Portaratrum holdichi, Bird, 2014

Bird, Graham J., 2014, Tanaidacea (Crustacea: Peracarida) of the North-east Atlantic: the genera Leptognathioides and Portaratrum of the ‘ Atlantic Margin’, Journal of Natural History 48 (29 - 30), pp. 1771-1815 : 1788-1799

Portaratrum holdichi n. sp.

Leptognathia (?) zezinae Kudinova-Pasternak, 1973 ; Holdich and Bird (1985): 444, Table 1 [probable synonym]

Material examined

Holotype ovigerous female (2.9 mm), BIOGAS Stn 3282 [IINH 27881]; Iceland Basin [slope], 62.48° N 16.16° E, 1810 m, 2.54°C.

Allotype preparatory male (2.6 mm), BIOGAS Stn 3282 [IINH 27882], details as for holotype.

Paratypes: nine non-ov. ♀♀, four prep. ♂♂, BIOICE Stn 2836 [IINH 27883]; one non-ov. ♀, BIOICE Stn 2859 [IINH27884]; four non-ov. ♀♀, BIOICE Stn 2860 [IINH 27885]; one non-ov. ♀, BIOICE Stn 2864 [IINH 27886]; one prep. ♂, BIOICE Stn 3069 [IINH 27887]; one non-ov. ♀, two ov. ♀♀, one prep. ♂, BIOICE Stn 3624 [IINH 27888]; nine non-ov. ♀♀ (one dissected on microslides), two ov. ♀♀, one prep. ♂, BIOICE Stn 3282 [IINH 27889]; one ov. ♀, BIOICE Stn 3504 [IINH 27900]; one non-ov. ♀, one ov. ♀, BIOICE Stn 3509 [IINH 27901]; one?non-ov. ♀, BIOICE Stn 3510 [IINH 27902]; one manca-III, two non-ov. ♀♀, one ov. ♀, two post-ov. ♀♀, eleven prep. ♂♂ (one partly dissected on microslide), BIOICE Stn 3522 [IINH 27903]; six non-ov. ♀♀, one ov. ♀, ten prep. ♂♂, BIOICE Stn 3524 [IINH 27904] .

Other material (examined 1982–1989): two non-ov. ♀♀, BIOGAS-III Stn DS 36; one non-ov. ♀, BIOGAS-IV Stn DS 64; one non-ov. ♀, BIOGAS-VI Stn DS 75; five non-ov. ♀♀, BIOGAS-VI Stn DS 86; one non-ov. ♀, BIOGAS-VI Stn DS 87; one non-ov. ♀, BIOGAS-XI Stn KG 212; one ov. ♀, INCAL Stn CP 02; one non-ov. ♀, INCAL Stn CP 03; two non-ov. ♀♀, INCAL Stn CP 04; four non-ov. ♀♀, INCAL Stn CP 07; one non-ov. ♀, one ov. ♀, one prep. ♂, INCAL Stn CP 08; four non-ov. ♀♀, two prep. ♂♂, INCAL Stn DS 01; two non-ov. ♀♀, INCAL Stn DS 02; three non-ov. ♀♀, INCAL Stn DS 05; nine non-ov. ♀♀, three prep. ♂♂, INCAL Stn DS 06; one prep. ♂, INCAL Stn DS 08; two non-ov. ♀♀, one prep. ♂, INCAL Stn DS 09; one manca-III, INCAL Stn KR 03; one non-ov. ♀, INCAL Stn KR 06; one non-ov. ♀, INCAL Stn ØS 01; three non-ov. ♀♀, INCAL Stn WS 02; one non-ov. ♀, IOS Stn 10111#8; two non-ov. ♀♀, POLYGAS Stn DS 15; two non-ov. ♀♀, POLYGAS Stn DS 20; one non-ov. ♀, one ov. ♀, SMBA ES4 ; 28 non-ov. ♀♀, one ov. ♀, three prep. ♂♂, six indet. (damaged/incomplete), SMBA Stn ES 10; four non-ov. ♀♀, one manca- III, SMBA Stn ES 34; one non-ov. ♀, SMBA Stn ES 56; one manca-III, one non-ov. ♀, SMBA Stn ES 105; one non-ov. ♀, SMBA Stn ES 118; three non-ov. ♀♀, one indet., SMBA Stn ES 135; three non-ov. ♀♀, one post-ov. ♀, SMBA Stn ES 137; two non-ov. ♀♀, one post-ov. ♀, SMBA Stn ES 143; three non-ov. ♀♀, SMBA Stn ES 147; one indet., SMBA Stn ES 172; two non-ov. ♀♀, SMBA Stn ES 180; nine non-ov. ♀♀, one ov. ♀, one prep. ♂, SMBA Stn ES 185; one non-ov. ♀, SMBA Stn ES 190; three non-ov. ♀♀, SMBA Stn ES 204; one non-ov. ♀, SMBA Stn ES 207; one manca-III, one non-ov. ♀, SMBA Stn SBC48; one ov. ♀, SMBA Stn SBC50; one manca-II, one non-ov. ♀, SMBA Stn SBC51; one manca-III, three non-ov. ♀♀, SMBA Stn SBC60; two non-ov. ♀♀, SMBA Stn SBC61; three manca-III, two non-ov. ♀♀, SMBA Stn SBC68; one manca-III, SMBA Stn SBC150; three manca-II, SMBA Stn SBC262; one non-ov. ♀, SMBA Stn SBC275 .

