Revision of the genus Peraeospinosus Sieg, 1986 (Crustacea: Peracarida: Tanaidacea)

Ten species, four new to science, five formerly belonging to genus Typhlotanais, and Peraeospinosus pushkini (Tzareva, 1982) are congeneric species, based on the following set of characters: a row of setae is present on the dorsal margin of the cheliped carpus, the distal seta of pereopods 4–5 exceeds the bifurcated unguis, large prickly tubercles on pereopods 4–6 surrounded by well‐calcified spines, the pleopods semi‐elliptical, and the rami of the uropod subequal in length. The new definition of the genus is proposed together with a key for identification of the females. The present‐day distribution of the genus does not in itself indicate geographical origin, although the possibility of a deep‐water origin cannot be excluded. It is assumed that phylogenetically young, blind Peraeospinosus could have colonized Antarctic free niches and then radiated.


Introduction
The genus Typhlotanais was erected by Sars (1882) for tanaids characterized by an elongated, almost straight body; a carapace narrowly truncated in front or slightly produced in the middle, with no traces of an ocular lobe (blind); the first pereonite shorter than the others; the three-articled antennule, with article 2 shorter than other articles; the elongated cheliped, with the narrow propodus subequal in length to the carpus; pereopod 1 longer than the next two limbs, and the three last pereopods of a clinging type; the biramous uropod, with both rami with two articles or at least one ramus with one article. Typhlotanais sensu lato includes 56 described species (Anderson et al. 2005) and is the most speciose genus of the family Nototanaidae sensu Larsen and Wilson (2002). Sieg (1986), in his monograph on Tanaidacea from the Antarctic Peninsula and the most southern part of South America, created a new genus Peraeospinosus for species bearing spiniform setae (5spines in Sieg's terminology) on the carpus and merus of pereopods 2 and 3. He included three typhlotanaid species in that genus: Peraeospinosus (5Typhlotanais) pushkini (Tzareva, 1982), P. (5T.) adipatus (Tzareva 1982), and P. (5T) mixtus (Hansen, Peraeospinosus Sieg, 1986 Diagnosis Female. Body robust, elongated, usually 5.6-10 times as long as wide, preserved specimens are often stiff and straight (stick-like). Some of pereonites 1-5 with collar-like grooves, usually anteriorly or posteriorly. Carapace usually oval or rounded, rarely narrow, rostrum well-developed. Dorsal margin of cheliped carpus with row of minute setae. Labrum hoodshaped, with upper part covered with needle-like setae. Molar process with row of setae on lower margin of crushing edge. Maxillule with nine spiniform setae distally, two semi-fused (10th short seta centrally usually not observable). Labium external lobes with row of minute setae on edges. Maxilliped bases wide, heart-shaped, endites with two small flat setae (tubercles) on distal margins. Epignath sharply tipped, often bifurcated. Pereopods 1-3 walking type. Pereopods 4-6 clinging type. Distal seta on propodus of pereopods 4 and 5 longer than unguis; prickly tubercles on pereopods 4-6, surrounded by blunt, calcified spines; unguis of pereopods 4-6 bifurcated. Exopod of pleopods semi-elliptical. Uropod rami usually uni-articled, equal or subequal. Uropod exopod tipped by diminutive and robust seta (at basis almost as wide as exopod).

Distribution
Members of newly defined Peraeospinosus have so far been recorded from the Pacific Ocean (off Alaska, Kurile-Kamchatka Trench, Japan Trench), the Indian Ocean (Sri Lanka, off Dunbar), the Atlantic (off Argentina), and the Southern Ocean (Kerguelen Island, Bransfield Strait, South Shetlands, Ross Sea). The genus is widely distributed in abyssal and hadal depths. Only in the Antarctic has it been found on the continental shelf at 300-400 m ( Figure 25).
Body ( Figure 1A, B). Length 4.6 mm. Body about six to seven times as long as wide.
Antennule ( Figure 2A). Article 1 massive, about one-third longer than articles 2 and 3 combined, with three groups of simple and pinnate setae; article 2 one-third as long as article 3, with one simple seta; article 3 with seven simple and one pinnate apical setae.
Antenna ( Figure 2B). Article 2 twice as long as article 3, with one simple seta; article 4 less than twice as long as article 5, with three minute rod setae and two pinnate setae distally; article 5 with one simple seta distally; article 6 very short, with seven terminal setae.
Mouthparts. Labrum ( Figure 2C) hood-shaped, covered by numerous short needle-like setae. Mandible ( Figure 2D, E) robust, molar process well-developed with undulated but spineless margins, bunch of delicate setae at ''lower'' margin ( Figure 2E9), lacinia mobilis well-developed, crenulated. Maxillule ( Figure 2F) endite as long as palp, with nine apical spiniform setae; two of them are fused together; palp lost during dissection. Maxilla lost during dissection. Both lobes of labium ( Figure 2G) poorly separated and hirsute in distal parts; inner lobe with tubercle distally; each ''accessory lobe'' with row of short simple setae and comb of setae along outer margin.
Maxilliped ( Figure 2H). Basis (typical for genus) fused in heart-shaped plate; endite with two simple setae and two flat setae (tubercles) distally; palp article 1 unarmed, article 2 wedge-shaped, with two weakly serrated and one strongly serrated setae on inner margin and one minute seta on outer margin; article 3 trapezoidal, with four weakly serrated setae on inner margin; article 4 slender, with one simple seta on outer margin and five weakly serrated distal setae.
Cheliped ( Figure 3A). Basis robust, slightly rounded, 1.75 times as long as wide; merus wedge-shaped, with one rod seta; carpus with row of six small rod setae dorsally and two relatively long rod setae ventrally; propodus with distal seta on inner side; fixed finger (propodus projection) tipped with a strong spine, with two to three teeth and three rod setae dorsally and two setae ventrally; one seta near insertion of dactylus; dactylus slightly curved, with two strong spiniform setae ventrally and one short rod seta proximally on dorsal margin.
Pereopod 1 ( Figure 3B). Slender (walking type); basis with two pinnate seta on proximal part only and short setae along article; ischium short with one seta; merus subequal to propodus, with two setae distally; carpus with three simple and one rod setae; merus and carpus combined longer than propodus; propodus with one simple and two rod setae distally, propodus length: width ratio 5.75; dactylus half unguis length, with long seta.
Pereopod 4 ( Figure 3E). Clinging type; basis twice as long as wide, with two simple and two pinnate setae; ischium with two setae; merus subequal to carpus, with two strong spiniform setae on ventral margin and combs of blunt spines; carpus with two distal hooks, one seta dorsally and large tubercle covered by little spines and surrounded by row of calcified ( Figure 3E9), blunt spines ventrally; propodus, with two spiniform setae ventrally and distal seta twice as long as propodus and dactylus combined length; dactylus tipped by weakly bifurcated unguis; two teeth on ventral margin.
Pleopods ( Figure 1D). All pleopods similar in structure; exopod and endopod with a row of plumose setae on outer margin (length: width ratio of both exopod and endopod 3.0); no gaps between the most proximal and other setae.
Uropod ( Figure 3H). Both rami uni-articled, exopod little shorter than endopod; endopod with two pinnate setae at middle, tipped by four simple terminal setae (one very short) and two pinnate setae; exopod with short simple middle seta on outer margin, tipped by strong and minute simple setae.

