Tanaidacea (Crustacea: Peracarida) of the northeast Atlantic: Chauliopleona Dojiri and Sieg, 1997 and Saurotipleona n. gen. from the ‘Atlantic Margin’

Two akanthophoreid taxa, Chauliopleona and the new genus Saurotipleona, are modest contributors to tanaidacean diversity in the benthos of seas from Iceland to the British Isles along the ‘Atlantic Margin’. Three of H.J. Hansen’s ‘Ingolf’ species, originally within the genus Leptognathia, are rediagnosed, i.e. Chauliopleona amdrupii, C. armata and C. hastata. One new species, C. bamberi, from British waters is described and a new genus and species, Saurotipleona julii, is described from bathyal depths in the Irminger and Iceland basins. The latter is similar to Chauliopleona in having a sternal spur on pleonite-5 but this is of a slightly different form and is ventrally directed; it also has two superodistal spines on the propodus of pereopod-5, a distinctly plesiomorphic character in the family. A distribution map and key to the identification of these species are given. http://zoobank.org/urn:lsid:zoobank.org:pub:E7EF8C72-D1C6-438E-B9C2-A5CE637FB75A


Introduction
In a previous paper on the peracarid crustacean group Tanaidacea Dana from the 'Atlantic Margin' (Bird 2014), two akanthophoreid-like taxa, Leptognathioides Holdich, 1984 andPortaratrum Guerrero-Kommritz, 2003 were studied, but the taxonomy of two genera genuinely belonging to the Akanthophoreidae Sieg, 1986 are examined here. The first, Chauliopleona Dojiri and Sieg, 1997, was originally known from the Ingolf Expedition (Hansen 1913) as Leptognathia 'group a, subdivision γ' that included Leptognathia armata Hansen, 1913, L. hastata Hansen, 1913and L. Amdrupii Hansen, 1913, all easily recognized by the recurved sternal spur on pleonite-5. However, a single pleonal spur is no longer diagnostic after the publication of Portaratrum and a new genus described in this paper.
These Chauliopleona species are widely distributed but never abundant tanaidaceans in the soft sediments of the northeast Atlantic at bathyal and abyssal depths, including the Norwegian Sea and the 'cold-water' province north of Iceland. The type species, C. dentata Dojiri and Sieg, 1997, was incompletely described because the authors did not give details of mouthparts (apart from the mandibles) and pereopods 2-6. I feel justified in offering new figures of Hansen's species as those given by Table 1. List of samples in which Chauliopleona and Saurotipleona species were recorded (excluding stations reported in Bird 2004aBird , 2004bBird , 2010Bird , 2014 (Larsen and Araújo-Silva 2014). Within a fairly conservative overall morphology, specialised characters such as high pleonal spurs, lateral pleotelson spurs, crenation or nodules on various regions of the cheliped, extension of a cheliped carpal shield, slender uropods with one or two-segmented exopods, and grooved and serrate dactylus of pereopods 4-6 are part of the morphological expression within this taxon.
The following two genera are typical akanthophoreids, from their overall habitus to the narrow mandibular molars that carry a palmate array of distal spines. The latter character is quite different from that expressed in akanthophoreid-like taxa such as Portaratrum and Leptognathioides where the molar is broader and has a coronal spine array (Bird 2014). Diagnosis (developed from Dojiri andSieg 1997, Larsen andShimomura 2009). Akanthophoreid with cephalothorax with parallel or sub-parallel lateral margins. Pleonites 1-4 sternites with or without low medial process, pleonite-5 sternite with acute recurved spur. Pleotelson lateral margins smooth. Mandible molar acuminate-palmate. Maxilliped bases with or without long seta. Cheliped carpus inferior shield very slight to strongly developed; fixed finger without proximal dentition, with two inferior bayonet spines; dactylus with crenate or smooth superior margin. Pereopods 1-3 basis not broader than that of pereopods 4-6, superior margin with large plumose sensory seta (PSS); pereopod-1 carpus with two bayonet spines, pereopods 2-3 with three. Pereopods 4-6 carpus with three bayonet spines and superodistal rod-like seta; pereopods 4-5 propodus with one superodistal spine, pereopod-6 with three (sometimes slender). Uropod peduncle simple [without spur]; exopod two-segmented, shorter than segment-1 of endopod.
Preparatory male. Pleon slightly larger than in female. Antennule five-articled, broader than female. Mouthparts similar. Pleopods slightly larger and/or with more setae than female. Swimming male: unknown or not proven.

