Machatrium thungku Bruce & Buxton, 2013, sp. nov.

Machatrium thungku sp. nov.

(Figures 11–14)

Material examined: Holotype. 3 (4.3 mm), Lizard Island region, Day Reef, 14.47119°S, 145.5297°E, 13 February 2009, outer reef front slope, coral rubble, 10 m, coll. M. Błażewicz-Paszkowycz (MTQ W31367). Paratypes. 3 (4.0 mm), 2 Ƥ (non-ovig. 4.2 juv. 2.7 mm), same data as holotype (MTQ W34000).

Description of male. Body length 4.7 as greatest width; pereonite 1 medial width 1.9 length; pleotelson length 1.2 width.

Cephalon length 0.6 width; lateral margins acute, sparsely setose; antennal spines rounded; eyes with 12–18 ommatidia, ommatidia dark brown, arranged in two parallel rows.

Antenna length 1.1 total body length; articles 5–6 length 4.4, 5 width respectively; each flagellum article with a cluster of 4 anteriorly projecting setae, the cluster position serially repeating every 4 articles.

Mandible right spine row with 8 spines; article 2 with submarginal row of 7 short serrate setae. Maxillula lateral lobe apex with 9 serrate setae; mesial lobe apex with 2 serrate setae. Maxilla mesial lobe mesial margin with 5 serrate setae. Maxilliped basis length 2.6 width, width 1.0 endite width; endite mesiodistal margin with 5 serrate setae, distal margin with 5 fan setae; palp article 2 length 0.8 basis width; epipod length 3.4 width, width 1.2 basis width, apex acute, mesial margin with 4 regularly spaced setae.

Pereopod 1 basis length 2.5 width, submarginal mesial ridge with regularly spaced setae along length. Ischium length 1.6 width; inferodistal margin with 3 short setae; superodistal margin produced, acute, densely covered with long setae; mediodistal margin with 3 long setae. Merus angular, length 0.7 width, length 1.1 carpus length; inferior margin densely covered with setae; inferodistal margin not produced; superodistal margin slightly produced, apex acute, densely covered with long setae. Carpus length 0.7 width; distal margin sinuous, without short setae; carpal process long, length 3.8 width, extending greater than two-thirds but not to propodal palm articulation, straight, spatulate; inferior margin smooth, straight, densely setose, with several rows of setae; superior margin concave with mesial submarginal extension, densely setose on extension. Propodus inferior half of article flattened, length 4.4 width; inferior margin length 0.7 superior margin length, lightly setose, regularly spaced setae restricted to distal half of margin; superior margin setae absent, superior mesial surface densely covered with long, bidenticulate setae; propodal palm with 5–6 medial teeth, row of long setae, row of short setae on each side of margin, cluster of setae at inflection, terminal end with short spine. Dactylus 4.3 times as long as basal width, length 1.0 propodal palm length, curved, distal margin setose, setae regularly spaced in clusters along entire length, opposing margin with regularly spaced rows of setae and serrate setae, mesial surface lightly setose. Pereopod 2 basis medial inferior margin with stiff seta absent, anterosuperior margin with 1 penicillate seta; ischium superior margin apex with 1 stiff seta; merus superodistal apex with 1 stiff seta, inferodistal margin with 2 long setae; carpus superodistal margin with 2 short and long setae, 1 penicillate seta, inferior margin with 4 flagellated RS, inferodistal margin with 1 RS, and 3 setae; propodus superior margin with regularly spaced setae, superodistal margin with 1 penicillate seta, 1 long seta, inferior margin with 4 flagellated RS. Pereopod 7 basis superior margin with 2 penicillate setae, inferior margin with 1 stiff seta; carpus inferior margin with 1 flagellated RS, propodus inferior margin with 3 flagellated RS.

Pleopod 1 protopod length 0.8 width, lateral margins with 1 seta, posterior lobes with pair of RS, surface setae absent; rami lateral margins with regular setae along distal half of margin, apex without clustering of setae, ventral surface without setae. Pleopod 2 protopod length 2.8 width; lateral margin with 1–2 setae; endopod proximal segment length 0.5 protopod length, without setae; appendix masculina length 1.4 endopod proximal length, 0.7 protopod length, lateral margin without distal groove, apex concave, depression fringed with setae, interior pocket with fine setae, 5 anteriorly projecting distolateral spines, mesial margin without setae. Pleopod 3 endopod apex with 4 plumose setae. Pleopod 4 exopod apex with 7 plumose setae.

Uropods length 0.5 pleotelson length.

Female. Pereopod 1 basis length 2.2 times as long as wide, mesial submarginal ridge with regular long setae; ischium superodistal process developed, acute; merus superodistal process developed, acute; carpus inferodistal process acute; propodus 2.6 times as long as wide, with 2 rows of setae, serrate setae absent; propodal palm length 1.7 times propodus proximal width, 7 teeth along margin, row of serrate setae absent; dactylus length 5.7 width, length 1.0 propodal palm length, proximal margin with 11 denticulate setae.

Pleopod 2 length 1.4 width; lateral margins with less than two setae, anterior half of margins slightly concave; apex notched, asymmetric, a seta on each lobe; ventral surface sparsely setose.

Size. Males 4.0– 4.3 mm, females 4.0– 4.2 mm.

Coloration. Freshly collected specimens possess dark to almost solid black dorsal pigmentation patterns. Cephalon with almost solid markings extending from anterior margin, encompassing the eyes to their posterolateral apex, without a thin band along the anterior margin. The pleotelson has a solid anterior margin band and two separate posteromedial bifurcated markings, similar to that of Hansenium monodi Nordenstam 1946 as illustrated by Kensley and Schotte (2002, fig. 15A). Juveniles have a dark, transverse band across the cephalon between the eyes, appearing like a ‘mask’.

Remarks. Machatrium thungku sp. nov. may be identified by the male pereopod 1 having a broad carpal blade that is widest distally and extends to just short of the palm; the process has a submarginal mesial blade, forming a V-shaped groove into which the inferior margin of the propodus fits; the palm has four or five short teeth. Females also have a distinct carpal lobe. The particularly dark coloration of this species is distinctive.

Distribution. Day Reef, Lizard Island group, Great Barrier Reef; 10 metres.

Etymology. The Aboriginal adjective ‘thungku’, part of the ‘sand beach’ language of the Kuuku Ya’u tribe, means black, in reference to the dark coloration of this species; noun in apposition.