Etymology

In honour of my former supervisor in the Department of Zoology, Nottingham University, and principal contributor to the renewed study of Tanaidacea in Britain during the late 1970s and early 1980s, Dr David Holdich DSc.

Type locality

Bathyal Iceland Basin ca. 1500–2100 m.

Diagnosis

Female: with cheliped basis with anterior mass clearly longer than posterior lobe; fixed finger with single distal tooth on incisive margin. Pereopods 1–3 propodus inferior margin smooth. Uropod exopod two-segmented, distal segment much smaller than proximal. Preparatory male pleon slightly longer than in female, wider than pereon. Antennule article-1 2.0 times ltb. Pleopod rami with nine distal setae.

Description

Female (ovigerous, post-ovigerous): habitus ( Figure 6A ) fairly slender, 6.9 times ltb; length 1.9–3.3 mm [post-ovigerous female 2.2–3.1 mm]; cuticle well-calcified, fragile. Cephalothorax ( Figure 6D, E ) 1.3 times ltb, with rounded lateral margins; rostrum rounded. Pereon 62% of body length, pereonites with lateral process at pereopod insertion, becoming more posterior from pereonite-1 to pereonite-6; pereonite-1 with two anterodorsal setae. Pleon ( Figure 6B ) 18% of body length, pleonites of equal width; epimera with simple seta. Pleotelson ( Figure 6C ) shorter than pleonites 4–5 together, with two simple setae and two PSS on posterior margin.

Antennule ( Figure 7A ) 0.7 times as long as cephalothorax; article-1 fairly stout, 2.4 times ltb, twice as long as article-2, with two lateral group of three PSS and distolateral simple seta; article-2 1.7 times ltb, with distolateral seta, at least two PSS, with stouter distomedial seta; article-3 subrectangular, 0.6 times length of article-2, with two stout distal setae; article-4 longer than article-3, with one weak subdistal seta, four longer terminal setae and one aesthetasc. Antenna ( Figure 7B ) just shorter than antennule; article-1 annular, naked; article-2 just longer than broad, with small superodistal seta; article-3 slightly smaller than article-2, with larger superodistal seta; article-4 slender, 7.5 times ltb, with very slight indication of fusion line at mid-length, with associated PSS, and with at least two distal PSS and two long inferodistal setae; article-5 slender, just under half as long as article-4, with distal seta; article-6 small, with five terminal setae.