Remarks
Chauliopleona is an Akanthophoreus or Parakanthophoreus-like genus with pleonite-5 supporting an acute, recurved, sternal spur. Diagnoses of this akanthophoreid genus have been given previously several times (see above). Twelve species have been described to date (Anderson 2013; Larsen and Araújo-Silva 2014) but it has been a problematic genus, mainly because it has been difficult to find diagnostic and phylogenetically valid characters that separate it from Akanthophoreus, Parakanthophoreus and Paraleptognathia, other than the pleonal spur. There has also been speculation that the pleonal spur might only be a sex-related character (Bamber, Larsen pers. comm.). Surprisingly, this was the only character in the original generic diagnosis (Dojiri and Sieg 1997, p. 231). Its status in mancae remains unresolved as none of these were identified as Chauliopleona in the present study; it is quite possible that the spur is absent in this developmental stage and they would be indistinguishable from mancae of Akanthophoreus or Parakanthophoreus. Diagnosis Cephalothorax 1.4 times longer than broad (ltb). Pereonites 1-6 all shorter than broad, with parallel lateral margins. Pleon shorter than cephalothorax, without posteriodorsal protuberances; pleonites 1-4 sternite with low recurved subrectangular process. Antennule article-1 (1.25 times) longer than rest of antennule. Maxilliped bases with short distal seta. Cheliped merus without inferior protuberance; carpus relatively slender, twice as long as broad, inferior shield shallow (aspect ratio ≈ 0.2), subtriangular, distal margin not angular; fixed finger with four teeth; dactylus superior margin smooth. Pereopods 1-3 basis with marginal setules; carpus and propodus inferior spinules fine to moderate; pereopods 2-3 carpus with distomedial seta. Pereopods 4-6 ischium with two short setae. Uropod exopod just over half the length of endopod segment-1; endopod slender, > three times longer than peduncle.

Remarks
This species of Chauliopleona is characterised by a relatively slender cheliped carpus that has a low-aspect ratio (shallow) sub-rectangular shield ( Figure 3H) and a slightly recurved sternal process on pleonites 1-4 ( Figure 2C). The basal setae of the maxilliped ( Figure 3G) are also relatively short compared to those in C. armata and C. hastata. There is some discrepancy between the present specimens and the specimen illustrated by Guerrero-Kommritz (2005) in the size of the inferior propodal spinules on pereopods 1-3: his material, one specimen from the Greenland Sea, has robust spinules (also on the carpus), whereas the current material has both weak and moderate setules ( Figure 4A-C). This better corresponds to Hansen's description of 'second pair of legs [pereopod-1] without spinules on the posterior margin of sixth joint [propodus]' (Hansen 1913, p. 81). The presence of a distomedial seta on the carpus of pereopods 2-3 is another possible distinguishing character from C. armata and C. hastata. This species is partly sympatric with C. armata and C. hastata in the Irminger Basin and its depth and geographic distributions indicate polar emergence.

Size
Non-ovigerous female. Body length 2.28-3.64 mm, cf. 3.6 mm as measured by Hansen (1913)  . Some of these were reported by Holdich and Bird (1985). These data are available from the author on request.
Remarks A significant problem in assessing any new records of C. armata is that the original type material consists of only two specimens ( Figure 1B-G) and this shows some differences from the specimens illustrated here that have a slightly shorter cephalothorax and somewhat weaker propodal spinules on pereopods 1-3 ( Figure 7A-C).
If these new records are genuine, Chauliopleona armata appears to be a eurybathic species, inhabiting both bathyal (200-2000 m) and abyssal zones (2000-6000 m). However, it is almost certain that the records of C. armata outside of the Atlantic Margin study area (see above) refer to more than one species, and the material needs re-examination.
Antennule ( Figure 8D) about 0.6 times length of cephalothorax; article-1 as long as distal articles combined, three times ltb; article-2 twice as long as broad, with lateral seta longer than article; article-3 half as long as article-2, with two setae; article-4 slender, just longer than article-2, with six setae and aesthetasc; without caplike terminal segment; other setation as figured. Antenna ( Figure 8E) about 0.75 times length of antennule; article-2 with superior and lateral setae; article-3 half as long as article-2; article-4 about seven times ltb, with pseudo-suture; article-5 about as third as long as article-4; article-6 small, as long as broad; other setation as figured.
Cheliped ( Figure 9L-M) basis with posterior lobe about as long as anterior mass; carpus 1.8 times ltb, carpal shield shallow, aspect ratio 0.22; chela longer but as wide as carpus, fixed finger incisive margin with four teeth; dactylus superior margin nodulose.

Etymology
For my much esteemed colleague Dr. Roger Bamber, for his tireless work and contributions on Tanaidacea (and much else besides).

Distribution records from the AFEN, BIOICE and BIOFAR area
Eleven records from the AFEN surveys: nine from the North and West Shetland Shelf and Slope, 120-243 m, and two from the Hebrides Slope, 301-398 m, in sandy substrata.

Distribution elsewhere
North Sea (via Roger Bamber); no site data available.

