Hansenium hanseni (Nobili, 1906)

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 : 451-456

Hansenium hanseni (Nobili, 1906)

( Figures 3–6 )

Stenetrium Hanseni Nobili, 1906: 266 .—1907: 414, Pl. 3, fig. 3.

Stenetrium hanseni .—Nierstrasz 1941: 281.—Müller 1991a: 57, fig. 21–37.—Miller 1941: 311.—Serov and Wilson, 1995: 81. Hansenium hanseni . —Serov and Wilson 1995: 72.

Type locality: Viatape, Bora Bora, French Polynesia, 16°30.526'S, 151°45.101'W

Material examined. Neotype (here designated). 3 (3.4 mm), Bora Bora, fringing reef near Vaitape, Feb– March 1988, dead coral, 1 m (SMF 43367).

Other material. 3 #1 (3.5 mm), 3 #2 (3.5 mm), Ƥ #1 (ovig. 3.2 mm), 19 3 (2.8–3.4 mm), 13 Ƥ (ovig. 2.4–3.4 mm), same data as neotype (SMF43368). Not measured: 36 3, 26 Ƥ, 34 juveniles, same data as neotype (SMF 18624).

Additional material. 3 (3.3 mm), Mooréa, fore-reef near Cook’s Bay, 17.4761°S, 149.831°W, 7 November 2010, coral rubble, 10–11 m, coll. S. McKeon (MTQ W33526). 3 (mature 2.8 mm), Ƥ (ovig. 2.9; non-ovig. 2.9, 2.6 mm), juvenile (1.6 mm), Mooréa, Cooks Bay Hook, 17.4815°S, 149.8250°W, 11 November 2010, coral rubble and Halimeda , coll. C. Watson (MTQ W33634).

Description of male. Body length 3.7 as long as greatest width; pereonite 1 medial width 2.4 length; pleotelson length 1.0 width.

Cephalon length 0.6 width; lateral margins acute, sparsely setose; antennal spines acute; eyes with 18–21 ommatidia, ommatidia orange, arranged in two parallel rows.

Antennula length 1.1 cephalon width; article 1 length 1.9 width, mesial margin with 1 short penicillate seta, anterolateral margin with 1 large penicillate seta; article 2 length 1.5 width, mesial margin with 1 cluster of setae, 1 penicillate seta, anterolateral margin with 2 clusters of setae, 1 penicillate seta; article 3 length 2.1 width, medial margin with 2 clusters of setae, anterolateral margin with 2 clusters of setae; article 4 length 0.5 width, anterior margin with 2 short setae, 1 penicillate seta; flagellum with 8 articles, flagellar article 1 distinctly longer than other flagellum articles, length 2.7 flagellar article 2 length. Antennae length 1.1 total body length, lateral margin with cluster of 3 setae; article 2 length 0.63 width, anterior margin with 2 short setae, lateral margin with cluster of 3 setae; article 3 length 1.5 width, mesiodistal margin with 2 clusters setae, 1 seta posterior to squama; article 4 length 0.5 width, distal margin with 2 short setae, mesiodistal margin with cluster of 2 setae; articles 5–6 length 3.1, 7.4 width respectively; each flagellum article with a cluster of 4 anteriorly projecting setae, the cluster position serially repeating every 4 articles.

Mandible left spine row with 4 spines, right spine row with 11 spines; palp article 1 distolateral margin with 2 long setae; article 2 with submarginal row of 7 short serrate setae. Maxillula lateral lobe apex with 6 serrate setae; mesial lobe apex with 2 serrate setae. Maxilla mesial lobe mesial margin with 7 serrate setae. Maxilliped basis length 2.4 width, width 0.98 endite width; endite mesiodistal margin with 4 serrate setae, distal margin with 5 fan setae; palp article 2 length 0.9 basis width; epipod length 3.4 width, width 1.1 basis width, apex acute, mesial margin with 7 regularly spaced setae.

