Diastylis implanus Gerken, 2015, n. sp.

Diastylis implanus n. sp.

(Figs. 18–20)

Material examined. Holotype: adult male, NIWA 0 93194, TAN0707/139, 39.6373°S, 172.1532°E – 39.6457°S, 172.1522°E, 264–266 m, 7 June 2007. Paratypes: ovigerous female (dissected), NIWA 0 93211, TAN0707/139, 39.6373°S, 172.1532°E – 39.6457°S, 172.1522°E, 264–266 m, 7 June 2007; adult male (dissected), NIWA 0 94978, TAN0707/139, 39.6373°S, 172.1532°E – 39.6457°S, 172.1522°E, 264–266 m, 7 June 2007. Non-type material: 2 adult males, NIWA 0 94978, TAN0707/139, 39.6373°S, 172.1532°E – 39.6457°S, 172.1522°E, 264–266 m, 7 June 2007.

Diagnosis. Female and subadult male. Carapace elongate, with single partial ridge, strongly rugose; ventral margin smooth; antennal notch oblique. Eyelobe without lenses. Pseudorostrum acute, 0.16 times carapace length anterior of eyelobe. Antennule article 2 shorter than article 3. Maxilliped 3 ischium not produced. Pereopod 1 basis ischium merus together shorter than carpus propodus dactylus together, carpus shorter than propodus, propodus shorter than dactylus. Pereopod 2 carpus 2.5 times propodus length. Pereopods 3–4 with rudimentary exopods in female. Telson with 5 lateral setae, more than 0.5 times length of uropod peduncles.

Adult male. Carapace similar to female. Antennule with brush of setae. Telson produced dorsally, with 4–5 lateral setae.

Etymology. From the Latin implanus meaning uneven, in reference to the rugose surface of the carapace.

Description. Adult male holotype 4.4 mm, adult male paratype 4.6 mm. Body (Figs. 18 A–B). Carapace rugosities short, not connected into longer ridges. Pereonite 5 produced bluntly posteriorly. Pleon unornamented.

Antennule (Fig. 19 A) article 1 longest, with plumose and simple setae; article 2 with few simple setae; article 3 shortest, unarmed. Main flagellum of 6 articles, article 1 expanded with many simple setae, with 2 aesthetascs terminally; accessory flagellum of 3 articles, extending past distal border of main flagellum article 3, with 2 long simple setae terminally.

Antenna (Fig. 19 B) peduncle of 5 articles, article 1 and 2 with pappose seta each, article 5 with small ranks of short setae; flagellum extending past posterior border of pleonite 6.

Mandibles–maxilliped 3 not examined.

Pereopod 1 (Fig. 19 C) missing after basis; basis with many plumose setae; exopod basal article more than 4 times as wide as flagellum.

Pereopod 2 (Fig. 19 D) 100:6:26:50:18:28; basis produced as strong spine distally, with plumose setae; merus with long plumose setae; dactylus with simple setae; exopod subequal to basis, basal article 4 times as wide as flagellum.

Pereopod 3 (Fig. 19 E) 100:8:26:16:10:8; basis with plumose, pappose and pedunculate setae; ischium with plumose setae; merus with simple setae; carpus with simple and annulate setae; propodus with annulate seta; dactylus terminal seta long and simple; exopod as long as basis, basal article 3 times as wide as flagellum.

Pereopod 4 (Fig. 19 F) 100:9:28:19:9:9; basis with plumose and pappose setae; ischium and merus with simple setae; carpus with simple and annulate setae; propodus with annulate seta; dactylus terminal seta long and simple; exopod subequal to basis, basal article 3 times as wide as flagellum.

Pereopod 5 (Fig. 19 G) 100:21:42:50:17:17; basis with plumose setae; ischium and merus with simple setae; carpus and propodus with simple and annulate setae; dactylus terminal seta long and simple.

Pleopods (Fig. 19 H) endopod longer than exopod, basal article stout, with moderately long plumose setae.

Telson (Fig. 19 I) 2.7 times length of pleonite 6; with 4–5 simple setae laterally, terminal setae broken.

Uropods (Fig. 19 I) peduncles with many short microserrate setae medially; exopod triarticulate, with short microserrate setae medially, article 3 longest, terminal seta short and simple; exopod shorter than endopod, with simple setae, terminal seta long.

Ovigerous female paratype 4.3 mm.

Body (Figs. 18 C–D). Carapace more rounded than in male; pseudorostrum more acute than in male. Pereonite 5 not produced posteriorly. Pleon unornamented.

Antennule (Fig. 20 A) article 1 with pappose and simple setae; article 2 with plumose and simple setae; article 3 longest, with simple setae. Main flagellum of 3 articles, with 2 aesthetascs; accessory flagellum of 1 article, more than half length of main flagellum article 1, with short simple setae.

Antenna (Fig. 20 A) of 2 articles, with pappose seta.

Mandibles (Fig. 20 B) navicular, lacinia mobilis with 3 cusps, with row of 10–11 microserrate setae medially.

Maxillule (Fig. 20 C) with 2 endites; palp with 2 short simple setae.

Maxilla (Fig. 20 D) with 3 endites; broad endite medial row of setae pedunculate; narrow endites long, with simple setae.

Maxilliped 1 (Fig. 20 E) dactylus slender.

Maxilliped 2 (Fig. 20 F) ischium visible.

Maxilliped 3 (Fig. 20 G) 100:5:9:14:18:12; basis expanded distolaterally, with 5 plumose setae, medial marting with plumose setae; ischium and merus broad.

Pereopod 1 (Fig. 20 H) 100:13:16:63:71:78; very long; basis with many plumose setae; carpus, propodus and dactylus with short simple setae.

Pereopod 2 (Fig. 20 I) 100:3:23:51:21:33; basis margin with few strong spines, many long plumose setae; ischium unarmed; merus with long plumose setae; carpus and propodus with short simple setae; dactylus with long simple setae; exopod longer than basis.

Pereopod 3–4 not examined, broken.

Pereopod 5 (Fig. 20 J) 100:18:45:41:23:23; basis to merus with short simple setae; carpus with stout and small simple setae and pedunculate seta; propodus with stout simple seta; dactylus terminal seta long and simple.

Telson (Fig. 20 K) 2.0 times length of pleonite 6; with 5 setae with single setule laterally, terminal setae with single setule.

Uropods (Fig. 20 K) peduncles with many short setae with single setule; endopod triarticulate, with setae with single setule medially, terminal seta short with single setule; exopod subequal to endopod, with simple setae, terminal seta long.

Distribution. Challenger Plateau, New Zealand, 264– 266 m.

Remarks. Within the New Zealand fauna, the rugose carapace of D. implanus is unique.