Expanathura collaris (Kensley)

Poore, Gary C. B., Lew, Helen M. & Ton, 2002, Expanathuridae (Crustacea: Isopoda) from the Australian region, Zootaxa 82, pp. 1-60 : 26-32

Expanathura collaris (Kensley) ( Figs 16–19 , 20 a)

Panathura collaris Kensley, 1979: 823 –827, figs 7–9.— Kensley & Poore, 1982: 635

Expanathura collaris .— Wägele, 1981: 89, 121–122.— Negoescu, 1999: 214 –220, figs 9–11.— Negoescu & Wägele, 1984: 118.— Negoescu & Brandt, 2002: 121 –129, figs 14–18.

Material examined.– Australia. New South Wales, Lord Howe I., between Comet Hole and Reef (31°33'S, 159°05'E), 2 m, assorted algae, some coral, AM P41456 (1 female, 3 slides); AM P41555 (1 submale, 2 slides); AM P41454 (3). Queensland. Heron I. (23°27'S, 151°55'E), intertidal, QM W7832 (1), W8089 (1), W8089 (1), W8758 (1), W16302 (1 female), W16308 (1 male, 1 juvenile), W16309 (2 females), W16310 (1 juvenile), W16311 (1 female). Britomart Reef (18°17'S, 146°38'E), 5–15 m, encrusting algae and coral rubble, NMV J17136 (1 juvenile); NMV J17143 (1 juvenile); J17149 (1 juvenile); J17127 (1 female); J17128 (1 female, 2 juveniles). Lizard I. (14°40'S, 145°28'E), NMV J9802, J17114 – J17120 , J17122 – J17126 J17129 , J17150 , J17152 , J1754 (39 specimens). Off Townsville, NMV J17121 (24), J17151 (2). Northern Territory. McCluer I. (11°6'S, 133°0'E), NMV J17131 (1 female, 1 juvenile, 1 manca); J17133 (5 females, 20 juveniles); J17145 (1 male, 1 juvenile); J17153 , (1, 2 slides); J17142 (2 mancas); J17138 (1 juvenile). New Year I. (10°54'S, 133°2'E), NMV J17132 (1 female, 23 juveniles); J17135 (2 juveniles, 1 manca); J17137 (1 female, 2 juveniles); J17144 (1 juvenile); J17147 (2 males); J17140 (1 juvenile). Oxley I., W side (11°0'S, 132°49'E), NMV J17134 (8 females, 13 juveniles); J17139 (1 female, 19 juveniles); J17141 (1 female); J17146 (1 male, 1 slide). Fannie Bay, W of East Point (11°24'S, 130°48'E), 8 m, mainly sponges, NMV J17148 (1 male).

Coral Sea. Mellish Reef (17°S, 156°E), back reef and lagoon, 6–10 m, QM W16300 (1 female carrying 2 mancas); NMV W16301 (1 juvenile); W16304 (2 females); W16305 (1). Chesterfield Reefs (19°52'S, 158°19'E), 0–12 m, QM W16297 (2 juveniles); W16298 (1 juvenile); W16298 (1 juvenile); W16303 (1 juvenile); W16306 (1 juvenile); W16307 (1 juvenile).

Description of juvenile, 2.6 mm, NMV J17154 : ( Figs 16 & 17 ). Head longer than wide, with prominent broad rostrum between bases of antennae 1, with 3 pairs of lateral setae; eyes small, anterolateral. Pereonites of equal width, 5 the longest and 7 0.2 length of pereonite 6. Pleonites 1–4 of approximately equal length, 5 twice as long, 1–5 about as long as pereonite 6, pleotelson as long as pereonite 6–pleonite 5; pleonites 5 and 6 each with dorsal submedian pair of setae. Telson base 0.6 width of widest point, three­quarters along; apex evenly rounded, with 2 pairs of dorsal setae and its apex with 7 setae on each side, starting from middle, second the longest, and third and sixth longer than others.

