Scallasis amboinae Bate, 1888

Komai, Tomoyuki, Poore, Gary C. B. & Fujita, Yoshihisa, 2020, Redescription of the poorly known ghost shrimp species, Scallasis amboinae Bate, 1888, review of the genus, and description of a new species from the Ryukyu Islands, Japan (Decapoda: Axiidea: Callianassidae), Zootaxa 4766 (3), pp. 401-420 : 402-407

Scallasis amboinae Bate, 1888

( Figs 1–3 )

Scallasis amboinae Bate, 1888: 34 , pl. 2 figs 3, 4.— Manning & Felder 1991: 780.— Tudge et al. 2000: 145.— Poore et al. 2019:

143 (list). Callianassa (Scallasis) amboinae .— Borradaile 1903: 547.—De Man 1928: 30, 93. Callianassa (Cheramus) pygmaea De Man 1928: 27 , 93, 99, 155–159, pl. 16 fig. 24– 24g (type locality: Ambon Anchorage, 54

m). Callianassa amboinae .— Sakai 1999: 12, 37–38, fig. 5d–f.— Sakai 2005: 68, figs 15, 16. Callianassa pygmaea .— Tudge et al. 2000: 143.— Sakai 2005: 102. Trypaea amboinae .— Sakai 2011a: 391 (see too discussion on pp. 364–365). Trypaea pygmaea .— Sakai 2011a: 407.

Type material. Holotype: Indonesia, Ambon (as Amboina), 6 October 1874, HMS Challenger stn, male (5.2 mm), NHM 1888.22 .

Other material examined. Papua New Guinea, Madang Province, Alexishafen, 05°05.3'S 145°48.0'E, 8–13 m, 16 November 2012 (stn PS 14), ovigerous female (5.5 mm), MNHN IU- 2013-610 (Genbank sequences, MN 237932 , MN 238140 ). Madang Harbour, E of Nui I., 05°12.3'S 145°47.9.0'E, 10–15 m, 11 November 2012 (stn PD 14), postovigerous female (3.5 mm), MNHN IU- 2013-12303.

Diagnosis. Pleomere 6 1.1–1.2 times as long as wide, with lateral notches posteriorly. Telson 1.2 times as long as wide; greatest width 1.3 times posterior width. Maxilliped 3 ischium-merus 3 times as long as wide; merus free distal margin oblique. Female major cheliped ischium lower margin with 7 spines; merus lower margin with fine oblique proximal spine, sometimes with small accessory proximal tooth; palm 0.7–1 times as long as carpus. Minor cheliped ischium lower margin with 3–5 spines; merus lower margin with 1 oblique spine at midpoint. Uropodal endopod anterior margin with small spine about two-thirds along; dorsal surface with 1 long proximal spiniform seta, usually plus 1 shorter submarginal seta; exopod anterior margin with small spiniform seta about three-quarters along.

Redescription. Rostrum narrowly triangular, spiniform, directed forward, with slight ventral carina, falling slightly short of distal ends of eyestalks. Carapace shorter than length of pleomeres 1 and 2 combined; orbital margins concave; anterolateral projections rounded; excavation inferior to anterolateral projections deep, U-shaped; cervical groove across 0.75 length of carapace, without postrostral transverse groove; linea thalassinica distinct, extending to posterolateral margin of carapace.

Thoracic sternite 7 subpentagonal with rounded anterior margin; ventral surface with shallow median groove.

Length ratio of pleomeres 1–6 measured along midline 1: 2.3: 1.3: 1: 1.8: 2.0. Pleomere 1 narrowing anteriorly in dorsal view; pleuron with poorly defined ventral margin. Pleomere 2 pleuron posterolateral margin rounded. Pleomeres 3–5 pleura each with patch of plumose setae. Pleomere 6 1.1–1.2 times as long as wide, narrowing posteriorly, with shallow lateral oblique groove at about posterior 0.2. Telson trapezoidal, narrowing posteriorly, 1.2 times as long as wide, broadest at anterior 0.2; greatest width 1.3 times posterior width; dorsal surface medially with 2 pairs each of spiniform setae and long setae in short transverse row anterior to midlength; lateral margin unarmed; 2 pairs of small spiniform setae at rounded posterolateral angles; posterior margin shallowly concave medially, with minute median spine.

Eyestalks each with flat, acute distal projection, contiguous, reaching distal margin of article 1 of antennular peduncle; lateral margin convex. Cornea subterminal, submedial, darkly pigmented, third–half as wide as eyestalk.

Antennular peduncle) slightly longer than to antennal peduncle; article 1 distal margin visible in dorsal view; article 2 about as long as article 1; article 3 3.3 times as long as article 2; articles 2 and 3 with longitudinal ventral row of sparse long setae.

Antennal peduncle with distal 2 articles subcylindrical; article 4 1.5 times as long as article 5; scaphocerite minute, acute.

