Discorsotheres subglobosus ( Baker, 1907 ), 2018

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 554-557

Discorsotheres subglobosus ( Baker, 1907)

( Figs. 8 , 9 )

Pinnoteres subglobosa Baker, 1907: 179 (type locality: Gulf St. Vincent, South Australia).

Ostracotheres (?) (‘ Pinnotheres ’) subglobosus . — Tesch, 1918: 287 (list).

Pinnotheres subglobosa . — Rathbun, 1923: 96–97, fig. 1, pl. 16 fig 1. — Hale, 1927a: 173–174, fig. 174; 1927b: 312. — Silas & Alagarswarmi, 1967: 1186, 1191, 1210–1211. — Springthorpe & Lowry, 1994: 113.

Pinnotheres subglobosus . — Tesch, 1918: 262. — Schmitt et al., 1973: 6, 8, 9, 88. — Davie, 2002: 434.

Ostracotheres subglobosus . — Pregenzer, 1988: 17–21, figs. 1–9. — Takeda & Konishi, 1989: 1222. — Ahyong & Brown, 2003: 12. — Poore, 2004: 484, 486, fig. 154d, pl. 26H. — Ng et al., 2008: 250. — McDermott, 2009: tab. 1.

Ostracotheres subglobosa . — An et al., 2014: tab. 1.

Type material. Lectotype: AM P151 , female (cl 10.6 mm, cw 12.4 mm), Gulf St. Vincent, South Australia, 34°53′17″S, 138°08′14″E, 17 fm [31 m], dredged, in pectens, coll. J.C. Verco. Paralectotypes: AM P102300 , 1 ovigerous female (cl 8.7 mm, cw 9.9 mm), collected with lectotype ; SAM C1390 , 4 ovigerous females (cl 7.8 mm, cw 9.3 mm to cl 8.9 mm, cw 10.4 mm), 1 parasitised female (cl 7.8 mm, cw 10.3 mm), collected with lectotype .