Head with dorsal U­shaped brown band and laterally pereonites 1–6 with prominent brown spot (may fade in preservative).

Antenna 1 peduncle with stout article 1, shorter and progressively narrower articles 2 and 3; flagellum shorter than last peduncle article, of short article 1 with pappose seta, articles 2 and 3 minute, last with 2 aesthetascs and 3 setae. Antenna 2 peduncle longer than antenna 1, articles 4 and 5 longer than wide; flagellum of 3 minute articles.

Mouthparts conically produced ventrally. Upper lip fused to epistome, ventrally with short notch. Mandible with produced simple incisor, lamina dentata denticulate, molar process obscure; palp article 2 longer than 1, with 2 distal setae, article 3 half as long as 2, with 4 short distal setae. Maxilla 1 with 1 seta on inner lobe; 4 teeth on outer lobe. Maxillipedal endite reaching to end of palp article 3, acute, with 1 mesial and 1 distal seta; palp articles 1–3 broad, article 2 with 1 mesial seta, article 3 longest and with 2 simple mesial setae and 1 lateral pectinate seta, article 4 tapering and with 2 mesial setae, article 5 short and with 4 apical setae; epipod rounded distally.

Pereopod 1 subchelate, with stout proximal articles; carpus cupping propodus, with 3 setae on posterior margin; propodus obliquely swollen, palm axial with 2 proximal teeth alternating with 2 short setae, another longer seta more distally, mesial face with 1 stout setae and 2 finer setae; dactylus closing on palm, unguis about one­quarter its length. Pereopod 2 more slender than first; merus cupping triangular carpus; carpus with weakly setose posterior margin; propodus moderately swollen, palm with weak proximal teeth, few palmar and mesial setae. Pereopod 3 similar to pereopod 2. Pereopods 4–6 similar; carpus triangular; carpus and propodus each with 2 posterior marginal short spiniform setae; dactylus curved, unguis one­third length. Pereopod 7 carpus more elongate than in more anterior pereopods, with 1 spiniform seta; propodus with 2 simple spiniform setae on posterior margin, plus 3 mesial­posterior and 2 anterodistal double­pectinate setae.

Pleopod 1 operculiform but scarcely thickened, not indurate, overlapping all other pleopods; endopod one­third as wide as exopod and shorter, distally setose; exopod 1.8 times as long as wide, marginally setose. Pleopods 2–5 about two­thirds as long as pleopod 1; endopods more rectangular and narrower than exopods, distally truncate and setose; exopods distally and laterally setose. Uropodal peduncle and endopod of similar size, reaching to end of telson; endopod about as wide as length in midline, distally and laterally setose; exopods meeting in midline, 1.6 times as long as wide, much wider anteriorly than posteriorly, with shallow marginal excavation, marginal setae well spaced.

Description of male, 2.6 mm, NMV J17116 : ( Fig. 18 ). Differs from juvenile in: Eyes grossly enlarged. Pleonites 1–5 of equal length, 1–4 with few short setae carpus with toothed flange; along posterior margins, 5 with marginal row of c. 40 plumose setae. Antenna 1 peduncle articles shortened and swollen; flagellum article 1 swollen, hemispherical, with numerous aesthetascs, articles 2 and 3 slender and with 2 aesthetascs each, articles 4–6 with setae only. Mandible incisor, lamina dentata and molar process obsolete. Maxilla 1 obsolete, without teeth. Maxillipedal endite obsolete. Pereopods generally narrower, Pereopod 1 propodus less swollen, palm with weak proximal teeth, mesial face with 1 stout seta plus 4 fine setae; dactylus narrower. Pereopod 7 propodus with 2 simple spiniform setae on posterior margin, plus 5 mesial­posterior and 2 anterodistal double­pectinate setae, all setae longer than in juvenile. Pleopod 2 with appendix masculina extending beyond endopod by about one­third its length, apically curved; exopod 2­articled.