Maxilliped 3 without exopod; ischium-merus narrowly subrectangular, non-operculiform, 3.0 times as long as wide; ischium tapering, twice as long as wide, crista dentata row of 14 uneven erect spines; merus, about half as long as ischium measured along dorsal margin, about as wide as long, wider than merus, distolateral margin obliquely truncate, unarmed; carpus cup-shaped, slightly shorter than merus; propodus narrowing distally, 1.7 times as long as wide, longer than carpus; dactylus slender, digitiform, about 0.7 times as long as propodus, with dense oblique setae along distal half of lower margin.

Pereopods 1 (chelipeds) greatly unequal, dissimilar. Female major cheliped carpus-chela as long as carapace length. Ischium upper margin sinuous, unarmed; lower margin with row of 7 oblique spines. Merus shorter than ischium; upper margin convex, unarmed; lower margin with narrow oblique spine proximal to midpoint. Carpus 2.3 times as long as wide; upper and lower margins carinate, smooth. Chela about as long as carpus; palm 0.6 times as length of carpus, 1.5 times as long as wide; upper margin carinate, almost glabrous; lateral surface smooth, convex; mesial surface slightly convex; lower margin carinate, with submarginal row of tufts of setae extending onto fixed finger; fixed finger 0.7 times as long as palm, occlusal margin unarmed. Dactylus as long as palm, curved distally, closing on fixed finger; upper surface with blunt ridge laterally and with tufts of long setae; occlusal margin sinuous.

Female minor cheliped carpus-chela slightly shorter than that of major cheliped. Ischium slightly curving; upper margin smooth, lower margin armed with row of 5 oblique spines. Merus 0.8 times as long as ischium; upper margin convex, unarmed; lower margin with narrow oblique spine at midpoint. Carpus 1.7 times as long as merus, 4.2 times as long as wide; upper margin straight, rounded; lower margin convex proximally, carinate. Palm wider distally, 1.6 times as long as wide; upper margin straight, bluntly carinate, with row of setae; lower margin carinate, with row of tufts of setae extending onto fixed finger; lateral and mesial surfaces slightly convex, smooth; fixed finger about as long as palm, slightly curving, with acute tip; occlusal margin slightly concave; lateral surface with row of tufts of setae along cutting edge. Dactylus 1.2 times as long as palm, as long as fixed finger; dorsal margin rounded, with row of long setae; occlusal margin unarmed.

Pereopod 2 ischium short, lower distal angle produced; merus with sinuous lower margin, upper margin almost straight; carpus subtriangular, twice as long as wide; chela subtriangular; palm 2.5 times as wide as upper margin; occlusal margins of fingers bordered by thin corneous ridge; dactylus 2.5 times as long as palm. Pereopod 3 carpus subtriangular, lower margin concave, twice as long as wide; propodus suboval with produced lower proximal margin, upper margin 1.3 times width, lateral face obtusely carinate medially, lower margin convex, faintly undulate, with 1 slender spiniform seta subdistally; dactylus nearly straight, about 0.7 times as long as propodus upper margin. Pereopod 4 coxa flattened ventrally, immovable; basis and ischium partially fused, extended posterolaterally; merus longer than ischium; carpus wider distally; propodus compressed, as long as carpus, with dense grooming setae distally on lower margin, scattered stiff setae on outer surface; dactylus slightly curving, 0.4 times as long as propodus. Pereopod 5 slender, with chela as long as carpus, slightly curving; dactylus about 0.3 times as long as palm, with minute teeth.

Female pleopod 1 uniramous; peduncle straight; exopod almost as long as peduncle, with slight shoulder slightly proximal to midlength on inner margin. Female pleopod 2 subequally biramous; peduncle curved outward, inner margin angular; endopod tapering distally, slightly shorter and broader than exopod; exopod slightly curved inward. Pleopods 3–5 with appendix interna slender, rod-like.

Uropod endopod and exopod subovate, overreaching posterior margin of telson. Endopod about 1.8 times as long as wide; upper surface shallowly concave in mesial half, with 1 long spiniform seta near anteroproximal angle, sometimes with adjacent ancillary spiniform seta; anterior margin slightly sinuous, with small subdistal spine at about distal 0.35; posterodistal margin convex, with fringe of setae, with 2 short distal spiniform setae. Exopod 1.6 times as long as wide, exceeding endopod by half length; anterior margin convex, bearing 1 subdistal spiniform seta; posterior margin with about 10 blade-like distal setae, connected to distal margin continuously or by rounded corner; upper surface faintly slightly carinate in midline, sometimes with submarginal spiniform seta near anterior margin; dorsal plate extending about one-third–one-half distal exopod width, with distal row of stiff setae separated from setal row of distal margin.

Variation. The shapes, position of the uropodal tooth, and the number of dorsal spiniform setae on the exopod of the uropodal rami differ between the holotype and the two newly discovered specimens. With few individuals we attribute this to individual differences, possibly size-related. The size and shape of the eyestalks appear to differ between individuals; the apical tubercles ( Fig. 2G ) were only visible at high magnification. The posterior concavity of the telson was more pronounced in some individuals than others; Sakai’s (1999: fig. 5e) illustration of the telson of the holotype is much longer than it actually is, which could be artistic error.