Pereopod 1 basis length 2.2 width, submarginal mesial ridge without setae. Ischium length 1.9 width; inferodistal margin with 3 short setae; superodistal margin not produced, setae absent; mediodistal margin with 8 long setae. Merus rectangular, length 1.6 width, length 3.0 as long as carpus; inferior margin densely covered with setae; inferodistal margin slightly produced; apex rounded; densely covered with long setae; superodistal margin not produced, with short setae. Carpus length 0.5 width; distal margin convex, short setae along margin length; carpal process length 2.3 width, extending to propodal palm articulation, curved, bladelike; inferior margin smooth, convex, sparsely setose, 1 row of stiff setae, 2 rows of long serrate setae; superior margin straight, setae regularly spaced. Propodus robust, length 1.4 width; inferior margin length 0.3 superior margin length, lightly setose, regularly spaced setae restricted to distal half of margin; superior margin sparsely setose, setae widely spaced, restricted to distal two-thirds of margin, superior mesial surface lightly covered with long, bi-denticulate setae; propodal palm oblique, margin with 1 medial tooth, short setae inserting between teeth, cluster of setae at articulation, terminal end with large, curved tooth. Dactylus 3.9 as long as basal width 1.3 propodal palm length, curved, distal margin sparsely setose, setae regularly spaced in clusters along entire length, opposing margin with regularly spaced short setae, mesial surface without setae. Pereopod 2 basis medial inferior margin with 1 stiff seta, superodistal 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, 1 short seta; carpus superodistal margin with 4 short and long setae, 1 penicillate seta, inferior margin with 4 flagellated RS setae, inferodistal margin with 1 RS, and 2 setae; propodus superior margin with regularly spaced setae, superodistal margin with 1 penicillate seta, 1 long seta, inferior margin with 4 flagellated RS. Pereopod 3 carpus inferior margin with 4 flagellated RS; propodus inferior margin with 3 flagellated RS. Pereopod 6 basis superior margin with 5 penicillate setae, inferior margin with 1 stiff seta; carpus inferior margin with 1 flagellated RS; propodus inferior margin with 3 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 0.7 width, lateral margins with 1 seta, posterior lobes without pair of RS, surface setae present; rami lateral margins with regular setae along distal half of margin, apex with clustered setae, ventral surface with setae. Pleopod 2 protopod length 3.3 width; lateral margin with 1–2 setae; endopod proximal segment length 0.4 protopod length, without setae; appendix masculina length 1.4 endopod proximal length, 0.7 protopod length, lateral margin with distal groove, apex mediodistal margin hardened, without interior pocket of setae, 1 anteriorly projecting distolateral spine, 1 cluster of short setae distal to spine, mesial margin with evenly spaced setae. Pleopod 3 endopod apex with 5 plumose setae. Pleopod 4 exopod apex with 9 plumose setae. Pleopod 5 apex with 5 plumose setae.

Uropods length 0.6 pleotelson length; protopod length 1.8 width; endopod length 1.7 protopod length, 2 latitudinal rows of sensillate setae, distal and sub-distal margins with 8 penicillate setae; exopod length 1.0 protopod length, 2 latitudinal rows of sensillate setae.

Female. Pereopod 1 basis length 2.4 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 2.5 times as long as wide, with one row of setae and one row of serrate setae; propodal palm length 1.5 times propodus proximal width, 4 teeth along margin, row of serrate setae present; dactylus length 3.5 width, length 1.0 propodal palm length, proximal margin with 10 denticulate setae.

Pleopod 2 length 1.5 width; lateral margins with 2–5 setae, anterior half of margins straight and tapering; apex notched, asymmetric, 1 seta on each lobe; ventral surface without setae.

Size. Adult males 2.9–3.5 mm (mean 3.1 mm, n=22); ovigerous females 2.4–3.3 mm (mean 2.9 mm, n=18). Largest specimen, male 3.5 mm (male topotype #1).

Variation. Müller (1991a) describes the pereopod 1 carpal process as having five teeth (serrations) on the inferodistal margin. Although most mature males possess five serrations, the serration count varies between 4–5 serrations in specimens examined.

Colour. The cephalon has a ‘butterfly-shaped’ pattern mesial to the eyes and a band along anterior margin of cephalon extending just medial of antennal teeth apex. Pereonites 1–4 with medial markings along anterior margins only. Pereonite 7 without pigmentation, pleotelson speckled across entire dorsal surface.

Remarks. Hansenium hanseni may be identified by the male pereopod 1 having a strongly produced, terminally acute, serrated carpal process and an elongate and quadrate merus. H. remocarpus differs from H. hanseni by the pereopod 1 carpal process being weakly serrated and a far shorter merus (1.6 longer than wide in H. remocarpus vs 2.0 in H. hanseni ).

Distribution. Bora Bora and Mooréa, Society Islands; ‘Laguna di Fakahina, Polinesia’ (Nobili 1906, 1907), Fakahina Atoll, Tuamotus (approximately 700 km East of Bora Bora).

Figures

FIGURE 3. Hansenium hanseni Nobili, 1906. A, B, male neotype (SMF 43367). A, dorsal view; B, dorsal view of cephalon; C – F, male (SMF 18625); C, antennula; D, antenna with enlargement of articles and squama; E, uropod; F, enlargement of antenna flagellum articles; G, female (SMF 43368), enlargement of antenna flagellum articles.

FIGURE 4. Hansenium hanseni Nobili. Male (SMF 43368). A, right mandible with palp; B, left mandible; C, left maxilla with enlargements of setal types; D, left maxilliped with enlargement of coupling hooks; E, detail of left maxilliped endite; F, left maxillula with detail of mesial lobe.

FIGURE 5. Hansenium hanseni Nobili. A, B, male neotype (SMF 43367): A, pereopod 1; B, detail of dactylus; C – F, male # 1: C, pereopod 2; D, pereopod 3; E, pereopod 6; F, pereopod 7, with enlargement of dactylus; G, H, female: G, pereopod 1; H, enlargement of dactylus of pereopod 1 (SMF 43368).

FIGURE 6. Hansenium hanseni Nobili. A – E, male # 1, A, pleopod 1; B, pleopod 2; C, pleopod 3; D, pleopod 4; E, pleopod 5; F, female, pleopod 2 (SMF 18624).