Myopiarolis, 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 : 38-40

Myopiarolis gen. n.

urn:lsid:zoobank.org:act:F4F859DF-3982-4749-B42D-CD8F1AAF8C62

Caecoserolis . – Poore and Brandt 1997: 161 (part).

Type species. Myopiarolis systir sp. n., here designated.

Diagnosis. Eyes minute (less than 5% greatest width of head) elliptical (lenticular/ ovoid) when present, or absent; coxae of pereonites 2–4 distal margin truncate; coxae 6 extending to between posterior of uropods and pleotelson posterior margin; pleonites 2 and 3 distally narrow or acute, laterally overlapped by coxae 6, extending posteriorly along pleotelson; antenna peduncle articles 4 and 5 slender (4.6–6.3 and 8.6–10.3 as long as wide respectively); left mandible lacinia mobilis three-quarters as wide as incisor or larger; propodal palm setae all RS, alternating straight and flattened; pleopod 2 endopod lamellar part slightly shorter than ramus; uropods biramous, inserted on pleotelson mid-laterally. Uropodal rami positioned ventrally, less than one-third as long as pleotelson (less than 0.3).

Description. Head lateral lobe mesial margin with two concavities; anterolateral lobes forming of continuous margin with pereonite 1; anterior submarginal ‘ridge’ entire; posterior margin with or without median tubercle. Pereonites 5–7 fused mid-dorsally; pereonite 1 anterior margin not strongly bent dorsally, dorsally with or without median tubercles on some or all of pereonites and pleonites. Coxae of pereonites 2–4 articulated, with dorsal sutures; 2–4 and pereonite 6 entirely lacking coxal keys; coxae 6 wide, posteriorly produced. Ventral coxal plates 2–4 meeting midline; simple, smooth, or with anterior and posterior ridge, or strongly punctate, or with mesial ridges forming X-shape; plates 6 and 7 entirely separate. Sternites 5–7 visible, fused. Sternal plates of pleonites 1–3 tri-cornered, with acute median point, with distinct median ridge (occasionally absent in plate 1). Pleotelson dorsal surface with paired sublateral carinae; posterior margin converging to caudomedial point, without distinct median excision.

Antennule flagellum 2.0–3.0 as long as peduncle articles 3 and 4, extending to between pereonites 3 and pereonite 5. Antenna peduncle articles 4 and 5 slender, article 5 8.6–10.3 times as long as greatest width; flagellum about as long as or longer (0.8–1.9) than peduncle article 5.

Epistome with blunt or acute median point. Mandible incisor even or minutely irregular; right mandible lacinia mobilis distally multicuspid, mandibular spine simple. Maxilla lateral lobe with 2 distal simple setae, middle lobe with 2–5 long simple setae. Maxilliped palp with 3 articles, article 3 cordiform, longer than wide.

Pereopod 1 carpus RS distally pilose; propodus wide, RS with finely ridged margins or with serrate margins, narrow RS distally bifid, with simple flagellum or distally bifid, with pilose flagellum. Pereopod 2 propodus inferior margin with distinct heel, palm straight or angled or weakly concave; inferior margin RS simple, acute or simple, blunt, smooth or pilose; unguis simple, slender. Pereopods 6 and 7 not sexually dimorphic.

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

Pleopods 1–3 peduncles triangular, pleopod 1–3 peduncles with coupling setae.

Uropods not forming part of continuous body outline, endopod distally rounded.

Remarks. Myopiarolis gen. n. can be distinguished from all other genera of Serolidae by the following combination of characters: small (<5% head width) lenticular eyes (when present), coxae 2–4 distally truncate forming continuous body outline, broad but posteriorly produced coxae 6 that extend laterally along the pleotelson, pleonites 2 and 3 that curve posteriorly and run along the side of the pleotelson, but are laterally overlapped by coxae 6, antenna with slender peduncle articles 4 and 5 (4.6–6.3 and 8.6–10.3 as long as wide respectively) and very short uropods (<0.3 pleotelson) that are ventrally inserted about halfway along the pleotelson lateral margins, the rami of which are consistently bluntly rounded. Th ese character states are entirely consistent within the genus including several undescribed species from New Zealand (personal observation).

The most similar genus is Caecoserolis Wägele, 1994 , known only from the southwestern Indian Ocean, off the Natal coast of South Africa. Th at genus differs from Myopiarolis in having broad antennal articles 4 and 5 (less than 5.0 times as long as wide), all pereonites dorsally articulated and a weakly domed pleotelson that lacks sublateral carinae. Difference between the two genera are discussed in more detail under the remarks for Caecoserolis .

