Oahutanais makalii , a new genus and species of colletteid tanaidacean ( Crustacea , Peracarida ) from shelf-waters off Hawaii , with a taxonomic key

A new colletteid tanaidacean, Oahutanais makalii gen. et sp. n., is described from Hawaiian coastal waters at depths ranging from 19 to 102 m. The new taxon is tentatively designated as a new genus, although it displays many features in common with the genus Leptognathiella. The new species is distinguished from the morphologically similar tanaidomorphans by having (1) a small body, less than 1.0 mm (reproductively active specimens), (2) a maxillule with two bifid spiniform setae; (3) a maxilliped palp article-2 with geniculate, finely pectinate spiniform seta on sub-distal inner margin, (4) a cheliped attachment ventrally via sclerite not connected to the carapace, and (5) the pereopods 1 to 6 with ischial seta shorter than the merus. A key to the five extant genera of Colletteidae in the North Pacific Ocean is presented herein.


Introduction
The Tanaidacean fauna from the Hawaiian Islands has received little attention so far.Recently, David and Heard (2015) described a new metapseudid, Cryptapseudes lerory David & Heard, 2015 from Niihau Island. They

Materials and methods
Bulk sediment collections were made by divers or with benthic grabs, depending upon depth, sieved through 0.5 mm screens and preserved in 10% buffered formalin.
Specimens were dissected under an Olympus ZS-16 stereomicroscope.Appendages were mounted on glass slides in glycerine and observed with an Olympus BX41 microscope, and drawings were made with a camera Lucida.Additional material was examined under the Hitachi S-4800 Scanning Electron Microscope (SEM) at the Pacific Biosciences Research Center (PBRC) Biological Electron Microscope Facility (BEMF).Illustrations were prepared with Adobe Illustrator CS6 Extended.
Type material has been deposited in the National Museum of Natural History, Smithsonian Institution, Washington DC, (USNM), Gulf Coast Research Laboratory Museum, Ocean Springs, Mississippi MS, (GCRL), and the Bernice Pauahi Bishop Museum (BPBM), Honolulu Hawaii.All measurements are in millimetres (mm).Total body length (TL) is measured from the tip of the rostrum to the end or tip of the telson.Terminology used in this description follows that of Larsen (2003).In our description the total length of the dactylus includes the unguis.dated-benthic-community-monitoring at four Honolulu wastewater treatment plant outfalls (Fig. 1).
The family Colletteidae was erected during a phylogenetic revision of the superfamily Paratanaoidea Lang, 1949 to accommodate genera not assigned to any family, most being anarthurids (sensu Guţu and Sieg 1999) and leptognathiids: nevertheless, the systematic support for creating this family was admittedly weak (Larsen and Wilson 2002: 215) and incomplete (Larsen 2005;Bird and Larsen 2009).After thirteen years, the family currently holds 15 genera, which have been reported from the North and South Pacific Ocean, North and South Atlantic Ocean, Gulf of Mexico, Indian Ocean, Arctic Ocean and Antarctic Ocean (   Generic diagnosis.Female: Small, 0.8-0.9mm, slender body, parallel-sided.Carapace extending laterally to cover (dorsally) the cheliped attachments.Carapace not connected with the cheliped sclerites Pereonites wider than long.Antennule with four articles and minute terminal segment, shorter than carapace, article-2 with dorsal symmetric projection overlapping basal part of article-3, terminal segment minute and covered by article-4 (only visible with scanning electron microscope image).Antenna with six articles.Labium without distolateral spines.Maxillule with seven distal spiniform setae (two bifid); maxillipedal palp article-2 with geniculate, finely-pectinate spiniform seta on distal inner margin (serrations visible at magnification 100×).Cheliped attached via sclerite just anterior to the posterior margin of the cephalothorax, very close to the midventral line.Pereopods 1 to 6 attached ventrally.Pereopods 1-3 relatively slender; ischial seta shorter than merus.Pereopods 4-6 not stouter than pereopods 1-3; ischial setae shorter than merus.Pleopods absent in females.Uropods longer than pleotelson; basal article shorter than pleotelson, without distal apophyses; exopod uni-articulated, slightly longer than endopod article-1.
Male unknown.
Etymology.Named after "O'ahu Island", where the material used in this study was collected, plus suffix -tanais.

