Halacarsantia acuta, Shimomura, Michitaka & Bruce, Niel L., 2012

Shimomura, Michitaka & Bruce, Niel L., 2012, A new species of Halacarsantia Wolff, 1989 (Crustacea, Isopoda, Asellota, Santiidae) from Wistari Reef, southern Great Barrier Reef, Australia, ZooKeys 173, pp. 1-9 : 3-5

Halacarsantia acuta sp. n. Figs 13

Material examined.

Holotype. ♀ (0.83 mm, with 4 eggs), Wistari Reef, Great Barrier Reef, Australia, 23 November 2009, 23°27.257'S, 151°52.840'E, northern side of reef, rubble on bommie, 3 m, stn HI09-084F, coll. N. L. Bruce & K. Schnabel (MTQ W34048).

Paratype. 1♀ (0.83 mm), same data as holotype (MTQ W31550).

Description of the holotype female.

Body (Fig. 1A) 1.9 times as long as maximum width, with dark reddish brown pigment in patches. Head 1.4 times as broad as long, narrower than pereonite 1, with 1 robust seta on anterior part of eyes; frontal lobe broad and long, 0.32 times as wide as maximum width of head, with 6 long robust setae on anterior margin; lateral margins of head, each with 1 slender and 3 robust setae; posterior margin of head convex. Eyes each with 7 ommatidia. Pereonites laterally rounded; pereonites 1, 4 and 7 with 2 long robust setae near lateral margin on each side; pereonite 2 with 2 short slender setae on each side of lateral margins and 2 long robust setae near lateral margin on each side; pereonites 3, 5 and 6 with 1 short slender setae on each side of lateral margins and 3 robust setae near lateral margin on each side. Pereonites 1 to 3 increasing in length; pereonites 3 and 4 subequal in length; pereonites 5-7 subequal in length. Pereonites 1 to 3 increasing in width; pereonite 4 slightly narrower than pereonite 3; pereonites 4 to 7 decreasing in width. Coxal plates dorsally visible on all pereonites, laterally rounded; coxal plate of pereonite 1 with 1 short seta; coxal plates of pereonites 2 and 3 each with 1 robust seta; coxal plates of pereonites 4-6 each with 2 robust setae; coxal plate of pereonite 7 with 1 short seta. Pleotelson (Figs 1A, 3E, 3F) pyriform, about 1.3 times as long as wide, with 7 robust setae near dorsolateral margin on each side and 4 robust setae near ventrolateral margin on each side.

Antennula (Figs 1B, 1C) composed of 5 articles. Article 1 broadest, with 1 simple seta mediodistally and 1 broom seta laterodistally; article 2 slightly shorter than article 1, with 1 simple seta and 4 broom seta distally; article 3 with 1 simple seta mediodistally; article 4 as long as article 3, without setae; article 5 twice as long as article 4, with 3 simple setae, 1 broom seta and 1 aesthetasc apically.

Antenna (Fig. 1D): peduncle composed of 4 short stout and 2 long slender articles, and flagellum of 8 short slender articles. Article 1 with 1 simple seta laterodistally; article 2 without setae; article 3 with 1 simple seta mediodistally and 1 stout seta on lateral protrusion; article 4 with 3 simple setae mediodistally; article 5 shorter than articles 1-4 combined, with 1 simple and 1 biramous setae laterally and medially; article 6 longer and slender than article 5, with 1 lateral and 1 medial simple setae, and 3 simple and 2 broom setae; flagellar articles 1-7, each with 2 or 3 simple setae distally; flagellar article 8 with 6 simple setae apically.

Left mandible (Fig. 1E) palp article 1 with seta distally; article 2 longest, laterally with 2 setae; article 3 as long as article 1, with 2 apical setae and few short setae; molar process with 2 setae; lacinia mobilis with 2 teeth; setal row with 4 setae. Right mandible (Fig. 1F) palp article 1 with seta distally, article 2 longest, laterally with 2 setae, article 3 as long as article 1, with 2 apical setae and few short setae; incisor with 4 cusps, setal row with 4 setae; molar process stout, with 2 setae.

