Shenius anomalus ( Shen, 1935 )

Ng, Peter K. L., Clark, Paul F. & Cuesta, Jose A., 2010, Establishment of a new subfamily for Shenius anomalus (Shen, 1935) (Crustacea: Decapoda: Brachyura: Dotillidae), Journal of Natural History 44 (25 - 26), pp. 1531-1553 : 1534-1541

publication ID	https://doi.org/ 10.1080/00222931003616362
persistent identifier	https://treatment.plazi.org/id/415987FD-8375-FFB5-1499-DDD6AE1E2A2F
treatment provided by	Felipe
scientific name	Shenius anomalus ( Shen, 1935 )
status

Treatment

Shenius anomalus ( Shen, 1935) View in CoL

( Figures 1–10 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 View Figure 8 View Figure 9 View Figure 10 )

Camptandrium anomalum Shen, 1935: 31 , text figs 8B, 9; Tweedie 1937: 162.

? Camptandrium anomalum, Serène 1968: 1010 .

Shenius anomalum, Serène 1971: 917 View in CoL , plate 5C; Serène and Umali 1972: 94, plate 9, figs 5–7, text figs 124, 125; Serène 1974: 66; Tan and Ng 1994: 84; Ng, Wang and Lim, 2008: 126.

Shenius anomalus, Serène 1971: 903 View in CoL ; Yang 1979: 42; Manning and Holthuis 1981: 200; Dai et al. 1986: 441, fig. 247 (1–3); Dai and Yang 1991: 483, fig. 247 (1–3); Ng, Guinot and Davie 2008: 235.

Material examined

Type. Da Pu Xu (= Taipo), Guangdong Province, (= Canton), southern China, coll. 2 June 1932; holotype male (4.5 × 3.5 mm) ( CAS CB-02060a) ; paratype female (3.8 × 2.9 mm) ( CAS CB-02060b) .

Others. Nine males, 4 ovig. females ( NHM 1937.11.15.132-141), Kranji River, Singapore; pres. Raffles Museum; 2 males, 1 ovig. female, 5 females ( ZRC 1965.7.15.1–8), Kranji , Singapore, coll. M. W. F. Tweedie, June 1935 ; 1 female ( ZRC 1993.488 View Materials ), Sungei Buloh Nature Reserve , Singapore, coll. D. Wee, 10 August 1992 ; 1 male (5.5 × 4.9 mm), 1 female (6.8 × 5.5 mm) ( NHM, ex ZRC 1987.338 View Materials – 339 View Materials ), Lim Chu Kang , Singapore, coll. P. K. L. Ng, March 1986 ; 1 male, 1 female ( ZRC 1999.1176 View Materials ), Lim Chu Kang , Singapore, coll. P. K. L. Ng, April 1995 ; 1 female ( ZRC 2000.1111 View Materials ), Lim Chu Kang , Singapore, coll. P. K. L. Ng, 23 March 2000 ; 2 females (larger 5.0 × 4.0 mm) ( ZRC 1987.333 View Materials – 334 View Materials ), Mandai , Singapore, coll. P. K. L. Ng, 21 February 1987 ; 2 males (3.0 × 2.8 mm, 2.6 × 2.4 mm), 1 female (4.3 × 3.5 mm) ( ZRC 1987.335 View Materials – 337 View Materials ), Lim Chu Kang , Singapore, coll. P. K. L. Ng, 19 March 1987 ; 1 female (4.7 × 4.1 mm) ( ZRC 1987.1181 View Materials ), Lim Chu Kang , Singapore, coll. S. Harminto, 30 July 1987 ; 1 female ( ZRC 2002.611 View Materials ), Sungei Buloh Nature Reserve , Singapore, coll. P. K. L. Ng, August 2002 ; 2 females ( ZRC 1993.486 View Materials – 487 View Materials ), Sungei Buloh Nature Reserve , Singapore, coll. D. Wee, 28 July 1992 ; 2 males, 1 ovig. female, 1 female ( ZRC 1965.7.9.18–20), Johore Straits , coll. M. W. F. Tweedie, October 1934 ; 1 female ( ZRC 1965.7.15.9), Muar , Johor, Peninsular Malaysia, coll. M. W. F. Tweedie, February. 1935; 5 males (largest 4.6 × 3.8 mm), 11 females ( ZRC 1965.7.15.14–23), Mersing , Johor, Peninsular Malaysia, coll. M. W. F. Tweedie, November 1938 ; 1 male, 1 ovig. female, 2 females ( ZRC 1965.7.15.10–13), Prai , Province Wellesley, Peninsular Malaysia, coll. M. W. F. Tweedie, December 1938 .