Distribution
Peraeospinosus kerguelenensis is known from the region of the Kerguelen Islands (Southern Ocean) ( Figure 25) where it was collected at depths from 17 to 1390 m (Beddard 1886a;Shiino 1978). Peraeospinosus kerguelenensis can be distinguished from the other members of Peraeospinosus by the relatively long pleon that is slightly longer than the carapace. Also, Peraeospinosus magnus (Kudinova-Pasternak 1990) also has a pleon slightly longer than the carapace but its carapace is long and narrow (length: width ratio 1. 24) which distinguishes it from the former species. The carapace of P. kerguelenensis is round (length: width ratio 0.94) and resembles that of P. emergensis n. sp., but the last species, unlike P. kerguelenensis, has pereonites 2-4 longer than wide. The uropod exopod slightly shorter than the endopod is a character shared by P. kerguelenensis, P. rectus (Kudinova-Pasternak, 1966), P. peculiaris (Lang, 1968), and P. peculiaroides n. sp. Each of the last three species, however, has one seta on the propodus of pereopod 6 reaching far over the unguis, while P. kerguelenensis has all three setae not longer than the dactylus.

Diagnosis
Female. Carapace 1.3 times as long as wide, oval; pereonites 1-5 longer than wide; pereonite 1 relatively long (three-quarters length of carapace). Pereonite 6 one-third as long  Propodus of pereopod 6 with one long seta distally. Pleopod endopod with one dorsal seta and six setae in distal part.
Body. Body about eight times longer than wide.
Pereonites. Pereonites 1-5 longer than wide, with only slightly rounded corners; pereonite 6 three times wider than long and a little narrower than pereon 5, one-quarter as long as carapace.
Antennule ( Figure 4B). Article 1 narrow, four times as long as wide, with group of pinnate setae distally and two short rod setae along article; article 2 three times as long as article 3, with one rod seta and one pinnate seta distally; article 3 with six sharply tipped setae (three long and three short).
Antenna ( Figure 4C). Article 2 a little longer than article 3; both articles naked; article 4 is 1.6 times longer than article 5, with three pinnate and two rod setae distally; article 5 with one simple seta distally; article 6 very short, with six terminal setae (four long and two short).
Pereopod 1 ( Figure 5A). Basis with one pinnate seta in proximal part and three rod setae along article; ischium with one rod seta; merus subequal to propodus, with two rod setae distally; carpus with five rod setae distally; propodus five times as long as wide, with two rod setae dorsally and minute spiniform seta ventrally; dactylus as long as half unguis, with short seta (not longer than dactylus).
Pereopod 2 ( Figure 5B). Basis little shorter than merus, carpus and propodus combined; with two rod setae in the middle of article and one pinnate proximal seta; ischium with rod seta; merus little longer than carpus, with two rod setae and two spiniform setae; carpus with five rod setae and one spiniform seta distally; propodus little shorter than merus and carpus combined, with one spiniform seta ventrally and one rod seta and one trifurcate seta dorsally; propodus length: width ratio 5.5; dactylus with one simple distal seta. Unguis twice as long as dactylus.
Pereopod 4 ( Figure 5D). Basis 2.6 times as long as wide, with two pinnate setae and one rod seta dorsally and two pinnate setae ventrally; ischium with one seta; merus with two spiniform setae and combs of blunt teeth ventrally; carpus with two distal hooks and large, prickly tubercle surrounded by row of blunt, calcified spines; propodus with two spiniform setae ventrally, pinnate seta dorsally and distal seta reaching over unguis; dactylus tipped by bifurcated unguis.
Pleopods ( Figure 5F). All pleopods similar in structure; endopod (length: width ratio 2.6) with one seta on dorsal margin; six plumose setae in distal part and one plumose seta proximally; large gap between distal and proximal setae; exopod with a row of 18 plumose setae on outer margin (length: width 3.9); relatively short gap between the most proximal and the other setae.