Labrum ( Figure 7C ) as long as broad, distally truncate, setulate. Mandibles ( Figure 7D–H ) delicate; left mandible incisor tricuspid, lacinia acuminate, molar acuminate, with about twelve terminal spines, in sub-coronal array; right mandible incisor tetracuspid, molar acuminate with curved terminal spines. Labium ( Figure 7J ) with sub-triangular inner lobe, distally setose. Maxillule ( Figure 7K ) slender, endite with sparse rows of setules and eight (?) terminal spines; palp typical of genus. Maxilla ( Figure 7L ) sub-ovate, half as long as maxilliped bases and endites together. Maxilliped ( Figure 7M, N ) bases together cardiform, with small seta near articulation with palps, margin projecting distally over endite; each endite weakly flared, with setose distolateral margin, distolateral lobe, small rounded medial tubercle, and medial seta; palp article-1 naked; article-2 with long lateral seta overreaching article-3, with three inner setae, one serrulate on oral margin; article-3 larger than article-2, with three inner setae (two long, one weak); article-4 about half as long as article-3, with subdistal seta and five unequal terminal setae. Epignath not recovered.

Cheliped ( Figure 8A, B ) robust; basis as long as broad, with superolateral seta; merus inferior margin as long as carpus margin, with one seta; carpus 1.5 times ltb, with two superior setae and two inferior setae; chela longer than carpus; propodus palm with two spines on medial comb; fixed finger longer than palm, with three setae proximal on incisive margin, with large distal tooth, terminal spine rounded; dactylus with small medial seta and two spines on inferior margin, distal larger.

Pereopod-1 ( Figure 9A ) annular coxa with seta; basis slender, four times ltb (at widest breadth), smooth; ischium with stout seta; merus with weakly oblique articulation with carpus, about twice as long as broad, with inferodistal bayonet spine; carpus subrectangular, three times ltb, with one superodistal and one inferodistal bayonet spine; propodus slender, six times ltb, 1.2 times longer than carpus, with small superodistal seta and inferodistal bayonet spine; dactylus and unguis just longer than propodus, dactylus slightly shorter than the unguis, which has a rounded tip (possibly denoting a spinning pore). Pereopod-2 ( Figure 9B ) similar to pereopod-1 but carpus with two, unequal, inferodistal bayonet spines. Pereopod-3 ( Figure 9C ) similar to pereopod-2 but merus slightly shorter.

Pereopod-4 ( Figure 9D ) coxa annular, with seta; basis broader than pereopods 1–3, 3.3 times ltb, with two inferior PSS; ischium with two setae; merus just over twice as long as broad, with two inferodistal bayonet spines; carpus subrectangular, as long as merus, with superodistal rod-shaped seta and three bayonet spines; propodus slender, about 1.2 times longer than carpus, inferior margin setulate, with two inferodistal bayonet spines and one superodistal bayonet spine half as long as dactylus; dactylus almost as long as carpus, with inferior spinulation; unguis slender, shorter than dactylus, together longer than propodus. Pereopod-5 ( Figure 9E ) similar to pereopod-4 but basis with long PSS on inferior margin and with shallow superior groove. Pereopod-6 ( Figure 9F ) similar to pereopod-5 but propodus without superodistal PSS, and with three superodistal spines.

Pleopod ( Figure 10A ) peduncle visible from dorsal view of pleon, slender, three times ltb, subovate; endopod slender, seven times ltb, with distomedial seta (weaker than remainder) and four distolateral setae; exopod longer and broader than endopod, six times ltb, with seven distolateral setae; all setae sparsely plumose.

Uropod ( Figure 8C ) as long as pleotelson; peduncle longer than broad; endopod two-segmented, segment-1 slightly longer than segment-2, with two long PSS, segment-2 with one subterminal seta, three terminal setae and one PSS; exopod two-segmented, segment-1 with distal seta, segment-2 cap-like, with larger, longer seta.

