Pooredoce, Bruce, 2009

Bruce, Niel L., 2009, A new genus and new species of Sphaeromatidae (Crustacea: Isopoda) from the Great Barrier Reef, Australia, Memoirs of Museum Victoria 66 (1), pp. 35-42 : 35-37

Pooredoce gen. nov.

Type species. Pooredoce garyi , sp. nov., here designated and by monotypy.

Diagnosis. Adult male. Pereonite 7 narrower than pereonite 6, not extending to lateral body margin. Pleon dorsal surface without process; posterior margin with plate-like extension. Pleotelson dorsally flat, posterior margin with two small submedian foramens, with hardened boss anterior to median notch, with ventral thickened rim; lateral margins forming dorsally directed ridge. Maxilliped palp articles 2–4 medial margins extended, forming finger-like lobes. Uropod exopod reduced, mobile, round in section, inserted near midpoint of lateral margin of peduncle-endopod, distally with hard terminal spike; endopod round in section, distally with hard terminal spike.

Description of male. Body vaulted, dorsal surfaces granular, densely setose, unable to conglobate; strongly sexually dimorphic. Head with rostral point present, dorsally visible, separating antennular bases; without paired incisions in front of eyes, lateral margins not laterally extended to body outline (antennules more or less ventral). Eyes lateral, posteriorly lobed. Pereonite 1 lateral margins not anteriorly produced, not laterally enclosing head, anteriorly without ‘keys’; pereonites 2– or 5–7 with posterior margin raised, forming broad and low transverse ridge. Sternite 1 without cuticular mesial extensions. Pereonite 7 narrower than pereonite 6, coxal margin free. Coxae distally narrow, distally rounded, coxae without ventral ‘lock and key’ processes or ventral groove, those of pereonite 6 not large, not overlapping those of pereonite 7. Pleon consisting of 4 visible segments (as determined by lateral sutures); pleonite 1 entire, posterior margin even, as wide as remainder of pleon, extending to pleon lateral margins; sutures (except first) running to lateral margin, all separate, long; pleonal sternite short relative to width; dorsal surface without process; posterior margin with plate-like extension, without ‘keys’. Pleotelson flat, anteriorly as wide as pleon; posterior margin with two small submedian foramens; with hardened boss anterior to median notch, with ventral thickened rim; lateral margins forming ridge.

Antennule peduncle with basal articles medially not in contact, peduncle 1 and 2 robust, article 3 slender; inferior margin without hard cuticular spines; article 2 approximately 0.5 as long as article 1; with articles 2 and 3 colinear, article 3 longer than article 2; longer than peduncular article 3. Antenna peduncle articles less robust than antennule, peduncular articles all of similar thickness.

Epistome anteriorly narrow, with median constriction, elongate. Mandible incisor wide, multicuspid; lacinia mobilis present, tricuspid; molar process gnathal surface with transverse ridges, rounded. Maxillule lateral lobe RS with some or all serrate, mesial lobe with 4 major RS, these setae being heavily serrate. Maxilla with setae on middle and lateral lobes serrate. Maxilliped palp articles 2–4 medial margins extended, forming finger-like lobes, article 2 not expanded; endite distal margin truncate, without clubbed RS.

Pereopod 1 ambulatory. Pereopod 2 similar in proportion to pereopod 3. Pereopods with inferior margins of ischium to carpus not bearing dense setulose fringe; ischium superior margin with sinuate acute RS, pereopods 1–3 or 4 ischium superior margin without long stiff slender setae. Pereopods 1–3, inferior margins of merus, carpus and propodus palm with widely-spaced conspicuous RS along inferior margins. Dactylus of all pereopods with simple secondary unguis.

Penial processes entirely separate, basally in contact, short (not extending beyond pleopod peduncles), tapering smoothly from base, apex bluntly rounded.

Pleopod 1 rami not operculate; exopod lamellar, of similar proportions to exopod, longitudinal axis weakly oblique, mesial margin lamellar, proximomedial heel absent; exopod distally subtruncate, margins not serrate. Pleopod 2 endopod about as long as exopod; exopod distal margins not deeply serrate; appendix masculina inserted basally, margins curving weakly to lateral, 1.25 times as long as endopod, distally bluntly rounded. Pleopod 3 exopod transverse suture present; endopod of similar proportions to exopod. Pleopod 4 rami without PMS; exopod transverse suture present, thickened transverse ridges absent, lateral margin not thickened, without short simple marginal setae; endopod thickened transverse ridges present, mesial margin without deep distal notch, without proximomedial lobe. Pleopod 5 exopod transverse suture present, entire, thickened transverse ridges absent, lateral margin without short simple setae, not thickened, 3 discrete scale patches, scale patches forming protruding lobes. Pleopod 5 endopod with thickened transverse ridges absent, with proximomedial lobe.