Distribution
The species has a discontinuous distribution: in the North Pacific (off California, off Japan and Alaska), the South Atlantic (Argentina), and the West Antarctic (Bransfield Strait) ( Figure 25). Depth range: 1170-5225 m.

Remarks
The only specimen of P. magnificus available for the study lacks some of the appendages and pleotelson. The remaining appendages and the figures presented in Kudinova-Pasternak (1970, p 350) are enough for recognition and placement of the present species in Peraeospinosus. Peraeospinosus magnificus most resembles P. emergensis n. sp. and P. exiliremis n. sp. having pereonites 1-3 slightly narrowed in the middle and antennule article 3 three times longer than article 2. However, it has a much more elongated carapace than the two last species. Also, only P. magnificus has six, fully developed setae on the lower margin of the pleopod endopod, while P. emergensis has 15 setae on lower margin of the pleopod endopod and P. exiliremis has a few short simple setae there.
Body. Body about seven to eight times longer than wide.
Pereonites and pleonites. Pereon 1 is two-thirds as long as carapace and subequal to pereonite 6; pleon longer than carapace; all pleonites similar in size; pleotelson truncated posteriorly.
Antennule ( Figure 6B). Article 1 a little longer than articles 2 and 3 combined, with three pinnate setae distally and three minute setae along article; article 2 is one-third as long as article 3, with one simple seta distally; article 3 with seven simple apical setae.
Antenna ( Figure 6C). Article 2 twice as long as article 3, both with short rod seta; article 4 twice as long as article 5, with five setae distally; article 5 with one simple seta distally; article 6 very short, with seven terminal setae.
Mouth parts and pereopods. Missing.
Pleopods ( Figure 6D). All pleopods similar in structure; endopod with two dorsal (inner) setae, exopod and endopod with a row of plumose setae on outer margin (length: width ratio of exopod 3.75; of endopod 2.9); no clear gap between the most proximal and other setae.
Uropod ( Figure 6E). Both rami uni-articled, subequal; endopod with one pinnate seta at the middle, tipped by four simple terminal setae and three pinnate setae; exopod with short simple middle seta on outer margin, tipped by strong and minute simple seta.

Distribution
Known only from the type locality ( Figure 25).

Remarks
Peraeospinosus magnus is known only from the holotype, a specimen which lacks most appendages. The combination of characters observed in the antennule, antennae, pleopods, and uropods is enough to recognize P. magnus as a valid species. It is the only member of Peraeospinosus with two setae on the inner margin of the pleopods.
Body ( Figure 7A). Length 8.6 mm. Body about 8.5 times as long as wide.
Antennule ( Figure 7B). Article 1 massive, about one-third longer than articles 2 and 3 combined, with three rod setae marginally and two pinnate setae distally; article 2 one-third length of article 3, with one simple seta and two pinnate setae distally; article 3 with six apical setae.
Antenna ( Figure 7C). Article 2 a little longer than article 3, both articles without setae; article 4 twice as long as article 5, with two pinnate setae distally; article 5 with one simple seta distally; article 6 very short, with six terminal setae.
Mouthparts. Labrum missing. Mandible ( Figure 7D, E) typical for genus: robust, molar process well-developed with undulated margins with bunch of delicate and long setae at ''lower'' margin, lacinia mobilis well-developed, crenulated. Maxillule ( Figure 7F) typical for genus: with nine apical spiniform setae; two of them fused together; palp missing. Maxilla missing. Labium ( Figure 7G, G9) typical for genus; both lobes poorly separated and hirsute in distal parts; inner lobe with tubercle distally; each external lobe with row of  short simple setae and comb of setae along outer margin. Maxilliped missing. Epignath (not drawn) simply tipped (not bifurcated distally).
Cheliped ( Figure 7H). Basis robust, slightly rounded, 1.6 times longer than wide; merus wedge-shaped with one seta ventrally; carpus with row of seven small rod setae dorsally and two relatively long rod setae ventrally; propodus robust, 1.6 times as long as wide; fixed finger (propodus projection) tipped with a thick spine, with three setae dorsally and two setae ventrally; dactylus slightly curved.
Pereopod 1 ( Figure 8A). Basis with two rod setae dorsally in proximal part, one short seta ventrally in distal part; ischium short, with one seta; merus subequal to propodus, with one rod seta, one simple and one spiniform seta distally; carpus with three rod setae distally; merus and carpus combined longer than propodus; propodus with one spiniform seta and two rod setae distally, propodus length: width ratio 6.25; dactylus half as long as unguis, with long seta.
Pereopod 2 ( Figure 8B). Basis little shorter than rest of articles combined, with one simple and one pinnate setae proximally, one rod seta distally, with numerous combs of setae along article; ischium with combs of setae; merus and carpus subequal, merus with one simple and one spiniform seta distally, with numerous combs of setae; carpus with three simple setae and one thick spiniform seta distally, with many combs of robust setae; propodus little shorter than merus and carpus combined, with blunt spiniform seta ventrally and rod seta dorsally, covered with numerous combs of setae; propodus length: width ratio 3.85; dactylus with one simple seta.
Pereopod 4 ( Figure 8D). Basis twice as long as wide, with three rod setae and two pinnate setae along article; ischium with two rod setae ventrally; merus little longer than carpus, with two strong spiniform setae and strong blunt spines ventrally; carpus with two distal hooks, one seta dorsally, and large prickly tubercle surrounded by row of calcified, blunt spines ventrally; propodus, with two spiniform setae ventrally and one long distal seta, one pinnate seta dorsally; dactylus tipped by clearly bifurcated unguis.
Pleopods ( Figure 8G). All pleopods similar in structure; exopod and endopod with a row of plumose setae on outer margin (length: width ratio of exopod 3.5, of endopod 4.1); clear gaps between the most proximal and other setae at both rami, endopod with one plumose seta on dorsal margin.
Uropod ( Figure 8H). Both rami uni-articled, exopod little shorter than endopod; endopod with two pinnate setae at the middle, tipped by four simple terminal setae, one rod and two pinnate setae; exopod with short simple middle seta on outer margin, tipped by one strong seta and one minute simple seta.

