Alpheus microrhynchus sensu De Man 1897
Creators: name: Anker, Arthur
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Alpheidae
Alpheus
Alpheus microrhynchus

description: Alpheus microrhynchus De Man, 1897
(Figs. 2A–E, 19–22, 51D)
Alpheus microrhynchus De Man 1897: 754, pl. 36, fig. 65 (as Alpheus sp.).
Alpheus microrhynchus. — De Man 1898: 318, pl. 4, fig. 3; Nobili 1900: 479; Johnson 1965: 9 (part.?); Banner & Banner 1966: 133 (part.?), fig. 50; Johnson 1976: 39 (part.?); Banner & Banner 1985: 24 (footnote); Naiyanetr 2007: 173.
Crangon microrhynchus.— Suvatti 1937: 48.
(?) Alpheus paludicola. — Kemp 1918: 273 (not A. paludicola Kemp, 1915).
Not Alpheus microrhynchus. — De Man 1911: 413 (part.), pl. 23, fig. 99 [= A. takla sp. nov.]; Johnson 1965: 9 (part.); Johnson 1976: 39 (part.?) [possibly = A. takla sp. nov. and/or A. mangalis sp. nov.]; Yeo & Ng 1996: 56, fig. 8a, b [= A. takla sp. nov.].
Type material. Neotype, male (cl 16.3 mm, tl 37.0 mm, chl 21.0 mm), ZRC 2000.2193, Indonesia, Kalimantan Barat, Kabupaten Sambas, Sambas Pasar, fish market, leg. H.H. Tan, 18.04.1998 [THH-9833].
Additional material. Thailand: 1 male (cl 15.0 mm), 1 female (cl 14.9 mm, in poor condition), OUMNH. ZC. 2019.06.49, Bangkok, aquarium trade market, leg. P.K.L. Ng, 06.2001; 1 male (cl 13.4, in poor condition), 1 male (16.8 mm, tl 45.0 mm, chl 28.0 mm), MNHN-IU-2018-5739, Bangkok, aquarium trade market, leg. F. Fasquel, 06.2001; 3 males (cl 12.6–13.0 mm), 1 ov. female (13.1 mm), ZRC 2012.0399, between Bangkok and Chonburi, river mouth, local collectors, leg. P.K.L. Ng, 04.2012.
Vietnam: 1 male (cl 17.1 mm), MNHN-IU-2013-14789, near Ho Chi Minh City, mangrove, water brackish (“very slightly salty”), in burrow in mud, leg. N. Ngoc-Ho, 05.1993.
Malaysia: 2 females (cl 14.3, 14.7 mm), ZRC 2014.0670, Sarawak, Kuching prawn farm, no further data.
Tentative identification. Alpheus cf. microrhynchus. Thailand: 1 male (cl 7.4 mm), 1 female (cl 8.7 mm), USNM 65477 /1, Bang Pakong River, leg. H. Smith, 01.07.1923.
Redescription. See Figs. 19, 20 and Banner & Banner (1966: fig. 50). Medium-sized species of Alpheus (maximal cl 16.8 mm, tl ~45.0 mm). Carapace glabrous, minutely and sparsely pitted, without pubescence, with weak grooves. Rostrum very short, subtriangular, broader than long, narrowing towards apex, distally subacute, not reaching 0.3 length of first article of antennular peduncle, obliquely ascendant or pointing straight-forward (see remarks below); rostral carina present as faint broad elevation flattening posterior to orbital hoods; rostro-orbital furrows very shallow; anterior margin of orbital hoods very shallowly concave, almost perpendicular to rostrum. Pterygostomial angle broadly rounded; cardiac notch deep.
