Synidotea poorei, Cai & Teo, 2012

Cai, Yixiong & Teo, Serena L. M., 2012, Synidotea poorei, a new isopod from the fouling community in Singapore waters (Valvifera, Idoteidae), Memoirs of Museum Victoria 69, pp. 237-243 : 237-238

Synidotea poorei sp. nov.

Figures 1-4

Material examined. Holotype: male, tl 11.4 mm, ZRC.2005.0118, North Pandan Buoy , 1°15'48.12" N, 103°45'10.81" E, Terumbu Pandan, Singapore, coll. Y. Cai, S. L. M. Teo, K. S. Tan and T. M. Sin, 11 Apr. 2002 . Paratypes: 25 males, tl 4.6–12.2 mm, 15 females, tl 5.6-8.1 mm, ZRC.2005.0119, data same as holotype ; 2 females, 7.4, 10.2 mm; 4 ovigerous females, tl 6.9-8.6 mm; 4 males, tl 10.2-12.9 mm, NVM J62812 , data same as holotype .Other specimens: 4 males, tl 6.0- 9.1 mm, 2 females, tl 7.0- 7.4 mm, ZRC.2005.0120, North West Sudong Buoy , 1°13'07.22" N, 103°42'59.10" E, near Pulau Sudong, Singapore, 19 Jul. 2002 ; 1 female, tl 8.4 mm, ZRC.2005.0121, Perimbi Buoy , 1°25'45.11" N, 103°53'14.75" E, East Johor Strait, Singapore, coll. Y. Cai, 21 May 2002 ; 1 male, tl 12.0 mm, ZRC.2005.0122, Retan-D Buoy , 1°17'35.63" N, 103°45'25.48" E, off Sungei Pandan, West Coast, Singapore, coll. Y.Cai, K.S. Tan & S. C.Lim, 17 Oct.2003 ; 1 female,tl 5.9 mm, ZRC.2005.0123, Sirdhana Buoy , 1°14'43.00" N, 103°52'55.02" E, off Marina Bay, Singapore, coll. Y. Cai, K. S. Tan, T. M. Sin & S. L. M Teo, 5 Jun. 2002 ; 6 males, tl 6.2-10.8 mm, 1 female, tl 7.0 mm, ZRC.2005.0124, Mooring Buoys at Marina Bay, Singapore, 1°17'06.26" N, 103°51'20.09" E, coll. K. S. Tan & S. C. Lim, 14 Jul. 2003 ; 84 males, tl 6.8-13.2 mm, 54 females, tl 7.3-10.0 mm, ZRC.2005.0125, CAAS2 Buoy , 1°23'38.65" N, 103°59'37.13" E, off Changi Beach, Singapore, coll. Y. Cai, S. L. M. Teo & T. M. Sin, 23 Apr. 2002 ; 3 males, tl 4.8-10.3 mm, 1 female, tl 8.0 mm, ZRC.2005.0126, Jetty of St John’s Island , 1°13'20.95" N, 103°50'56.33" E, Singapore, coll. Y. Cai, 22 Mar. 2004 .

Description of male. Maximum size: 11.4 x 4.0 mm (holotype). Body 2.9–3.1 times as long as wide; depressed and smooth, without tubercles or carina, lateral margin smooth. Colour brownish with darker spots. Cephalon frontal margin almost straight, with indistinct median excavation, dorsal surface with anterior and posterior transverse grooves and longitudinal lateral grooves. Eyes bulge outward, forming part of contour of lateral margin of head. Ratio of post-orbital head width to width of pereonite 3 (widest pereonite) 0.56.

Antenna 1 flagellum uniarticulate, with 10 pairs of jointed aesthetascs. Antenna 2 0.6 body length; article 4 2.4 times as long as wide; article 5 3.6 times as long as wide; flagellum with 16-22 articles, 1.2 length of peduncle.