Remarks
Peraeospinosus peculiaris was described by Lang (1968) based on two specimens, one obtained from the area of Seychelles-Ceylon [5Sri Lanka] (1u549N, 77u059E) and one from the vicinity of Durban (32u009S, 32u419E, depth 3530 m). The re-examination of fragments and dissected appendages of both specimens held in the Zoological Museum University of Copenhagen revealed that each of those two specimens represent two nominal species. The description of P. peculiaris (Lang, 1968) is confusing. Lang (1968, p 161-166) used the specimen from off Durban for describing external characters (body, carapace, pereonites, and pleon), while the description of the appendages was based on the specimen from the Seychelles-Ceylon region. Nevertheless, Lang clearly stated that the Durban specimen (Sta. 192) was the type specimen, and therefore the specimen from Seychelles-Ceylon is considered to be an undescribed species, described here as Peraeospinosus peculiaroides n. sp.
Body. Body about six times as long as wide.
Antennule ( Figure 10A). Article 1 massive, about 1.5 times as long as articles 2 and 3 combined, with three groups of pinnate setae and one simple seta distally; article 2 shorter than article 3, with one simple seta; article 3 with five simple setae and two pinnate setae distally.
Antenna ( Figure 10B). Article 2 a little longer than article 3; article 3 with four simple setae; article 4 twice as long as article 5, with two minute and two pinnate distal setae; article 5 with two simple seta distally; article 6 very short with, six terminal setae.
Maxillipeds ( Figure 10H). Basis fused in heart-shaped plate, with one seta on distal margin; endite with two setae and two tubercles on distal margin; palp article 1 naked; article 2 wedge-shaped, with three plumose setae on inner margin and one minute seta on outer margin; article 3 trapezoidal, with four serrated setae and one simple seta on inner margin; article 4 more slender than the others, with one simple seta in outer margin and with a group of five serrated terminal setae.
Cheliped ( Figure 10J). Basis robust, slightly rounded, 1.8 times as long as wide, fused with the body; merus wedge-shaped, with one seta ventrally; carpus with rounded dorsal margin armed with two setae on ventral margin and row of 10 minute setae on dorsal margin; propodus with seta on inner side; fixed finger (propodus projection) tipped with a strong spine, with two to three teeth and three setae on dorsal margin, two setae on ventral margin; dactylus slightly curved, with minute seta on dorsal margin.
Pereopod 1 ( Figure 11A). Basis smooth, with one pinnate seta in proximal part only and nine short rod setae, longer than ischium, merus and carpus together; ischium short, with one seta; merus subequal to propodus, with one spiniform and two simple setae distally; carpus with four setae and one rod seta distally; propodus with three setae, propodus length: width ratio 6; dactylus as long as unguis, with one long seta.
Pereopod 2 ( Figure 11B). Basis little shorter than the rest of articles combined, with five rod setae; ischium short with one simple seta; merus and carpus subequal, both with one spiniform seta distally; additionally two simple setae on merus and four simple setae on carpus; propodus as long as merus and carpus combined, with one short simple seta and two spiniform distally; propodus length: width ratio 5; dactylus with one simple seta, tipped by subequal unguis.
Pereopod 3 ( Figure 11C). Similar to pereopod 2 but spiniform setae on merus and two distal setae on carpus are modified to strong spines.
Pereopod 4 ( Figure 11D). Basis wide, one-fifth as long as wide and clearly shorter than length of rest of articles combined, with one rod seta ventrally; ischium with two setae (one broken off); merus subequal to carpus; merus with combs of setae and two spiniform setae; carpus with two distal hooks and one seta distally; large prickly tubercles surrounded by short, blunt and well-calcified spines; propodus longer than carpus, with one pinnate setae on dorsal margin; propodus with one long seta distally and two spiniform setae ventrally; dactylus tipped by relatively short, bifurcated unguis.
Pereopod 6 ( Figure 11F). Similar to pereopod 5; basis with one simple seta and one pinnate seta; propodus tipped by three relatively short terminal setae (not longer than dactylus).
Pleopods ( Figure 9D). All pleopods similar in structure; exopod and endopod with a row of plumose setae on outer margin (length: width ratio of exopod 2.6; of endopod 3.2); the most proximal seta on the exopod and endopod, separated from remainder by a gap; one plumose seta on inner margin of endopod.
Uropod ( Figure 11I). Exopod uni-articled a little shorter than endopod; endopod with two articles; endopod article 1 with two pinnate setae distally; endopod article 2 tipped by four long and one short simple setae and two pinnate setae; exopod with short simple seta in proximal part of outer margin, one strong seta and one minute simple seta distally.

Distribution
Peraeospinosus pushkini so far has been found only at the Antarctic Peninsula at the depth range of 33-600 m (Figure 25).

