Myopiarolis systir, 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 : 58-64

Myopiarolis systir sp. n.

urn:lsid:zoobank.org:act:11B00636-BB4E-498D-9381-6B8908C963DC

Figs 20–23

Caecoserolis novaecaledoniae Poore & Brandt, 1997: 161 (part).

Material. Holotype: 3 (11.6 mm), New Caledonia, ‘sudest fairway’, 21° 27.008 – 24.374´S, 162° 36.457 –37.187´E, 23 Oct 2005, EBISCO stn CP2652, 1019– 1147 m ( MNHN Is.6012) . Paratypes: 18 3 (11.0– 12.5 mm; 2 immature 9.7, 9.9 mm; 11.4 mm [dissected]), ♀ (8 ovig. with eggs 12.5, 14.0, without eggs, 11.5–14.1 mm, 1 nonovig. 10.5 mm), 1 manca (7.5 mm), same data as holotype ( MNHN Is.6013; 1 microslide). 43 (11.3, 11.5, 11.5, 12.1 mm), 2♀ (ovig. 13.9, 14.5 mm), New Caledonia, ‘sudest fairway’, 21° 29.187 –26.855´S, 162°32.559–959´E, 23 Oct 2005, EBISCO stn CP2650, 825– 894 m ( MNHN Is.6014). 23 (11.0, 11.3 mm), ♀ (ovig. 14.5 mm), New Caledonia, ‘sudest fairway’, 21°28.134–711´S, 162° 33.911 –36.110´E, 23 Oct 2005, EBISCO stn CP2651, 883– 957 m ( MNHN Is.6015) .

Additional material. ♀ (imm. 12.2 mm), Chesterfield Is., 21°02.77´S, 160°55.00´E, 21 July 1988, 700– 705 m, CORAIL stn DE13 ( MNHN Is.4083; part of non-type material of misidentified by Poore and Brandt (1997) as Caecoserolis novaecaledoniae ) .

Description. Body 1.3 as long as wide, widest at coxae 3, dorsal surfaces punctate. Head anterolateral lobes weakly convex, anterior submarginal ‘ridge’ entire; dorsally without tubercles, posterior margin without median tubercle. Eyes present. Pereonite 1 anterolateral margin continuously convex; dorsal surfaces without tubercles. Coxae distal margins truncate; coxae 4 extending to mid-pleonite 1; coxae 5 extending posteriorly along 0.3 of pleotelson length; coxae 6 extending to between posterior of uropods and pleotelson posterior margin, and along 0.7 (to 0.9) of pleotelson

length. Ventral coxal plates 2 mesially elevated, plates 2–4 mesially with ridges forming X-shape; plates 6 and 7 entirely separate. Pleonites extending posteriorly along 0.5 pleotelson lateral margin; pleonite 1 sternal plates 3-cornered, sternal plate 1 without median ridge. Pleotelson 1.04 times as long as anterior width, dorsal surface without median longitudinal carina, with paired sublateral carinae (weak); lateral margins weakly sinuate, posterior margin converging to angled caudomedial point, without distinct median excision.

Antennule peduncle article 2 2.2 times as long as wide; articles 3 and 4 2.4 times as long as article 2; article 3 7.4 times as long as wide; flagellum 3.0 as long as peduncle articles 3 and 4, with ̴60 articles, extending to pereonite 5. Antenna peduncle article 4 5.5 times as long as wide, 3.0 times as long as article 3; article 5 1.1 times as long as article 4, 9.6 times as long as wide; antennal flagellum 1.0 as long as peduncle article 5, with ̴20 articles, extending to middle of pereonite 4.

Epistome with blunt median point. Mandible incisor even or minutely irregular, left mandible lacinia mobilis 0.9 as wide as incisor, right mandible lacinia mobilis distally multicuspid, mandibular spine simple; palp article 2 with 22 distolateral setae, article 3 with 26–27 biserrate setae. Maxilla mesial lobe with 11 long, finely serrate setae; middle lobe with 2 long simple setae; lateral lobe with 2 distal simple setae. Maxilliped palp article 2 proximomesial margin with 6 setae, distomesial margin with 18 setae, lateral margin distally with 4 setae; article 3 lateral margin with 3 setae, distal margin with 14 setae; endite distal margin RS simple.

Pereopod 1 carpus RS distally pilose; propodus 2.1 times as long as wide, inferior margin with ̴56 RS; wide RS with finely ridged margins, narrow RS distally bifid, with simple flagellum; dactylus with acute unguis. Pereopod 2 basis 4.5 times as long as greatest width; 0.7 times as long as basis, ischium 3.4 times as long as wide; merus 0.4 as long as ischium, 1.8 times as long as greatest width, inferior margin with 1 cluster of setae (as 2), superior distal angle with 3 setae; carpus 0.6 as long as ischium, 2.5 times as long as wide, inferior margin with 3 clusters of setae (as 1, 1 and 1); propodus 0.5 as long as ischium, 2.4 times as long as wide, inferior margin with distinct heel, palm angled, inferolateral margin with 4 RS, inferomesial margin with 7 RS, inferior margin RS simple, blunt, smooth, distal margin with ̴12 setae; dactylus 0.8 as long as propodus, unguis simple, slender. Pereopod 6 basis 4.2 times as long as greatest width; ischium 0.8 as long as basis, 4.1 times as long as wide, inferior margin with 0 clusters setae, superior distal angle with 1 robust seta; merus 0.4 as long as ischium, 2.1 times as long as wide, inferior margin with 5 clusters of setae (as 1, 1, 1, 1 and 4), superior distal angle with 1 seta; carpus 0.8 as long as ischium, 4.6 times as long as wide, inferior margin with 7 clusters of setae (as 1, 1, 2, 2, 3 and 3), superior distal angle with ̴9 setae; propodus 0.8 as long as ischium, 6.2 times as long as wide, inferior margin with 9 clusters of setae (as 1, 2, 2, 3, 3, 2, 3, 3 and 1), distal margin with ̴12 setae, inferior distal angle with 0 RS; dactylus 8.8 as long as proximal width. Pereopod 7 similar to, but 0.8 as long as pereopod 6. Setae on inferior margins of pereopods 4–7 densely plumose. Inferior margins of pereopods 2–7 setulose fringe weakly developed.

