A New Species of Cryptopontius (Crustacea: Copepoda: Siphonostomatoida) from Easter Island

Abstract A new species of artotrogid copepod (Siphonostomatoida), Cryptopontius tanacredii n. sp., associated with the scleractinian coral Pocillopora damicornis (Linnaeus) from Easter Island, is described. The new species can be distinguished from its 20 congeners by the combination of the following six characters: (1) 9-segmented antennule, (2) terminal segment of leg 4 exopod armed with nine elements, (3) second segment of P1 endopod with two setae, (4) two setae on outer lobe of maxillule, (5) inner lobe of the maxillule tipped with two setae, and (6) free segment of P5 present and armed with three setae. This is the first record of the genus from the eastern Pacific and the first occurring in association with a scleractinian coral.


INTRODUCTION
The distribution of the genus Cryptopontius Giesbrecht, family Artotrogidae, was previously known to be nearly worldwide, with species present in the Mediterranean Sea, Atlantic and Indian Oceans, and the western Pacific. The discovery of a new species collected from Easter Island is the first occurrence of the genus in the eastern Pacific, and shows the genus to be truly circumglobal. The si-phonostomatoid fauna of Easter Island was also previously unknown, and the description of this new species of Cryptopontius is the first record of the order for the island. The association of the new species with Pocillopora damicornis (Linnaeus, 1758), a scleractinian coral belonging to the Pocilloporidae, is also unique, as most of the other 20 species of Cryptopontius have been recorded in algal associations, but none with corals. NO . 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).
Antenna ( 2c) five-segmented, comprising syncoxa 80 m long, armed with small seta on inner margin, basis 250 m long with small seta subproximally on outer margin, and tooth subdistally on inner margin. Endopod three-segmented, 33, 61, and 48 m long, respectively. First endopodal segment with two setae distally; second segment with single seta; and third segment bearing curved, 106 m long claw and seta.
Swimming  rami 39 ϫ 54 m, wider than long, with row of hairs on inner margin and armed with six setae. Seta I absent. Length of setae 50,80,252,417,65, and 47 m, respectively. Setae II and VII smooth, remaining setae plumose.
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.
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.