Discorsotheres camposi, Ahyong, 2018

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 557-559

Discorsotheres camposi new species

( Fig. 8 , 10 )

Type material. Holotype: ZRC 2003.0299 , spent female (cl 10.8 mm, cw 10.3 mm), near Toula Village , SE coast of Vava’u Island, Tonga, 18°41′S, 173°59′W, 88-016, 5–30 m, from large oval clams, coll. T. Iliffe & S. Sarbu, 17 March 1988 . Paratypes: CBM ZC13153 , 1 ovigerous female (cw cl 13.6 mm, cw 15.5 mm), 2 spent females (cl 10.8 mm, cw 11.5 mm; cl 12.0 mm, cw 13.3 mm), Vava’u, Tonga, 10 March 1992 ; MNHN-IU-2017-11712, 1 ovigerous female (cl 12.9 mm, cw 14.0 mm), in front of Peng Beach , Sandal Bay, Loyalty Islands, 20°54.0′S, 167°07.3′E, 12 m, between coral heads, from Spondylus Bi 77, LIFOU Stn 1423, 14 November 2000 ; USNM 104989 , 2 spent females (cl 15.3 mm, cw 16.4 mm; cl 14.9 mm, cw 16.4 mm), Thokotamon Coral Knoll , Kapingamarangi, Caroline Islands, 01°04′N, 154°46′E, 9 m, No. 191, Pacific Science Board, coll. C. Hand, 12 July 1954 .

Description. Female: Carapace ( Fig. 10A–C ) firm but not hard; subquadrate, slightly wider than long, glabrous, surface finely rugose under magnification; strongly vaulted longitudinally, bluntly polygonal in lateral view; front rounded, usually distinctly produced, with or without shallow transverse groove on dorsal surface immediately behind front ( Fig 10A, O, R, U ); anterolateral margins, unarmed, forming bluntly rounded rim; lateral surface almost vertical; dorsal surface finely rugose, distinctly raised medially forming broad, rounded, longitudinal ridge, with peaks in gastric and cardiac regions; cardiac peak extending laterally onto branchial regions forming broad blunt transverse swelling; combined transverse and longitudinal swellings appearing cross-like in dorsal view.

Epistome ( Fig. 10D ) with narrow interantennular septum; median buccal margin with short median point. Antennular sinus size subequal to orbit, aligned distinctly obliquely in anterior view; antennules folded obliquely. Antenna short, free antennal articles extending to about one-third height of eye; antennal articles 1 and 2 fused to epistome. Eyes usually visible in dorsal view, filling orbit, cornea pigmented.

Maxilliped 3 ( Fig. 10E ) ischiomerus surface glabrous, length about twice width; inner proximal two-thirds weakly concave, distomesial angle obtuse, blunt; distal margin not produced beyond palp articulation; outer margin convex. Carpus about half propodus length. Propodus spatulate, length about twice width, distally widened, apex blunt, subtruncate. Exopod margins straight to gently convex.

Cheliped (pereopod 1) ( Fig. 10A, F, N ) dactylus gently curved to straight, pollex relatively straight, apices crossing distally, without gape, irregularly, setose. Dactylus 0.7–0.8 × length of dorsal margin of propodus palm, outer occlusal margin with triangular proximal tooth, and row of short corneous denticles and setae extending to distal two-thirds of margin; inner occlusal margin with row of short setae, margin smooth. Pollex ( Fig. 10N ) outer occlusal margin weakly crenulate, with 2 small, blunt triangular proximal teeth; inner occlusal margin setose, with row of small denticles along proximal three-fourths; inner ventral margin with row of setae. Propodus palm dorsal margin length 2.0–2.5 × 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. 10A, G–M ); relative lengths: pereopod 3(both)>pereopod 4>pereopod 2>pereopod 5. Pereopods 2, 4, 5 merus to dactylus unarmed, glabrous; propodus flexor and extensor margins subparallel, not widening distally; dactyli stout, length subequal, strongly falcate, apices spiniform, turning perpendicular to main axis, pereopod 2 dactylus 0.5 × propodus length, pereopod 4–5 dactylus 0.4 × propodus length. Pereopod 3 asymmetrical in length and dactyl form; “normal” pereopod 3 with merus to dactylus glabrous; dactylus apex spiniform, strongly falcate, similar to but slightly longer than pereopod 2 dactylus. Longer P3 1.1–1.2 × length of “normal” pereopod 3; merus 1.3 × length of pereopod 4 merus; propodus not expanded distally, glabrous; dactylus with blunt, often apex, longer, stouter than dactylus of opposite side, setose.