Pleopod 1 peduncle 1.6 times as long as wide, mesial margin with 3 coupling setae; exopod 1.8 as long as wide, with 36 PMS; endopod 2.3 times as long as wide, 0.6 as long as exopod, with 18 PMS. Pleopod 2 peduncle 1.6 as long as wide, mesial margin with 2 coupling setae; exopod 1.6 as long as wide, with 38 PMS; endopod 2.9 as long as greatest width, lamellar part 3.6 as long as wide, with 18 PMS; appendix masculina 4.2 times as long as endopod. Pleopod 3 exopod with 42 PMS, endopod with 22 PMS. Pleopod 4 exopod with complete transverse suture, endopod with complete transverse suture. Pleopod 5 exopod with complete transverse suture, endopod with incomplete transverse suture.

Uropods (rami + peduncle) 0.3 as long as pleotelson, peduncle 0.8 as long as endopod. Endopod 2.4 as long as wide; distally broadly rounded. Exopod 0.7 as long as endopod, 2.2 times as long as wide, distally broadly rounded.

Females. Similar to males, slightly larger; coxae 6 not as produced as in males, rarely extending beyond the uropods.

Size. Males 11.0– 12.5 mm, mean = 11.6 mm; immature males 9.7–9.9 mm (2 only); females–with eggs 12.5–14.5 mm (mean 13.7 mm), with oostegites only 11.4– 14.5 mm (mean = 12.7 mm); non-ovig. 10.5 mm.

Colour. Dark grey–green, pale bands on dorsal somites and coxae noticeably broad.

Variation. Coxae 6 extends posteriorly to about the midpoint of the uropodal rami (tip of exopod) to a little beyond the rami (as in the holotype), with most (7 of 10) extending at least to the apex of the endopod or further. Ovigerous females have slightly shorter coxae, most (5 of 7) not extending beyond the uropodal exopod.

Setation of male pereopod 2 propodus (n=18) is variable, ranging from 3+6 RS (mesial + lateral margins) to 6+7 and 4+8, with no clear combination; lateral margin ranging from 5 to 8 RS, most frequently with 8 (16%), 7 (28%) and 6 (33%) (damaged limbs were discounted from the counts); mesial margin ranging from 3 to 6 RS, most frequently with 5 (22 %) or 4 (50%).

Remarks. Myopiarolis systir sp. n. can be identified by the lack of dorsal ornamentation, long coxae 6 which extend posteriorly to between the mid-point of the uropods to just short of the pleotelson apex, short pleonites that extend along the anterior onethird of the pleotelson, the strong sculpting of sternal coxae 2–4, and lack of median dorsal carina on the pleotelson.

Myopiarolis systir is similar in general appearance to M. novaecaledoniae , but differs consistently at least seven characters (state for M. novaecaledoniae in parentheses): small body size, with males averaging 11.6 mm, adult females 12.7 mm (males 16.9, 16.7 mm; females ovig. 18.5 mm); coxal sternites 2–4 are medially elevated and strongly ornamented with ridges forming a prominent median excavation (not elevated, weakly ornamented); coxae 6 extend to and beyond uropods (not beyond uropods); pleonites extending posteriorly along anterior one-third of pleotelson (along anterior half of pleotelson); pleotelson without longitudinal median carina (longitudinal carina present) and pleotelson apex sub-acute (rounded); male pereopod 2 propodus with short, blunt robust setae (robust setae longer, acute) and a different pattern of robust setae (3–4+7–8 RS in M. systir vs. 6+ 6 in C. novaecaledoniae ); pereopod 2 propodal ‘heel’ distinct (less distinct); and the setae on the inferior margins of pereopods 5–7 are prominently plumose from mid-length (weakly plumose). In addition the two species occupy somewhat different though potentially overlapping depth ranges: M. systir has been collected at depths from 500 to 1210 metres, while C. novaecaledoniae s. str. from 1395 to 1410 m

Distribution. New Caledonia, depths of 700–1147 metres.

Etymology. The Old Norse word for sister, alluding to the close ‘relationship’ between this species and Caecoserolis novaecaledoniae (noun in apposition).

Figures

Figure 20. Myopiarolis systir sp. n. Holotype, except G, H, paratype 3 11.4 mm, Is.6013. A dorsal view B lateral view C frons (labrum and clypeus) D sternites and ventral pleonites E pleotelson, ventral view F coxae 2–5, ventral G antennule H antenna.

Figure 21. Myopiarolis systir sp. n. Paratype 3 11.4 mm, Is.6013. A maxilliped B right mandible, distal margin C left mandible, distal margin D maxillule E maxilla F mandible palp.

Figure 22. Myopiarolis systir sp. n. Paratype 3 11.4 mm, Is.6013, except H, holotype. A–D pereopods 1 2, 6 and 7 respectively a detail of pereopod 1 propodal palm setae E pereopod 2 carpus and propodus F pereopod 6 carpus and propodus.

Figure 23. Myopiarolis systir sp. n. Paratype 3 11.4 mm, Is.6013. A–E pleopods 1–5 respectively F pleopod 2 endopod detail G uropod.