(Figs. 17, 18, 46F–G, 51C)
Alpheus richardsoni Yaldwyn 1971: 88; Fransen et al. 1997: 36; Poore 2004: 106, fig. 27c, d, 28l, 29s, t, pl. 9b; Gowlett-Holmes 2008: 215; De Grave & Fransen 2011: 389.
Alpheus euphrosyne.— Hutchings & Recher 1974: 106 [not A. euphrosyne De Man, 1897].
Alpheus euphrosyne richardsoni.— Banner & Banner 1982: 235, fig. 74 (part.?); Morgan & Jones 1991: 485; Morrison et al. 2014: 88, fig. 37c.
Alpheus sp. — Richardson & Yaldwyn 1958: 37, fig. 35.
Not Alpheus euphrosyne richardsoni.— Miya 1995: 275, fig. 2; Yang & Kim 1996: 106, figs. 1–3; Hayashi 1998: 292, figs. 353c, g, 354c, 355c, e [= A. nomurai sp. nov.]; Binh & Van 2021: 132 [= Alpheus sp., possibly A. euphrosyne De Man, 1897 or A. eurydactylus De Man, 1920].
Not Alpheus richardsoni. — Kunishima et al. 2022: 134, fig. 5 [= Alpheus sp. from A. malabaricus complex, possibly A. dolichodactylus Ortmann, 1890].
Material examined. Australia: 1 male (cl 9.5 mm), OUMNH. ZC. 2009.09.16, Queensland, Moreton Bay, Gold Coast, Loders Creek, 27°57.232’S 153°24.617’E, under rocks on muddy sand at high tide mark, leg. A. Anker & S. De Grave, 11.03.2009; 1 male (cl 8.3 mm), FLMNH UF 18694, same collection data as for prevous specimen [AUS-009]; 1 ov. female (cl 8.3 mm), FLMNH UF 18693, same collection data as for previous specimen [AUS-008]; 1 male (cl 9.3 mm), OUMNH. ZC. 2009.09.15, Queensland, Cleveland, Raby Bay Marina, 27°30.245’S 153°24.341’E, muddy lower intertidal, leg. A. Anker & S. De Grave, 12.03.2009 [AUS-055]; 1 male (cl 13.8 mm), USNM 106164, Queensland, North Stradbroke Island, Dunwich, leg. J.M. Moulton, 03.09.1960; 1 male (cl 10.0 mm), OUMNH. ZC. 2003.20.27, New South Wales, Clarence River, Thorny Island, ungated drainage system, leg. “H.K”, 07.2000; 1 male (cl 11.7 mm), OUMNH. ZC. 2003.20.24, same collection data as for previous specimen; 1 ov. female (cl 15.5 mm), RMNH Crus.D. 49642, New South Wales, north of Sydney, Broken Bay, Pittwater, Bayview, 17.04.1955, mud beach at low tide, near low tide mark, leg. L.B. Holthuis; 1 female (cl 10.0 mm), NMV J41038, Victoria, Port Phillip Bay, central muddy region, 3759.77’S, 14457.43’E, depth: 17 m, Smith MacIntyre grab, leg. R. S. Wilson, G. Walker-Smith & S. Heislers, 03.04.1995; 2 males (cl 12.4, 13.0 mm), 1 ov. female (cl 13.8 mm), NMV J40239, Victoria, Mallacoota Inlet, 37°32.7’S, 149°45.5’E, under wharf, depth: 1 m, oyster bag, leg. M.F. Gommon, 06.04.1989; 1 male (cl 12.7 mm), 1 ov. female (cl 14.6 mm), NMV J43683, Victoria, Port Phillip Bay, Corio muddy region, 38°07.0’S, 144°23.1’E, depth: 9 m, Smith MacIntyre grab, leg. R. S. Wilson & S. Heislers, 17.10.1995; 2 ov. females (cl 8.7, 10.8 mm), NMV J37327, Victoria, reef north of San Remo, intertidal, under rocks, leg. G. Poore et al., 28.04.1994; 1 male, 2 ov. females (cl 11.5–13.1 mm), NMV J21603, Victoria, Chesapeake Island, French Island, Western Port, collector unknown, 21.01.1972; 2 males (cl 11.5, 12.4 mm), NMV J21643-1, Victoria, Crib Point, Western Port, leg. G. Westcott, 22.06.1973; 2 ov. females (cl 11.5, 15.2 mm), NMV J21601, Victoria, Toora Beach, leg. S.W. Gunn, 01.09.1983; 1 male (cl 15.5 mm), 1 ov. female (cl 17.5 mm), NMV J21606, Victoria, Miller’s landing, Western Port, leg. Marine Research Group, 17.10.1981; 1 male (cl 13.2 mm), 1 ov. female (cl 13.8 mm), NMV J21642, South Australia, Pine Point, 19.11.1983; 1 ov. female (cl 10.2 mm), NMV J22006-2, Investigator Strait, leg. J.E. Watson, 17.01.1971.
