Machatrium falcensis, Bruce, Niel L. & Buxton, Chad, 2013

Bruce, Niel L. & Buxton, Chad, 2013, Review of the marine isopod crustacean genus Hansenium Serov and Wilson, 1995 (Asellota: Stenetriidae) from tropical Australia and Papua New Guinea, with description of a new genus, Zootaxa 3664 (4), pp. 445-478 : 457-463

Machatrium falcensis sp. nov.

( Figures 7–10 )

Material examined: Holotype. 3 (5.0 mm), east of South Direction Island, southwestern reef slope at High Rock, 14.82428°S, 145.5527°E, 11 September 2010, coralline algae-covered coral rubble, 30 m, coll. S. Smith (MTQ W33805).

Paratypes. 3 (3.5 mm), 7 Ƥ (4 ovig. 3.8–4.6; non-ovig. 5.0, 3.5, 3.5 mm), 3 mancas (1.8–1.9 mm), same data as holotype (MTQ W33808). 3 (4.7 mm [dissected]), Ƥ (ovig. 4.6 m), Lizard Island, lagoon entrance from Bird Islet, 14.689°S, 145.4671°E, 19 April 2008, dead robust Acropora branches, 15 m, coll. M. Błażewicz-Paszkowycz (MTQ W33806). 3 (3.4 mm), Ƥ (ovig. 4.1 mm), Lizard Island, Granite Bluff, 14.64823°S, 145.44999°E, 17 April 2008, large coral rubble, 15 m, coll. M. Błażewicz-Paszkowycz (MTQ W33807). 2 3 (4.1, 3.3 mm), Ƥ (ovig. 3.3; non-ovig. 4.0 mm), juvenile (2.4 mm), Lizard Island, Granite Bluff, 14.64823°S, 145.44999°E, 17 April 2008, coral rubble in depression on coral reef, 15 m, coll. M. Błażewicz-Paszkowycz (MTQ W14061). 6 3 (3.3–5.5 mm), 2 Ƥ (ovig. 4.0; non-ovig. 3.0 mm), 2 juv. (3.4, 2.0 mm), McGillivray Reef, 14.6583°S, 145.4917°E, 29 August 2010, coral rubble, 15 m, coll. CB (MTQ W32591). 2 3 (4.0, 4.3 mm North Direction Island, 14.7511°S, 145.5126°E, 3 September 2010, coral rubble, 28 m, coll CB (MTQ W32771, W32772).

Character Pseudojaniridae Hansenium Machatrium gen. nov. Stenetrium 1. Antenna 2, article 1 without lateral spine without lateral without lateral spine with lateral spine

spine

Description of male. Body length 4.3 greatest width; pereonite 1 medial width 2.9 length; pleotelson length 1 width.

Cephalon length 0.6 width; lateral margins acute, sparsely setose; antennal spines acute; eyes with 14–16 ommatidia, ommatidia pale brown, arranged in two parallel rows.

Antennula length 1.1 cephalon width; article 1 length 1.9 width, mesial margin with 6 short penicillate setae, anterolateral margin with 1 large penicillate seta; article 2 length 2.1 width, mesial margin with 1 cluster of setae, 1 penicillate seta, anterolateral margin with 1 cluster of setae, 1 penicillate seta; article 3 length 2.4 width, medial margin with 1 cluster of setae, anterolateral margin with 1 cluster of setae; article 4 length 0.4 width, anterior margin with 2 short setae, 1 penicillate seta; flagellum with 15 articles, flagellar article 1 distinctly longer than other articles, length 2.1 flagellar article 2 length. Antennae length 1.0 total body length; articles 5–6 length 7.2, 9.5 width respectively; each flagellum article with a cluster of 3–4 anteriorly projecting setae, the cluster position serially repeating every 4 articles.

Mandible left spine row with 4 spines, right spine row with 8 spines; palp article 1 distolateral margin with 1 long seta; article 2 with submarginal row of 7 short serrate setae. Maxillula lateral lobe apex with 10 serrate setae; mesial lobe apex with 2 serrate setae. Maxilla mesial lobe mesial margin with 8 serrate setae. Maxilliped basis length 2.3 width, width 0.92 endite width; endite mesiodistal margin with 6 serrate setae, distal margin with 5 fan setae; palp article 2 length 0.8 basis width; epipod length 3.1 width, width 1.2 basis width, apex acute, mesial margin with 6 regularly spaced setae.

