddle”; fifth pleonite with small, whitish, dorsal patch; chelipeds with yellow tinge, especially on merus and carpus, and ochre-red stripes and patches on palms and fingers; distal half of fingers hyaline-white with pinkish tinge; antennules and antennae bright yellow with ochre-orange spots and streaks, especially on antennular peduncles and scaphocerite; antennular and antennal flagella almost colourless, with yellowish or bluish tinge, respectively; second pereiopods and walking legs uniform yellow; pleopods yellowish; uropods mainly yellow with whitish areas and few ochre-orange spots on endopod; telson yellow with two ochre-red longitudinal bands flanking white mid-dorsal band ( Fig. 3 ; see also Fig. 8A, B ).

Etymology. This new species is named after the author’s friend and colleague, Dr. Andrew Thompson, an expert of ecology and evolution of goby-shrimp symbioses (Thompson 2004, 2005; Karplus & Thompson 2011).

Distribution. Indo-West Pacific: so far confirmed only from Papua New Guinea (Madang); numerous photographic records (as “ A. ochrostriatus ” or Alpheus sp. ) ranging from the Red Sea ( Karplus et al. 1981) to Indonesia ( Randall et al. 2007; Kuiter & Debelius 2009) and Japan ( Anker 2000; Karplus & Thompson 2011); also recorded, possibly based on colour photographs, from New Caledonia ( Poupin 2010, as “ A. ochrostriatus ”); however, all records from outside of the type locality require confirmation as more than one species might be involved (see below).

Ecology. Coral reefs and adjacent reef flats; associated with numerous gobies, including Amblyeleotris wheeleri (Polunin & Lubbock) , and possibly also A. steinitzi (Klausewitz) , A. guttata (Fowler) , Ctenogobiops pomastictus Polunin & Lubbock , and C. tangaroai Lubbock & Polunin ( Fig. 8A, B ; see also Karplus et al. 1981; Anker 2000; Debelius 2001; Randall et al. 2003, 2007; Kuiter & Debelius 2009; Jaafar & Randall 2009; Karplus & Thompson 2011; however, see discussion below).

Remarks. Alpheus thompsoni sp. nov. has a very striking colour pattern ( Figs. 3 , 8A, B ), which is characterised by the long, narrow, longitudinal bands of ochre-red to brick-red colour on a generally pale-yellow body and chelipeds, sharply contrasting with the bright yellow colour of the remaining appendages (antennules, antennae, walking legs and uropods). The white “saddle” between the carapace and pleon, which is also present in several other goby-associated species (e.g. Karplus et al. 1981; Kuiter & Debelius 2009; Minemizu 2013) is very conspicuous. This colour pattern separates the new species from A. bellulus (see Miya & Miyake 1969; Debelius 2001; Kuiter & Debelius 2009; Minemizu 2013; see also Fig. 8F ), A. macellarius (see Anker et al. 2015; Anker & De Grave 2016), A. fenneri (see Bruce 1994; Kuiter & Debelius 2009), and A. mannarensis (see Purushothaman et al. 2021), as well as the strikingly coloured species reported as A. djiboutensis by Holthuis (1958), A. djeddensis s. lat. by Anker & De Grave (2016) and A. djeddensis by Dehghani et al. (2019).

The above described colour pattern of A. thompsoni sp. nov. is identical or at least very similar to that of many snapping shrimps associated with gobies across the Indo-West Pacific. This species was sometimes identified as “ A. ochrostriatus ”, a nomen nudum first used by Karplus et al. (1981), or as “ Alpheus sp. ” Upon the author’s request, Dr. Ilan Karplus provided scans of two colour slides of a snapping shrimp identified as “ A. ochrostriatus ” from Eilat, Israel, which were taken during his ecological studies in the 1980s. Although the photographed specimen was not deposited (or at least is untraceable), the shrimp on these slides is indeed similar to the holotype of A. thompsoni sp. nov. both in general morphology and colour pattern. This fact combined with numerous in situ colour photographs (e.g. Randall et al. 2003; Kuiter & Debelius 2009; Jaafar & Randall 2009; Karplus & Thompson 2011; Minemizu 2013) suggest that A. thompsoni sp. nov. may be distributed from the northern Red Sea to southern Japan and New Caledonia. However, the taxonomic status of the Red Sea populations originally reported as “ A. ochrostriatus ” ( Karplus et al. 1981) will need to be confirmed morphologically and genetically, in view of high level of endemism of the area and differences in some colour pattern details (A. Anker, pers. obs.). Therefore, A. thompsoni sp. nov. remains known with certainty only from the type locality in Papua New Guinea, until more material is collected and analysed morphologically and genetically. More generally, the name “ A. ochrostriatus ” should not be used in the future, even if the Red Sea material is confirmed to be a distinct, undescribed species, since (1) it represents a nomen nudum ( De Grave & Fransen 2011) and (2) was apparently used for at least two colour morphs (e.g. Debelius 2001; Randall 2007; see also discussion in Anker 2000). This is also true for the two other unavailable (and therefore invalid) names in Karplus et al. (1981). The second colour morph of “ A. ochrostriatus ” (shown in Fig. 8E ) could represent the recently described A. mannarensis , despite some differences in the shape and of the reddish lines on the pleon and the much less conspicuous white “saddles” in A. mannarensis .