Pleon smooth, finely pitted, without pubescence. Telson broad, ovate-rectangular, gently tapering towards posterior margin, about 1.3 times as long as maximal width near proximal margin; lateral margins with weak convexity at about mid-length; dorsal surface finely pitted, without longitudinal median depression, with two pairs of stout spiniform setae inserted in deep pits at some distance from lateral margins, first pair at about telson mid-length, second pair at about 0.7 of telson length; posterior margin broadly rounded, with two pairs of minute spiniform setae at posterolateral angles, lateral shorter than mesial.
Antennular peduncle with stylocerite slightly convex laterally, with acute tip, latter not overreaching distal margin of first article; ventromesial carina with broadly triangular tooth, latter longer than high and without acute point; second article about 1.8–1.9 times as long as wide. Antennal peduncle with distoventral margin of basicerite unarmed or with minute tooth; carpocerite reaching slightly beyond scaphocerite; scaphocerite with lateral margin nearly straight; blade broad, separated from broad strong distolateral tooth by deep cleft; anterior margin of blade rounded and reaching slightly beyond distolateral tooth.
Third maxilliped with antepenultimate article not particularly broadened, rather slender; penultimate article almost 3.2 times as long as wide, with long setae on lateroventral and mesioventral margins, latter not surpassing ultimate article; ultimate article with dense transverse rows of short serrulate setae on mesial surface and some much longer setae on dorsal and lateral surfaces, especially near or on apex; coxal lateral plate bluntly protruding dorsally; exopod reaching end of antepenultimate article.
Major cheliped of A. edwardsii - type. Merus very stout, about 1.8 as long as wide; ventromesial margin unarmed distally. Carpus very short, cup-shaped. Chela large, massive, with fingers about 0.6–0.7 length of palm. Mesial face of palm with feebly developed mesial transverse ridge in proximal half, extending from proximal edge of subtriangular mesial longitudinal groove to ventral surface of palm; surface smooth, without granules. Lateral face of palm smooth, without granulation; lateral longitudinal groove moderately deep, subrectangular; proximal half of palm without transverse ridge. Dorsal shoulder rounded, sloping gently with angle inferior to 45° into broad transverse groove, not overhanging. Ventral shoulder pronounced, slightly protruding in lateral view, rounded. Pollex with mesial face smooth over most of its surface, with prominent mesial subdistal ridge marked by low protuberance proximally and extending to subdistal angle of pollex; area ventral to mesial subdistal ridge noticeably depressed; distomesial angle distinctly superior to 90°, blunt; lateral face smooth; distolateral angle about 90°, rounded. Dactylus slightly longer than pollex, with moderately developed dorsal ridge, latter twisted mesially, rounded, not protruding; both mesial and lateral surfaces smooth; dactylar plunger moderately large, stout, clearly distinct from ventral dactylar margin; distal surface of plunger with obliquely flattened ventromesial area, without deep transverse groove. Adhesive discs small.
Male minor cheliped with chela strongly balaeniceps.Merus somewhat slenderer than that of major cheliped,about 2.5 times as long as wide; ventral margin with distomesial angle unarmed. Chela moderately swollen, with fingers about 0.9 length of palm; all surfaces smooth, without granulation. Palm subcylindrical, slightly swollen; mesial face with subdistal swelling; mesial longitudinal and lateral longitudinal groove indistinct or poorly demarcated; dorsal shoulder absent; dorsal transverse groove noticeable as shallow sinus; ventral transverse groove reduced to shallow sinus; ventral shoulder poorly marked as low bump or indistinct. Pollex with row of balaeniceps setae on low crest extending from base to just before mid-length of pollex; lateral surface with similar row of balaeniceps setae as on mesial surface. Dactylus with moderate lateral expansion (balaeniceps expansion) in proximal half, about twice as long as maximal width; lateral and mesial dactylar ridges each with dense rows of balaeniceps setae. Cutting edges of both fingers shallowly excavated on each side of sharp, blade-like ridge.
Female minor cheliped simple, not balaeniceps. Chela slender, not particularly swollen, with fingers of about same length as palm. Palm surface smooth, without granulation, without noticeable sculpture, i.e., without mesial and lateral longitudinal grooves, and without shoulders. Fingers simple, with sharp cutting edges, not gaping when closed; fingertips curved and crossing.