Remarks
Peraeospinosus pushkini is the only member of the genus which has a two-articled endopod of the uropod.

Diagnosis
Female. Carapace rounded, as long as wide, a little swollen. Pereonites 2 and 3 as wide as long. Pereonite 1 relatively long (two-thirds length of carapace). Pleon little longer than carapace, truncated posteriorly. Antennule article 3 twice as long as article 2. Propodus of pereopod 2 length: width ratio about 4.6. One distal seta on propodus of pereopod 6 reaching over the unguis. Pleopod endopod elongated (over four times as long as wide). Pleopod endopod with one dorsal seta. Uropod exopod slightly shorter than endopod.
Body ( Figure 12A, B). Body about 5.5 times longer than wide.
Cephalothorax. Rounded, only slightly longer than wide, twice as long as pereonite 6; rostrum rounded.
Pleon. Pleon as long as carapace. All pleonites similar in size; pleotelson rectangular.
Antennule ( Figure 13A). Article 1 massive, about three times as long as wide and a little longer than articles 2 and 3 combined, with group of pinnate setae at middle, and one simple seta distally; article 2 with two pinnate setae distally; article 3 with six simple apical setae (four long and two short).
Antenna ( Figure 13B). Article 2 twice as long as article 3, article 2 with short seta; article 4 twice as long as article 5, with one simple seta and two pinnate setae distally; article 5 with one long simple setae distally; article 6 with five terminal setae.  Mouthparts. Labrum missing. Mandible ( Figure 13C) typical for genus: robust, molar process well-developed with strongly undulated margins and short setae at ''lower'' margin; lacinia mobilis well-developed, crenulated. Maxillule ( Figure 13D) typical for genus: with nine apical spiniform setae; two of them fused together; palp lost during dissection. Maxilla semi-oval ( Figure 13E). Labium ( Figure 13F) typical for genus; both lobes poorly separated and hirsute in distal parts; inner lobe with tubercle distally; each ''accessory lobe'' with row of short simple setae and comb of setae along outer margin.
Maxilliped ( Figure 13G). Basis (typical for genus) fused in heart-shaped plate; endite with two rod setae and two flat setae (tubercles) distally; palp article 1 unarmed, article 2 wedgeshaped, with two weakly serrated and one strongly serrated setae on inner margin and one minute seta on outer margin; article 3 trapezoidal, with four weakly serrated setae on inner margin; article 4 slender, with one simple seta on outer margin and five weakly serrated distal setae. Epignath ( Figure 10H) simply tipped (not bifurcated distally).
Cheliped ( Figure 14A). Basis robust, slightly rounded, 1.5 times as long as wide; merus wedge-shaped with one rod seta ventrally; carpus with row of six small rod setae dorsally and two short rod setae ventrally; propodus robust, 1.5 times as long as wide; fixed finger (propodus projection) tipped with a thick spine, with three setae dorsally and two setae ventrally; dactylus slightly curved with one rod seta dorsally and two spines ventrally.
Pereopod 1 ( Figure 14B). Basis with one pinnate seta in proximal part and four rod setae along article; ischium with one rod seta; merus subequal to propodus, with three rod setae distally; carpus with five rod setae distally; propodus five times as long as wide, with two rod setae dorsally and minute spiniform seta ventrally; dactylus subequal to unguis, with one seta not longer than unguis.
Pereopod 2 ( Figure 14C). Basis a little shorter than merus, carpus, and propodus combined, with two rod and one pinnate seta; ischium naked; merus a little longer than carpus, with two setae and one spiniform setae distally; carpus with three spiniform, one simple, and one tubercle distally; propodus a little shorter than merus and carpus combined, with spiniform seta ventrally and two rod setae dorsally; propodus length: width ratio 5.6; unguis twice as long as dactylus.
Pereopod 4 ( Figure 14E). Basis 2.6 times as long as wide, with pinnate setae and one rod seta along article; ischium with one seta; merus ventral margin with spiniform setae and combs of blunt teeth; carpus with two distal hooks and large, prickly tubercle surrounded by row of blunt, strongly calcified spines; propodus with two spiniform setae ventrally, pinnate seta dorsally and distal seta reaching over unguis; dactylus tipped by bifurcated unguis.
Pleopods ( Figure 12C). All pleopods similar in structure; exopod with row of 16, and endopod with row of 10 plumose setae on outer margin (length: width ratio of exopod 3.1; of endopod 3.4); most proximal seta on exopod, as well as on endopod, is separated from remainder by a gap; one plumose seta on inner margin of endopod.
Uropod ( Figure 14H). Exopod with one article. Endopod with suture at place of fusion of two articles; endopod clearly longer than exopod; endopod with two pinnate setae at the middle, tipped by four simple terminal setae and three pinnate setae; exopod with short simple seta in proximal part of outer margin, tipped by strong and minute simple setae.

Distribution
The species has two centres of distribution: Pacific Ocean (Kuryl-Kamchatka Trench, Japan Trench) and West Antarctic ( Figure 25). Depth range 4664-7370 m.

