A new genus of Cletopsyllidae (Copepoda, Harpacticoida) from Gulf of Mexico

Abstract A new genus and new species of the family Cletopsyllidae Huys & Willems, 1989 from deep-sea sediment in the Gulf of Mexico, are reported and fully described and illustrated. The new genus Pentacletopsyllus (type species: P. montagni sp. n.) can be distinguished from the four known genera of the family by antennule segmentation, length ratio of first and second endopodal segments of P1, and armature pattern on P5 exopod. It also differs from its sister genera by the rostrum being bifid at the tip, third segment of the female antennule having a smooth posterior margin, the baseoendopod of P5 with biarticulate outer setophore bearing basal seta, and female caudal rami without lobate expansion. A revised key to species of the family Cletopsyllidae Huys & Willems, 1989 is provided.


Introduction
The Gulf of Mexico is a large semi-enclosed oceanic basin surrounded by the North American continent and the island of Cuba. The continental slope of the northern Gulf of Mexico is topographically complex and shows a high species diversity of benthic fauna (Haedrich et al. 2008). Baguley et al. (2006) estimated the harpacticoid species richness of the northern Gulf of Mexico to be approximately 2200 species with a maximum diversity found at mid-slope water depths of 1200-1500 m. Harpacticoid diversity in this area is thought to be maintained by both small scale heterogeneity and large scale food supply mechanisms (Baguley et al. 2006). In total, Baguley et al. (2006) recorded 696 species of benthic harpacticoids, belonging to 175 genera and 22 families.
The subfamily Normanellinae was elevated to family level by Huys and Willems (1989), and they established two subfamilies, the Normanellinae and Cletopsyllinae. Subsequently, Huys and Lee (1999) raised the subfamily to the family Cletopsyllidae and it was divided into four genera, the type genus Cletopsyllus Wiley, 1935, and three new genera Bathycletopsyllus, Isocletopsyllus and Retrocalcar. At that time, they considered Pseudocletopsyllus Vervoort, 1964 to be a genus inquirendum in Cletopsyllidae because of the inadequate description of the type species P. spiniger, which was very similar to the copepodid V of R. sagamiensis (Itô, 1971).
During a recent deep-sea benthic survey to assess impacts of the Deepwater Horizon oil spill in the northern Gulf of Mexico, a new genus and species of Cletopsyllidae was collected. Recent investigations have uncovered significant benthic community impacts from the Deepwater Horizon (Montagna et al. 2013), stressing the need to more completely describe and understand the biodiversity and community structure of the region. Here, we describe the new genus and species based on the newly collected specimens and provide an updated key to genera and species of Cletopsyllidae.

Material and methods
Samples were collected from the northern Gulf of Mexico in May/June 2011 as part of the Deepwater Horizon Natural Resource Damage Assessment (NRDA) follow-up cruise aboard the R/V Sarah Bordelon. Sediments were sampled with an Osil multicorer and were fixed with buffered formalin and stained with Rose Bengal. Meiofauna was extracted from sediments by Ludox isopycnic centrifugation (Burgess 2001). Harpacticoids were sorted and enumerated under a Leica S8APO dissecting microscope, and stored in 70% ethanol.
Specimens were dissected in lactic acid and the dissected parts were mounted on slides in lactophenol mounting medium. Preparations were sealed with transparent nail varnish. All drawings have been prepared using a camera lucida on a Leica DM 2500 differential interference contrast microscope. Specimens are deposited at the Smithsonian National Museum of Natural History.
Genital double-somite ( Fig. 4C), completely fused ventrally with original segmentation indicated by a transverse surface ridge dorsally and laterally. Genital field located near anterior margin with gonopore and copulatory pore located in median depression. P6 with 1 bare seta on a small protuberance. Anal somite with well-developed rounded operculum bearing row of setules (Fig. 4D).
Caudal rami cylindrical, about 7 times as long as wide, each ramus with 7 setae: setae I-II small, closely set, seta III subapical, setae IV-V bipinnate, seta V longest, seta VI bare and small, seta VII tri-articulate at base; tube pore presented dorsally near proximal inner margin (Fig. 1F).
Maxilliped (Fig. 2G) comprising syncoxa, basis, and 1-segmented endopod. Syncoxa with 3 plumose setae and several short rows of spinules. Basis with 1 longitudinal row of spinules along palmar margin. Endopodal segment produced into strong and distally pinnate curved claw; accessory armature consisting of 1 long naked seta and 1 small seta at base.
Fifth pair of legs (P5) (Fig. 6G) fused medially. Baseoendopod with outer setophore bearing the basal seta. Endopodal lobe with 1 inner and 2 distal bipinnate setae.      Exopod shorter than in female, about three times as long as wide, with 1 inner, 1 distal and 2 outer pinnate setae. P6 (Fig. 5C) asymmetrical, bearing 1 naked seta on a cylindrical process. Etymology. The species is named in honor of Dr. Paul Montagna, Endowed Chair for Ecosystem Studies and Modeling at the Harte Research Institute, Texas A&M University Corpus Christi. Dr. Montagna has had a long and distinguished career studying meiofauna, hapacticoid systematics, and marine ecosystem dynamics, particularly in the Gulf of Mexico.

