Tanaidaceans (Crustacea) from the Central Pacific Manganese Nodule Province. I. The genera Collettea, Robustochelia and Tumidochelia

Abstract Three new species of are described from the manganese nodule province between the Clarion and the Clipperton Fracture Zone of the equatorial North Pacific Ocean, and collected during the Nodinaut expedition on board the r/v l´Atalante in the summer of 2004. The new species belongs to three genera as: Collettea (Collettea longisetosa), Robustochelia (Robustochelia pacifica), and Tumidochelia (Tumidochelia tuberculata). A key to the genus Tumidochelia is presented and the validity of the genera Robustochelia and Collettea is discussed.


Introduction
Th e aim of this paper is to present the fi rst part of the taxonomic results from a survey of the Central Pacifi c Manganese Nodule Province between the Clarion and the Clipperton Fracture Zone of the equatorial North Pacifi c Ocean. Th is region has, due to the rich manganese deposits, been a tempting area for mineral exploration. Th is fact has made the area one of the best surveyed deep-sea regions in the Pacifi c. For the Tanaidacea alone this has resulted in a couple of publications (Wilson 1987;Larsen 1999b; and more are under way (Gurreo-Kommritz pers comm.; Larsen research in progress).
Th e phylogeny and systematics of the Tanaidacea is still very much unresolved despite recent advances. Large groups of genera are still left without family affi liation and the diagnoses of many families are incomplete or even contradictory. Unfortunately the reduced general morphology of tanaidaceans, the conservative morphology of many otherwise not closely related taxa, and the huge diversity of especially the deep-sea taxa, makes it hard to resolve the systematic confusion without genetic data (Larsen and Froufe 2010).
Any collection in remote deep-sea habitats will reveal a signifi cant proportion of undescribed species relative to known species (Larsen and Froufe 2010): the ratio of unknown/known species in deep-sea sampling is estimated to be about 80/20 and even higher at remote or previously unstudied locations (Larsen unpublished data). An additional problem is the fact that most species are represented by one specimen only further hampering systematic treatment.

Material and methods
Samples were taken during the Nodinaut expedition (17 May -28 June 2004) from on board of the research vessel l´Atalante using an Usnel Box corer and the submersible Nautile with a spade corer (Carottier a lame). Th e material was sieved over a 0.5 mm sieve and fi xed in 4% buff ered formalin and stored in 70% alcohol afterwards.
Dissections were made in glycerine using chemically sharpened tungsten wire needles. Body length was measured from the tip of the cephalothorax to the apex of the pleotelson. Th e terminology in the descriptions is based on Larsen (2003). Types are deposited in the Museum National d'Histoire Naturelle Paris (MNHN). Diagnosis. (Modifi ed after Larsen 2005) Female. Body almost completely cylindrical. Carapace longer than wide. Eye-lobes small but present, without visual ele-ments. Pleon and pleotelson not fused. Pleotelson mostly longer than last three free pleonites combined, terminating in dorsal plate covering uropods. Antennule with 4-5 (minute terminal article) articles. Antenna with 6-7 (fusion line) articles. Mandibles with small, but not pointed crushing area. Maxillule setal number varying, some setae may be bifurcate or setulose. Maxillipedal endites without inner distal setae. Maxilliped palp article 2 without multifurcate seta. Chelipeds attached via lateral sclerite. Pereopods slender, with coxae, and with dactylus and unguis not fused to hook. Pleopods absent in females. Uropods biramous; endopod with one or two articles; exopod uniarticulated.

Taxonomy
Male. Similar to female. Functional mouthparts retained in adult. Antennule thicker than in female. Pleopods present, most often with simple setae.
Remarks. Collettea is a genus well represented in all major oceans from less than 100 meters (G.O. Sars 1896) to abyssal depths exceeding 5000 meter (Kudinova-Pasternak 1973;1983). It is recognized by elongated pleotelson. Th e genus currently consists of 18 species including the one described herein.
Etymology. Named to refl ect the long setae of the pleopods. Description. Adult male, 2.9 mm (body and appendages of holotype). Body (Fig. 1A) strongly elongated, 19 times as long as broad.