Second pereiopod with ratio of carpal subarticles ranging from 4: 1.7: 1: 1: 1.5 to 5: 1.8: 1: 1: 1.6. Third pereiopod moderately robust; ischium armed with small spiniform seta on lateroventral surface; merus about four times as long as maximal width, unarmed; propodus with about five spiniform setae on ventral margin and one pair of spiniform setae on distoventral margin adjacent to dactylus; dactylus close to 0.3 of propodus length, trigonal-conical, tapering, not broader than propodus in dorsal view. Fourth pereiopod generally similar to third pereiopod, slenderer; merus about 4.8 times as long as maximal width; dactylus about 0.3 length of propodus. Fifth pereiopod much slenderer than third and fourth pereiopods; ischium unarmed; propodus with at least two slender spiniform setae (or robust setae) and well-developed setal brush; dactylus trigonal-subspatulate, about 0.3 length of propodus.
Male second pleopod with appendix masculina ~1.2 length of appendix interna. Uropod with each protopodal lobe ending in sharp tooth distally; exopod and endopod broad, ovate; diaeresis of exopod complete, almost straight, with two subacute teeth fringing small distolateral spiniform seta (occasionally two spiniform setae); lateral margin convex.
Eggs not numerous (10 in one ovigerous female examined, ZRC 2012.0399, less than 40 in ovigerous females in Fig. 21A, D), very large; egg diameter about 1.4 mm.
Colour pattern. Carapace pale olive-brown, sometimes with purplish or bluish tinge; posterior margin of carapace and each pleonite with one narrow, transverse, dark grey-blue or dusky band; antennular peduncles and scaphocerite pale brown-green or greenish blue; antennular and antennal flagella bluish or greenish; mesial face of major chela olive-green to bluish green or bluish grey, with some olive-beige, pale orange or yellowish areas; fingers pinkish distally; minor chela dark olive-grey to brown or bluish green; walking legs reddish; telson greyish blue distally; uropods mostly greyish blue with some reddish tinge; exopod with conspicuous brick-red patch above distolateral spiniform seta; area posterior to transverse suture intense deep blue (Figs. 21, 22).
Type locality. Pontianak, Kalimantan (west coast of Borneo). Neotype from Kabupanten Sambas, Kalimantan Barat (west coast of Borneo), Indonesia.
Distribution. South-East Asia (Fig. 51D): Thailand (vicinity of Bangkok and possibly Songkhla Lake and Bang Pakong), Indonesian and Malaysian parts of Borneo (Kalimantan Barat, Sarawak) (De Man 1897, 1898; Nobili 1900; present study); records from eastern Java, Indonesia (De Man 1911), and Singapore (Johnson 1965, 1976) require confirmation.
Common name proposed. Klang snapping shrimp.
Ecology and biology. Alpheus microrhynchus can be qualified as an stenohaline snapping shrimp, confined to oligohaline habitats, such as rivers, creeks, lagoons and artificial canals (man-made for navigation or irrigation of rice fields) under slight tidal influence, living in deep burrows dug into muddy bottom or riverbanks. The small number of eggs and their large size suggest a highly abbreviated larval development in this species (H. Coutière in De Man 1898), although it remains to be studied in more details.
Alpheus microrhynchus is occasionally sold on fish or pet markets, mainly in Thailand (e.g., Chatuchak market in Bangkok). According to observations of F. Fasquel (pers. comm.), the species needs a low percentage of salt added to freshwater since all shrimps kept in pure freshwater unexpectedly died after only a few weeks.