Diagnosis

Carapace hexagonal, dorsal surface not convex with regions well defined, covered with short stiff setae. Outer surface of chelipeds covered with short stiff setae; dactylar finger of adult male chela with prominent sub-basal tooth; distal parts of cutting margins of fingers spatuliform. Ambulatory legs with dorsal margin of P2 meri armed with two spines, those of P3 and P4 with three spines, that of P4 with one spine; outer surface with submarginal carina; outer surfaces of meri with numerous short stiff setae; propodus and dactylus long, slender, unarmed. Male and female sternoabdominal cavity reaching to base of buccal cavity Male abdomen with somite 5 hourglass-shaped. G1 sinuous, slender, with several short and long spines distally.

Description of male

Carapace hexagonal, regions well defined, separated by broad depressions, prominently raised, peaks with tubercle ( Figures 1 View Figure 1 , 2A,C View Figure 2 , 3A,B View Figure 3 ); dorsal surface covered with very short black setae, denser near raised parts of regions ( Figure 2A,C View Figure 2 ). Carapace margins, including front, lined with small, fine rounded granules ( Figures 1 View Figure 1 , 2A,C View Figure 2 , 3A,B View Figure 3 ). Front sinuous, weakly bilobed, each lobe rounded with broadly concave median depression; separated from low inner orbital tooth by shallow cleft, without fissure ( Figures 1 View Figure 1 , 2A,C View Figure 2 , 3A,B View Figure 3 ). Supraorbital margin sinuous, without cleft ( Figures 1 View Figure 1 , 3A,B View Figure 3 ). External orbital tooth prominent, triangular, directed obliquely outwards ( Figures 1 View Figure 1 , 3A,B View Figure 3 ). Anterolateral margin with two distinct triangular teeth, first tooth smaller than second tooth ( Figures 1 View Figure 1 , 3A,B View Figure 3 ). Posterolateral margin sinuous, median part with low raised lobe on posterolateral region ( Figures 1 View Figure 1 , 2A,C View Figure 2 , 3A,B View Figure 3 ). Posterior carapace margin almost straight ( Figures 1 View Figure 1 , 3A,B View Figure 3 ). Pterygostomial, subhepatic and suborbital regions smooth but covered with numerous short setae ( Figure 3C View Figure 3 ). Suborbital margin distinctly sinuous, finely granulated, with two large, broad rounded lobes ( Figure 3C View Figure 3 ). Orbits complete; eyestalk relatively short, stout; cornea large ( Figure 3C View Figure 3 ). Basal antennal segment mobile, flagellum relatively short, only reaching to external orbital tooth ( Figure 3C View Figure 3 ). Antennules folding obliquely ( Figure 3C View Figure 3 ). Posterior margin of epistome with large triangular median lobe and a small triangular lobe on each side ( Figure 3C View Figure 3 ). Buccal cavity wide, occupying most of face; third maxillipeds short, broad, without any gape when closed ( Figures 3C View Figure 3 , 5A View Figure 5 ); merus and ischium squarish; merus larger than ischium, anteroexternal margin rounded; ischium without teeth or grooves; palp (carpus, propodus and dactylus) relatively short, inserted submedially on distal margin of merus; exopod long, reaching just beyond distal edge of merus, with long flagellum ( Figure 5A View Figure 5 ).

Outer surfaces of cheliped segments covered with short, stiff setae; with very small granules ( Figures 1B,D View Figure 1 , 4E View Figure 4 ). Merus relatively short, with blunt subdistal angle on dorsal margin; distal part of ventral margin with denticulated margin. Carpus longer than broad with low inner angle. Chela with fingers shorter than palm; fingers with distal third of cutting margin spatuliform ( Figure 4E View Figure 4 ), inside surface of distal third of fingers with numerous long plumose setae; dactylus with prominent subtruncate basal tooth, cutting edge lined with numerous denticles; fingers forming small gape when closed ( Figure 4E View Figure 4 ).