Dorsum of each pereonite smooth, margin slightly arched; dorsomarginal areas of pereonites 2–7 slightly enlarged, distinctly depressed, lateral margins slightly upturned, marginal areas becoming progressively less depressed, and sloping gently on posterior pereonites; lunettes on pereonites 2–4 with posterior margin subtriangular or rounded; distolateral angle of pereonites 1–4 rounded, those of pereonites 5–7 subrectangular.

Pleotelson about 1.4 times as long as wide, dorsum smooth, evenly convex, lateral margin sub- parallel over anterior twothirds, then tapering beyond curved margin to rounded posterior margin, with a shallow medial excavation.

Mandible incisor with 4 strong, unequal cusps. Lacinia mobilis stout, 4-cusped, with additional large serrate spine-like process. Molar process large, truncate, surrounded by short spines, bearing laterally 3 stiff setulose setae and many denticles along distal end.

Mesial lobe of maxilla 1 with 2 stout distally serrated robust apical setae with mesial setules; outer lobe with 9 robust tooth-like serrated setae.

Maxilla 2 3-lobed, with plumose, simple and comb setae on endopod as figured; mesial lobe of exopod lined with comb setae, Outer lobe enlarged, recurved laterally, fringed with extremely long plumose setae.

Endite of maxilliped with 1 recurved coupling hook, lined with 7-10 apical moderately slender plumose setae. Palp 3-articulate, last article expanded and fringed with 6-10 long setae. Epipod laminar, distal margin rounded, outer and distal margin fringed with fine setae.

Pereopod 1 carpus triangular, flexor margin densely lined with simple setae and denticles; propodus 1.9 times as long as greatest depth, tapering and curving distally, flexor margin with long simple setae; dactylus elongated, with simple setae.

Pereopods 2-7 similar in form and size, slightly longer than pereopod 1; carpus subrectangular; flexor margins of ischium to propodus densely fringed with simple setae and pubescence; extensor margins of carpus and merus armed with 1 or 2 simple setae; dactylus more elongate and straighter than that of pereopod 1. Pereopod 2 propodus as long as merus and carpus together, 2.8 times as long as wide. Pereopod 4 propodus 2.4 times as long as wide. Pereopod 7 propodus 3.5 times as long as wide.

Penes fused along entire length, 1.6 times as long as wide, swollen distally, with notched lateral and distal margins.

Pleopods 1 and 2 with plumose marginal setae on endopods and exopods, both rami without sutures. Pleopods 1-3 with about 11, 5 and 3 coupling hooks on inner margin of peduncles respectively. Pleopod 2 with appendix masculina elongated, reaching beyond distal margin of endopod by one-sixth of its length, mostly straight, distal quarter slightly curving medisally, with numerous spinules distally. Pleopods 3-5 with few and short simple marginal setae, incomplete transverse suture present from near middle of the outer margin of exopod.

Uropod 2.9 times as long as distal peduncle width, with short, simple setae, no oblique ridges on peduncle, distolateral angle with 3 plumose setae; endopod 0.3 length of peduncle, mesial length 0.7 proximal suture length, suture at 75° to long axis, distal margin truncate, at 75° to long axis, lateral margin gently convex between lateral and distal margins

Female. Maximum size, 7.6 x 3.1 mm (one of paratypes). Body stouter than male, 2.3-2.6 times as long as wide; pleotelson 1.2 times as long as wide; pereonal margins more evenly curved than in male. Antenna 2 with 13-15 articled flagellum. Maxilla 2 3-lobed, with plumose, simple and comb setae on endopod as figured; both inner and outer lobes of exopod lined with comb setae; no dense pubescence on pereopods 2-7. Oostegites lamellar on pereonites 1-4.

Etymology. The new species is named after Gary C. B. Poore, who has contributed significantly to our understanding of marine isopods in the Indo-Pacific region.

Habitats. The new species was most commonly found in association with macroalgae and hydroids in the fouling community of Singapore waters.