Remarks
Peraeospinosus rectus can be distinguished from the other members of the genus by the presence of strong, blunt, and well-calcified spines on the merus and carpus of pereopods 4-6. Similar spines can be observed in P. exiliremis, which has also other distinguishing characters such as pleon narrower than pereonite, weakly developed pleopods, and uropod exopod little longer than endopod.
Body. Body about 10 times as long as wide.
Antennule ( Figure 15B). Article 1 massive, about twice as long as articles 2 and 3 combined, with three groups of simple and pinnate setae; article 2 half length of article 3, with one pinnate seta and two rod setae; article 3 with five simple apical setae.
Antenna ( Figure 15C). Articles 1-3 subequal; article 4 twice as long as article 5, with three minute distal setae; article 5 with one simple seta distally; article 6 very short with five terminal setae.
Maxillipeds ( Figure 15G). Basis fused in heart-shaped plate, with plumose seta on distal margin; endite with two setae and two tubercles distally; palp article 1 unarmed, second wedge-shaped, with three plumose setae on inner margin and one minute seta on outer margin; article 3 trapezoidal, with three setae on inner margin and one simple seta on outer margin; article 4 more slender than the others, with one simple seta in outer margin and five plumose terminal setae.
Cheliped ( Figure 15H). Basis robust, slightly rounded, 1.5 times as long as wide, fused with the body; merus rectangular with one seta ventrally; carpus with rounded dorsal margin armed with two setae on ventral margin and row of 11 minute setae on dorsal margin; propodus with seta on inner side; fixed finger (propodus projection) tipped with a strong spine, with two to three teeth and three setae on dorsal margin, two setae on ventral margin; one seta near insertion of dactylus; dactylus slightly curved, with minute seta on dorsal margin.
Pereopod 1 ( Figure 16A). Basis smooth, with two pinnate setae in proximal part only, longer than ischium, merus, and carpus together; ischium short, naked; merus subequal to propodus, with two simple setae and one rod seta distally; carpus with two setae and one long rod seta distally; propodus with one calceolus and two setae, propodus length: width ratio 6.25; dactylus as long as unguis.
Pereopod 2 ( Figure 16B). Basis almost equal to the rest of articles combined, with two minute setae on ventral margin; ischium short, naked; merus and carpus subequal, both with one spiniform seta distally; additionally two simple setae on merus and three simple and one pinnate seta on carpus; propodus as long as merus and carpus combined, with one short simple seta and one spiniform seta distally; propodus length: width ratio 7.7; dactylus with one simple seta, tipped by subequal unguis.
ereopod 4 ( Figure 16D). Basis wide, twice as long as wide and a little shorter than total length of carpus and propodus combined, with four pinnate and three simple setae; ischium with one seta; merus subequal to carpus; carpus with prickly tubercle surrounded by short, blunt and calcified spines, two distal hooks and one spiniform seta distally; propodus twice as long as carpus, with one middle seta; in distal part of propodus one long seta and two spiniform setae ventrally; dactylus tipped by relatively short bifurcated unguis.
Pleopods ( Figure 16G). All pleopods similar in structure; exopod and endopod with a row of plumose setae on outer margin (length: width ratio of exopod 3.1; of endopod 3.4); the most proximal seta on the exopod and endopod, separated from remainder by a gap; one plumose seta on inner margin of endopod.
Uropod ( Figure 16I). Both rami uni-articled, subequal, three times as long as basal article; endopod with two pinnate setae at the middle, tipped by four simple terminal setae and two pinnate setae; exopod with short simple seta in distal in proximal part of outer margin, tipped by one strong seta and one minute simple seta.

Remarks
Peraeospinosus emergensis n. sp. is distinguished by the presence of long calceoli on the distodorsal corner of pereopod 1 (a character easily seen also in small specimens). It is also characterized by a long merus, carpus (about twice as long as wide), and propodus (eight times as long as wide) of pereopod 2. The other members of the genus Peraeospinosus have carpus and merus as long as wide, and propodus 4.5-6 times as long as wide. Pereonites 2-4 long and rectangular, narrowed in the middle is a character shared by P. emergensis n. sp., P. magnificus, and P. exiliremis n. sp., but P. magnificus has an oval carapace (longer than pereonite 1) and P. exiliremis has a pleotelson much narrower than the pereon, and the uropod exopod a little longer than the endopod. The sixth pereonite is smooth and has rounded margins in dorsal view.