Gender. Masculine.
Distribution.Hawaii Islands at depths ranging from 19 to 102 meters.
Remarks.The family Colletteidae has been considered as polyphyletic (Larsen and Wilson 2002;Błażewicz-Paszkowycz and Poore 2008;Błażewicz-Paszkowycz et al. 2013) and it is currently composed of 15 genera (WoRMS); unfortunately, most of the genera included within this diverse family need revision (e.g.Leptognathiella Hansen, 1913 andFilitanais Kudinova-Pasternak, 1973).The females of Oahutanais gen.n. can be identified by having a small body (less than 1 mm in length of reproductively active specimens), cheliped attached just anterior to the posterior margin of the cephalothorax, very close to the midventral line, not in contact with carapace lateral margin, and pereopods 1 to 6 attached ventrally.Oahutanais gen.n. appears to be most closely related to the genera, Leptognathiella Bird and Holdich, 1984 from the Atlantic or Gulf of México (Larsen 2005;Larsen et al. 2006), Leptognathiopsis Holdich & Bird, 1986 from the North Atlantic (Holdich and Bird 1986), and several species of Leptognathia G.O. Sars, 1882 sensu stricto (see Larsen and Shimomura 2007: 12) in having pereonites wider than long, pointed molars, females without pleopods (only in some species of Leptognathiella and Leptognathia), and uropod structure.However, the Oahutanais can be distinguished from the Atlantic species of Leptognathiopsis and Leptognathiella by having 1) the maxilliped palp article-2 with geniculate, finely pectinate spiniform seta on sub-distal margin, 2) pereopods 1-3 with basis slender, and 3) pereopod ischial setae shorter than merus.
The new genus also shows similarities with the monotypic genus Nippognathiopsis Błażewicz-Paszkowycz, Bamber & Jóźwiak, 2013, recently described from 517-1356 m in waters off Japan.However, Oahutanais can be differentiated by 1) its pereonites are wider than long, 2) the antennal article-1 is longer than the distal three articles and minute terminal segment combined (shorter in Nippognathiopsis), 3) the maxilliped endites have a medial small process (two oval tubercles in Nippognathiopsis), 4) the maxilliped palp article-2 has a geniculate, finely pectinate spiniform seta on the sub-distal margin, and 5) pereopods 1-6 are slender.Although the presence of the geniculate, finely pectinate spiniform seta in the maxilliped palp article-2 separates Oahutanais from the other genera within the family Colletteidae, it is possible that this spiniform seta has been overlooked in the original description of Nippognathiopsis, as well as in other colletteids due to their small overall size.Unfortunately, no information is available on the form of the cheliped attachment in Nippognathiopsis.Bird and Larsen (2009) mentioned that this character, the cheliped-cephalothorax attachment position, is an important feature that has been overlooked or has not been recorded or illustrated by many authors, even today.So far within the family Colletteidae, only Błażewicz-Paszkowycz and Bamber (2012) and this study have included detailed information and illustrations showing the real point of insertion of the cheliped and how far it is located from pereonite-1.Thus, Oahutanais can be separated from Bascestus Błażewicz-Paszkowycz & Bamber, 2012 by having 1) the cheliped attached just anterior to the posterior margin of the cephalothorax (more anterior in Bascestus), 2) females without pleopods (pleopods present in Bascestus), and 3) exopod uni-articulated (bi-articulated in Bascestus).
The ventral cheliped attachment without contact with the carapace lateral margin (Fig. 8B-C) is an interesting and rare character among tanaidomorphans, and it has so far only been recorded from another colletteid, Isopodidus Larsen & Heard, 2002, but   Etymology.The species name, makali'i, is Hawaiian for tiny or minute and reflects both where the material used in this study was collected and its small size relative to other tanaidaceans within this benthic community.Description.Based in holotype female, length 0.9 mm (USMN 1283305).).
Antennule (Figs 3A, 6A-B): slightly longer than 2/3 length of cephalothorax.Article-1 about 3.1 times long than wide, longer than distal three articles, with three setulose setae and one simple seta along lateral margin.Article-2 about 1.1 times longer than wide, with distodorsal simple seta; with two setulose setae and one long (longer than articles 2 to 4 combined) simple seta on distoventral margin.Article-3 about 1.5 times wider than long, with two simple setae dorsally and one simple seta lateral.Article-4 about 1.4 times longer than wide, with four simple setae of different length.Terminal segment minute and covered by article-4, with one seta and one aesthetasc (only visible with SEM images) (Fig. 6B).
Antenna (Figs 3B, 6B): article-1 short, asetose.Article-2 about 1.2 times wider than long, with distolateral short seta.Article-3 about 1.3 times wider than long, with distodorsal long simple seta.Article-4 about 3.0 times longer than wide, longer than articles 2 and 3 combined, with one setulose seta and two simple setae on distoventral setae margin.Article-5 about 2.0 times longer than wide, with one simple seta on distolateral margin.Article-6 minute, with five simple setae of unequal length.
Cheliped: (Figs 4A-B, 6A-C, 8): cheliped attached just anterior to the posterior margin of cephalothorax and very close to the midventral line, via sclerite (Figs 6B-C, 8).Basis about 1.9 times longer than wide, with subdistal short seta.Merus triangular, with simple seta on ventral margin.Carpus about 1.8 times longer than wide, anterior margin with distodorsal seta; ventral margin with two simple setae of different length.Propodus about 1.4 times longer than wide, with small simple seta near insertion of dactylus.Fixed finger with crenulated ventral margin, with two ventral setae and three simple setae on outer incisive margin, with two to three sharp denticles on inner margin.Inner surface (Fig. 4B) with three short simple setae (one distinctly longest) at articulation with dactylus.Dactylus with long simple proximal seta on inner side.
Pereopod-4 (Figs 5D, 8): attached ventrally, basis about 4.0 times longer than wide, with setulose seta on proximal dorsal margin.Ischium wider than long with two simple setae of unequal length on posterior margin, long seta shorter than merus.Merus about 2.0 times longer than wide, with two distoventral pectinate setae.Carpus about 2.0 times longer than wide, with four pectinate setae of unequal length.Propodus about 3.5 times longer than wide; distodorsal margin with long pectinate setae, reaching beyond the dactylus; distoventral margin with two pectinate setae.Dactylus and unguis longer than propodus, dactylus shorter than unguis.
Male.Unknown.Ovigerous female.As above.When embryos were present, six (smaller embryos) was the most observed; typically only three or fewer were present.
Remarks.Among the family Colletteidae, Oahutanais makalii sp.n. shows some similarities with Cetiopyge mira Larsen and Heard, 2002, Isopodidus janum Larsen and Heard, 2002, and Collettea minima Hansen, 1913(see Larsen 2000) in having the unusual presence of bifurcate spiniform terminal setae on the maxillule endite; however, the presence of this kind of setae has also been reported in some species of other families such as the Tanaellidae Larsen & Wilson, 2002(Arthrura andriashevi Kudinova-Pasternak, 1966), Cryptocopidae Sieg, 1977(Curtichelia expressa Kudinova-Pasternak, 1987), and Paratanaoidea incertae sedis (Parafilitanais mexicanus Larsen, 2002).Larsen and Heard (2002) suggested that this setal character could have a wider occurrence in the deep-sea species, since it has only been reported in specimens collected in deep waters.Our results indicated that the presence of these unusual setae is not restricted to deep-sea Tanaidacea, since Oahutanais makalii was found in shallow waters (<105 m).Remarks on ecology.A complete description of the surrounding benthic communities at these four study areas is beyond the scope of this paper, although the following observations are offered.Oahutanais makalii occurs from 19 to 102 m.A single specimen per replicate correlated to a minimum density of 220 ind.m 2 .The maximum density for this species observed at any station was 5,070 ind.m 2 ; far below densities recorded for the most abundant small crustaceans (over 50,000 ind.m 2 ).No associated tubes were observed with the specimens.

