Insulamon unicorn Ng & Takeda, 1992

Freitag, Hendrik, 2012, Revision Of The Genus Insulamon Ng & Takeda, 1992 (Crustacea: Decapoda: Potamidae) With Description Of Four New Species, Raffles Bulletin of Zoology 60 (1), pp. 37-55 : 39-41

Insulamon unicorn Ng & Takeda, 1992

( Figs. 2 A–C; 3A–F)

Insulamon unicorn Ng & Takeda, 1992 : (part) 157–160, Figs. 4 , 5 ; Esser & Cumberlidge, 2008 (IUCN red list); Ng et al., 2008: 163 (checklist).

Type locality. — Barangay [= municipal district] Salvacion, Busuanga Island/Municipality, Palawan Province, Philippines.

Material examined. — 1 male (38.8 by 30.2 mm) ( ZRC 2010.0330 ), Busuanga , Coron , San Nicolas / Borac, small mount. fall, residual pools, rock, boulders, leaves, secondary vegetation, c. 100 m asl, 12°03'26"N, 120°14'31"E (164a), coll. H. Freitag, 2 Feb.1995 ; 1 female (25.1 by 19.6 mm) (SMF-38291), Busuanga , 5 km NW Coron town, Mabintangen River tributary, mountain creek upstream of artificial pool, secondary forest, riffle & run, gravel, roots, leaves, c. 50 m asl, 12°01'44"N, 120°12'19"E (167b), coll. H. Freitag, 2 Feb.1995 ; 1 male (37.4 by 29.1 mm) (NMCR-39034), Busuanga , Coron; Tagumpay, small lowland river,pool, CPOM, leaflitter, secondary vegetation, c. 50 m asl, 12°01'00''N, 120°17'14''E (171b), coll. H. Freitag, 4 Feb.1995 .

Diagnosis. — Carapace ( Fig. 2A, B ) 1.28–1.29 times as broad as wide, moderately high; cervical grooves moderately deep; suborbital margin obliquely connecting to external orbital angle; epigastric cristae not distinctly projected over postorbital cristae; mesogastric cristae rather low. Progastric, mesogastric, cardiac and intestinal regions slightly convex; branchial regions distinctly convex; medio-posterior carapace margin straight in dorsal view.

Male abdominal somites ( Fig. 2C ) moderately broad; telson c. 1.15 times as broad as long; sixth abdominal somite c. 1.75 times as broad as long; telson c. 1.15 times as long as sixth abdominal somite in males, and also longer than sixth abdominal somite in females ( Fig. 2D ).

Mandible with moderately broad and rather shallow incision opposite of palpus insertion; terminal segment of palp moderately long, evenly slender almost up to apex. Second maxilliped ( Fig. 3A ) exopod rather flat, partly membranous, lateral margin distinctly indented at c. half length; propodus almost as long as broad; outer distal margin of carpus slightly dilated. Third maxilliped ( Fig. 3B ) with dactylus only slightly longer than carpus; propodus about 1/4 shorter than carpus; merus rather long, more than 2/3 as long as broad, margins almost straight, outer distal edge rather sharp.

Larger cheliped in adult males with dactylus almost half as broad as entire chela length.

G1 ( Fig. 3 C–E) slightly sinuously bent, distal attenuate part and dilated proximal base of terminal segment subequal in length. Distal part of terminal segment narrow, attenuate, almost straight, entirely slightly laterad directed. Dilated proximal base of terminal segment as broad as or slightly narrower than distal subterminal segment; ventral setae rather short. Collar only slightly protruding dorsad; ventral collar region only slightly notched. G2 flagellum c. 0.6 times as long as basal segment; enlarged proximal portion of basal segment subrectangular to subtrapezoidal ( Fig. 3F ).

Remarks. — The species appears most similar to I. palawanense , new species, but can be distinguished by the carapace proportions (width/length ratio ≤1.29), the longer distal portion of the terminal G1 segment (as long as proximal portion), the more slender proximal base of the terminal segment (as broad as or slightly narrower than distal subterminal segment) and the comparably straight and somewhat elongate overall shape of the G1 (see remarks for I. palawanense , new species).

The holotype male (34.7 by 26.8 mm) (Salvacion, Busuanga, Palawan, coll. Gonzales et al., Mar.1976) was not accessible for re-examination despite intense search. It is most likely still deposited, but misplaced, in NSMT. However, the measurements, drawings and remarks by Ng & Takeda (1992) provide enough evidence for the determination of the material listed above. All specimens from the island of Palawan designated as paratypes of this species (Ng & Takeda, 1992) were re-examined and all of them were found to belong to I. palawanense , new species, due to the shape of the G1 (distal portion of the terminal G1 segment distinctly shorter than proximal portion and somewhat twisted towards ventral side; dilated base of terminal segment broader than distal subterminal segment; entire G1 stout and strongly bent), and the broader carapace (width/length ratios: 1.36 [ZRC 1992.8360], 1.37 [NSMT-Cr11222], 1.34 [NSMT-Cr11223a], 1.35 [NSMT-Cr11223b], 1.36 [NSMT-Cr11223c]).Although the immature male specimens (NSMT-Cr11223a & b) do not display the mature gonopod characters that are necessary for a proper determination, at least the carapace measurements allow their identification. Furthermore, the copious collection of Insulamon material studied suggests that I. unicorn is restricted to Busuanga Island or the Calamian Group.

Distribution. — Busuanga Island

Figures

Fig.2. Insulamon unicorn, male (38.8 by 30.2 mm) from San Nicolas (164a): A, dorsal view; B, frontal view; C, ventral view.

Fig. 4. Insulamon palawanense, new species.Paratype male (35.3 by 26.3 mm) from Dumarao (135):A, dorsal view; B, frontal view; C, ventral view. D, paratype female (28.5 by 22.2 mm) from Bagong Bayan (129c), ventral view.

Fig. 5. Insulamon palawanense, new species. Holotype male:A, left G1 ventral view; B, left G1 dorsal view; C, tip of left G1 ventral view (SEM picture); D, left G2 ventral view; E, left third maxilliped; paratype males, left G1 tip ventral, gradual variations from southern to northern specimens: F, from Salugon (147c), (30.5 by 23.3 mm); G, from Luzviminda (155) (24.7 by 19.1 mm); H, from Irawan (60), (33.7 by 25.0 mm); I, from Tarabanan (16b), (26.1 by 20.2 mm); J, from Dumarao (135), (29.3 by 22.1 mm); K, from Bagong Bayan (129c), (31.1 by 23.5 mm). Scale bars = 1 mm.

Fig. 3. Insulamon unicorn, male (38.8 by 30.2 mm) from San Nicolas (164a): A, left second maxilliped; B, left third maxilliped; C, left G1, ventral view; D, tip of left G1, ventral view (SEM picture); E, left G1, dorsal view; F, left G2 basal segment (flagellum broken off), ventral view. Scale bars = 1 mm.