Acutiserolis Brandt, 1988

Poore, Gary & Storey, Melissa, 2009, Brucerolis gen. n., and Acutiserolis Brandt, 1988, deep-water southern genera of isopods (Crustacea, Isopoda, Serolidae), ZooKeys 18 (18), pp. 143-160 : 144-146

Acutiserolis Brandt, 1988

Acutiserolis Brandt, 1988: 21 .– Brandt 1991: 131, 138–139.

Serolis (Acutiserolis) .– Wägele 1994: 53, 59.

Not Acutiserolis .– Poore and Brandt 1997: 152 (= Brucerolis gen. nov.)

Cuspidoserolis Brandt, 1988: 23 .– Brandt 1991: 131, 138–139. – Wägele 1994: 52, 59–60 (type species: Serolis luethjei Wägele 1986 by original designation). syn. n.

Type species. Serolis spinosa Kussakin, 1967 by original designation.

Diagnosis. Body deeply incised between extremely long, attenuating, posteriorly directed coxal and epimeral plates; middorsal line dominated by strong middorsal spine (prominent in lateral view) on posterior margin of head, pereonites 2–4 and pleonites 1–3. Pereonite 6 to pleonite 1 fused middorsally and midventrally. Eyes contiguous with head margin posteriorly, 3 times as long as wide, with concave mesial margin. Coxal dorsal plates 2–4 delimited from tergite by suture; coxal dorsal plates 2–5 with proximal anterior margins straight, slotting into grooves on preceding coxae, with no aperture between; coxa 6 with blunt process on anterior margin slotting into groove on coxa 5 and isolating an oval aperture. Pleotelson with sharp middorsal keel, upturned posteriorly; dorsal surface with sublateral sharply defined longitudinal keels ending acutely, and obscure irregularities along a submarginal posterolateral ridge. Pereonal sternite 1 with defined blunt medial lobe anteriorly and saddle posteriorly; ventral coxal plates 2–4 meeting in midline, with pair of contiguous teeth on anteromesial corners of sternites 2, smaller pair on sternites 3; pleonal sternites 1–3 with acute posterior ridged margin. Antenna 2 article 5 about 10 times as long as wide. Mandible, incisor smooth, chitinised, hoof-like; left lacinia mobilis expanded, half as wide as mandibular incisor; right lacinia mobilis diverging, with obsolete apical dentition; spine simple; mandibular palp, article 2 with row of setae confined distally along mesial margin. Maxilla 1 inner lobe a simple expanded plate, outer lobe with ̴11 robust terminal setae. Maxilla 2 inner lobe broad, distally richly setose, middle and lateral lobes each with 2 apical setae. Maxilliped, endite with 2 strong distal robust setae; maxillipedal palp of 3 articles; palp article 2 distally dilated, distomesially lobed, with shallow indentation on mesial margin separating two clusters of setae; epipod more or less semicircular. Pereopod 1, palm of propodus with alternating flagellate cylindrical setae and flagellate plate-like setae. Pereopod 2 of male subchelate; palm of propodus with robust setae surrounding an oval palm; dactylus with small terminal unguis. Pereopod 7 of male sexually differentiated, propodus broader than in female, with felt of fine scale setae, dactylus simple, curved. Pleopod 4 endopod simply triangular, not bilobed. Uropod biramous, inserting sublaterally at about midpoint of pleotelson. Oostegites of female present on pereopods 1–4.

Included species (all originally described in Serolis ).

Acutiserolis spinosa ( Kussakin 1967) – Ross Sea, Antarctica, 500–900 m

A. gerlachei ( Monod, 1925) comb. n. – Bellingshausen Sea, Antarctica, 400 m

( Monod 1926).

A. johnsoni ( Hale 1952) comb. n. – Eastern Antarctica, 540–2267 m ( Kussakin

1967).

A. luethjei ( Wägele 1986) new combination – Weddell Sea, 189– 481 m.

Remarks. The most significant features of Acutiserolis are: coxal dorsal plates 2–5 slot into each other with no aperture between; coxal plate 6 has a blunt process on its anterior margin slotting into a groove on coxa 5 and isolating an oval aperture; prominent middorsal pereonal and pleonal spines; pleotelson with a sharp middorsal keel, upturned posteriorly; and sharply defined longitudinal sublateral pleotelson keels ending acutely.

Brandt (1988) relied on the extreme length of the coxal plates and pleonal epimera to characterise Acutiserolis but in our opinion this was unwarranted. Coxal plate 6 of Acutiserolis spinosa exceeds the pleotelson by one-third its length whereas in the remaining species included, the overlap of coxa 6 is at least as great as the pleotelson length and usually much greater. Acutiserolis spinosa is more similar to species of Cuspidoserolis Brandt, 1988 in this and other features than to the other species in- cluded by Brandt (1988) and Wägele (1994) in Acutiserolis . Brandt (1988) agreed that the two genera were similar in having long coxal dorsal plates and pleonal epimera although none overlap the pleotelson in Cuspidoserolis . The distinguishing feature of Cuspidoserolis , according to Brandt, is the elongate spine on the posterior margin of the head but this is found also in A. spinosa (fig. 1). She treated the two genera as sister taxa sharing a middorsal spine on the head in a phylogenetic analysis ( Brandt, 1991) but this is not true of the species we remove to Brucerolis . The type species of Cuspidoserolis , Serolis luethjei Wägele, 1986 , differs from A. spinosa only in having a more rugose surface and more compact coxal plates and epimera. It shares prominent middorsal spines, ridges on pereonite 1, medial and sublateral keels on the pleotelson, and similar male pereopods 2 and 7. Brandt (1988) also included in Cuspidoserolis , Serolis gerlachei Monod, 1925 (illustrated by Monod 1926) and S. johnsoni Hale, 1952 . They too have a long middorsal posterior spine on head, coxal plates contiguous proximally, middorsal pleotelson keel and similar sublateral keels on the pleotelson. All three differ from A. spinosa only in having coxal plate 6 not reaching beyond the end of the pleotelson. Other authors have remarked on these similarities: Hale (1952) remarked on similarities between his S. johnsoni and S. gerlachei ; Kussakin (1967) likened S. spinosa to S. johnsoni . Brandt remarked on the extreme length of the pleotelson of Cuspidoserolis , being about as long as wide, but this is true too of all species of Acutiserolis and Brucerolis .

In his phylogenetic analysis of the family, Wägele (1994) placed Cuspidoserolis and what he called Serolis (Acutiserolis) in sister-clades. Th e clade containing Cuspidoserolis was characterised by a sexually dimorphic pereopod 7, the male having broader and finely setose articles than the female. However, this is true too of Acutiserolis and Brucerolis . Th e apomorphies of the sister clade (dealing with male pereopod 2, pleopod 4 and coxal plates) are equally unconvincing. Held’s molecular analysis placed two species of Cuspidoserolis ( C. luethjei and C. johnsoni ) close together and close to “ Acutiserolis bromleyana ”.

We conclude that Cuspidoserolis is a junior synonym of Acutiserolis which now includes its type species plus the three species of Cuspidoserolis . We assign other species previously included in Acutiserolis to Brucerolis .