Remarks. Currently, 14 species of the genus Synidotea belong to the ‘ S. hirtipes group’, which was defined as a group of similar species characterized by a smooth body, entire or slightly excavate front of the head, and excavated pleotelson apex ( Monod, 1931; Menzies and Miller, 1972; Poore, 1996). The group contains: S. hirtipes ( Milne Edwards, 1840) , S. laevidorsalis ( Miers, 1881) , S. laticauda Benedict, 1879 , S. harfordi Benedict, 1879 , S. variegata, Collinge, 1917 , S. marplatensis Giambiagi, 1922 , S. fluviatilis Pillai, 1954 , S. worlinensis Joshi and Bal, 1959 , S. brunnea Pires and Moreira, 1975 , S. hunumantharoei Kumari and Shyamasundari, 1984 , S. keablei Poore and Lew Ton, 1993 , S. grisea Poore and Lew Ton, 1993 , S. oahu Moore, 2004 , and S. fosteri Schotte and Heard, 2004 . Two more species, S. innatans and S. karumba from Australia, were just described and added into the group ( Poore, 2012).

Synidotea poorei sp. nov. can be separated from S. hirtipes easily by its smooth uropodal peduncle (vs. two ridges in S. hirtipes ). The new species is superficially similar to S. lavidorsalis , S. laticauda , S. grisea and S. keablei , but it can be separated from these species by the sub-parallel lateral margin of the pleotelson. It also differs from S. laevidorsalis by the shape of uropodal endopod (fig. 3G vs. fig. 1f in Poore, 1996) and the fused penial plates (fig. 3H vs. fig. 1k in Poore, 1996); from S. laticauda by the less excavated posterior end of the pleotelson; and from S. keablei by sexual dimorphism of the maxilla 2, and the elongated pleotelson. Synidotea poorei sp. nov. can be distinguished from S. harfordi by the shape of the lunette on the pereonites 2-4 (rounded vs. triangular) and the overall body form, which is more slender in the latter. Synidotea poorei is also similar to S. brunnea from which it can be separated by the more elongated antennae 1 and 2, and the shape of uropodal endopod (fig 3G vs. fig. 38 in Pires & Moreira, 1975). Synidotea poorei , also resembles S. variegata (cf. Collinge, 1917; Pillai, 1963) from which it differs by the more stout peduncle of antenna 2 (fig 3 in Collinge, 1917 vs. fig. 2C), stouter pleotelson (1.3 times as long as wide in female and 1.5 times in male of S. poorei vs. 1.7 times in S. variegata ); and the shallower pleonal suture. With respect to the body form, the cephalon and the pleotelson, S. poorei is very similar to the Argentinean species S. marplatensis . It can be separated by the much longer appendix masculina ( Fig. 3C, D vs. Fig. 4 in Giambiagi, 1922); and the smooth uropodal peduncle (vs. with an oblique ridge). Synidotea poorei can also be easily separated from the two recently described species, S. fosteri and S. oahu by its much longer antenna 2, and the smooth uropodal endopod.

Figures

Figure 1. Photographs of Synidotea poorei, sp. nov. A. female, tl 7.4 mm, B. male, tl 12.9 mm, NMV. Scale bar = 1 mm.

Figure 2. Synidotea poorei, sp. nov. A. dorsal view of male specimen, B. dorsal view of female specimen, C. antenna 2, D. right mandible, E. left mandible, F. right maxilla, G, I. maxilla 2, male, H. inner and median lobes of left maxilla 2, male, close up. Scales: A, B=1.5 mm, C=0.5 mm, D, E=0.2 mm, F, H=0.1 mm, G=2 mm.

Figure 3. Synidotea poorei, sp. nov. A. left maxilliped, B. pleopod 1, male, C. pleopod 2, male, D. appendix masculina of pleopod 2, E. base of pleopod 1, F. pleopod 3, G. right uropod, H. penial papilla. Scales: A, D, E, G, H=0.2 mm, B, C, F=0.6 mm.

Figure 4. Synidotea poorei, sp. nov.A. left antenna 1, B. left pereopod 1, C. left pereopod 2, D. left pereopod 4, E. left pereopod 7. Scales:A-E=0.2 mm.