Figure 1 .
Figure 1.Map of study area, indicating the sampling stations where Oahutanais makalii gen.et sp.n., were found.

Figure 6 .
Figure 6.Oahutanais makalii gen.et sp.n., paratype female (SEM images): A enlargement of anterior end showing part of the carapace, antennules, and carpus to dactylus of left cheliped, dorsal view; B enlargement of the cephalothorax and pereonites-1; C enlargement of anterior part showing how the carapace covers the antennules, antennas, mouthparts, and left cheliped, ventral view.

Figure 8 .
Figure 8. Oahutanais makalii gen.et sp.n., paratype female (SEM images): A ventral view of habitus; B enlargement of mid-anterior part of habitus, lateral view; C enlargement of union of cephalothorax and pereonite-1.

Table 1 .
Listing of the 16 currently recognized genera within the family Colletteidae, including information on distribution and depth range.NW = northwest; NE = northeast; SW = southwest; SE = southeast; and GoM = Gulf of Mexico.

Order Tanaidacea Dana, 1849 Suborder Tanaidomorpha Sieg, 1980 Superfamily Paratanaoidea Lang, 1949 Family Colletteidae Larsen & Wilson, 2002 Oahutanais gen. n.
).The description of this new Hawaiian genus and species as well as an identification key to the five extant genera of Colletteidae in the North Pacific Ocean is presented here.