Taxonomic remarks. The neotype of A. microrhynchus from western Borneo corresponds to De Man’s (1897) description in all but a few minor details. The first small discrepancy is the direction of the rostrum, which was described as pointing obliquely upwards (= “schräg nach oben gerichtetes Spitzchen”). In most examined specimens of A. microrhynchus, including the neotype, the rostrum is directed straight forwards (Fig. 20A), although in one male specimen from Thailand (ZRC 2012.0399), it is directed slightly obliquely upwards. In addition, a clearly obliquely upwards-pointing rostrum can be seen in the illustrated (but not preserved) specimen from Thailand (Fig. 21A). Some variation in the direction of the rostrum is also present in the closely related A. cyanoteles (see below). The second difference is the armature of the antennal basicerite, which according to De Man (1897) has a rudimentary, hardly 1.0 mm long tooth (= “rudimentäres, kaum mm langes Stachelchen”). In the neotype of A. microrhynchus from Kalimantan and all specimens from Thailand, the distoventral margin of the basicerite is smoothly rounded, i.e., has no tooth, exactly as in the material from Thailand reported by De Man (1898) and Banner & Banner (1966). Because of its small size, this tooth may break off or get blunter after each moult, to the point of eventually becoming obsolete in full-grown adults. However, the development of the tooth on the basicerite may be simply variable in A. microrhynchus. Noteworthy here is that a similar variation in the armature of the basicerite was observed in A. euphrosyne (see above).
Two further characters of A. microrhynchus, viz. the proportions of the carpal subarticles of the second pereiopod (P2) and the shape of the dactyli of the third to fifth pereiopods need to be discussed in more detail. In the original description of A. microrhynchus (material from Pontianak, as Alpheus sp.), De Man (1897) described the proportions of the carpal subarticles of the second pereiopod as 3.5: 1.3: 0.6: 0.6: 0.96, which is roughly similar to his observations (De Man 1898) of the material from Bangkok, 4.3: 1.6: 0.8: 0.72: 1.04 (right P2), and 4.0: 1.5: 0.8: 0.72: 1.1 (left P2). These numbers show that the ratio of the first to second subarticle is proportionally higher in the material from Thailand, 2.7–3.0, as illustrated by Banner & Banner (1966: fig. 50F), compared to the material from Borneo, where this ratio is at most 2.4. Regarding the condition of the dactylus of the ambulatory pereiopods, De Man (1897: 754) stated that the third to fifth pereiopods are somewhat similar to those of A. euphrosyne (“gleichen ungefähr denen von A. euphrosyne ”). No specific details on the dactylus were provided in the complementary description, where De Man (1898: 321) only noted that the ambulatory pereiopods agree with those of the material from Pontianak. However, Banner & Banner (1966) noted that the dactylus of A. microrhynchus, at least in the material from Thailand, is not spatulate, as in A. euphrosyne, but rather “conical, tapering”. Yeo & Ng (1996) examined several specimens identified as A. microrhynchus in the ZRC holdings and concluded that the dactylus in this species is “subconical to subspatulate”, which is essentially the same as trigonal-subspatulate in the above description.
Alpheus microrhynchus can be separated from A. euphrosyne, A. eurydactylus and A. richardsoni by the ischium of the third and fourth pereiopods unarmed (vs. usually armed with a spiniform seta in the other three species); the much larger size of eggs, with the diameter around 1.4 mm (vs. equal to or less than 0.7 mm in the other species); the less expanded, trigonal-conical (at most weakly subspatulate) dactyli of the third to fifth pereiopods (vs. spatulate, much more expanded, in the other species; see also below); the perfectly smooth mesial surface of the major chela (vs. with a small distal field of granules in A. richardsoni and with large granulated areas in A. euphrosyne and A. eurydactylus); and the absence of a median longitudinal depression on the dorsal surface of the telson (present in the other species, especially well demarcated in A. euphrosyne and A. eurydactylus). In addition, A. microrhynchus differs from A. eurydactylus and A. richardsoni by the much shorter rostrum; from A. euphrosyne and A. eurydactylus by the absence of dorsal and ventral transverse grooves on the palm of the male minor chela (well developed in A. euphrosyne and A. eurydactylus); specifically from A. euphrosyne by the dorsal shoulder of the major chela smoothly sloping into the adjacent transverse groove (vs. protruding and overhanging the transverse groove in A. euphrosyne); and specifically from A. richardsoni by the much stronger distomesial ridge on the mesial face of the major chela pollex (which is feebly developed in A. richardsoni). In life, A. microrhynchus (Figs. 21, 22) can be distinguished from A. euphrosyne (Fig. 8–10) and A. richardsoni (Fig. 17, 18) by its colour pattern, which is more similar to that of A. eurydactylus (Fig. 16). There also seem to be an ecological separation between A. microrhynchus, A. euphrosyne, A. eurydactylus and A. richardsoni, with only the former species being confined to oligohaline habitats (sections of rivers, lagoons and canals under weak tidal influence). For separation of A. microrhynchus from other species treated in this study see below or refer to Table 1.