Maxilla 1 (Fig. 1G) with inner lobe bearing 4 apical and 2 medial setae; outer lobe with 11 irregular and 1 simple setae distally. Maxilla 2 (Fig. 1H) with inner lobe bearing 16 setae on margin; outer 2 lobes each with 4 apical setae.

Maxilliped (Fig. 1I) palp slender: article 1 shortest, with 1 seta mediodistally; article 2 about 1.9 times as long as article 1, with 1 medial seta; article 3 slightly longer than article 2, with 1 seta laterodistally and 2 setae medially; article 4 as long as article 3, with 1 seta laterodistally and 2 setae medially; article 5 narrowest, with 2 slender and 2 stout setae apically; endite broad, bearing 2 simple setae ventrally, with 8 pectinate setae distally, 1 simple and 2 fan-shaped setae on subdistal margin, and 2 coupling hooks medially; epipod lanceolate, moderately broad, with acute apex.

Pereopod 1 (Fig. 2A): basis the longest article, with short projection ventrally, and with 3 ventral and 1 dorsal setae; ischium 0.8 as long as basis, bearing 1 ventral and 1 dorsal setae; merus trapezoidal, with 4 ventral and 2 dorsal setae; carpus trapezoidal, 0.8 as long as merus, wider than merus, ventrally with 2 stout and 6 slender setae, dorsally with 1 slender seta; propodus ovate, with 8 ventral and 3 dorsal setae; dactylus shorter than propodus, with 1 curved unguis and 1 short accessory claw.

Pereopods 2-3 (Fig. 2B, C) subequal in shape and length; bases with 2-3 ventral and 1 dorsal setae; ischia as long as bases, with 0-1 ventral and 2 dorsal setae; meri as long as ischia, with 2 setae ventrally, 1-2 simple and 1 robust setae dorsodistally; carpi shorter than meri, with 3-4 simple, 1 broom and 5-7 robust setae; propodi shorter than carpi, with 3-5 simple and 1 robust setae; dactyli with 1 short setae, 1 curved unguis and 1 curved accessory claw. Pereopods 4-6 (Fig. 2 D–F) decreasing in length posteriorly; bases with 2 short and 1 long setae ventrally, and with 0-1 short seta dorsally; ischia with 0-1 short seta; meri with 2 short distal setae, and with 1-3 robust setae and row of short setae dorsodistally; carpi with 2-3 robust setae ventrally and 3-6 robust setae distally; propodi with 1-2 short setae and 0-1 robust seta; dactyli with 1 short seta, 1 curved unguis and 1 curved accessory claw. Pereopod 7: basis shorter than those of pereopods1-6, with 1 long and 2 short setae ventrally and 1 short seta dorsally; ischium with 1 dorsal and 1 ventral setae; merus with 2 short setae ventrodistally and 3 robust setae and row of spinules dorsodistally; carpus with 4 robust setae ventrally and 1 robust seta dorsodistally; propodus with 2 short setae; dactylus with 1 short seta, 1 curved unguis and 1 curved accessory claw.

Operculum (Fig. 3A) 1.2 times as broad as long, with 2 lateral, 2 subapical setae, and many fine marginal setae. Pleopod 3 (Fig. 3B) with endopod bearing 3 stout, plumose setae distally; exopod narrower than endopod, bearing 1 lateral, 1 apical long simple setae, and many fine setae on convex lateral margin. Pleopod 4 (Fig. 3C) with ovate endopod; exopod uniramous, narrow, with 1 plumose seta distally, and many fine setae on lateral margin. Pleopod 5 (Fig. 3D) ovate, uniramous, about 2.8 times as long as broad, without setae.

Remarks.

Halacarsantia acuta sp. n. may be distinguished from its congeners in having long robust setae on the pereonites. The body shape of Halacarsantia acuta is similar Halacarsantia kussakini Müller, 1992 from the Society Islands, French Polynesia (type locality), but H . acuta can be separated from Halacarsantia kussakini by the (those of Halacarsantia kussakini in parentheses): 3 robust setae on each side of the head (2 setae); antenna flagellum composed of 8 articles (11 articles); maxilliped epipod apically acute, without setae (apically blunt, with 2 slender setae); maxilliped endite broad (moderately narrow); and pereopod 1 basis with a conspicuous short projection (without conspicuous projections).

Etymology.

The species is named after the apically acute maxilliped epipod.