Myopiarolis tona, Spong, Keren & Bruce, Niel L., 2015

Spong, Keren & Bruce, Niel L., 2015, A new deep-water species of Myopiarolis Bruce, 2009 (Crustacea: Isopoda: Serolidae) from New Zealand waters, Zootaxa 4057 (2), pp. 257-264 : 258-263

Myopiarolis tona sp. nov.

( Figures 1–4 )

Material examined. Holotype: ♂ (8.0 mm), Challenger Plateau, off the West coast, South Island, New Zealand, 40.83o S, 168.24o E, 17 April 1980, depth 1009 m, stn P927 ( NIWA 99811).

Paratypes: 2 ♂ (8.5 [dissected and drawn], 8.0 mm). 2 ♀ (ovig. 10 [dissected allotype], 8.5 mm), same data as holotype ( NIWA 32396). 1 ♀ (non-ovigerous 9.0 mm), North West Slope, off West coast, North Island, New Zealand, 38o S, 173.31o E, 14 March 1968, depth 1247–1250 m, stn E90–TAM ( NIWA 32414).

Other material: 1 ♂ (7.7 mm), South Lord Howe Rise, 36.92067o S, 167.5268o E, 30 May 2007, depth 1216 m, stn TAN0707/52 ( NIWA 31571). 1 ♂ (7.5 mm), Challenger Plateau, 39.54367o S, 169.7145o E, 4 June 2007, depth 634 m, stn TAN0707/93 ( NIWA 31574).

Description of male. Body 1.3 times as long as wide, widest at pereonite 2, dorsal surfaces sparsely punctate. Head anterolateral lobes weakly convex; dorsally without tubercles, posterior margin with low rounded median tubercle and pair of low lateral tubercles. Eye minute (less than 5% greatest width of head), elliptical (lenticular/ ovoid), ommatidia not distinct. Pereonites, pereonite 1 anterolateral margin continuously convex; dorsal surfaces with medial posterially directed prominent blunt tubercle on fused pereonites 5–7; small median tubercles on pereonites 2–4, and pleonite 1 and 2; posterolateral margins of pereonite 1 with row of small tubercules; pereonites 3 and 4 with single small tubercule at posterodistal corner. Coxae, distal margins weakly convex; coxa 4 not posteriorly extended; coxa 5 extending posteriorly along 0.3 of pleotelson length; coxa 6 extending to insertion of uropod, and along 0.8 of pleotelson length. Ventral coxal plate s 2–4 meeting midline, mesially elevated, plates 2–4 mesially with ridges forming X-shape, 5 and 6 incompletely separate, 7 separate; sternites 5–7 visible, fused.

Pleonites extending posteriorly along 0.8 of pleotelson lateral margin; pleonite 1 sternal plate with weak median ridge. Pleotelson 1.0 times as long as anterior width; dorsal surface with low median longitudinal carina; lateral carinae entirely carinate, pleotelson lateral margins convex, posterior margin converging to rounded caudomedial point, without distinct median excision.

Antennula peduncle article 2 1.8 times as long as wide; articles 3 and 4 2.6 times as long as article 2; article 3 7.8 times as long as wide; flagellum 2.8 times as long as peduncle articles 3 and 4, with 39 articles, extending to pereonite 4. Antenna peduncle article 4 5.8 times as long as wide, 2.9 times as long as article 3; article 5 1.1 times as long as article 4, 9 times as long as wide; antennal flagellum 1.5 times as long as peduncle article 5, with 16 articles, extending to posterior of pereonite 3 or posterior of pereonite 4.

Epistome with obtuse median point and median ventral projection. Mandible incisor even, without cusps. Left mandible lacinia mobilis 0.8 times as wide as incisor; palp article 2 with 20 distolateral biserrate setae, article 3 with 21 distolateral biserrate setae. Maxilla mesial lobe with 11 long, finely serrate setae; middle lobe with 2 long simple setae (terminal); lateral lobe with 2 distal simple setae. Maxilliped palp article 2 proximomesial margin with 6 setae, distomesial margin with 9 setae, lateral margin distally with 5 setae (continuously along margin); article 3 lateral margin with 3 setae, distal margin with 13 setae; endite distal margin RS simple.