Unusually the setation of the maxilla middle lobe varies. This is a character that is generally consistent within serolid genera, with the middle and lateral lobes each having two apical setae. Two large species, M. koro sp. n. and M. carinata ( Bruce, 2008) have the middle lobe with 5 or 6 long apical setae and one mid-length on the mesial margin.

Relationships of Myopiarolis . Atlantoserolis Wägele, 1994 , Caecoserolis and Glabroserolis Menzies, 1962 form a monophyletic group according to Wägele (1994), to which Myopiarolis gen. n. also belongs. Th at group was characterised ( Wägele 1994, Fig.36) by lack of eyes, oval body shape, body widest at pereonites 1 or 2 and, more basally, Wägele’s ‘group B’ was defined by having a ‘stalked appendix masculina’. Loss of eyes is a frequent homoplasious occurrence within the Isopoda , and cannot be reliably used to characterise genera or groups of genera (in contrast to eye shape which is usually consistent). Body width and where the body is widest varies considerably within larger genera (in Myopiarolis body width ranges from 1.1–1.4 as long as greatest width, and is widest at coxae 3 or 4). Neither Myopiarolis nor Caecoserolis are widest at pereonites 1 and/or 2, and neither genus has a stalked appendix masculina.

A character not used by Wägele’s (1994) is the shape of the coxae of pereonites 2–4. All of Wägele’s ‘group B’ is characterised by having approximately quadrangular coxae, that is with the anterior, posterior and distal margins clearly demarcated, with the exception of Serolina . Wägele’s (1994) ‘Group C’ has coxae that are distally acute, in effect three sided. Myopiarolis (and Caecoserolis ) then belongs with the ‘Group B’ genera, but with unclear affi nities with the remainder of that group, differing from most of the Group B genera in having triangular peduncles to pleopods 1–3, the state for Caecoserolis ; Heteroserolis and Sedorolis gen. n., being quadrate or sub-quadrate.

The minute lenticular eye shape is a unique, probably apomorphic, character for Myopiarolis . Th e state of short uropods (0.2–0.3 length of pleotelson), also probably apomorphic, is shared only with Caecoserolis Wägele, 1994 , that genus being distinguished by the broad antennal peduncle articles 4 and 5, separate penial openings, all pereonites unfused, coxae 6 not extending posteriorly beyond the pleonites and a weakly domed pleotelson that lacks sub-lateral carinae.

Taxonomically useful characters. Dorsal ornamentation, including pattern and size of pereonal and pleonal tubercles, and of the pleotelson carinae; ornamentation of the ventral coxal plates of pereonites 2–4; extent that coxae 4–6 are posteriorly produced; extent that pleonites are produced along the pleotelson; body length to width ratio; relative proportions of the antennule and antenna peduncle articles and their flagellae (the latter of which vary considerably in relative length); extent, number and morphology of robust setae on pereopod 2 palm; shape of pereopod 2 palm; number, size and morphology of setae on the inferior margins of posterior pereopods; relative size of uropods and uropodal rami; presence or absence of eyes. Minor differences can be seen in the proportions of the pereopod articles and the relative length of pereopod 7 in relation to pereopod 6.

Species included. In addition to the type species, Myopiarolis antarctica ( Beddard, 1884, sensu lato) comb. n., southern Indian Ocean and tropical Brazil ( Beddard 1884); M. apheles (Schotte, 1992) comb. n., Mozambique Channel, southwestern Indian Ocean; M. bicolor ( Bruce, 2008) comb. n., northeastern New Zealand; M. carinata ( Bruce, 2008) comb. n., northwestern New Zealand; M. koro sp. n., Fiji; M. norfanz sp. n., Lord Howe Plateau, Tasman Sea; M. novaecaledoniae ( Poore and Brandt, 1997) comb. n., New Caledonia; and M. lippa sp. n., northern Coral Sea.

There are least three known undescribed species: one recorded here, one from off the South Island of New Zealand ( Bruce 2008), and the species from off Norfolk Island recorded by Poore and Brandt (1997); a further six probable new species are known from around New Zealand (NIWA NIC collections, personal observation).

Distribution. The genus is known from the Western Indian Ocean eastwards to Fiji and New Zealand, the Southern Ocean and the northern Coral Sea in the Gulf of Papua; at depths from 700 to 3184 metres.

Etymology. From the Greek ‘myopia’ in combination with [Se]-rolis; alluding the tiny or absent eyes. Gender neuter.