Using the key to the A. brevirostris group in Bruce (1994), A. thompsoni sp. nov. would key out to A. djeddensis , a species described based on three male and two female specimens from Djeddah, Saudi Arabia ( Coutière 1897). However, several elements of the morphology of A. djeddensis mentioned and/or illustrated by Coutière (1897, 1899) and De Man (1909) separate A. thompsoni sp. nov. from A. djeddensis . In the new species, the scaphocerite blade exceeds the adjacent distolateral tooth ( Fig. 1A ), whereas in A. djeddensis , the blade has the same length as the distolateral tooth ( De Man 1909: fig. 26). In A. thompsoni sp. nov., the fingers of the female minor chela are not balaeniceps, whereas the dorsal surface of the palm is smooth, without discernable grooves. In contrast, in A. djeddensis , the minor chela fingers are strongly balaeniceps in both sexes, whereas the palm has a longitudinal groove departing from a distinct transverse groove and running parallel to the palm’s dorsal margin, as seen in the very detailed illustration of the minor chela provided by Coutière’s (1899: fig. 232, as A. rapax var. Djeddensis). Both characters were verified in the male and female syntypes of A. djeddensis (RMNH.CRUS.D.1781) , although the palmar grooves seem to be less developed in the female minor chela. However, some other distinguishing features were found during the examination of the type material of A. djeddensis . The stylocerite of A. thompsoni sp. nov. appears to be somewhat longer and less swollen than in A. djeddensis (reaching or slightly overreaching the distal margin of the antennular peduncle in the new species vs. not reaching it in A. djeddensis ), whereas the antennal carpocerite is shorter (not reaching the distal margin of the scaphocerite in the new species vs. overreaching it in A. djeddensis ). Their major chelae are also somewhat different, for instance, in the proportion of the fingers to the palm (0.4 in A. thompsoni sp. nov. vs. 0.6 in A. djeddensis ), and in the cutting edge of the dactylus (with a less developed plunger and feebly bulging in A. thompsoni sp. nov. vs. with a more pronounced plunger and with a strong anterior bulge in A. djeddensis ). It must be noted, however, that in the A. brevirostris group, the major and minor chelipeds of females are generally smaller than their male counterparts and may exhibit slightly different proportions.

Alpheus thompsoni sp. nov. can be separated from A. djiboutensis , as described by De Man (1909), by the shape of the antennal scaphocerite, more precisely, by the blade reaching slightly beyond the adjacent distolateral tooth in the new species ( Fig. 1A ) vs. by the distolateral tooth by far overreaching the blade in A. djiboutensis ( De Man 1909: fig. 19; see also Banner & Banner 1982: fig. 55a, m). In addition, in A. thompsoni sp. nov., the first subarticle of the second pereiopod carpus is almost as long as the second ( Fig. 1F ), whereas in A. djiboutensis , the first subarticle is noticeably longer than the second ( De Man 1909: fig. 23). The two species also seem to differ by the proportions of the major and minor chelae, which are much stouter in A. djiboutensis (cf. Fig. 2 and De Man 1909: 20, 21), although this character needs to be confirmed in the presence of adult male specimens in the future [same remark as above]. According to De Man (1909), the ventromesial margin of the major cheliped merus of A. djiboutensis is armed with a stout and sharp tooth, which is blunt and poorly developed in A. thompsoni sp. nov. ( Fig. 2B ).

An ongoing study of the goby-associated snapping shrimps of the Red Sea, largely based on material collected off the Red Sea coast of Saudi Arabia in 2012 (FLMNH UF), enabled to distinguish five morphotypes, each with a different, highly diagnostic colour pattern. One of them corresponds to “ A. ochrostriatus ” (nomen nudum) of Karplus et al. (1981), as mentioned above, and may or may not be the same as A. thompsoni sp. nov. (Anker, in prep.). The second is a very distinctive morphotype with a unique colour pattern type, reported as “ A. rubromaculatus ” (nomen nudum) by Karplus et al. (1981); this clearly new species will be described elsewhere (Anker, in prep.). The remaining three morphotypes are morphologically in line with A. djeddensis and A. djiboutensis , although one of them represents yet another, possibly undescribed species (Anker, in prep.). Although the latter three taxa are still being evaluated taxonomically, their colour patterns are very different from that of A. thompsoni sp. nov., which strengthens its separation from A. djeddensis and A. djiboutensis .