Other material examined (all Australia). SOUTH AUSTRALIA: AM P64674, 2 ovigerous females (cl 8.6 mm, cw 10.6 mm; cl 9.5 mm, cw 11.7 mm), off Grange, Gulf St. Vincent, 34°54′S, 138°30′E, 15–20 m, inside scallops, 22 December 1971 ; SAM C7190 , 1 spent female (cl 8.4 mm, cw 9.5 mm), Glenelg, Gulf St. Vincent, 35°00′S, 138°30′E, on reef in Spondylus tenellus , 37 ft [11 m], coll. N.N. Holmes, 21 September 1985 ; SAM C12812, 2 ovigerous females (cl 6.9 mm, cw 8.8 mm; cl 7.8, cw 9.5 mm), 2 spent females (cl 6.7 mm, cw 7.9 mm; cl 7.0 mm, cw 8.4 mm), 1 female (cl 7.2 mm, cw 8.5 mm; with rhizocephalan parasite), Seacliff Reef, Gulf St. Vincent, 35°01.8′S, 138°30.6′E, from 57 scallops, coll. F. Anderson, 1 April 1982 ; SAM C12813, 3 ovigerous females (cl 5.4 mm, cw 6.4 mm to cl 6.8 mm, cw 8.0 mm), 2 spent females (cl 5.1 mm, cw 6.0 mm; cl 6.0 mm, cw 6.7 mm), 1 female (cl 5.9 mm, cw 7.1 mm; with pair of epicaridean isopods), Gulf St. Vincent, in scallop ( Pecten bifrons ), 40 ft [12 m], coll. N. Holmes, June 1982 ; AM E4519 , 1 ovigerous female (cl 7.3 mm, cw 9.4 mm), off Marsden Point, Kangaroo Island , 35°34′S, 137°38′E, 17 fathoms [31 m], FIS Endeavour ; SAM C11032, 1 ovigerous female (cl 6.9 mm, cw 8.2 mm), Hardwicke Bay, Yorke Peninsula , 34°53′29″S, 137°27′12″E, from scallop, coll. L. Brake, 11 February 1983 ; USNM 205905 , 2 ovigerous females (cl 7.3 mm, cw 8.8 mm; ~ 7.1 mm, cw ~ 7.9 mm), Port Giles, Yorke Peninsula , 35°00′S, 137°46′E, from Equichlamys bifrons , coll. A.J. Butler, 25 November 1978 ; AM P64673, 4 ovigerous females (cl 7.1 mm, cw 8.4 mm to cl 8.6 mm, cw 10.5 mm), off Edithburgh, Yorke Peninsula , 35°05′S, 137°45′E, 9 m, broken rubble & sponges, coll. N. Coleman, 16 December 1970 ; SAM C11037 ( PCO455 photo), 1 ovigerous female (cl 6.3 mm, cw 7.2 mm), Edithburgh, Yorke Peninsula , 35°05′05″S, 137°44′45″E, 45 m, in Equichlamys bifrons , coll. K. Gowlett-Holmes, 18 April 2005 ; WAM C15774, 1 spent female (cl 5.2 mm, cw 6.0 mm), Edithburgh, Yorke Peninsula , 35°05′S, 137°44′E, jetty area, from Queen Scallop, coll. N. Beach, 4 March 1985 ; AM P13500, 2 ovigerous females (cl 5.5 mm, cw 7.2 mm; cl 6.5 mm, cw 7.9 mm), Backy Point, near Whyalla, Spencer Gulf , 32°55′S, 137°48′E, from purple pecten, coll. B. Flounders ; SAM C7092 , 1 ovigerous female (cl 8.2 mm, cw 9.8 mm), opposite Nicholas Bay, between Reevesby & Partney Islands , Sir Joseph Banks Group , Spencer Gulf , 34°30′S, 136°16′E, 20 ft [6 m], sand and Posidonia , in scallop, coll. W. Zeidler, 8 January 1984 ; SAM C12814, 1 ovigerous female (cl 8.1 mm, cw 10.1 mm), Sir Joseph Banks Group, N Point, Marum Island, Spencer Gulf , 34°30.6′S, 136°15.0′E, 15–25 ft [4.5–7.5 m], reef, rubble, sand, sparse Posidonia , coll. K. Gowlett-Holmes & N. Holmes, 19 January 1986 ; AM P19997, 1 ovigerous female (cl 7.2 mm, cw 8.7 mm), Cape Donington, Spencer Gulf , 34°44′S, 136°00′E, 8 fathoms [15 m], rough bottom, coll. N. Coleman, 21 December 1970 ; SAM C11038, 1 ovigerous female (cl 7.9 mm, cw 9.3 mm), N side of St Francis Island, Nuyts Archipelago , 32°29′35″S, 133°17′06″E, 20–30 m, in Spondylus tenellus , coll. D. Howlett, December 1979 .

WESTERN AUSTRALIA: WAM C12228, 1 spent female (cl 7.6 mm, cw 9.0 mm), ¾ mile S of City Beach Groin , 31°56′S, 115°45′E, in living Spondylus shell, coll. J. Brouwer, 29 July 1961 .

Description. Female: Carapace ( Fig. 9A–C ) soft, thin, rounded-subquadrate, slightly wider than long, glabrous, surface smooth, appearing polished; strongly vaulted longitudinally, evenly rounded in lateral view; front, transverse, straight or weakly concave, slightly produced, with or without shallow transverse groove on dorsal surface immediately behind front ( Fig. 9A, N, O ); anterolateral margins, unarmed, forming bluntly rounded rim; lateral surface almost vertical; dorsal surface smooth, gently raised medially forming broad, low, rounded ridge.

Epistome ( Fig. 9D ) with narrow interantennular septum; median buccal margin with short median point. Antennular sinus slightly larger than orbit, almost transversely aligned in anterior view; antennules folded slightly obliquely. Antenna short, free antennal articles to about mid-height of eye; antennal articles 1 and 2 fused to epistome. Eyes visible in dorsal view, filling orbit, cornea pigmented.

