Cryptopontius tanacredii, new species Figures 1–4

Material Examined: ex Pocillopora damicornis, offshore from Ahu Tepeu, Easter Island (Rapa Nui), 15.1 m, 29 August 1999, coll. H. Tonnemacher: 1 female, holotype (AMNH 18380), 1 male, allotype (AMNH 18381); ex P. damicornis, from Motu Iti islet, off the southwest coast of Easter Island (Rapa Nui), 47.88 m, 28 August 1999, coll. H. Tonnemacher: 1 female, paratype (MNRJ 15429).

Description of Holotype Female (figs. 1–3c): Body length (excluding caudal setae) 1167 ;gmm, greatest body width 667 ;gmm; thus body 1.75 times longer than wide. Body shape cyclopiform (fig. 1a), with sensilla covering prosome; cephalosome and pedigerous somites 2 to 4 not imbricated, with epimera moderately pointed. Ratio of length to width of prosome 1.3:1, ratio of length of prosome to urosome 2.6:1. Pedigerous somite 3 with posterior margin showing denticles (fig. 1b).

Urosome (fig. 1c) five-segmented. Genital double somite 127 ;ts 221 ;gmm, ratio of length to width 0.6:1, rounded medially, armed with one plumose and one smooth seta near genital aperture. Three abdominal somites, all wider than long (66 ;ts 139 ;gmm, 48 ;ts 125;gmm, 64 ;ts 105 ;gmm), ratio of length to width 0.5, 0.4, and 0.6:1, respectively. All somites showing sensilla. Caudal rami elongated, 57 ;ts 43 ;gmm, 1.3 times longer than wide, with row of hairs on inner margin and armed with six setae. Seta I absent. Length of setae II–VII, 52, 127, 350, 525, 189, and 70 ;gmm, respectively. Setae III–VI plumose, setae II and VII smooth.

Antennule (fig. 1d) 357 ;gmm long (not including setae), and nine-segmented. Length of segments 1–9 measured along their posterior margin: 64 ;gmm (60 ;gmm along anterior margin), 26, 69, 31, 16, 31, 27, 36, and 57 ;gmm, respectively. Segmental homologies and setation as follows, romans numerals indicate the original segments followed by the number of setae in Arabic numbers, according to Huys and Boxshall (1991): I–1; II–2; III–VIII–11; IX–XIII–8; XIV–2; XV–XVI–2; XVII–XVIII–2; XIX–XX–2; XXI–XXVIII–9+ae. All setae smooth. Aesthetasc (ae) on segment XXI 100 ;gmm long.

Antenna (fig. 1e) 172 ;gmm long (including distal seta), with basis 55 ;gmm long. Endopod two-segmented; first segment 24 ;gmm long, unarmed; second segment 42 ;gmm long with one smooth proximal seta, one smooth subdistal seta, and two plumose distal setae (51 and 62 ;gmm long), none of them modified into a claw.

Oral cone (fig. 1a) produced into long, siphonlike distal portion, 447 ;gmm long, 0.4 times the body length. Mandible (fig. 1f) comprising a distally toothed stylet, palp absent. Maxillule (fig. 2a) bilobed, inner lobe 127 ;gmm, almost twice as long as outer lobe, armed with long plumose seta and short hirsute seta. Outer lobe 67 ;gmm long, armed with two pinnate setae.

Maxilla (fig. 2b) with syncoxa 286 ;gmm long and curved slender claw 295 ;gmm long, with pinnate extremity and showing small spine and tooth subdistally. Maxilliped (fig. 2c) five-segmented, comprising syncoxa 80 ;gmm long, armed with small seta on inner margin, basis 250 ;gmm long with small seta subproximally on outer margin, and tooth subdistally on inner margin. Endopod three-segmented, 33, 61, and 48 ;gmm long, respectively. First endopodal segment with two setae distally; second segment with single seta; and third segment bearing curved, 106 ;gmm long claw and seta.

Swimming legs 1–3 (P1–P3; figs. 2d, e, 3a) biramous, all with three-segmented rami, P4 (fig. 3b) with three-segmented exopod and without endopod. Leg 2 with distal element plumose proximally and spinulated distally. Armature formula of legs 1–4 shown in table 1.

Fifth leg (fig. 3c) with long smooth seta near insertion of small, free segment armed with three smooth setae, two distal and third on outer margin.