Ambulatory legs inserted laterally on thorax, distinctly unequal in length; P2 shortest; P3 and P4 longest ( Figures 2A,C View Figure 2 , 4A–D View Figure 4 ). Coxa with outer margins denticulated; ventral surface of base of coxa without setae. Basis-ischium with distal margin finely granulated. Merus broadest medially; outer surfaces of meri finely granulated, with numerous short, stiff setae, with low but distinct subdorsal granulated ridge which spans proximal two-thirds length, not reaching distal margin; with distinct, blunt distal tooth on dorsal margin; dorsal and ventral margins lined with numerous low but outwardly directed granules; dorsal margin of P2 merus with one small submedian spine and one large subdistal spine, dorsal margins of P3 and P4 meri each with three prominent spines on distal two-thirds, dorsal margin of P5 merus with one small subdistal tooth ( Figure 4A–D View Figure 4 ). Carpus, propodus and dactylus smooth, glabrous; propodus longest; dactylus gently curved.

Thoracic sternum transversely broad; sternites 1–3 completely fused, just visible between bases of ischia of third maxillipeds; sternoabdominal cavity reaching to base of buccal cavity ( Figure 2B View Figure 2 ); part of sternoabdominal cavity covered by hourglasslike abdominal somite 4 exposed. Press button present as low rounded knob on distal edge of sternite 5. Male abdomen relatively slender, all somites and telson mobile; somite 1 mostly hidden under posterior edge of carapace; somite 2 transversely narrow; somites 1 and 2 not wider than somite 3, not reaching coxae of P5; somite 3 subrectangular with gently convex lateral margins; somite 4 trapezoidal, as long as somite 3; somite 5 hourglass-shaped with prominent median constriction which exposes sternoabdominal cavity and G1 beneath; somite 6 trapezoidal, lateral margins gently concave; telson triangular in general shape but with median part of lateral margin prominently concave and edges convex, structure appears almost trilobate in form ( Figure 5B View Figure 5 ). G1 slender, sinuous, S-shaped, distal part with several small and large spines; tip open ( Figure 6A–D View Figure 6 ). G2 very short, tip without flagellum ( Figure 6E View Figure 6 ).

Female characters

Females are similar to males but the chelipeds are relatively weaker, smaller; manus not inflated; fingers with sub-basal dactylar tooth smaller, spatuliform margin extending most of length. Abdomen rounded, with all somites and telson free, completely covering thoracic sternal surface, telson reaching base of buccal cavity; telson broad, tip gently rounded, margins sinuous; somites 1 and 2 very broad, longitudinally narrow, somite 2 with granulated median transverse ridge. Vulva simple, subovate, between thoracic sternites 5 and 6, submedian in position, without cover or ridges. Eggs small.

Remarks

Shen (1935) described Camptandrium anomalum on the basis of one male measuring 4.5 × 3.5 mm, and one female from Taipo, near Canton in southern China. The specimens were from muddy flats. The two type specimens in CAS were examined by N.K. Ng at our request ( Figure 1 View Figure 1 ). Both specimens are in extremely poor condition, with only the carapace still present, and the male abdomen has been detached. The holotype male agrees well with the original descriptions and figures in Shen (1935).

Biology

The species is a wholly mangrove species and has not been found outside this habitat. They prefer areas nearer the edge of the mangroves but only those that have substantial shade and are flooded only by the highest tides. They are often found under planks, wood or rafts of decaying vegetation, the substrate usually been sandy-mud. They are also not uncommon among the mangrove pneumatophores where the mud is soft and moist (see Ng, Wang and Lim 2008). Tweedie (1937: 162) commented that at Kranji mangroves in Singapore, numerous individuals can be found “... inhabiting burrows in soft mud...”. They have been observed foraging during the day. Their movements on the mud are similar to those of grapsoids and camptandriids, with the carapace generally close to the ground. They dart about when disturbed but usually do not move far. In life, they are always covered with mud that is trapped by the numerous short setae all over their carapace and pereiopods. This makes them difficult to spot in the low light conditions of the covered mangrove forest.

Distribution

Shenius anomalus View in CoL is known only from southern China (type locality), Peninsular Malaysia and Singapore ( Tweedie 1937; Serène and Umali 1972; Yang 1979; Tan and Ng 1994). It is almost certainly also found in mangroves in many other parts of Southeast Asia; but because of its small size and cryptic habitats, it is rarely encountered.