Remarks
Until the publication of Chauliopleona bamberi n. sp., three species of this genus had originally been recorded with a nodulose or crenate superior margin of the cheliped dactylus: C. dentata, C. paradoxa and C. sinusa, but with the discovery of the female of C. hansknechti, Błażewicz-Paszkowycz, Bamber, Jóźwiak (2012) showed that this also has a finely crenulate cheliped dactylus. Chauliopleona bamberi is therefore the most similar of the four known northeast Atlantic Chauliopleona to the type species in possessing this character. This is also shared by several species in Akanthophoreus and Parakanthophoreus. The relatively long cephalothorax and slender, almost smooth, propodus of pereopods 1-3 appear to be other useful or diagnostic characters.
The records from west of the Shetland Isles at shelf and shelf-break depths, 120-243 m, mean at least that it is another (somewhat unexpected) addition to the shallow-water fauna (< 200 m) from the British Isles, following the discovery of Zeuxo holdichi Bamber, 1990 in the Scilly Isles (Bamber 2011). Twenty-seven species were reported by Holdich and Jones (1983) with additions made by Jones and Holdich (1983) and Holdich and Bird (1986), bringing the published total now to 32. It is probable that this species is the source of some records of 'Leptognathia gracilis' or 'Akanthophoreus' in British waters if the pleonal spur was not observed. In the outer shelf and shelf-break area from where C. bamberi has been found, the tanaidacean fauna is sparse (Bird 2001) and same-sample records include Akanthophoreus gracilis sensu lato, Araphura brevimanus (Lilljeborg, 1864), Akanthophoreus longiremis (Lilljeborg, 1864) and Tanaopsis graciloides (Lilljeborg, 1864), in descending order of abundance (all lower than that of C. bamberi). The first and last of these taxa have a crenulate cheliped dactylus.

Remarks
This species is recognised by its stout cheliped carpus (1.6 times ltb, Figure 12J) with its deep and rounded inferior shield, while its pereopods 1-3 ( Figure 13A-C) are more robust compared to those of C. amdrupii and C. armata. The pleonal sternites are also lower than in C. armata and C. amdrupii. The cheliped shown by Guerrero-Kommritz (2005, fig. 7b, f) based on non-type material from the Greenland Sea at 188-191 m is far more massive and angular than those illustrated here from the cotype and new topotypical material, and is more similar to that of the new genus described below. Similarly, his drawing of the pereopod-5 (Guerrero-Kommritz 2005, fig. 8l) suggests that it may not be C. hastata. Another Atlantic species, C. amftae from the abyssal Angola Basin, also has a robust cheliped but this taxon differs from C. hastata at least by having a proportionately longer cephalothorax (> pereonites 1-2), a small protuberance/apophysis on the cheliped merus and fewer pleopodal setae.
Chauliopleona hastata is a cold-water species with an overall recorded depth range of 400-3709 m, i.e. it is primarily characteristic of the Arctic area of the Norwegian Sea, but there is a single, possibly spurious, record from the West Shetland Slope at 400 m (SEA-4 Stn 57075#1). The record of a preparatory male from the Irminger Basin (BIOICE Stn 3187) also looks anomalous but the specimen appears to have characters consistent with C. hastata, such as its robust cheliped ( Figure 17A).
Akanthophoreus: Holdich and Bird 1989: in part;Bird 2001: in part, see below
Preparatory male similar to female but pleon slightly larger; antennule fivearticled, stouter than in female.
Swimming male not known.

Etymology
From the Greek saurotos, 'spiked', and suffix pleona; a similar name to Chauliopleona; gender female.

Remarks
Two superodistal spines (rather than one) on the propodus of pereopod-5 are plesiomorphic relative to most paratanaoids other than leptocheliids, teleotanaids, pseudozeuxids, heterotanoidids and a few others, such as Tangalooma . The presence of this character in an akanthophoreid genus is surprising, although it was apparently observed, but for pereopod-4 and without comment, by Guerrero-Kommritz (2005) for C. hastata. The validity of this is discussed below.
Cheliped ( Figure 15H-J) basis with posterior lobe of similar size to anterior mass; carpus fairly slender, 1.8 times ltb (excluding shield), superior margin with setules and two setae, with large, rounded shield (aspect ratio 0.5 on holotype), inferior setae attached medial to this; chela longer than basis and as wide (excluding shield); propodus with two inferior setae attached along ridge or groove, medial comb of about eight spines, and a distolateral seta near the dactylus attachment; fixed finger incisive margin with proximal spine (of group of three) thickest, with low distal teeth; dactylus with smooth superior margin and small proximomedial seta.
Pereopod-1 ( Figure 16A) coxa with seta; basis as wide as those of pereopods 4-6, as long as ischium, merus and carpus combined, with superior PSS; ischium with small seta; merus twice as long as broad, with distomesial seta and inferodistal (lateral) spine as long as carpus; carpus twice as long as broad, with superior and inferior distal bayonet spines and inferior margin with weak to moderate spinules; propodus four times ltb, with inferodistal spine, superodistal seta and palmate array of spinules, inferior margin with weak to robust spinules; dactylus and unguis subequal, former with accessory seta, together two thirds as long as propodus. Pereopod-2 ( Figure 16B) similar to pereopod-1 but carpus and propodus slightly shorter, carpus with additional inferodistal spine and mesial seta; (PSS on basis probably detached on drawn specimen). Pereopod-3 ( Figure 16C) similar to pereopod-2.