Description of Allotype Male (figs. 3d, 4): Body similar to female, but much smaller (fig. 3d). Length (excluding caudal setae) 935 ;gmm long, greatest body width 555 ;gmm, 1.7 times longer than wide. Prosome covered with sensilla. Ratio of length to width of prosome 1.7:1. Ratio of length of prosome to urosome 3.2:1. Cephalosome and pedigerous somites 2–4 not imbricated, with epimera slightly pointed. Urosome (fig. 4a) five-segmented. Genital somite 61 ;ts 167 ;gmm, ratio of length to width 0.4:1, rounded anterolaterally, with three plumose setae posteriorly. Three abdominal somites, all wider than long, 43 ;ts 130, 35 ;ts 120, 59 ;ts 117 ;gmm, ratio of length to width 0.3, 0.3, and 0.5:1, respectively. Caudal rami 39 ;ts 54 ;gmm, wider than long, with row of hairs on inner margin and armed with six setae. Seta I absent. Length of setae II–VII, 50, 80, 252, 417, 65, and 47 ;gmm, respectively. Setae II and VII smooth, remaining setae plumose.

Antennule (fig. 4b) 256 ;gmm long (not including setae), and eight-segmented. Length of segments 1–8 measured along their posterior margin 62 ;gmm (61 ;gmm along anterior margin), 54, 23, 12, 21, 17, 21, and 46 ;gmm, respectively. Segmental homologies and setation as follows: I-1; II-VIII-14; IX-XIII-6+spine; XIV-1+spine; XV-XVI-2; XVII-XVIII-2; XIX-XX-2; XXI-XXVIII-10+ae. All setae smooth, aesthetasc on segment XXI 78 ;gmm long. Maxilla (fig. 4c) with long syncoxa, 180 ;gmm long, with small tooth proximally on inner margin, curved claw 221 ;gmm long, toothed distally and showing two small setae subdistally.

Maxilliped (fig. 4d) five-segmented, with syncoxa 50 ;gmm long, armed with smooth seta. Basis 160 ;gmm long, with small seta medially and subdistal tooth on inner margin. Endopod three-segmented, 36, 43, and 33 ;gmm long, respectively. First segment armed with two setae distally, second segment with one seta and third segment with one seta and claw curved distally, 71 ;gmm long.

Leg 5 (fig. 4e) with free segment armed with three plumose setae. All other appendages as in the female.

Etymology: The specific name “tanacredii” honors Dr. John T. Tanacredi of the U.S. National Park Service, Gateway National Recreation Area, whose efforts made the Invertebrate Survey of Easter Island possible.

Discussion: The 21 species of Cryptopontius can be divided into three groups according to the number of segments on the antennules (8, 9, or 10). Cryptopontius tanacredii, n. sp., belongs to the group having nine-segmented antennules, which also includes C. brevicaudatus (Brady, 1899); C. brevifurcatus (Giesbrecht, 1895); C. graciloides Ummerkutty, 1962; C. gracilis Wilson, 1932; C. longipes Nicholls, 1944; a new species from Madeira, Portugal (fide Johnsson, in press); C. orientalis Ummerkutty, 1962; C. paracapitalis Eiselt, 1961 (new name for C. latus Nicholls, 1944, non C. latus (Brady, 1910); erroneously credited to Nicholls by Eiselt, 1961); C. proximus Nicholls, 1944, and C. tenuis (Giesbrecht, 1895).

Among these 11 species, C. longipes is the only one with eight elements on the third exopodal segment of P4 (Nicholls, 1944), while the other 10 species, including C. tanacredii, n. sp., all have nine elements. Cryptopontius tanacredii, n. sp., has its second endopodal segment of P1 with two setae, as is also true of C. brevifurcatus, C. paracapitalis, C. graciloides, the new species from Madeira, and C. brevicaudatus. The remaining four species (C. proximus, C. gracilis, C. tenuis, and C. orientalis), have only one seta on the second endopodal segment of P1 (Giesbrecht, 1899; Wilson, 1932; Nicholls, 1944; Ummerkutty, 1962).

Of the six species cited above as having the second endopodal segment of P1 with two setae, Cryptopontius brevifurcatus is the only one with three setae on the outer maxillule lobe (Giesbrecht, 1899); all other species have two setae on the outer lobe. Cryptopontius paracapitalis has one seta on the inner maxillule lobe (Nicholls, 1944); C. brevicaudatus has three setae (Eiselt, 1961); and C. tanacredii, n. sp., C. graciloides, and the new species from Madeira have two setae each (Ummerkutty, 1962; Johnsson, in press).

Cryptopontius graciloides has the free segment of leg 5 reduced to a group of setules, the maxilliped with two endopodal segments, the antennal exopod with one seta, and the second endopodal segment with two setae. Cryptopontius tanacredii, n. sp., differs in having the free segment of P5 present with three setae, a three-segmented endopod of the maxilliped, an antennal exopod with two setae and the second endopodal segment bearing three setae distally. The new Cryptopontius species from Madeira has only two setae distally on the second endopodal segment of the antenna, one of them modified into a claw; this is not present in C. tanacredii. Additionally, the antennule of the new species from Madeira has the proximal pattern of I, II-VII, VIII, while in C. tanacredii it is I, II, III–VIII.