Sedorolis, Bruce, 2009

Bruce, Niel, 2009, New genera and species of the marine isopod family Serolidae (Crustacea, Sphaeromatidea) from the southwestern Pacific, ZooKeys 18 (18), pp. 17-76 : 30-31

Sedorolis gen. n.

urn:lsid:zoobank.org:act:31C90C50-CE3E-4240-9A18-0539D38C5624

Type species. Sedorolis simplex sp. n., here designated.

Diagnosis. Male. Pereonites with all segments indicated by entire suture lines, coxae 2–4 articulating; distal margin truncate; coxae 6 wide, laterally or distally broad, extending to mid-length of uropod peduncle; pleonites 1–3 sternal plate trilobed, lobes gently rounded, without median ridge; pleotelson posterior margin broadly truncate; pereopod 1 propodal palm setae all slender, bifid, all similar; antennule peduncle article half as long as wide; antenna peduncle articles 4 and 5 broad (less than 5 times as long as wide); pleopods 1–3 peduncles sub-rectangular, without coupling setae; pleopod 2 endopod lamellar part about half as long as ramus (= stalked); uropods inserted on pleotelson at anterolateral angle; rami positioned in a dorsal groove on pleotelson lateral margin.

Description. Male. Head Lateral lobe mesial margin with single concavity; anterolateral lobes forming of continuous margin with pereonite 1; anterior submarginal ‘ridge’ on lateral lobes only; posterior margin without tubercle, or with prominent median spine. Eyes absent. pereonite 1 anterior margin not strongly bent dorsally, dorsally without tubercles. Coxae of pereonites 2–4 articulated, with dorsal sutures. Ventral coxal plates simple, smooth; plates 6 and 7 incompletely separated (sutures partly fused). Pleonites 2 and 3 distally narrow or acute, laterally overlapped by coxae 6, not extending posteriorly along pleotelson. Sternites 5–7 visible, sternite 5 not mesially demarcated by suture. Pleotelson dorsal surface with median longitudinal carina (weak), without paired sublateral carinae; without distinct median excision.

Antennule flagellum 1.2–2.0 as long as peduncle articles 3 and 4, extending to between pereonite 3 (anterior). Antenna peduncle articles 4 and 5 broad, article 5 less than 5 times as long as greatest width; flagellum two-thirds as long as peduncle article 5.

Epistome with obtuse median point. Mandible incisor with two posterior cusps; left mandible lacinia mobilis two-thirds as wide as incisor, right mandible lacinia mobilis distally multicuspid, mandibular spine distally serrate. Maxilla lateral lobe with 2 distal simple setae, middle lobe with 2 long simple setae. Maxilliped palp with 3 articles, article 3 cordiform, longer than wide.

Pereopod 1 carpus RS with prominent pilose flagellum; propodal palm RS distally pilose. Pereopod 2 propodus inferior margin with indistinct heel, palm straight; inferior margin RS distally bifid, smooth. Pereopods 6 and 7 not sexually dimorphic.

Penial openings narrowly separated, penes opening flush with surface of sternite 7.

Uropods Biramous, uropods not forming part of continuous body outline, uropods more than half (0.8) as long as pleotelson. Uropod endopod distally rounded.

Remarks. Probable derived character states (putative apomorphies) that uphold Sedorolis and that also serve to distinguish the genus from both Serolina and Heteroserolis are the broad antennal articles 4 and 5 and the unique position of the uropodal rami, which sit on a dorsal groove on the lateral margin of the pleotelson. The robust setae on pereopod 1 are all slender, bifid, all similar. Sedorolis is the only serolid genus to have a weakly vaulted pleotelson with a broadly truncate and flat posterior margin.

Serolina is distinguished from Sedorolis by numerous derived states, including a narrow posterior margin to pleotelson; male pereopod 2 merus and carpus inferior margins with long plumose setae; clubbed pereopod 2 dactylar unguis; ischium and carpus of pereopods 6 and 7 highly setose or with acute robust setae, in having sexually dimorphic pereopod 7 and the maxilla mesial and middle lobes with 2+1 long terminal setae (rather than the more usual 2+2). Heteroserolis is distinguished by the uropods being inserted at a mid-lateral or just anterior to mid-lateral position on the pleotelson; pleonal sternite 1 with large posteriorly-directed median spine, a unique apomorphy for the genus; slender antennal peduncle articles 4 and 5 (most species); and a clearly excavate (Australian species) or rounded and medially indented (Northern Hemisphere species) pleotelson apex.

Relationships of Sedorolis . Sedorolis belongs in the group of two genera, Heteroserolis and Serolina , characterised in part ( Wägele 1994, see dendrogram, figure 37) by having ‘enlarged’ uropodal rami (at least the endopod is long) which reach to about the posterior margin of the pleotelson. These two genera belong to Wägele’s ‘Group B’ part of a group defined by the presence of a ‘stalked’ pleopod 2 endopod (‘stalked appendix masculina’ in Wägele’s terminology). All of ‘Group B’ and ‘Group C’ are characterised by having the ‘palm of pereopod 1 each second spine scale-like’. Wägele (1994) considered the large uropods to be potentially plesiomorphic, but also that it was ‘a character secondarily acquired in the stem-line of the group.’

On the basis of uropod and pleopod 2 morphology Sedorolis belongs with this pair of genera. Further character states, not previously recognized by Brandt (2001) or Wägele (1994) is that the peduncles of pleopods 1–3 are quadrate, or slightly narrower distally, lacking the mesial projection (with coupling hooks) the presence of which creates a triangular shaped peduncle, as in all other Serolidae . Both the elongate quadrate state and triangular states can be recognised as derived from a short quadrate state as shown in the Basserolidae ( Poore 1985, 1990). The quadrate pleopod peduncle further upholds the monophyly of this group of genera.

Species included. Sedorolis simplex sp. n., the type species and Sedorolis sp.

Distribution. The genus is known only from New Caledonia, at depths of 440– 680 metres.

Etymology. Sedorolis –from the Latin sedo smooth, in combination with [Se]-rolis indicating family affinity.