Description. See Yaldwyn (1971) for original description and Banner & Banner (1982) for detailed redescription and illustrations (as A. euphrosyne richardsoni); a complementary, fully revised diagnosis is provided below.
Diagnosis. Large-sized species of Alpheus (maximal cl 20.0 mm, tl 65.0 mm). Carapace and pleon smooth, without pubescence. Rostrum subtriangular, acute, reaching or slightly overreaching mid-length of first article of antennular peduncle; rostral carina present, blunt, gently sloping into moderately deep rostro-orbital furrows. Orbital hoods broadly rounded in dorsal view. Pterygostomial angle broadly rounded. Telson ovate-rectangular, gradually tapering towards posterior margin, about 1.3–1.4 times as long as maximal width; dorsal surface with shallow, longitudinal, median depression, latter without setae, and two pairs of spiniform setae inserted at some distance from margin; posterior margin broadly rounded; posterolateral angle with two small spiniform setae. Antennular peduncle with stylocerite convex laterally, with tip subacute, not overreaching distal margin of first article; ventromesial carina with subtriangular tooth bearing small acute point; second article about 2.0–2.2 times as long as wide. Antennal basicerite with small distoventral tooth; scaphocerite with lateral margin shallowly concave; blade not broadened, separated from strong distolateral tooth by deep cleft; anterior margin of blade rounded, not reaching beyond distolateral tooth. Third maxilliped with antepenultimate article not broadened; penultimate article 2.5 times as long as wide. Chelipeds with ventromesial margin of meri unarmed distally. Major chela of A. edwardsii - type, with fingers about 0.4–0.5 length of palm; mesial face of palm smooth, with narrow mesial longitudinal groove, without mesial transverse ridge; lateral face of palm largely smooth, except for small field of minute granules above ventral shoulder (sometimes absent), with subrectangular lateral longitudinal groove; dorsal shoulder pronounced, rounded, sloping with angle superior to 45° into dorsal transverse groove, not overhanging; ventral shoulder pronounced, slightly protruding in lateral view, broadly rounded; mesial face of pollex faintly granulated, with poorly developed mesial subdistal ridge, without proximal protuberance and groove; lateral surface of pollex, as well as mesial and lateral surfaces of fingers smooth; dactylus with dorsal ridge slightly curved mesially, not protruding; dactylar plunger stout, distinct from dactylar ventral margin; distal portion of plunger with obliquely flattened ventromesial area; adhesive discs small. Male minor chela stout, strongly balaeniceps, with fingers about 0.8 length of palm; all surfaces smooth, without granulation; mesial face of palm with shallow mesial longitudinal groove; lateral face of palm with well-marked lateral longitudinal groove; dorsal shoulder not distinct, at most present as slight sinus; ventral transverse groove constriction-like; ventral shoulder poorly developed, rounded; dactylus with proximal balaeniceps expansion about 1.5 times as long as maximal dactylar width, with rows of balaeniceps setae. Female minor chela not balaeniceps; palm smooth, without sculpture; fingers slightly longer than palm, simple, with sharp cutting edges, not gaping. Second pereiopod with ratio of carpal subarticles approximately equal to 3.8: 2.2: 1: 1: 1.5. Third pereiopod with ischium typically armed with spiniform seta; merus about 4.0 times as long as maximal width, unarmed; propodus with six to eight stout spiniform setae on ventral margin and one pair of spiniform setae on distoventral margin adjacent to dactylus; dactylus about 0.4 length of propodus, spatulate. Fifth pereiopod with ischium unarmed. Male second pleopod with appendix masculina ~1.2 times length of appendix interna. Uropod with both protopod lobes ending in sharp tooth distally. Eggs numerous (> 100 in large females), small; egg diameter: 0.7 mm.
Colour pattern. Carapace brownish to olive-green with more or less conspicuous, whitish, transverse, crescentshaped band and some white spots or whitish mottling; each pleonite with two transverse, greenish or brown-green bands, sometimes with some additional bands on first two or three somites; antennular peduncles and scaphocerite brownish or pale brown-green; antennular and antennal flagella bluish or bluish green; mesial face of major chela olive-green to bluish green, with some greyish and paler beige areas; fingers pinkish distally; minor chela dark olive-grey or brown-green; walking legs pinkish or yellowish; telson greyish blue; uropods greenish or brownish with large bluish areas, blue colour being more intense posterior to transverse suture (Figs. 17, 18; see also colour photographs in Poore 2004: pl. 9b; Gowlett-Holmes 2008: 215).
Type locality. Bay of Islands, North Island, New Zealand.
Distribution. Southern temperate and subtropical Indo-West Pacific (Fig. 51C): Australia (Western Australia, South Australia, Victoria, Tasmania, New South Wales, southern Queensland) and New Zealand (North Island).
Common name proposed. Richardson’s snapping shrimp.