Uropod rami not strongly flattened, not forming part of continuous body outline; exopod (of adult male) reduced, mobile, exopod round in section, inserted near midpoint of lateral margin of peduncle-endopod, distally with acute; endopod round in section, distally with hard terminal spike.

Female. Body surfaces densely setose. Pleon posterior margin not produced. Pleotelson dorsally domed, posterior margin obscurely trilobate, median lobe overriding lateral lobes, ventrally with single simple exit channel. Uropod rami flat, exopod about half as long as endopod; appendages otherwise similar to male.

No ovigerous females were present in the material but the close relationship of this genus to other genera in the Cymodoce -group of genera would strongly suggest that the mouthparts would be metamorphosed.

Remarks. Pooredoce gen. nov. can be identified by, in males, the cylindrical uropods, with the exopod smaller than the endopod, both rami being terminally acute, and the bi-perforate posterior pleotelson margin, which also has a median boss. Females have conspicuously setose dorsal surfaces, and that character together with the details of the uropods and pleotelson (as figured) serve to identify females in the absence of males.

Pooredoce is allied to a group of genera within the Sphaeromatidae characterised by a trilobate pleotelson posterior margin, the maxilliped palp articles 2–5 being greatly elongate (‘finger-like’), the inferior margins of the merus–propodus of pereopods 1–3 with conspicuous robust setae, and uropods with a cylindrical in section endopod and a small exopod (50% or less than the length of the endopod) set about mid-length on the fused endopod peduncle. These genera in the broadest sense include the Indo-Pacific species of Cymodoce Leach, 1814 (see Harrison and Holdich 1984; Bruce 1997, generic remarks), Oxinasphaera Bruce, 1997 and Koremasphaera Bruce, 2003 . In Cymodoce the uropodal exopod is flattened and comparatively larger than the other genera mentioned; in Koremasphaera the trilobate pleotelson is scarcely evident. The Cilicaea – Cilicaeopsis – Paracilicaea group of genera share the maxilliped, pleotelson and pereopod characters but differ conspicuously to the other genera mentioned in having the uropodal exopod cylindrical in section and large, while the endopod is reduced to a small lobe (see figures in, for example, Harrison and Holdich 1984; Benvenuti and Messana 2000).

The pleotelson posterior margin of Pooredoce gen. nov. is complex, essentially trilobate, and conforming to the structure of ‘two sub-median notches’ or ‘median notch with median process’. Such a pattern is present in the genera Cymodoce , Cilicaea , Cilicaeopsis , Paracilicaea (see Harrison and Holdich, 1984) and Oxinasphaera Bruce, 1997 (although Cilicaeopsis lacks a lobe within the median sinus). In the new genus the pleotelson lateral ‘lobes’ meet at the midline and the median lobe is posteriorly in contact with the lateral ‘lobes’ leaving the sinuses posteriorly closed off and forming two holes (figs. 1E–G).

This form of pleotelson, with the submedian sinuses posteriorly closed off, is not unique, occurring in the species Cilicaea caniculata ( Thomson, 1879) (see Hurley and Jansen 1977). A pleotelson morphology approaching that of the new genus can be seen in some Paracilicaea Stebbing, 1910 such as P. stebbingi Baker, 1926 (see Harrison and Holdich 1984), P. mirabilis Benvenuti and Messana, 2000 and also in Cilicaea calcarifera Harrison and Holdich,1984 , but in all these species the submedian notches are posteriorly open. These genera are characterized by, among other characters, a uropod exopod that is round in section and the endopod reduced to a stub.

Pooredoce has one presumed derived or apomorphic character that is shared only with Oxinasphaera , that of the uropods having a cylindrical uropodal endopod and an exopod that is about half the length of the endopod and cylindrical or semi-cylindricalinshape;eachramusistippedwithahardened ‘spike’. Koremasphaera is similar, but the uropodal exopod is large, about as long as the endopod. Oxinasphaera is defined by the unique apomorphy of hardened spikes on the antennule peduncle; the present genus lacks these, but does have a unique and defining pleon and pleotelson morphology.