Makrokylindrus semiechinata n. sp.

(Figs. 37–38)

Material examined. Holotype: subadult female, NIWA 0 93172, TAN0705/251, 42.9958°S, 178.9957°E – 42.9910°S, 179.0052°E, 520–530 m, 24 April 2007. Paratypes: 1 subadult male (dissected), NIWA 0 93207, TAN0707/29, 38.6177°S, 168.9428°E – 38.6258°S, 168.9490°E, 480–482 m, 29 May 2007; 1 subadult female, NIWA 0 94876, TAN0707/29, 38.6177°S, 168.9428°E – 38.6258°S, 168.9490°E, 480–482 m, 29 May 2007. Nontype material: 13 specimens, NIWA 0 46230, TAN0705/136, 43.2903°S, 175.5522°W – 43.2933°S, 175.5630°W, 638–644, 15 April 2007; 3 specimens, NIWA 0 95004, TAN0705/24, 44.1208°S, 174.8432°E – 44.1242°S, 174.8448°E, 512–513 m, 4 April 2007; 1 specimen, NIWA 0 95005, TAN0705/251, 42.9958°S, 178.9957°E – 42.9910°S, 179.0052°E, 520–530 m, 24 April 2007; 4 specimens, NIWA 0 95006, TAN0705/127, 43.0650°S, 174.9325°W – 43.0732°S, 174.9348°W, 933–940 m, 13 April 2007.

Diagnosis. Females and subadult males. Carapace with small spines scattered on anterior half. Eyelobe narrow, without lenses. Pseudorostrum extending 0.2 times carapace length anterior of eyelobe. Telson post-anal 0.2 times total telson length, with 2–3 pairs lateral setae, several rows of fine hair-like setae dorsally at the proximal end of the post-anal section, shorter than uropod peduncles. Uropod endopod of 3 articles; uropod exopod much longer than endopod.

Adult male. Unknown.

Etymology. The species name semiechinata is a combination of the Latin semi meaning half, and echinata meaning spine, referring to the spines present only on the anterior half of the carapace.

Description. Subadult female holotype 6.4 mm, subadult male paratype 4.2 mm. Body (Figs. 37 A–B). Carapace with dorsal depression posteriorly. Pleon unornamented.

Subadult male paratype.

Antennule (Fig. 37 C) long, slender, article 1 longest, with few simple setae, article 2 with simple and pedunculate setae; article 3 shortest. Main flagellum of 3 articles, with 2 aesthetascs terminally; accessory flagellum of 2 articles, not as long as main flagellum article 1, with few simple setae.

Antenna not examined.

Mandibles (Fig. 37 D) navicular, lacinia mobilis with 2 cusps, with row of 6–7 microserrate setae medially.

Maxillule (Fig. 37 E) of 2 endites; palp with 2 short microserrate setae.

Maxilla (Fig. 37 F) of 3 endites, broad endite missing, narrow endites with microserrate setae.

Maxilliped 1 (Fig. 37 G) basis short and stout; dactylus small.

Maxilliped 2 (Fig. 37 H) ischium visible.

Maxilliped 3 (Fig. 38 A) 100:11:13:18:24:18; basis expand distolaterally with 4 plumose setae, with plumose setae medially.

Pereopod 1 (Fig. 38 B) 100:6:19:39:49:39; basis with plumose setae; merus with plumose setae; carpus and propodus with short simple setae; dactylus with long setae terminally.

Pereopod 2 (Fig. 38 C) 100:3:24:46:16:32; basis with plumose and simple setae; merus with several long plumose setae; carpus and propodus with short simple setae; dactylus terminal seta long; exopod missing.

Pereopod 3 (Fig. 38 D) 100:9:28:24:11:13; basis, ischium, and merus with simple and plumose setae; carpus with plumose and annulate setae; propodus with annulate seta; dactylus terminal seta shorter than subterminal seta.

Pereopod 4 (Fig. 38 E) 100:11:40:40:14:17; basis, ischium, merus with plumose setae; carpus with plumose and annulate setae; propodus with annulate seta; dactylus terminal seta shorter than subterminal seta.

Pereopod 5 (Fig. 38 F) 100:20:35:65:25:20; basis with simple and plumose setae; merus with plumose seta; carpus unarmed; propodus with annulate seta; dactylus seta longer than subterminal seta.

Telson (Fig. 38 G) 2.5 times pleonite 6 length; with ranks of fine hair-like setae proximally on post-anal part, with 1–2 setae with single setule laterally, terminal setae short and simple.

Uropods (Fig. 38 G) peduncles with setae with single setule medially, small simple setae laterally; endopod triarticulate, with few setae with single setule medially, pedunculate and simple setae laterally, terminal seta short and microserrate; exopod much longer than endopod, with many simple setae, terminal and lateral subterminal setae long and microserrate.

Distribution. Chatham Rise, Challenger Plateau, New Zealand, 480– 940 m.

Remarks. The most similar carapace is Diastylopsis senta Gerken, 2014 from Australia, with a similar pattern of scattered spines on the anterior half of the carapace. However, in D. senta the carapace spines increase in length anteriorly and the telson is much longer than the uropod peduncles, while in Makrokylindrus semiechinata the carapace spines are uniformly small and the telson is distinctly shorter than the uropod peduncles.

It is worth noting that the diagnoses of Diastylis, Leptostylis and Makrokylindrus have been recognized as insufficient for cleanly discriminating amongst these genera since at least Day (1980). In the context that one cannot cleanly discriminate between these genera based on the current definitions, and the definitions of these three genera have been expanded since Day (1980), an alternate generic placement within Diastylis could be argued for this species. It is placed in Makrokylindrus on the basis that the pre-anal portion of the telson is much longer than the post-anal section of the telson.