Description of submale, 2.5 mm, NMV J17151 : ( Fig. 19 ). Eyes enlarged. Antenna 1 peduncle articles swollen; flagellum article 1 enlarged, with single bush seta, articles 2–4 short, 3 with 2 aesthetascs.

Ovigerous females, several specimens, up to 2.6 mm: Similar to juveniles except: Pleonite 5 with c. 40 marginal plumose setae (as in adult male). Oostegites on pereopods 2–5; carrying up to 4 ova or 2 mancas.

Size: Most to 2.6 mm, rarely to 3.5 mm.

Distribution: Fiji (type locality); Cook Is; Coral Sea, Moorea, Chesterfield and Mellish Reefs; Tasman Sea, Lord Howe I.; Papua New Guinea; Australia, Northern Territory, Queensland (shelf and Great Barrier Reef); mostly shallow coral reef environments.

Remarks: This is a widespread species in coral reef rubble of the south­eastern Pacific. The numerous specimens in museum collections, over 100, has enabled variability and sexual differentiation to be examined.

Expanathura collaris is very similar to E. haddae and E. macronesia but small and consistent differences distinguish them. Most obvious are the shape and setation of the telson, more evenly curved laterally in E. collaris than in the others ( Fig. 20 ). The terminal setae, seven pairs of which the second, third and sixth are longer than the others, are remarkably consistent. In E. haddae and E. macronesia the sixth seta is as long as its neighbours. Material from Aldabra, eastern Indian Ocean, resembles E. collaris but its systematic position is uncertain (see below). Occasional specimens from Australia differ from the pattern described: a 3.5 mm juvenile from Heron I. (QM W8089) possesses an extra long seta near the midpoint, and a juvenile from Lord Howe I. (AM P41454) possesses only three setae of different lengths lateral to the long third seta. Setation of the uropodal exopod is usually as figured but in a few specimens 1–2 extra setae occur on the posterodorsal margin.

Colour pattern of a U­shaped stripe dorsally on the head and lateral spots at the bases of pereopods 1–6 is apparent in most of the material (including that from Aldabra). Its absence in some specimens might be put down to loss in preservation.

Adult males and females differ from the more common undifferentiated juveniles in having a pronounced row of marginal plumose setae on pleonite 5. Males are further differentiated in enlargement of the eyes, elongation of the limbs, obsolescence of the mouthparts and the swollen antenna 1. The adult male antenna is attained in two instars, in the first the peduncle is swollen and in the second the proximal article of the flagellum supports numerous aesthetascs, a callynophore ( Lowry, 1986).

Kensley (1979) described the species but did not note the lateral pigment spots that are characteristic of most specimens. He also probably misinterpreted the structure of the male first antenna although his figure represents it fairly. His figure and mention of a "fringed scale distally on the terminal segment" of the maxilliped was not confirmed by our examination of a paratype but otherwise his description and figures agree with the Australian specimens. Negoescu (1999) redescribed and illustrated the species from Fijian material and Negoescu & Brandt (2002) described and illustrated in detail material from Papua New Guinea.

Figures

FIGURE 16. Expanathura collaris (Kensley, 1979). Juvenile, NMV J 17154. Scale = 1 mm.

FIGURE 17. Expanathura collaris (Kensley, 1979). Juvenile, NMV J 17154.

FIGURE 18. Expanathura collaris (Kensley, 1979). Male, NMV J 17116.

FIGURE 19. Expanathura collaris (Kensley, 1979). Submale, NMV J 17151.

FIGURE 20. Expanathura spp.: Telsons and right uropods. a, E. collaris (Kensley, 1979), juvenile, NMV J 17154. b, E. haddae (Kensley & Poore, 1982), paratype juvenile, NMV J 1709. c, E. macronesia (Kensley, 1980), paratype female, USNM 171724. d, E. sp., Aldabra NMV J 17155.