Caecoserolis carinata, Bruce, Niel L., 2008

Bruce, Niel L., 2008, Two new deep­water species of Caecoserolis Wägele, 1994 (Isopoda, Sphaeromatidea, Serolidae) from off North Island, New Zealand *, Zootaxa 1866, pp. 453-466 : 455-459

Caecoserolis carinata sp. nov. ( Figs 1–3 )

Material. All Tasman Sea, New Zealand.

Holotype: ď (19.8 mm), New Caledonia Trough, 34.5250 S, 166.3500 E, 23 Sep 1982, stn. U195, 2930 m ( NIWA 27939).

Paratypes: 2 ď (17.0, 19.4 [pre­dissected] mm), Ψ (ovig. 23.3 mm), plus two heads and one body piece, same data as holotype ( NIWA 27534). 2 ď (17.3, imm 13.6 mm), New Caledonia Trough, 35.5850 S, 160.9517 E, 27 Sep 1982, stn. U0200, 3180–3184 m ( NIWA 27533).

Description. Body 1.3 as long as wide, widest at coxae 3, dorsal surfaces coarsely pitted. Head anterolateral lobes weakly convex, anterior submarginal 'ridge' entire; dorsally without tubercles, posterior margin with prominent blunt median tubercle. Eyes minute (less than 5% greatest width of head), elliptical (lenticular/ ovoid), ommatidia not distinct. Pereonites 5–7 fused mid­dorsally; pereonite 1 anterolateral margin continuously convex; dorsally with median tubercle on all pereonites and pleonites. Coxae of pereonites 2–4 articulated, with dorsal sutures, distal margins weakly convex; coxae 4 extending to mid­pleonite 2; 5 extending posteriorly along 0.2 of pleotelson length; 6 extending to between posterior of uropods and pleotelson posterior margin, and along 0.7 of pleotelson length. Ventral coxal plate s 2–4 mesially strongly punctate. Pleonites extending posteriorly along 0.6 pleotelson lateral margin; pleonite 1 sternal plates 3­cornered, with acute median point, sternal plate 1 with median ridge and 2 sub­median depressions. Pleotelson 1.0 as long as anterior width, dorsal surface with median longitudinal carina, with paired sublateral carinae; lateral margins weakly sinuate, posterior margin converging to angled caudomedial point, without distinct median excision. Antennule peduncle article 2 1.9 as long as wide; articles 3 and 4 2.7 as long as article 2; article 3 10.5 as long as wide; flagellum 2.4 as long as peduncle articles 3 and 4, with ~58 articles, extending to pereonite 5. Antenna peduncle article 4 5.9 as long as wide, 3.1 as long as article 3; article 5 1.2 as long as article 4, 8.6 as long as wide; antennal flagellum 1.1 as long as peduncle article 5, with ~16 articles, extending to posterior of pereonite 4.

Epistome with obtuse median point. Mandible incisor with single posterior cusp, left mandible lacinia mobilis 0.8 as wide as incisor, right mandible lacinia mobilis distally multicuspid, mandibular spine simple. Maxilla mesial lobe with 12 long, finely serrate setae; middle lobe with 5 long simple setae (1 mesial, 4 terminal); lateral lobe with 2 distal simple setae. Maxilliped palp article 2 proximomesial margin with 6 setae, distomesial margin with 146 setae, lateral margin distally with 2 setae; article 3 lateral margin with 5 setae, distal margin with 12 setae; endite distal margin RS simple.

Pereopod 1 carpus RS simple; propodus 2.1 as long as wide, inferior margin with ~66 robust setae; wide RS with serrate margins, narrow RS distally bifid, with simple flagellum; dactylus with acute unguis. Pereopod 2 basis 5.0 as long as wide; 0.7 as long as basis, ischium 3.5 as long as wide; merus 0.5 as long as ischium, 2.0 as long as wide, inferior margin with 2 clusters of setae (as 1 and 3), superior distal angle with 1 seta; carpus 0.5 as long as ischium, 2.3 as long as wide, inferior margin with 1 cluster of setae (as row of 10); propodus 0.7 as long as ischium, 2.2 as long as wide, inferior margin with indistinct heel, palm weakly concave, inferolateral margin with 3 RS (and 5 setae), inferomesial margin with 6 RS (and 6 setae), inferior margin RS simple, blunt, distally pilose, distal margin with ~10 setae; unguis simple, slender. Pereopod 6 basis 3.9 as long as greatest width; ischium 0.7 as long as basis, 3.8 as long as wide, inferior margin with 1 cluster of setae (2), superior distal angle with 0 robust setae; merus 0.5 as long as ischium, 2.5 as long as wide, inferior margin with 3 clusters of setae (as 1, 1, and 3), superior distal angle with 0 RS; carpus 0.6 as long as ischium, 3.0 as long as wide, inferior margin with 7 clusters of setae (as 2, 2, 1, 4, 5, 7 and 6), superior distal angle with 3 setae; propodus 0.5 as long as ischium, 3.0 as long as wide, inferior margin with 6 clusters of setae (as 1, 1, 2, 3, 4, 3), distal margin with ~14 setae, inferior distal angle with 1 RS; dactylus 5.5 as long as proximal width. Pereopod 7 similar to, but 0.9 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 mutually adjacent, penes opening flush with surface of sternite 7.