Discussion
The subfamily Cletopsyllinae of the family Normanellidae was raised to familial rank by Huys and Lee (1999). They provided a new diagnosis and revised the genera of the family, and the family Cletopsyllidae was divided into four genera and nine species. Since then, two new species have been added by Song et al. (2010: Isocletopsyllus maximus) and Addis et al. (2011: I. sardus), the family Cletopsyllidae currently includes four genera and 11 species. Huys and Lee (1999) provided the following morphological diagnosis of the family Cletopsyllidae: (1) body elongated, body somites well defined with dentate or crenulate posterior margins, (2) female antennule 4-or 6-segmented, posterior margin of second segment with two distinct conical process, each bearing an apical seta; apical acrothek in both sexes represented by two setae only, (3) male antennule 7-segmented and typically subchirocerate with geniculation between segments 5 and 6; posterior margin of segment 2 with proximal spinous and distal cylindrical process, (4) antenna exopod 1-segmented and bisetose; endopod with 3 lateral and 6 distal element, (5) P1-P4 biramous with 3-segmented exopod and 2-segmented endopod, (6) baseoendopod of P5 with elongated, tri-articulate setophore, (7) the sexual dimorphism of P2 endopod is the most diagnostic character.
Pentacletopsyllus gen. n. is placed in the family Cletopsyllidae with the character sets of the presence of a crenulated posterior margin of body somite, posterior margin of female antennule second segment with 2 distinct conical processes, 1-segmented antenna exopod with 2 setae, armature formula of swimming legs, and P5 with separate exopod and baseoendopod in both sexes and baseoendopod with elongated basal seta. The new genus can be readily identified on the basis of the following three characters: 1) Antennule: The genus Bathycletopsyllus Huys & Lee, 1999 has a 6-segmented female antennule and the other genera -Cletopsyllus Willey, 1935, Isocletopsyllus Huys & Lee, 1999, and Retrocalcar Huys & Lee, 1999 -have a 4-segmented antennule. However, the new genus displays a 5-segmented female antennule. Generally the third segment of the antennule has a smooth posterior margin, but a crenulated posterior margin is presented in the genus Cletopsyllus. The new genus does not show any modifications as in the genus Cletopsyllus. Huys and Lee (1999) mentioned that the second segment of the male antennule has 2 processes along the posterior margin, however the genus Pentacletopsyllus has only one process on the posterior margin of antennule, moreover the fifth segment has an additional swelling at the posterior margin. 2) Structure of P1: Normally in the family Cletopsyllidae, P1 exopod is 3-segmented, shorter than endopod; P1 endopod 2-segmented, prehensile, enp-1 at least twice as long as enp-2, and consists of an elongate proximal segment with 1 inner seta. The setation on exopod and endopod of P1 in the genus Pentacletopsyllus is the same as above, but the proximal and distal segment of P1 endopod are nearly equal in length. 3) P5: Huys and Lee (1999) mentioned that the baseoendopod of both sexes in the family Cletopsyllidae is characterized by an extremely long extension bearing the outer basal seta, and this setophore is typically tri-articulate. The P5 exopod has six setae in the female and 4-5 setae in the male except for Cletopsyllus papillifer Willey, 1935 with seven setae in the female. The new genus has long setophore but not extremely long, and the P5 baseoendopod has a bi-articulate outer setophore in both sexes, and the female P5 has only five setae on the exopod.
Together with newly described P. montagni, the 5 genera and 12 species currently recognized as valid in the family Cletopsyllidae can be identified with the specific key given below. It is amended from Huys and Lee (1999) and Wells (2007). Caudal ramus 3.6 (male) and 6.5 (female) times as long as greatest width; outer spines on third exopodal segment of leg 3 modified in male .. was provided by representatives of the NRDA Trustees. We thank professor Wonchoel Lee, who reviewed our illustrations and preliminary descriptions prior to drafting this manuscript. We thank the two anonymous reviewers and the editor Danielle Defaye, whose comments greatly improved the quality of this manuscript.