Pleon long (about 75% as long as rest of body). All pleonites subequal, bearing long uniramous setae.
Pleotelson as long as combined length of three pleonites. Antennule ( Fig. 1B) with four articles, terminal article fused with article 4 and creating a dorsal projection. As long as cephalothorax. Article 1 marginally shorter than rest of antennule, with two setulated distal setae. Article 2 shorter than article 4, with one simple and two setulated distal setae. Article 3 half as long as article 4, with one simple distal seta. Article 4 half as long as article 1, with fi ve simple distal setae and one short but wide aesthetasc.
Antenna (Fig. 1C) length 0.8 times length of antennule. Article 1 naked and fused to the cephalon. Article 2 elongated and widening distally, with one robust dorsodistal seta. Article 3 shorter than article 2, with one robust dorsodistal seta. Article 4 longer than other articles, with one medial setulose seta but without recognizable fusion line, with one simple and two setulated distal setae. Article 5 longer than article 2, with one simple distal seta. Article 6 minute with four distal setae.
Cheliped (Fig. 3A) basis divided unequally by sclerite, marginally shorter than carpus. Merus triangular with one ventral seta. Carpus longer than propodus including fi xed fi nger, with two small simple ventromedial setae and one small simple seta dorsoproximal and dorsodistal. Propodus with setulose inner ridge, with two robust setae, with one simple outer seta at dactylus insertion; fi xed fi nger with multiple prominent sharply pointy processes and three inner seta and one ventral seta arising from a prominent tubercle; with ventral ridge terminating in unguis. Dactylus with conspicuous inner seta, row of setules and one inner spine.
Pereopod 1 (Fig. 3B) coxa with one simple seta. Basis fairly robust, shorter than three succeeding articles together, naked. Ischium with one robust simple seta. Merus shorter than carpus, widening distally, with one simple ventrodistal seta. Carpus shorter than dactylus, with one spiniform and two simple distal setae. Propodus more than half as long as basis, with three spiniform subdistal setae, row of scales and dorsal spine. Dactylus and unguis combined shorter than propodus. Unguis with subdistal ventral expansion at exit of spinning gland. Pereopod 2 (Fig. 3C) as pereopod 1 except: basis with medioventral setulated seta, merus with one spiniform distal seta, propodus with two spiniform and one simple subdistal setae and dorsal spine; ventral margin with row of spines.
Uropod (Fig. 1E) basal article shorter than exopod, naked. Endopod with two articles subequal length articles; article 1 with two setulated distal setae; article 2 with one long subdistal, four long simple and two setulated distal setae. Exopod longer than endopod article 1, with one medial and two unequally length distal setae.
Remarks. It is hard to compare C. longisetosa and other Collettea species given that it is a male and most other species are described from females only. Th e sexual dimorphism of Collettea, know from the species, which have described male (C. minima (Larsen, 2000) C. elongate (Larsen, 2002) and C. lilliputa (Błażewicz-Paszkowycz & Larsen, 2005) indicate only minor diff erences between the sexes in the antennule and absence of pleopods in the females. Th e remarkable uniramous pleopods and their equally remarkable setae of this species separate it from any other male described.
A similar armament of the cheliped fi xed fi nger with its strong inner serration and transverse row of inner setae/setules is also seen in C. subtilis Kudinova-Pasternak, 1981 and C. rotundicauda Kudinova-Pasternak, 1983, but none of these species have the ventral fi xed fi nger setae arising from a tubercle or the prominent dactyli seta. Furthermore in the case of C. subtilis the pereonites 2-5 are of similar size and in C. rotundicauda the antennule is much more robust (despite being a female, which usually have slender antennules than male), a shorter antennule article 4, and a shorter pleon. Th e powerful setae of the pereopods is also recorded from C. longipleona Błażewicz-Paszkowycz & Larsen, 2005, but this species have shorter and uniarticulated uropod. Another important feature of this species is the ischial setae on the pereopods 1-3, which are much more robust than usually seen in tanaidacean ischial setae. Th e crushing area of the mandibular molar, while not exactly pointed, is unusual small compared to what is seen in other species of Collettea. However, the long pleotelson still indicate that the species belong to Collettea, or to a new genus if/when Collettea is spilt into several genera. Th e only other genus that show some similarities, like the elongated body, cheliped structure and species with variable mandibular molar width, is Filitanais Kudinova-Pasternak, 1973 but the pleon is too short and the pleotelson too long in the new species to fi t the diagnosis of that genus.