Pereopod 1 propodus 2.2 times as long as wide, inferior margin with 48 robust setae; 24 wide RS finely pilose, 24 narrow RS distally bifid, with simple flagellum; dactylus with acute unguis. Pereopod 2 basis 4.8 times as long as greatest width; ischium 0.6 times as long as basis, ischium 3.1 times as long as wide; merus 0.5 times as long as ischium, merus 1.8 times as long as greatest width, inferior margin with 1 distal cluster of 4 setae, superior distal angle with 4 setae; carpus 0.6 times as long as ischium, 2.6 times as long as wide, inferior margin with 3 clusters of setae; propodus 0.6 times as long as ischium, 2.5 times as long as wide, inferior margin with distinct heel, palm weakly concave, inferolateral margin with 4 RS, inferomesial margin with 3 RS, inferior margin RS distally bifid, distally pilose, distal margin with 10 setae; dactylus 0.8 times as long as propodus, unguis blunt, with prominent secondary unguis. Pereopod 6 basis 4 times as long as greatest width; ischium 0.7 times as long as basis, ischium 3.5 times as long as wide, inferior margin with 1 cluster of setae, superior distal angle with 2 RS; merus 0.5 times as long as ischium, 2.2 times as long as wide, inferior margin with 4 clusters of setae, superior distal angle with 2 setae; carpus 0.8 times as long as ischium, 4.5 times as long as wide, inferior margin with 7 clusters of setae, superior distal angle with 7 setae; propodus 0.8 times as long as ischium, 7.6 times as long as wide, inferior margin with 7 clusters of setae, distal margin with 9 setae, inferior distal angle with 1 RS; dactylus 8 times as long as proximal width. Pereopod 7 similar to, but 0.8 times as long as pereopod 6. Setae on inferior margins of pereopods 4–7 finely plumose. Inferior margins of pereopods 2–7 setulose fringe weakly developed.

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

Pleopod 1 peduncle 1.9 times as long as wide, mesial margin with 3 coupling setae; exopod 1.7 times as long as wide, with 34 PMS; endopod 2.6 times as long as wide, 0.6 times as long as exopod, with 18 PMS. Pleopod 2 peduncle 1.2 times as long as wide, mesial margin with 2 coupling setae; exopod 1.7 times as long as wide, with 36 PMS; endopod 2.8 times as long as greatest width, lamellar part 3.1 times as long as wide, with 15 PMS; appendix masculina 4.1 times as long as endopod. Pleopod 3 exopod with 37 PMS, endopod with 23 PMS. Pleopod 4 exopod with complete transverse suture, endopod with complete transverse suture. Pleopod 5 exopod with complete transverse suture, endopod with complete transverse suture.

Uropods (rami + peduncle) 0.3 times as long as pleotelson, peduncle 0.8 times as long as endopod. Endopod 2.1 times as long as wide; distally broadly rounded. Exopod as long as endopod, 3 times as long as wide, distally broadly rounded.

Female. Similar to the male; ridges on ventral coxal plate 4 less raised than in males, no ridges on 5. Pereopods 1 and 2 similar to male pereopod 3. No sexual dimorphism of pereopod 7 or pleopod 3.

Size. Length: Males 7.5–8.5 mm (n= 5); females 9.0–10.0 mm (n=3).

Variation. The large triangular median nodule on fused pereonites 5-7 is always prominent, but varies in height and shape, with some being more ‘hooked’ than others.

Remarks. Myopiarolis tona sp. nov. can best be recognized by the head posterior margin with low rounded median tubercle and pair of lateral tubercles, small, low median tubercles present on pereonites 2–4 and 6, the large triangular median nodule on fused pereonites 5–7, and the coxae of pereonite 6 extend posteriorly to the insertion of the uropods. Myopiarolis tona sp. nov. is the only species of the genus with this ‘fin-shaped’ nodule. Myopiarolis tona is similar to M. koro Bruce, 2009 , M. lippa Bruce, 2009 , and M. novacaledoniae ( Poore and Brandt, 1997) in outline and pleotelson features, while the nodules on the posterior margin of the head are similar to M. norfanz Bruce, 2009 . In profile M. tona sp. nov. is most similar to M. carinata .

Distribution. Off western New Zealand: South Lord Howe Rise (634 m), Challenger Plateau (1009–1216 m) and off northwestern New Plymouth (1248 m).

Etymology. From the Maori word for nodule, referring to the prominent, posterior facing nodule on fused pereonites 5–7; noun in apposition.

Figures

FIGURE 1. Myopiarolis tona sp. nov., holotype (male, 8.0 mm): A, dorsal view. B, lateral view. Paratype (male, 8.5 mm): C, ventral view of head, pereonites, and pleonites (damaged area in grey). Female paratype (8.5 mm): D, ventral coxal plates, sternites and left oostegites. Male Paratype (8.5 mm): E, uropods (ventral view). F, antenna. G, antennula. Paratype (female, 10.0 mm): H, lateral view.

FIGURE 2. Myopiarolis tona sp. nov., male paratype (8.5 mm). A, maxilliped. B, left mandible, distal margin. C, right mandible, distal margin. D, maxillula. E, maxilla. F, mandible palp and detail of setae.

FIGURE 3. Myopiarolis tona sp. nov., male paratype (8.5 mm). A, pereopod 1, with details of palm setae and carpus. B, pereopod 2 with detail of propodus and carpus. C, pereopod 3 and detail of tip. D, pereopod 7 and detail of tip.

FIGURE 4. Myopiarolis tona sp. nov., male paratype (8.5 mm). A – C, D and E, pleopods 1 – 5, respectively.