Etymology
The name reflects the weakly developed pleopods that are used by tanaids for swimming or producing water current in tubes (Latin: exilis+remus5meagre+oar).
Body. Body about 8.5 times as long as wide.
Antennule ( Figure 17B). Article 1 a little longer than articles 2 and 3 combined, with three groups of simple and pinnate setae on outer margin; inner margin with row of four rod  setae. Article 2 one-third length of article 3, with three rod setae distally. Article 3 with seven simple setae and one pinnate apical setae.
Antenna ( Figure 17C). Article 3 with minute seta. Article 4 almost twice as long as article 5, with three rod setae and three pinnate setae distally. Article 5 with one simple seta distally. Article 6 very short, with five terminal setae.
Mouthpart. Labrum not dissected. Mandible typical for genus; molar process ( Figure 17D) well-developed, with undulated margins with bunch of well-calcified setae at ''lower'' margin. Maxillule ( Figure 17E) with nine apical spiniform setae (two of them fused together); three of the setae swollen and well-calcified distally. Maxilla and labium lost during dissection.
Maxilliped ( Figure 17G). Typical for genus. Basis fused in heart-shaped plate with two pinnate setae; endite with two simple setae and two flat setae (tubercles) distally. Palp article 1 naked. Article 2 wedge-shaped, with two weakly serrated setae and one simple seta on inner margin and one minute seta on outer margin. Article 3 trapezoidal, inner margin with one simple, one serrated seta and two weakly serrated setae swollen distally. Article 4 slender, with one simple seta in outer margin and five sparsely serrated distal setae (one seta distally swollen).
Cheliped ( Figure 17F). Basis robust; merus wedge-shaped with long, well-calcified rod seta; carpus with row of five small rod setae dorsally and two well-calcified rod setae ventrally; propodus 1.3 times as long as carpus, with seta on inner side and short seta distally on dorsal margin; fixed finger (propodus projection) tipped with a strong spine, with two to three teeth, three rod setae dorsally, and two setae ventrally; one setae near insertion of dactylus; dactylus slightly curved, with two strong spiniform setae ventrally and one short rod seta proximally on dorsal margin.
Pereopod 1 ( Figure 18A). Basis with one pinnate seta in proximal part only and three short rod setae along article; ischium naked; merus subequal to carpus, with three short setae distally; carpus with five simple setae and one rod seta; merus and carpus combined longer than propodus; propodus with one simple and two rod setae distally, propodus length: width ratio 5.75; dactylus half as long as unguis.
Pereopod 2 ( Figure 18B). Basis little longer than rest of articles combined, naked; ischium naked; merus and carpus subequal, each with one robust spiniform seta and two setae distally; propodus a little shorter than merus and carpus combined, with minute spine ventrally and two rod setae dorsally; propodus length: width ratio is 4.5; dactylus tipped with slightly longer well-calcified unguis.
Pereopod 4 ( Figure 18D). Basis half as long as wide, with two pinnate setae distally; ischium with two setae; merus a little longer than carpus with two strong spiniform setae on ventral margin and sharp, well-calcified spines; carpus with two distal hooks and one seta dorsally; ventrally, large prickly tubercles surrounded by row of well-calcified and sparsely distributed strong spines; propodus with two spiniform setae ventrally and long distal seta; dactylus tipped with weakly bifurcated unguis; row of teeth on ventral margin of dactylus.
Pleopods ( Figure 18G). All pleopods similar in structure; exopod with short and simple setae on distal part; endopod with five setae on lower margin two long, feather and three short, simple setae; one plumose seta on inner margin (length: width ratio of both exopod and endopod 3.0); no proximal setae on exopod or endopod.
Uropod ( Figure 18H). Both rami uni-articled, exopod a little longer than endopod; endopod with three pinnate setae at the middle, tipped with five simple terminal setae (two short); exopod with short simple seta on outer margin, tipped with one strong seta and one minute setae.

Distribution
Species known from Antarctic Peninsula and Weddell Sea ( Figure 25).

Remarks
Peraeospinosus exiliremis can be distinguished from the other species of Peraeospinosus by the pleon, which is narrower than the pereon, the weakly developed pleopods, and the uropod exopod being slightly longer than the endopod.

Diagnosis
Female. Pereonites 2-5 longer than wide; pereon almost half carapace length. Pleotelson rectangular posteriorly. Antennule article 3 four times as long as article 2. Propodus of pereopod 2 length: width ratio about 4. One of three distal setae on propodus of pereopod 6 reaching over dactylus, two others as long as dactylus. Pereopods 4-6 unguis without teeth below bifurcated tip. Pereopods 4-6 merus and carpus with small and numerous spines ventrally. Pleopod endopod with one dorsal seta; no clear gap between proximal seta and the remaining ones. Uropod exopod slightly shorter than endopod.