Manca-II: generally similar to non-ovigerous female but pleonite-5 without spur; without pereopods-6 or pleopods; length 0.98–1.04 mm.

Manca-III ( Figure 10C ): generally similar to non-ovigerous female but pleonite-5 without spur; with rudimentary pereopods-6 and pleopods; length 1.02–1.38 mm.

Neuter-non-ovigerous female: similar to ovigerous female; length 1.4–3.5 mm.

Preparatory male: habitus ( Figure 6F ) slender, seven times ltb, length 1.5– 2.8 mm. Cephalothorax 1.4 times ltb. Pereonite-6 sternite with small raised male pores. Pleon ( Figure 6G ) 21% of body length, slightly wider than pereon. Antennule ( Figure 8D ) stout, article-1 twice as long as broad. Pleopod ( Figure 10B ) rami stouter than female, endopod and exopod 3.2 and 3.6 times ltb respectively; setae more numerous, endopod with one distomedial and eight terminal setae, exopod with nine terminal setae. Otherwise as female.

Distribution in study area

Represented by two records from AFEN: Hebrides Slope and North Rockall Trough, 1612 m and 1859 m respectively; also seven records from AFEN-area SMBA stations: Hebrides Slope , North Feni Ridge, and (northern) Rockall Trough, at 1800–1993 m, 1600–2000 m , and 2150–2200 m respectively; three records from AFEN-area INCAL Stn 1.3: (northern) Rockall Trough, 2081–2091 m . Also by 12 records from BIOICE: nine from Iceland Basin (slope) 1607–1940 m and three from Iceland Basin , 2079 ‒ 2296 m .

Overall depth range 1600–2296 m. Temperature range 2.7–3.7°C (n = 10) in BIOICE samples from Iceland Basin. Where recorded, the sediment type was ‘silty sand’ for the BIOICE stations and ‘mud’ and ‘sandy mud’ for single AFEN-area stations on the Hebrides Slope and in the northern Rockall Trough, respectively .

Distribution elsewhere

Recorded in 61 samples from the South Feni Ridge, Malin Slope, Rockall Trough, Porcupine Slope, Porcupine Seabight, abyssal Porcupine, Porcupine Abyssal Plain, North Biscay, abyssal North Biscay, Armorican Slope, Armorican Seamount, South Biscay Slope, and South Biscay, 1635–4632 m (Appendix B). It was most abundant at the SMBA’ s Stn ES 10 in the Rockall Trough, at 2540 m.

Remarks

This is a widely distributed and eurybathic (bathyal-abyssal) species within the Northeast Atlantic, although it is absent from the cold-water area north of Iceland and the Faroes. It differs from the other two described species in having the cheliped incisive margin with essentially a single large distal tooth – several in P. afer and P. fascinatus . The unusual cap-like segment-2 of the uropod exopod of Portaratrum holdichi n. sp. is very similar to that of Leptognathioides biarticulata , which seems to be further evidence for the possible close relationship between these genera.

The mouthparts of Portaratrum holdichi n. sp. are proportionately small and delicate in relation to the general robustness and size of the cephalothorax, with weak and acuminate mandibular molars. This suggests they deal with food items that are not as tough as those eaten by shallow-water taxa such as leptocheliids, tanaids, and paratanaids, where the mandibles are robust and have broad triturative molars. Since there is a similar apparent contrast of the delicate mouthparts with the robust chelipeds, it is possible that Portaratrum is adapted to predation on shell-forming foraminiferans. As with Leptognathioides , this genus is well-calcified, smooth, bearing relatively few setae on the carapace, pereon, pleon, and pleotelson.