Maxilliped 3 ( Fig. 9E ) ischiomerus surface glabrous, length about twice width; inner proximal two-thirds sinuous to weakly concave, distomesial angle obtuse, blunt; distal margin not produced beyond palp articulation; outer margin convex. Carpus slighty shorter than half propodus length. Propodus spatulate, length about twice width, distally widened, apex blunt, subtruncate. Exopod margins gently convex.

Cheliped (pereopod 1) ( Fig. 9A, F ) dactylus gently curved to straight, pollex relatively straight, apices crossing distally, without gape, irregularly, setose. Dactylus almost 0.8 × length of dorsal margin of propodus palm; outer occlusal margin with triangular proximal tooth and row of short corneous denticles and short setae extending to about midlength of dactylus, otherwise smooth; inner occlusal margin with row of short corneous denticles and short setae. Pollex ( Fig. 9G ) outer occlusal margin weakly crenulate, with 2 small, blunt triangular proximal teeth; inner occlusal margin setose, with row of small corneous denticles along proximal threefourths; inner ventral margin with row of setae. Propodus palm dorsal margin length 1.9–2.2 × height; ventral margin gently sinuous, slightly concave at base of pollex. Carpus mesial margin with setal tuft, unarmed. Merus unarmed, about as long as propodal palm.

Walking legs (pereopods 2–5) slender, smooth, similar in form ( Fig. 9A, H–M ); relative lengths: pereopod 3(both)>pereopod 4>pereopod 2>pereopod 5. Pereopod 2, 4, 5 merus to propodus unarmed, glabrous; propodus flexor and extensor margins subparallel, not widening distally; dactyli stout, half propodus length, glabrous or with few isolated setae; pereopod 2 dactylus curved, apex spiniform, slightly longer than pereopod 4–5 dactyli; pereopod 4–5 dactyli subequal, strongly falcate, apices spiniform, turning almost perpendicular to main axis. Pereopod 3 asymmetrical in length and dactyl-propodal form; “normal” pereopod 3 with merus to dactylus usually glabrous, dactylus and propodus occasionally with setose disto-flexor margin; dactylus apex spiniform, usually falcate. Longer pereopod 3 1.1–1.2 × length of “normal” pereopod 3; merus 1.4–1.5 (usually 1.5) × length of pereopod 4 merus; propodus usually slight expanded distally, distoflexor margin irregularly setose; dactylus usually longer, stouter but with shorter apex than dactylus of opposite side, setose.

Egg diameter 0.2–0.3 mm.

Hosts. Bivalves molluscs. Pectinidae : Equichlamys bifrons ( Lamarck, 1819) , Pecten fumatus Reeve, 1852 (as Notovola meridionalis [ Tate, 1887]); Mytilidae : Modiolus areolatus ( Gould, 1850) (as Modiolaria australis [ Gray, 1826]); Spondylidae : Spondylus tenellus Reeve, 1856 ( Hale, 1927a, b; Pregenzer, 1988).

Remarks. Pregenzer (1988) synonymised D. subglobosus ( Baker, 1907) (South Australia) and D. subquadratus ( Sakai, 1939) ( Japan) , although most subsequent authors have either questioned or not accepted the synonymy ( Davie, 2002; Poore, 2004; Ng et al., 2008); both species are regarded here as valid based on comparison of Australian and Japanese material. In overall appearance, the two species are very similar, including carapace shape and morphology of the pereopod and maxilliped 3; they differ chiefly in the shape of the antennular fossa. In D. subglobosus , the upper margins of the antennular fossa are essentially transverse in anterior view, with the orbits and antennular fossae approximately transversely aligned ( Fig. 9D ). The upper margins of the antennular fossae in D. subquadratus , however, are oblique and slope downwards toward the midline, meeting at an obtuse angle, and the orbits are positioned at a distinctly higher level than the antennular fossae ( Fig. 12D ). Also, pereopod 3 is usually proportionally more elongate in D. subglobosus than in D. subquadratus with the longer pereopod 3 merus 1.4–1.5 (usually 1.5) times the length of the pereopod 4 merus (versus 1.4). Males of neither D. subglobosus nor D. subquadratus are presently known. The smallest examined specimen of D. subglobosus is mature (cl 5.2 mm, cw 6.0 mm; WAM C15774), and the largest specimen (cl 10.6 mm, cw 12.4 mm; AM P151) considerably outsizes the largest known specimen of D. subquadratus (cl 7.5 mm, cw 9.2 mm; CBM ZC5989).

