Metapontius walteri, Johnsson, Rodrigo & Neves, Elizabeth G., 2005

Johnsson, Rodrigo & Neves, Elizabeth G., 2005, A revision of Metapontius (Siphonostomatoida: Artotrogidae) with the description of a new species associated with an octocoral from Eniwetok Atoll, Marshall Islands (USA), Zootaxa 1035, pp. 51-59 : 53-57

Metapontius walteri sp. nov.

Figures 1–3

Material examined.— Holotype: female, associated with the octocoral, Pachyclavularia violacea , from 2 m depth, on the western side of reef, at northern end of David, Eniwetok Atoll, Marshall Islands, USA, 29 June 1969, coll. Dr. A.G. Humes. Holotype deposited in the National Museum of Natural History (Smithsonian Institution) reg. no. USNM 1074640.

Description of female. Body length (excluding caudal setae) 1210 µm, greatest body width 775 µm, body length 1.6 times width. Body shape cyclopiform (fig. 1a), with sensillae covering prosome, cephalosome not imbricate. Cephalosome and pedigerous somites 2 and 3 with epimera pointed. Pedigerous somite 4 with epimera rounded. Prosome length:width ratio, 1.2:1. Ratio of prosome length to urosome, 3:1.

Urosome 5­segmented. Genital double­somite (fig. 1b) 134 x 237 µm, length:width ratio, 0.6:1, area of genital aperture projected laterally and armed with smooth seta. Three abdominal somites, all wider than long (56 x 113 µm; 31 x 95 µm; 61 x 100 µm), length:width ratios, 0.5:1, 0.3:1 and 0.6:1, respectively. Caudal rami 31 x 43 µm, width 1.4 times length, with row of setules on inner margin and armed with 6 setae. Seta I absent, setae IV and V broken. Length of setae II, III, VI, and VII; 68, 137, 174, and 105 µm, respectively; all plumose.

Antennule (fig. 1c) 280 µm long (not including setae) and 8­segmented. Length of segments measured along their posterior margins: 30, 75, 24, 15, 29, 16, 29, and 63 µm, respectively. Segmental homologies and setation as follows. Roman numerals indicate the original segments followed by the number of setae in Arabic (Huys & Boxshall 1991): I­1; II­VIII­8; IX­XIII­5; XIV­2; XV­XVI­1; XVII­XVIII­1; XIX­XX­ 1; XXI­XXVIII­6+ae. All setae smooth. Aesthetasc on segment XXI 105 µm long. Antenna (fig. 1d) 150 µm long (including distal seta), with basis 38 µm long. Endopod 2­segmented; first segment 17 µm long, unarmed; second segment 35 µm long with 3 smooth setae, 1 medially placed and 2 distal, none modified as claw. Exopod 1­segmented, armed with 2 distal setae.

Oral cone (fig. 1a) produced into long, siphon­like distal portion, 406 µm long, 0.3 times body­length. Mandible (fig. 1e) comprised of distally toothed stylet, palp absent. Maxillule (fig. 1f) bilobed, inner lobe 93 µm, armed with 2 stout, pinnate setae. Outer lobe 80 µm long, armed with 2 smooth setae. Maxilla (fig. 2a) with syncoxa 310 µm long, slender claw, 398 µm long, distally curved and showing small seta subdistally. Maxilliped (fig. 2b) 5­segmented, comprising syncoxa 89 µm long, armed with small seta on inner margin, basis 242 µm long with small seta medially on inner margin. Endopod 3­segmented, segments measuring 19, 56, and 77 µm long, respectively. First endopodal segment with 2 setae distally; second segment with 1 seta and third segment bearing curved, 110 µm long, claw, and seta.

Swimming legs 1–3 (P1–P3; figs. 2c–d, 3a) biramous, all with 3­segmented rami. P4 (fig. 3b) with 3­segmented exopod and 2­segmented endopod. Armature formula of legs 1–4 shown in table 1.

Fifth leg (fig. 3b) consisting of short, smooth seta near insertion of small, free segment, armed with 2 distal, smooth setae.

Remarks. All other siphonostomatoids collected at the same location were described by Humes (Humes 1971a & b; 1972a & b; 1973a & b; 1981).

Etymology. The specific name “ walteri ” honors Dr. Chad Walter of the National Museum of Natural History, Washington, whose efforts in rescuing and preserving Dr. Humes’ samples and notes provided the possibility that his legacy would not be wasted.

Figures

FIGURE 1. Metapontius walteri n. sp .. Female Holotype: a) habitus, dorsal view, with oral cone indicated in dashed line; b) urosome, dorsal view; c) antennule; d) antenna; e) mandible; f) maxillule. Scale bars: a – f = 100 µm.

FIGURE 2. Metapontius walteri n. sp. Female Holotype: a) maxilla; b) maxilliped; c) leg 1; d) leg 2. Scale bars: a – d = 100 µm.

FIGURE 3. Metapontius walteri n. sp. Female Holotype: a) leg 3; b) legs 4 and 5. Scale bars: a – b = 100 µm.