Pleopod 1 peduncle 1.7 as long as wide, mesial margin with 3 coupling setae; exopod 1.9 as long as wide, with 42 PMS; endopod 2.2 as long as wide, 0.7 as long as exopod, with 26 PMS. Pleopod 2 peduncle 1.7 as long as wide, mesial margin with 2 coupling setae; exopod 1.5 as long as wide, with 42 PMS; endopod 3.3 as long as greatest width, lamellar part 4.3 as long as wide, with 26 PMS; appendix masculina greater than 2.8 as long (tips broken) as endopod. Pleopod 3 exopod with 52 PMS, endopod with 32 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 as long as pleotelson, peduncle 0.7 as long as endopod. Endopod 3.0 as long as wide; distally broadly rounded. Exopod 0.7 as long as endopod, 2.8 as long as wide, distally broadly rounded.

Size: Adult males 17.0 to 19.8 mm, females to 23.3 mm.

Colour: Brown, narrow pale bands on dorsal somites and coxae.

Va r ia ti o n: Dorsal fusion of pereonites 5–7: in the holotype the suture line is indistinct between 5 and 6, in the 17.3 mm male (NIWA 27533) all suture lines are evident; in all others both suture lines indistinct to absent. Extent of coxae 6: in all specimens coxae 6 extend to about the point of the uropod peduncle. Robust setae of pereopod 2: variation could not be reliably assessed as no male had both pereopods 2, and many setae were missing; indications suggest that some variation is present.

The relative size of pereopod 7 in relation to pereopod 6 appears to increase with increasing size. In the two largest specimens pereopods 6 and 7 are similar in appearance, with pereopod 7 just a little shorter (0.9) than pereopod 6. In smaller specimens, including mature males, pereopod 7 is weakly pigmented, less setose and evidently shorter (0.8) than pereopod 6.

Remarks. Caecoserolis carinata sp. nov. can be readily identified and distinguished from all other species in the genus by the presence of a distinct median nodule on the posterior margins of the head, pereonites 2–4 and 7 and pleonite 1, with an indistinct nodule on each of the remaining segments; these nodules giving the appearance of an articulating longitudinal median ridge. Other characters that support identification of this species are the large size for the genus (approximately 2 cm body length); long antennule and antennal flagellae extending to pereonites 4 and 5 respectively; distinct lateral and median carinae on dorsum of pleotelson; coxae 6 not strongly produced, extending to position of uropodal peduncle; coarsely pitted dorsal surfaces, including coxal plates medially; and a relatively prominent rostrum.

One character is inconsistent with the other species of the genus. The maxilla middle lobe has 5 setae rather than the more usual 2.

Etymology. Derived from the Latin carina (‘keel­shaped ridge or structure’), alluding to the longitudinal row of median tubercles giving a keel­like appearance to the dorsum.

Distribution. Southern New Caledonia Trough, at depths of 2930–3184 m.

Figures

FIGURE 1. Caecoserolis carinata sp. nov. A – E holotype, remainder ♂ paratype 19.4 mm, NIWA 27534. A, dorsal view; B, lateral view; C, anterior margin, pereonite 1; D, frons; E, pereonal and pleonal sternites; F, antenna; G, antenna, base of peduncular article 2; H, antennule; I, right mandible apex; J, left mandible apex; K, maxillule; L, maxilla; M, maxilliped.

FIGURE 2. Caecoserolis carinata sp. nov. Paratype ɗ 19.4 mm, NIWA 27534. A, pereopod 1; B, pereopod 1, carpal setae; C, pereopod 1, propodal setae; D, propodus and dactylus; E, pereopod 2, propodal robust seta; F, pereopod 2; G, pereopod 6; H, pereopod 7; I, pereopod 6, distal articles; K, mandibular palp, article 3.

FIGURE 3. Caecoserolis carinata sp. nov. Paratype ɗ 19.4 mm, NIWA 27534; G, holotype. A – F, pleopods 1 – 5 (D and E endopod and exopod of 4); G, uropods, ventral view; H, pleopod 2 endopod, dorsal view; I, ventral view, coxae 2 – 4; J, cuticle, dorsal pitting on coxae 4 and 5.