As mentioned above, A. thompsoni sp. nov. can be easily separated from A. bellulus , A. macellarius , A. fenneri and A. mannarensis by its diagnostic colour pattern and also, from each of them, by at least two morphological characters. For instance, A. thompsoni sp. nov. differs from A. bellulus by the rostrum much narrower and longer (vs. shorter and subtriangular in A. bellulus ), and by the different proportions of the female major and minor chelipeds, especially by the more slender meri, the more slender major and minor chelae, and the minor chela fingers subequal in length to the palm and non-balaeniceps (vs. with the minor chela fingers longer than the palm and sub-balaeniceps in A. bellulus , see Miya & Miyake 1969: fig. 2E, F). The new species can be morphologically separated from A. macellarius by the lateral margin of the antennal scaphocerite almost straight (vs. strongly concave in A. macellarius ), the ventromesial margin of the chelipeds distally unarmed (vs. armed with a sharp tooth in A. macellarius ), the much stouter minor chela (which is very slender in A. macellarius ), and the second pereiopod carpus with the two first subarticles subequal in length (vs. with the first subarticle much longer than the second in A. macellarius ) (see Chace 1988: fig. 6a, e, f, h). Furthermore, A. thompsoni sp. nov. differs from A. fenneri by the scaphocerite blade reaching far beyond the adjacent distolateral tooth (vs. not or barely reaching the distolateral tooth in A. fenneri ), the mesial surface of the major and minor chelae not granulated (vs. distinctly granulated in A. fenneri ), and the relatively shorter and more slender penultimate article of the third maxilliped (which is very stout in A. fenneri ) (see Bruce 1994: figs. 1C, 2A–D). Finally, A. thompsoni sp. nov. differs from A. mannarensis by the second pereiopod carpus with the two first subarticles subequal in length (vs. with the second subarticle distinctly longer than the first in A. mannarensis ), the mesial surface of the major and minor chelae not granulated (vs. faintly granulated in A. mannarensis ), and the longer stylocerite, reaching the distal margin of the first article of the antennular peduncle (vs. not reaching it in A. mannarensis ) (see Purushothaman et al. 2021: figs. 2B, 3B, D, G).

Figures

FIGURE 1. Alpheus thompsoni sp. nov., holotype, female (cl 13.3 mm) from Madang, Papua New Guinea (MNHN-2013- 16813): A, frontal region, dorsal; B, same, lateral; C, telson, dorsal, plumose setae omitted; D, tooth on ventromesial carina of first article of antennular peduncle, lateral; E, third maxilliped, lateral; F, second pereiopod, lateral; G, third pereiopod, lateral; H, same, distal portion of propodus and dactylus, ventrolateral, slender setae on propodus omitted; I, fifth pereiopod, lateral; J, same, propodus and dactylus, ventromesial; K, uropod, dorsal, plumose setae omitted.

FIGURE 2. Alpheus thompsoni sp. nov., holotype, female (cl 13.3 mm) from Madang, Papua New Guinea (MNHN-2013- 16813):A, major (left) cheliped, distal portion of merus, carpus and chela, lateral; B, same, mesial; C, same, ischium, merus and carpus, mesial; D, same, dactylus, lateral, setae omitted; E, minor (right) cheliped, ischium, merus and carpus, lateral; F, same, merus, mesial, setae omitted; G, same, chela, lateral.

FIGURE 3. Alpheus thompsoni sp. nov., holotype, female (cl 13.3 mm) from Madang, Papua New Guinea (MNHN-2013- 16813): A, shrimp in life, dorsal; B, same, lateral. Photographs by the author, taken during Our Planet Reviewed—Papua Niugini Expedition (MNHN).

FIGURE 8. Some goby-associated species of Alpheus mentioned in the text, photographed in situ: A, Alpheus thompsoni sp. nov. associated with Amblyeleotris wheeleri, Anilao, Philippines; B, same, associated with Amblyeleotris guttata, Sulawesi, Indonesia; C, Alpheus sciolii sp. nov. associated with Cryptocentrus inexplicatus, Papua New Guinea; D, Alpheus sp. aff. A. sciolii sp. nov. associated with Amblyeleotris steinitzi, Bali, Indonesia; E, Alpheus sp. cf. mannarensis Purushothaman, Abhilash, Kumar & Lal, 2021, Papua New Guinea; F, Alpheus bellulus Miya & Miyake, 1969, Sulawesi, Indonesia. Photographs courtesy of Andrey Ryanskiy (A–C, E, F) and Yury Ivanov (D).