Description. Manca II Body (Fig. 3A) length 1.9 mm. Ten times as long as broad. Cephalothorax shorter than combined length of pereonite 1 and 2. Pereon. Pereonites 1, 5, and 6 wider than long. Pereonite 2-4 longer than wide. Pleon relatively short, about half as long as rest of body. All pleonites subequal but progressively deeper towards pleotelson.
Pleotelson longer than combined length of three pleonites, deeper than pleonites. Pereopod 4 (Fig. 3B) dactylus with clear ventral spine at unguis insertion. Remarks. As this species was only recorded from one specimen of stage manca II it is not justifi able to erect a new species. Th e short uropods indicate however that it is not conspecifi c with C. longisetosa. Th is manca could be conspecifi c with Collettea sp. (Larsen 2000) which was collected in the same ocean basin (09°37.41'N, 151°45.00´W), however, since that species was not dissected, no further comparisons can be made. Several other species of Collettea share the ventral dactylus spine on pereopods 4-6 (C. alicjae Błażewicz-Paszkowycz & Larsen, 2005; C. humbolti Larsen, 2000;C. longipleona Błażewicz-Paszkowycz & Larsen 2005) and the species recorded here and thus this character is not good for species identifi cation.

Genus Tumidochelia Knight, Larsen & Heard, 2003
Type species. Tumidochelia randyi Knight, Larsen & Heard, 2003. Diagnosis. See Larsen and Shimomura (2007) Gender. Feminine. Remarks. Th e genus Tumidochelia is a much rarer genus than Collettea, but is fairly well defi ned by the combination of a large cheliped carpus shield and a biramous uropod with an additional spiniform distal process on inner margin of the basal article. Th e genus is encountered both in fairly shallow water around 100 meters (G.O. Sars 1896) and at abyssal depths below 5000 meters (this study). It currently consists of fi ve species including the one described herein.
Th e mouthparts of this genus are remarkably small relative to the size of the whole animal. When compared to a specimen of the genus Tanais or most other shallowwater tanaidomorphans of a similar body size, the diff erences in the size of the mouthparts are several hundred percent.

Diagnosis.
Female. Pereonites 2-4 longer than wide. Pleotelson longer than combined length of four pleonites. Antenna with six articles (+ fusion line), article 4 longer than other articles, with clear fusion line. Cheliped propodus with large paired dorsal tubercles near dactylus insertion. Pereopod 1 merus and carpus with long (longer than length of merus) robust setae.
Male. Unknown. Etymology. Th e species is named after the diagnostic character of the tubercles on the cheliped propodus.
Pleonites all wider than long, subequal, bearing pleopods. Pleotelson longer than combined length of four pleonites. Antennule ( Fig. 6A) with four articles. Stout at base-tapering distally, almost as long as carapace. Article 1 with one simple distal seta and three subdistal setulated setae; article 2 approximately 0.80 times as long as article 1, with two simple and three setulated distal setae; article 3 approximately 0.3 times length of article 2, with two simple distal setae; article 4 approximately twice length of article 3, with four long and one short simple distal setae and one prominent aesthetasc.
Antenna (Fig. 6B) approximately 0.7 times as long as antennule. Article 1 naked and fused to cephalon. Article 2 wider than other articles, with dorsodistal process and one stout dorsodistal seta. Article 3 band-shaped, with one dorsodistal seta, Article 4 longer than other articles, with clear fusion line, with one medial (distal on fi rst article component) setulose seta, with two long and one short simple setae distally and with one subdistal setulated setae. Article 5 with one simple distal seta. Article 6 approximately 0.25 length of article 5, with three simple distal setae and one aesthetasc.