Pereopod 1 basis length 3.9 width, submarginal mesial ridge with regularly spaced setae along length. Ischium length 1.8 width; inferodistal margin with 1 short seta; superodistal margin strongly produced, acute, densely covered with long setae; mediodistal margin with 6 long setae. Merus angular, length 1.0 width, length 1.2 carpus length; inferior margin lightly covered with setae; inferodistal margin not produced; superodistal margin strongly produced, apex acute, densely covered with long setae. Carpus length 0.8 width; distal margin convex, short setae along margin length; carpal process long, length 4.2 width, extending about halfway along propodal palm, curved, spatulate; inferior margin smooth, convex, densely setose, 1 row of stiff setae, 2 rows of long serrate setae; superior margin slightly concave, setae regularly spaced. Propodus inferior half of article flattened, length 3.7 width; inferior margin length 0.7 superior margin length, lightly setose, regularly spaced setae along entire length; superior margin setose, setae regularly spaced, restricted to distal two-thirds of margin, superior mesial surface densely covered with long, bi-denticulate setae; propodal palm with 3 medial teeth, row of long setae, row of short setae on each side of margin, cluster of setae at articulation, terminal end with single RS. Dactylus width 4.7 times as long as basal width, length 1.05 propodal palm length, curved, distal margin setose, setae widely spaced along entire length, opposing margin with regularly spaced rows of setae and serrate setae, mesial surface densely setose. Pereopod 2 basis medial inferior margin with stiff seta absent, anterosuperior margin with 3 penicillate setae; ischium superior margin apex with 1 stiff seta; merus superodistal apex with 1 stiff seta, inferodistal margin with 1 long seta, 2 short setae; carpus superodistal margin with 4 short and long setae, 1 penicillate seta, inferior margin with 5 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 5 flagellated RS. Pereopod 7 basis superior margin with 1 penicillate seta, inferior margin with 1 stiff seta; carpus inferior margin with 2 flagellated RS, propodus inferior margin with 5 flagellated RS.

Pleopod 1 protopod length 0.7 width, lateral margins with more than 1 seta, posterior lobes with pair of RS, surface setae absent; rami lateral margins with regular setae along distal two-thirds of margin, apex with clustered setae, ventral surface with setae. Pleopod 2 protopod length 2.8 width; lateral margin with greater than 2 setae; endopod proximal segment length 0.5 protopod length, without setae; appendix masculina length 1.5 endopod proximal length, 0.8 protopod length, lateral margin without distal groove, apex concave, depression fringed with setae, interior pocket present with fine setae, 2 anteriorly projecting distolateral spines, mesial margin without setae. Pleopod 3 endopod apex with 5 plumose setae. Pleopod 4 exopod apex with 9 plumose setae. Pleopod 5 apex with 4 plumose setae.

Uropods length 0.6 pleotelson length; protopod length 2.9 width; endopod length 1.0 protopod length, 2 latitudinal rows of sensillate setae, distal and sub-distal margins with 7 penicillate setae; exopod length 0.7 protopod length, 2 latitudinal rows of sensillate setae.

Female. Pereopod 1 basis length 3.3 times as long as wide, mesial submarginal ridge with regular short setae; ischium superodistal process developed, acute; merus superodistal process developed, acute; carpus inferodistal process rounded; propodus 3.7 times as long as wide, with one row of setae and one row of serrate setae; propodal palm length 1.8 times propodus proximal width, 4 teeth along margin, row of serrate setae present; dactylus length 3.8 width, length 1.0 propodal palm length, proximal margin with 11 denticulate setae.

Pleopod 2 length 1.4 width; lateral margins with 6 or more setae, anterior half of margins slightly concave; apex pointed, without setae; ventral surface without setae.

Size. Largest specimens: male 5.0 mm (holotype), female 5.0 mm (topotype). Adult males 3.3–5.0 mm (mean 4.07, n=8); ovigerous females 3.3–4.6 mm (mean 3.9 mm, n= 8).

Coloration. Eyes pale brown, cephalon with thin, solid line along anterior margin, two distinct pigmentation spots mesial to the eyes extending from anterior margin to eye mesial curvature, pigmentation on pereonites 1–4 on both anterior and posterior margins, pleotelson with a light ‘reticulated pattern (as opposed to simple spotting) across entire dorsal surface, this pattern visible on juveniles and mancas.

Remarks. Machatrium falcensis sp. nov. can be identified by the inferior propodal margin of male pereopod 1 abruptly narrowing proximally, giving a ‘hatchet-like’ appearance to the propodus; the carpal process is narrow (4.2 as along as width) and curved; and the propodal palm has three teeth. M. falcensis has relatively long antennula with more than 10 flagellar articles.

Distribution. Lizard Island and Bird Islet, Lizard Island Group and High Rock, east of South Direction Island; at depths of 15 to 30 metres.

Etymology. Derived from the Latin ‘falc’ meaning sickle and ‘ensis’ meaning sword, alluding to the carpal process on pereopod 1.

Figures

FIGURE 7. Machatrium falcensis sp. nov. Male holotype (MTQ W 33805). A, dorsal view; B, dorsal view of cephalon; C, antennula with detail of marginal setae; D, antenna flagellum articles; E, uropod.

FIGURE 8. Machatrium falcensis sp. nov. Male paratype (MTQ W 33806). A, right mandible; B, maxillula, with detail of mesial lobe; C, maxilliped; D, maxilliped endite; E, maxilla.

FIGURE 9. Machatrium falcensis sp. nov. A, B, male holotype (MTQ W 33805), pereopod 1; B, enlargement of pereopod 1 dactylus; C, D, male paratype (MTQ W 33806): C, pereopod 2; D, pereopod 7; E, F, female paratype (MTQ W 33806): E, pereopod 1; F, enlargement of pereopod 1 dactylus.

FIGURE 10. Machatrium falcensis sp. nov. A – E, male paratype (MTQ W 33806), A, pleopod 1, dorsal view; B, pleopod 2; C, pleopod 3; D, pleopod 4 with enlargement of plumose seta; E, pleopod 5; F, female paratype (MTQ W 33806), pleopod 2.