Kemp’s (1918) record of A. paludicola from Thale Sap (Songkhla Lake) in southern Thailand most likely refers to A. microrhynchus. Kemp noted that the Thale Sap specimens had a distinctly longer rostrum, “extending considerably beyond the end of the orbital hoods”. They also had a different colour pattern, described by the collector, Dr. N. Annandale, as “translucent, without definite markings, but tinged ... with reddish brown, ... palm and fingers of both chelae were deeply tinged with blue, especially on the dorsal surface ... eggs were pale green”. All females had very large eggs, 1.3–1.4 mm in diameter. This combination of characters agrees more with the diagnosis of A. microrhynchus than with that of A. paludicola, although in the latter species, females bear equally large eggs (Kemp 1915).
Johnson’s (1965, 1976) records of A. microrhynchus from Singapore are probably based on material containing at least two species. All large-sized specimens (tl> 50 mm) identified as A. microrhynchus by D.S. Johnson were herein reidentified as either A. eurydactylus or A. takla sp. nov. (see below), whereas two smaller problematic females (tl<30 mm) were included under A. cf. eurydactylus B. (see above). Although the historical occurrence of A. microrhynchus in Singapore cannot be excluded, it is rather unlikely that the species occurs there today, after most of transitional freshwater-to-brackish habitats were lost to urban development.
Two specimens from Bang Pakong River east of Bangkok, Thailand (USNM 65477/1), were tentatively identified as A. cf. microrhynchus, because they deviate even more from the present redescription of the species. The third pereiopod merus of these specimens is somewhat broader, reaching the proportions of its homolog in A. eurydactylus. Most importantly, the minor chela of the male specimen has a more broadened, balaeniceps-shaped dactylus, almost as broad as in A. eurydactylus. On the other hand, the major chela has no trace of granulation (which is present in A. eurydactylus) and its dorsal shoulder is sloping very gently into the adjacent transverse groove (vs. sloping with a stronger angle in A. eurydactylus). The antennal basicerite of these specimens is unarmed, as in A. eurydactylus, which contradicts De Man’s (1897) original diagnosis of A. microrhynchus (see above) and does not allow assigning them to A. cyanoteles, the latter with a well-developed tooth (see below). Furthermore, it remains unknown where in the river (i.e., at the mouth or more upstream) these specimens were collected. More fresh material from Bang Pakong River and other parts of Thailand, as well as other localities across South-East Asia, is needed for a molecular analysis of various populations of A. microrhynchus and confirmation of their identity.
description: Published as part of Anker, Arthur, 2023, Revision of Alpheus euphrosyne De Man, 1897 and A. microrhynchus De Man, 1897, with description of three new species and taxonomic remarks on several other morphologically and ecologically similar snapping shrimps (Malacostraca: Decapoda: Alpheidae), pp. 1-115 in Zootaxa 5282 (1) on pages 38-43, DOI: 10.11646/zootaxa.5282.1.1, http://zenodo.org/record/7912292