Remarks
The description and figures by Lang (1968, p 162, 164-165, Figures 99-101) are carefully and completely prepared. Some missing details of mandible molar and pereopods 5 and 6 are given in Figure 19. The type specimen of Peraeospinosus peculiaroides is missing the carapace, nevertheless the characters displayed by rest of the body and the dissected appendages distinguish it clearly from P. peculiaris s. str. Pereonite 1 of P. peculiaroides is almost subequal to pereonite 2 and pereonite 6 is half the length of pereonite 5, while in P. peculiaris pereonite 1 is clearly shorter than pereonite 2 and pereonite 6 is two-thirds the length of pereonite 5. The cheliped carpus of P. peculiaris is stout (1.6 times as long as wide) and armed with seven rod setae on the dorsal edge; in P. peculiaroides (Lang 1968, p 164) it is about twice as long as wide and armed with 16 rod setae dorsally. Bases of all pereopods in P. peculiaris have more (about six) rod setae and the merus and carpus of pereopods 4-6 are delicately setose (poorly calcified) on the ventral side. On the contrary, P. peculiaroides has fewer setae on the bases of the pereopods (not more than four) and the merus and carpus of pereopods 4-6 are armed ventrally with strong spines. Propodus of pereopod 6 has one long and two short setae distally in both species, but the two short setae are as long as the dactylus in P. peculiaroides and only half as long as the dactylus in P. peculiaris. The gap between the most proximal and the other setae is clear in both pleopod rami in P. peculiaris, while it is not obvious on the exopod and is absent on the endopod in P. peculiaroides. Other differences can be observed in the mouthparts of both species; the setae on the molar process of the mandible are long and relatively thin in P. peculiaris, while they are short but more calcified in P. peculiaroides.
Body. Body about seven times as long as wide.
Pleon. All pleonites similar in size. Pleon only a little shorter than carapace. Pleotelson truncated posteriorly.
Antennule ( Figure 21A). Article 1 massive, less than twice length of articles 2 and 3 combined, with three groups of simple and pinnate setae on outer edge and row of six simple setae on inner margin; article 2 with simple seta distally, half as long as article 3; article 3 tipped with eight simple setae, one pinnate seta, and one aestethasc.
Antenna ( Figure 21B). Articles 1 and 3 subequal; article 2 a little longer than article 3, with short distal seta; article 4 twice as long as article 5, with three minute and one pinnate setae distally; article 5 with one simple seta distally; article 6 very short with six apical setae.
Maxilliped ( Figure 21H). Basis fused in heart-shaped plate, with two plumose setae on distal margin; endite with numerous short setae on inner margins; distal margin with two flat setae (tubercles), one simple seta, and one rod-like seta; palp article 1 unarmed, article 2 wedge-shaped, with one small seta on outer margin and three setae on inner margin (simple, strongly pinnate and rod seta); article 3 trapezoidal, with four setae on inner margin (two simple, one serrated, and one rod seta); article 4 more slender than article 3, simple seta on outer margin and five serrated or simple terminal setae on inner margin.
Cheliped ( Figure 20C). Basis robust, slightly rounded distally; merus wedge-shaped with one rod seta ventrally; carpus with two setae on ventral margin and row of six minute setae on dorsal margin; propodus fixed finger (propodus projection) tipped with a strongly calcified, blunt spine, two to three strongly calcified teeth and three setae on dorsal margin, two setae on ventral margin; dactylus slightly curved, with minute seta on dorsal margin and two strong spiniform setae on ventral margin.
Pereopod 1 ( Figure 22A). Basis with six rod setae along article and one pinnate seta proximally; ischium with one seta; merus subequal to carpus, with two setae distally; carpus with two rod setae and two simple setae distally; merus and carpus combined longer than propodus; propodus with one simple and two rod setae distally, propodus length: width ratio 5.5; dactylus half as long as unguis, with one seta.
Pereopod 2 ( Figure 22B). Basis a little shorter than the rest of articles combined, with six rod setae along article and one pinnate seta proximally; ischium with one seta; merus subequal to carpus, with one tubercle and one seta distally; carpus with four blunt spiniform setae and one simple seta distally; merus and carpus with numerous well-calcified combs of setae; propodus length: width ratio 4.8; dactylus with one simple seta, unguis longer than dactylus.
Pereopod 4 ( Figure 22D). Basis wide, twice as long as wide, with two pinnate setae distally, one pinnate seta proximally and four simple setae along article; ischium with two setae; merus a little longer than carpus, with strong spiniform seta ventrally, carpus with two distal hooks and one seta distally; ventral margin of basis, merus, and carpus covered by strong spines; propodus with pinnate seta in middle, two spiniform setae ventrally and long seta distally; dactylus tipped by a bifurcated unguis.
Pleopods ( Figure 22G). All pleopods similar in structure; endopod with one plumose seta dorsally and 16 setae ventrally; exopod with 23 short simple setae on outer margin (length: width ratio of exopod 3.0; of endopod 3.0); proximal seta on exopod and endopod separated by gaps from the others.
Uropod ( Figure 22H). Both rami uni-articled; exopod subequal to endopod; exopod with one minute seta at the middle, tipped by strong and minute simple setae; endopod with two pinnate setae at the middle; with five terminal setae.
Pleon. Pleon 0.8 times as long as total body length; pleotelson elongated, with welldeveloped caudal process.
Antennule ( Figure 23A). With seven articles; articles 1 and 2 relatively robust, subequal, with groups of simple setae; articles 3-5 narrow, article 6 as long as article 7; article 3 with two long simple setae; articles 4-6 with row of aesthetascs; article 7 with four simple apical setae and one aesthetasc.
Antenna ( Figure 23B). With seven articles; articles 2-4 subequal; article 3 with one distal seta, articles 5 and 6 subequal, article 7 one-third length of article 6; last three articles with simple distal setae.
the deep sea''. Basing his interpretation on fossil records (Schram, 1986), global climate and water temperature in the Cretaceous and Eocene, the phylogenetic relationship of recent Tanaidacea, and some characteristics of deep-sea fauna, e.g. lack of eyes, he concluded that the Antarctic fauna had to be extinct during the Cenozoic climatic deterioration. As a result, cold-stenothermal eurybathic taxa could have invaded vacant niches, supporting the hypothesis of polar emergence (Hessler and Thistle 1975). Brandt (1999) argued that some phylogenetically old tanaidacean taxa that are poorly represented in the West Antarctic could have survived the ice ages in refugia on the Antarctic shelf (as the isopod families Antarcturidae and Serolidae). Study of the material of tanaidaceans collected in the Southern Ocean on board the Eltanin, Hero, and Polarstern from the 1960s to the 1990s, revealed that abyssal and shelf tanaid faunas in the Antarctic are represented by two different sets of species. The few exceptions such as Paranarthura fortispina (Sieg, 1986) and Typhlotanais greenwichensis Shiino, 1970, which are found both in shallow and deep waters, are much more likely to be eurybathic taxa than records supporting polar emergence. On the contrary, one sample taken by Eltanin (Cr 6 Sta 339, see Larsen and Blażewicz-Paszkowycz 2003) in the lower Antarctic shelf (500-570 m) may well illustrate the polar emergence phenomena, as it consisted of typical shallow-water species (Nototanais antarcticus, Paratanais oculatus, Synapseudes ideos) together with typical deep-water taxa such as Exspina typica and N. affinis. It is regretted that no more samples were taken in the lower sublittoral or upper continental slope to exclude a potential artefact. A present-day distribution of a genus does not in itself indicate its origin, although the possibility of a deep-water origin cannot be excluded. There is no reason to reject that a phylogenetically young and blind Peraeospinosus or Typhlotanais (typhlos [gr]5blind) could have colonized Antarctic free niches and then radiated. Without a phylogeny relating to primitive species in the deep sea, it is impossible to say.