Cheliped (Fig. 7A) attached to cephalothorax by a large sclerite. Basis naked, narrow in posterior part, approximately as long as carpus. Merus with one ventral seta. Carpus widening distally, with two small dorsal setae and two simple ventromedial setae, ventrodistal part infl ated into a large carpal shield, extending distally past propodus articulation. Propodus as long as basis, with two simple (thick) ventral setae mid-length and three (one longer than the other two) inner setae proximal to dactylus insertion, with paired dorsal crest next to dactylus insertion. Fixed fi nger with three inner setae and three blunt denticles. Dactylus as long as fi xed fi nger Pereopod 1 (Fig. 7B) longer than other pereopods. Coxa naked. Basis robust without seta. Ischium with one simple distal seta; merus widening distally, longer than carpus, with one ventrodistal, long (longer than merus) bayonet-shaped setae. Carpus rectangular, half as long as propodus, with two long (longer than merus) bayonetshaped distal setae. Propodus elongate, longer than merus, with one spiniform ventrosubdistal seta and dorsal spine. Dactylus and unguis combined shorter than propodus, dactylus with distal spine at unguis insertion. Unguis as long as dactylus.
Uropod (Fig. 7I) biramous, basal article naked, with dorsomedial spiniform process. Endopod with two subequal articles; article 1 with three simple distal setae; article 2 with one long simple subdistal seta, three long and two short simple distal setae. Exopod reaching beyond midlenght of fi rst endopod article, with two subequal articles; article 1 naked, article 2 with two simple but unequally length distal setae.
Remarks. Tumidochelia tuberculata can be separated from T. uncinata by the cheliped propodus having paired dorsal crest next to dactylus insertion; from T. dentifera by the pleotelson being longer than last three pleonites combined; from T. randyi by the pereonite 2 being longer than other pereonites; from the only other Pacifi c species, T. knighti, by the straight lateral margins (with no segment indentations), the longer pleotelson, the antenular fusion line, the cheliped propodus tubercles, and a longer uropodal exopod. Female. Antennule with four visible articles and one minute terminal article (often not visible in the compound scope as with Collettea and many other tanaidomorphans). Antenna with six articles, articles 2 and 3 with robust dorsodistal setae. Mandibular molar pointed. Labium consists of one pair of lobes with minute distal setulation, usually with medial processes (e.i. ´lobes´ sensu Józwiak and Błażewicz-Paszkowycz 2007). Maxillipedal palp robust; endites not fused, with distal setae but without distal denticles, narrower than basis. Chelipeds attached by ventral sidepiece, carpus and propodus massive, dactylus and fi xed fi nger shorter than rest of propodus, and heavily chitinized. Pereopods 1-3 with coxa, dactylus and unguis combined shorter than, or as long as, propodus, unguis longer than dactylus. Pereopods 4-6 without coxa, dactylus and unguis not fused to a claw. Pleopods present. Uropodal exopod uniarticulated, endopod consisting of one (with pseudoarticulation) or two articles.

Key to the species of
Male: Similar to female, but antennule articles 1-3 much wider than in female. Gender. Feminine. Species currently assigned to this genus. R. angusticephala Kudinova-Pasternak, 1986;R. longa Kudinova-Pasternak, 1983;R. pacifi ca sp. n.;R. robusta (Kudinova-Pasternak, 1970); R. virilis Józwiak and Błażewicz-Paszkowycz, 2007. Remarks. Th e genus Robustochelia is a rare, and exclusively deep-sea, genus (Larsen 2005;Józwiak and Błażewicz-Paszkowycz, 2007). It is primarily recognized by the heavy cheliped with a calcifi ed keel on the cheliped fi xed fi nger but despite the recent clarifi cations by Józwiak and Błażewicz-Paszkowycz (2007) it i still poorly defi ned and poorly studied genus, due to the rarity of both species and specimens. Th e genus currently consists of fi ve species including the one described herein. Apart from the heavy cheliped, the defi ning characters of Robustochelia are the combination of a 'general leptognatid´ morphology: consisting of an antennule with four plus one minute articles, a pointed mandibular molar, and a uniarticulated exopod. However the calcifi ed cheliped keel is found in species of other genera (Leptognathioides, Siphonolabium, Monstrotanais, and Robustochelia[?] solida) and the combination of the other ´general leptoganthid´ characters all present in several other deep-sea genera (Caudalonga, Filitanais, Forcipatia, Leptognathia, Leptognathiella, Stenotanais). No other synapomorphic characters are present and several of the species of Robustochelia are only incompletely described. Unfortunately it is not unusual for tanaid systematists to have to rely on a character combination as this for genus diagnosis, but the homoplastic nature of all the characters in Robustochelia indicates that it is probably not monophyletic. Further studies, particularly genetic studies, needs to verify the status of this genus (Larsen and Froufe in progress).