Ecology and biology. Alpheus richardsoni is an intertidal and shallow subtidal snapping shrimp, which is frequently encountered on mudflats and sandflats with abundant rocks and other types of shelters, in mangroves, as well as estuarine habitats, typically between the lower intertidal zone and about 5 m, sometimes down to 24 m. Being both an eurythermic and an euryhaline species, A. richardsoni is capable of tolerating marked seasonal variations, with surface water temperature fluctuating from 6°C to 28°C, and salinities ranging from 140 / 00 to 350 / 00, for instance, in Tasmania and New Zealand. It lives in complex burrow systems, often dug under large rocks, with several chambers and galleries descending 30 cm or more below the surface (Banner & Banner 1982; present study). As for A. euphrosyne and A. eurydactylus, the large number of eggs and their small size suggest an extended larval development in A. richardsoni. Banner & Banner (1982: 239, 240) provided a detailed summary of the biology of the Tasmanian populations of A. richardsoni using data from an unpublished PhD thesis (U [U Khin Khin] 1977).
Alpheus richardsoni is one of the largest snapping shrimps in southern Australia, with adult individuals reaching cl 20 mm and tl 65 mm (Banner & Banner 1982). Noteworthy is that the size of A. richardsoni gradually diminishes along the south-north gradient on the eastern coast of Australia. For instance, in the present material, the largest specimen from southern Queensland, near the northern limit of the species’ geographic range, is a female from Gold Coast (OUMNH. ZC. 2009.09.16) at cl 9.5 mm and tl 26 mm. The largest specimen from New South Wales in the present material is a male from Clarence River (OUMNH. ZC. 2003.20.24) at cl 12.5 mm and tl 30 mm. In contrast, several specimens from Victoria are significantly larger in size, often exceeding cl 13 mm, with one ovigerous female from Western Port (NMV J21606) reaching cl 17.5 mm and tl 56 mm.
Taxonomic remarks. Alpheus richardsoni is easily distinguishable from both A. euphrosyne and A. eurydactylus by the feebly developed distomesial ridge on the major chela pollex (vs. a very prominent one in A. euphrosyne and A. eurydactylus); the granulation of the mesial palmar face of the major chela reduced to a few granules above the ventral shoulder (vs. with a much more extensive granulation in A. euphrosyne and A. eurydactylus); the greatly reduced sculpture of the male major chela, for instance, the absence of a clear dorsal groove and shoulder (vs. with longitudinal grooves and a distinct dorsal shoulder in A. euphrosyne and A. eurydactylus); and the antennal basicerite armed with a small distolateral tooth (vs. usually unarmed in A. euphrosyne and A. eurydactylus) (Banner & Banner 1982: fig. 74; cf. Figs. 6, 7, 14, 15). Alpheus richardsoni differs specifically from A. euphrosyne by the non-overhanging dorsal shoulder of the major chela palm (vs. overhanging the transverse groove in A. euphrosyne); the presence of distinct rostro-orbital furrows (which are barely distinct or absent in A. euphrosyne); and the dorsal surface of the telson bearing only a very shallow, non-setose median longitudinal depression (vs. with a much deeper median depression, fringed laterally by numerous long setae, in A. euphrosyne) (Banner & Banner 1982: fig. 74; cf. Figs. 6, 7). The unique and diagnostic colour pattern of A. richardsoni (Figs. 17, 18) separates this species at once from A. euphrosyne (Fig. 8–10) and A. eurydactylus (Fig. 16), but also from all other species of Alpheus, including all species treated below. In addition, A. richardsoni is confined to subtropical and temperate waters of Australia and New Zealand and is thus geographically separated from A. euphrosyne (not known from Australia) and A. eurydactylus (known only from tropical northern Australia) (Fig. 51A–C). For separation of A. richardsoni from A. euphrosyne, A. eurydactylus and other species included in this study see below or refer to Table 1.
The specimens from two localities near Cairns, Queensland (Arlington Reef and an intertidal reef flat at Green Island), which were tentatively identified as A. euphrosyne richardsoni by Banner & Banner (1982), do not appear to belong to A. richardsoni. As noted by Banner & Banner (1982), these specimens “were from neither silty nor brackish conditions, yet morphologically they could not be distinguished from A. e. richardsoni.... However, they were markedly smaller than A. e. richardsoni, for none, including 3 ovigerous females, were over 25 mm in length, while A. e. euphrosyne and A. e. richardsoni both reach 65 mm in length at maturity”. According to these authors, these specimens may represent “yet another subspecies of the nominate species that has adapted to living in other than mud and brackish water”. Since all other eastern Australian populations of A. richardsoni occur to the south of Moreton Bay, Queensland (Figs. 17, 51C), the material from Arlington Reef and Green Island is also somewhat isolated geographically. Whatever the case may be, the taxonomic status of these specimens can only be determined after collection and examination of fresh material from reefs off or near Cairns.