Distribution. Indonesia, Papua New Guinea, possibly Gulf of Thailand; at depths of 8– 13 m.

Remarks. The holotype is incomplete and now somewhat damaged ( Fig. 1 A–D). The chelipeds and pereopods 2–4 are not present. Bate’s (1888) description and illustrations are not especially informative. The “globular” eyestalk is not obvious on the holotype 130 years later. Sakai (2011a) suggested the description did not match Bate’s figures and interpreted Bate’s drawing (1888: pl. 2 fig. 3i) as maxillipeds 3 with exopods – it is more probably of maxillipeds 2 and 3. Pleopod 1 is missing (or absent), pleopod 3 biramous with narrow rami, and pleopods 3–5 have a long appendix interna. Sakai’s (1999) reillustration of the holotype confirms that the maxilliped 3 is relatively narrow (ischium-merus 3.5 times as long as wide) with an oblique distal meral margin, the rostrum is attenuated to reach almost the end of the eyestalk, and the eyestalk has a triangular terminal lobe with its apex not adjacent to its pair. His illustration of the uropod and telson are inaccurate. Our own observations (GCBP 2011, 2017) show the rostrum to be directed anteriorly and the telson to be shorter (1.1 times as long as wide, said to be ‘quadrate’ by Bate) than figured by Sakai, having an excavate posterior margin, short median spine and two short spiniform setae on each posterolateral corner. The telson is half as long as the elongate pleomere 6. The uropodal endopod has two long proximal spiniform setae on the upper surface and the exopod a definite short dorsal plate close to the anterodistal angle (not as in Sakai, 1999: fig. 5e). The scaphocerite is acute.

The ovigerous females from Papua New Guinea reveal details not observed on the holotype. The uropodal exopod carries a prominent marginal subdistal spiniform seta and (in one specimen) another dorsally near the anterior margin (both lost or not observed on the holotype). The uropodal endopod has a tooth at the end of the anterior margin and one strong facial spiniform seta (two on one side of one individual).

Sakai (1999) treated Callianassa (Cheramus) pygmaea De Man, 1928 , collected at Ambon, the same locality as S. amboinae , as a junior synonym of Callianassa amboinae . In as far as its description reveals the rostrum, eyes, maxilliped 3, minor cheliped, pereopod 3, telson and uropod are virtually indistinguishable from S. amboinae . Notably, De Man figured tooth at the end of the anterior margin and the easily missed spiniform setae on the dorsal surface of the uropodal endopod, and the spiniform setae at the end of the anterior margin of the exopod. The species are treated as synonymous here.

Sakai (1999) referred specimens from southern Vietnam to “ Callianassa ” amboinae , but we did not re-examine these specimens. Sakai (2005) identified specimens from various Indo-West Pacific localities as “ Callianassa ” amboinae : Gulf of Thailand, 20 m depth, “off Burail Bay, Fiji Is., New Caledonia, 200 m depth” [sic], Arafura Sea, 54 m depth, Bay of Bengal, 50 m depth, and West Malay Peninsula, 14 m depth. The geographic and bathymetric range of this collection is considerable but we have not been able to re-examine this material. The illustrated specimen ( Sakai 2005: figs 15, 16; labeled ZMUC 10b) is said to be the 3.8 mm ovigerous female from the Gulf of Thailand (ZMUC CRU-3775) in the text. The female chelipeds are more elongate than the female from Papua New Guinea ( Fig. 2A, B ) but otherwise this female cannot be distinguished.

Figures

FIGURE 1. Scallasis amboinae Bate, 1888. Holotype, male (cl 5.2 mm), NHM 1888.22: A, anterior carapace, rostrum, right eyestalk, antenna, lateral view; B, rostrum, eyestalks, dorsal view; C, left antennal peduncle, lateral view; D, pleomere 6, telson, uropod, dorsal view. Post-ovigerous female (cl. 3.5 mm), MNHN IU-2013-12303: E, rostrum, eyestalks, dorsal view; F, telson, uropod, dorsal view.

FIGURE 2. Scallasis amboinae Bate, 1888. Ovigerous female (cl. 5.5 mm), MNHN IU-2013-610: A, B, body, dorsal, lateral views; C, pleomere 6, right margin, uropodal peduncle, ventral view; D, pleomere 6, right margin, lateral view; E, F, anterior carapace, eyestalks, antennule and antenna peduncles, lateral, dorsal views; G, telson, dorsal view; H, right uropod, dorsal view (perpendicular).

FIGURE 3. Scallasis amboinae Bate, 1888. Ovigerous female (cl. 5.5 mm), MNHN IU-2013-610: A, left major cheliped, mesial view; B, same, fingers, lateral view; C, right minor cheliped, mesial view; D–G, right pereopods 2–5; H, pereopod 5 fingers (lateral view in situ); I, right maxilliped 3, lateral view; J, maxilliped 3 crista dentata, anterior view; K, pereopod 4 left coxa and thoracic sternite 7, ventral view; L, M, pleopods 1, 2 (setae omitted).