Cheliped (Fig. 10A, B) basis shorter than carpus, naked. Merus prominent with one simple ventral seta. Carpus appears twisted in relation to propodus, shorter than propodus including fi xed fi nger, with two simple ventral setae and prominent distal process. Propodus massive, with one seta at dactylus insertion and ventral calcifi ed keel. Fixed fi nger with keel only on proximal part, but with a clear tubercle distally from the keel, with one ventral seta and two on inner margin, and with one large distal process. Dactylus as long as fi xed fi nger, with small medial process and small dorsoproximal seta.
Pereopod 1 (Fig. 10C) coxa with one simple seta. Basis longer than the three succeeding articles combined. Ischium with one ventral seta. Merus as long as carpus, widening distally, naked. Carpus shorter than 0.5 times propodus, with two spiniform and one simple distal setae. Propodus with spinnules and one distal seta on both margins and dorsal spine. Dactylus and unguis combined shorter than propodus, not fused, dactylus shorter than unguis.
Pereopod 3 (Fig. 10E) as pereopod 1 except: basis with ventromedial setulose seta. Pereopod 4 (Fig. 10F) with no visible coxa. Basis about as long as the three succeeding articles combined, naked. Ischium naked. Merus with one simple ventral seta. Carpus with two small spiniform and one simple distal setae. Propodus longer than carpus, with two spiniform ventral and one simple dorsal setae. Dactylus and unguis combined shorter than propodus, not fused, with spinnules on both margins. Unguis still longer than dactylus, but shorter than in pereopod 1-3.
Pereopod 6 absent in manca II. Pleopods absent in manca II. Uropod (Fig. 8B) longer than pleotelson. Basal article naked and about as long exopod. Endopod with weak traces of a medial pseudo-articulation, with two medial setulose setae, one subdistal seta and four distal setae. Exopod less than half of endopod length, with two distal setae of unequal length.
Remarks. Bacause the studied specimen represent manca stage it is diffi cult to compare it with the other species of the genus. Th e carapace being longer than combined length of pereonites 1 and 2 and the weak armament of the pereopods (particularly the carpus) diff erentiate R. pacifi ca sp. n. from R. longa. As for R. angusticephala, this species is only incompletely described and nothing is known about the mouthparts so comparison with this species is diffi cult. However, the weaker fi xed fi nger of R. pacifi ca and the shape of the cephalothorax indicates that these are not conspecifi c. Robustochelia pacifi ca most closely resemble R. robusta, Figure 10. Robustochelia pacifi ca sp. n. Holotype A left cheliped, inner view B right cheliped, outer view C pereopod 1 D pereopod 2 E pereopod 3 F Pereopod 4 G pereopod 5 H pereopod 6 I pleopod. Scale bar = 0.1 mm. but diff ers in the stout antennule (particularly article 4) and antenna, but also the more rectangular shape of the cephalothorax, the pereonites 2-5 being longer than wide, the large tubercle distally on the fi xed fi nger, and the much longer pleotelson. R. pacifi ca diff ers from R. virilis by the pereonite 4 and 5 being longer than wide and by the pereopods 1-3 propodus setae not reaching longer than unguis insertion.
Th e species R. solida Larsen, 2005 was removed from the genus by Józwiak and Błażewicz-Paszkowycz 2007, based primary on the present of the present of a broad molar. Th is removal is undoubtly correct and thus clearly illustrate that the heavy cheliped is not a suffi cient character for defi ning the genus Robustochelia.