Egg diameter 0.2–0.3 mm (in preservative).

Hosts. Spondylidae : Spondylus spp.

Etymology. Named after Ernesto Campos for his extensive contributions to pinnotherid taxonomy.

Remarks. Discorsotheres camposi is the first species of the genus to be recorded from the tropical western Pacific. Of the four species of Discorsotheres , D. camposi has the most pronounced median longitudinal swelling on the carapace in which the gastric and cardiac regions are most swollen. These swollen gastric and cardiac regions present two blunt peaks, which in lateral view appear as low humps giving a “hunched” profile ( Fig. 10C ). The cardiac peak also extends laterally as a low blunt swelling. The median longitudinal swelling on the carapace of D. camposi is further accentuated by the broad, depressed anterior branchial surfaces on either side of the midline, and to a lesser extent on the posterior branchial surfaces. The blunt longitudinal and transverse swellings on the carapace, together appear cross-like in dorsal view ( Fig. 10A ). As a result, the carapace of D. camposi has a somewhat angular appearance, having a more prismatic than the rounded-subcuboid form in other congeners. The carapace of D. camposi is also comparatively firm and rugose compared to the soft, very smooth carapace of other species of the genus. In addition, the pereopod 4–5 dactyli of D. camposi are proportionally shorter than in congeners (0.4 versus 0.5 × propodus length).

The propodus of the longer pereopod 3 (usually the left side) of D. camposi is at most scarcely widened distally, although the dactylus has a distinctly setose flexor margin and a short, blunt apex. The relative length of the longer pereopod 3 propodus varies slightly, with the dactylus length ranging from slightly less to slightly more than half the propodus length. The dorsal outline of the anterior margin of the carapace also ranges from sinuous to almost transverse according to the prominence of the front. As with D. subglobosus and D. subquadratus , a shallow groove or crease may be present on the carapace surface immediately behind the frontal margin ( Fig. 10A, O, R, U ). As in congeners, the cheliped palm becomes more slender with increasing body size.

Discorsotheres camposi is presently known only from coral reefs of the western Pacific from Spondylus sp. and “large oval clams”.

Distribution. Tropical western Pacific from Tonga, Lifou and the Caroline Islands; 9–12 m depth.

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. 10. Discorsotheres camposi new species. A–M, female holotype, cl 10.8 mm, cw 10.3 mm, Tonga, ZRC 2003.0299; N–Q, ovigerous female paratype, cl 12.9 mm, cw 14.0 mm, Lifou, MNHN-IU-2017-11712; R–T, ovigerous female paratype, cl 15.3 mm, cw 16.4 mm, Caroline Islands, USNM 104989; U–W, ovigerous female paratype, cl 14.9 mm, cw 17.5 mm, Caroline Islands, USNM 104989. 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–I, left pereopods 2–4; J–M, right pereopods 2–5; N, left cheliped pollex, oblique anterior view; O, R, U, carapace anterior margin, dorsal view; P, S, V, left pereopod 3 dactylus & propodus; Q, T, W, right pereopod 3 dactylus & propodus. Scale: A–C, G–M, O–W = 2.0 mm; D–F = 1.0 mm; N = 0.5 mm.