Oahutanais, Morales-Núñez & Larsen & Cooke, 2016

Morales-Nunez, Andres G., Larsen, Kim & Cooke, William J., 2016, Oahutanais makalii, a new genus and species of colletteid tanaidacean (Crustacea, Peracarida) from shelf-waters off Hawaii, with a taxonomic key, Zoosystematics and Evolution 92 (1), pp. 1-12 : 2

Oahutanais gen. n.

Generic diagnosis.

Female: Small, 0.8-0.9 mm, 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.

Type species.

Oahutanais makalii sp. n.

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 and Filitanais 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 this highly modified genus differs in many other aspects from Oahutanais .

Figures

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.