Like D. subquadratus , the carapace of D. subglobosus is weakly sclerotised and gently inflated longitudinally, forming a low, broad dorsomedian swelling, being broadest slightly posterior to the midlength. The swelling is much more prominent in D. camposi and absent in D. spondyli . Note that the dorsomedian prominence in D. subglobosus may appear artifically prominent in poorly preserved specimens in which the branchial carapace surfaces are partially collapsed.

In most specimens of D. subglobosus , the shorter pereopod 3 has a glabrous propodus and the typical falcate dactylus with one or two setae on the flexor margin; the longer pereopod 3 has a distally setose, often slightly expanded propodus and a straighter, blunt tipped, strongly setose dactylus ( Fig. 9H–M ). Some specimens, however, have setose propodi and dactyli on both pereopods 3 (as in the lectotype, AM P151; Fig. 9A ), although other aspects of asymmetry remain. As in the lectotype, in about 75% of specimens, the left pereopod is the longer.

Of the known species of Discorsopagurus , D. subglobosus appears to be most closely related to D. subquadratus from East Asia, despite their wide geographic separation. This strongly anti-tropical distribution of this presumed cognate species pair in southern Australia and East Asia, is independently paralleled in other major marine groups, including fishes and molluscs ( Randall, 1981; Norman & Kubodera, 2006; Gill & Mooi, 2017).

Two specimens from Gulf St. Vincent are parasitised, one with a rhizocephalan ( SAM C12812), and another with a pair of epicaridean isopods, apparently Rhopalione sp. ( SAM C12813) .

Distribution. Gulf St Vincent, Spencer Gulf and the Nuyts Archipelago, South Australia; Perth, Western Australia; 6– 45 m.

Figures

Fig. 8. Distribution of species of Discorsotheres new genus. (■) D. camposi new species; (●) D. spondyli (Nobili, 1905) new combination; (▲) D. subglobosus (Baker, 1907) new combination; (▼) D. subquadratus (Sakai, 1939) new combination.

Fig. 9. Discorsotheres subglobosus (Baker, 1907) new combination. A–G, female lectotype, cl 10.6 mm, cw 12.4 mm, Gulf St. Vincent, AM P151; H–I, ovigerous female paralectotype, cl 8.7 mm, cw 9.9 mm, Gulf St. Vincent, AM P102300; J–K, ovigerous female, cl 8.6 mm, cw 10.5 mm, Edithburgh, AM P64673; L–M, ovigerous female, cl 7.3 mm, cw 8.9 mm, Edithburgh, AM P64673; N–O, females, cl 7.8 cw 8.4, cl 7.8 cw 9.5 mm, Seacliff reef, SAM C12812. A, dorsal habitus; B, carapace, anterior view; C, carapace, right lateral view; D, cephalothorax, anterior view; E, right maxilliped 3; F, right chela, anterior view; G, right cheliped pollex, oblique anterior view; H, J, L, left pereopod 3; I, K, M, right pereopod 3; N, O, carapace frontal margin, dorsal view. Scale: A–C, H–M = 4.0 mm; D–F, N, O = 2.0 mm; G = 1.0.

Fig. 12. Discorsotheres subquadratus (Sakai, 1939) new combination. A–H, female neotype, cl 7.1 mm, cw 8.6 mm, Suruga Bay, NSMT Cr10028; I–M, ovigerous female, cl 7.5 mm, cw 9.2 mm, Boso Peninsula, CBM ZC5989. A, dorsal habitus; B, carapace, anterior view; C, carapace, right lateral view; D, cephalothorax, anterior view; E, I, carapace frontal margin, dorsal view; F, right maxilliped 3; G, right chela, anterior view; H, right cheliped pollex, oblique anterior view; J–K, left pereopods 3–4; L–M, right pereopods 3–4. Scale: A–C, J–M = 2.0 mm; D–I = 1.0 mm.