Etymology
For my wonderful son, Julius.
Distribution records from the AFEN, BIOICE and BIOFAR surveys Two records from AFEN surveys: one from the Hebrides Slope, 991 m, and one from the northern Rockall Trough, 1886 m. Six records from BIOICE: one from the Irminger Basin, 1209 m, and five from the Iceland Basin, 940-1074 m; temperature range 2.34-4.1°C, with a variety of sediment types including 'fine sand', 'medium sand' and 'gravelly sand'.

Distribution elsewhere
There are 21 records from various surveys ranging from the Rockall Trough to the abyssal South Bay of Biscay, 1400-4829 m (see under C. armata).

Remarks
As defined for the genus, this species is distinguished by a long, ventrally directed, pleonal spur and two superodistal spines on pereopod-5. The latter character shown for C. hastata by Guerrero-Kommritz (2005, fig . 8l); is possibly an error as pereopod-6 (Guerrero-Kommritz 2005, fig. 8m) is shown with only one superodistal spine, when typically for akanthophoreids there are three.
Most records of Saurotipleona julii n. sp. are from south of the main study area, at abyssal depths but with an overall depth range of 991-4829 m. An example is INCAL (Intercalibration) Stn 2.4, sample ØS.04, from the Biscay Abyssal Plain (46.05°N, 10.18°W, 4786 m); sketches of the individual presumed to be S. julii are shown in Figure 17C-E. This distribution pattern suggests a eurybathic tolerance but with some degree of polar emergence.

Discussion
Chauliopleona is widely distributed in the world's oceans and may be present in intermediate areas from which no records have yet been obtained (Larsen and Shimomura 2009). In the more local context of this study, no Chauliopleona species were recorded by Brandt (1993) or Błażewicz-Paszkowycz and Bamber (2011) from the Kolbeinsey Ridge or the Norwegian Margin, respectively, although the first is within the 'Atlantic Margin' region; the second is northeast of the Shetlands sector of this area. Another modern published account, Błażewicz-Paszkowycz and Sekulska-Nalewajko (2004), did not record any Chauliopleona species from Kongsfjorden on Figure 18. Distribution of Chauliopleona species in the Atlantic Margin area. Filled triangles C. amdrupii, filled squares C. armata, and filled circles C. hastata; crosses indicate Ingolf records of C. hastata. the northwest coast of Spitsbergen, although some of the samples were from a depth comparable to those in the Greenland Sea from where the genus had been obtained (Guerrero-Kommritz 2005).
Those results could be rationalised as, although there are about 96 records of these two genera within the context of the present study, they represent only 6.6% of the 1445 samples studied (Bird 2014). Similarly, the actual sampled abundance values are usually small: single specimen (singleton) counts for individual species are most frequent (63, or 66%), 2-5 individuals less frequent (28, 29%), and 6-10 individuals scarce (4, 4%). Only one sample, BIOICE Stn 2856, in the Iceland Basin at 2079 m, yielded a higher count, with 38 specimens of C. armata. Because the focus of this study is one area of the northeast Atlantic, it leaves unresolved the status of many published and unpublished records of Chauliopleona from elsewhere in the Rockall-Biscay area and further afield, many of which rest under the name Leptognathia armata (e.g. Holdich and Bird 1985). One undescribed species from the Celtic Slope at 860 m (THALASSA-73 Stn Z.426) exhibits a truly extreme and bizarre character in its cheliped propodus morphology, with five inferior spines ( Figure 17B).
It is also evident that some deep-sea and shallow cold-water environments support more than one species of Chauliopleona, making identification more difficult. While sympatry occurs with C. amdrupii, C. armata and S. julii, the other two species, C. hastata and C. bamberi, appear to be more specialised in their distribution, the former primarily from cold bathyal-abyssal Norwegian Sea water, and the latter from sandy sediments in the North Sea and outer shelf and upper slope northwest of the British Isles.

Addendum
Two errors appear in the 'Material examined' section for Portaratrum holdichi Bird, 2014 (p. 18): BIOICE Stn 3624 should read 3264, and BIOICE Stn 2836 should be 2856. These do not affect the maps or other distributional data.