Key to Portaratrum species

1. Cheliped fixed finger with single distal tooth; uropod exopod two-segmented

....................................................................................... Portaratrum holdichi

Iceland Basin to North-east Atlantic - Cheliped fixed finger with several distal teeth; uropod exopod one-segmented

..................................................................................................................... 2

2. Cheliped carpus slender, longer than broad; pereopods 1–3 propodus inferior

margin spinulate ................................................................................. P. afer

Angola Basin to South Atlantic - Cheliped carpus stout, as long as broad; pereopods 1–3 propodus inferior

margin smooth ........................................................................... P. fascinatus

Eastern tropical Pacific

Comparison of Portaratrum and Chauliopleona

As was briefly discussed by Guerrero-Kommritz (2003) there is general similarity in habitus of these two genera in addition to the presence of a sternal spur on pleonite-5 (two examples from Chauliopleona are shown in Figure 11B, C ). However, this apparently shared character is homoplastic and independently evolved. Several other paratanaoid genera that belong in a variety of families express sternal spurs, such as Akanthophoreus Sieg ( Figure 11A ), Cryptocopoides Sieg ( Figure 11D ), Insociabilitanais Larsen ( Figure 11E ), Leptognathia G.O. Sars sensu stricto ( Figure 11F ), and Paranarthrurella Lang ( Figure 11G , here illustrated by P. arctophylax (Norman and Stebbing)) . These processes are either heterogeneous or homogeneous in shape, recurved or not, or present on one or more pleonites.

While Chauliopleona belongs in the Akanthophoreidae Sieg (see Błażewicz- Paszkowycz and Bamber 2011), the classification of Portaratrum remains uncertain. These two genera are easily distinguished by the morphologies of the cheliped and uropod, inter alia ( Table 2). Principally, in Chauliopleona , the cheliped basis has a well-developed posterior lobe, the carpus possesses an inferior shield (sometimes highly developed, as in C. hastata ), the palm inferior and superior margins are *indicates also applicable to Leptognathioides .

divergent, and the uropods are markedly different in proportions. Those of Chauliopleona are much more slender and the relative size of the exopod and endopod more unequal.

Figures

Figure 6. Portaratrum holdichi n. sp. Holotype ovigerous female: (A) habitus; (B) pleon, lateral view (pleopods omitted); (C) pleotelson apex. Paratype non-ovigerous female (IINH 27899): (D) Cephalothorax, lateral; (E) cephalothorax, ventral. Allotype preparatory male: (F) Habitus (antennules somewhat down-curved); (G) pleon, lateral. Scale bars: i: 1 mm for (A, B, F, G), 0.5 mm for (C); ii: 0.5 mm for (D, E).

Figure 7. Portaratrum holdichi n. sp. Paratype non-ovigerous female (IINH 27899): (A) antennule; (B) antenna; (C) labrum; (D–F) left mandible with enlargements of incisor and molar, respectively; (G, H) right mandible and enlargement of molar, respectively; (J) labium; (K) maxillule; (L) maxilla; (M) maxilliped (terminal setae of article-4 omitted for one palp); (N) maxilliped endites inner view. Scale bar: 0.25 mm for (A–E, G, J–N), 0.125 mm for (E, F, H).

Figure 8. Portaratrum holdichi n. sp. Paratype non-ovigerous female (IINH 27899): (A) cheliped [right]; (B) cheliped [left] palm and dactylus medial spines; (C) uropod. Preparatory male (IINH 27903): (D) antennule. Scale bar: 0.25 mm.

Figure 9. Portaratrum holdichi n. sp. Paratype non-ovigerous female (IINH 27899): (A–F) pereopods 1–6 respectively. Scale bar: 0.25 mm.

Figure 10. Portaratrum holdichi n. sp. Paratype non-ovigerous female (IINH 27899): (A) pleopod. Preparatory male (IINH 27903): (B) pleopod. All seta sparsely plumose as indicated. Manca-III (IINH 27903): (C) pereonite-6, pleon, and pleotelson, lateral. Scale bars: i: 0.25 mm for (A, B); ii: 0.125 mm for (C).

Figure 11. Pleonal spurs of several tanaidacean species from the Atlantic Margin: (A) Akanthophoreus longiremis (Lilljeborg), BIOICE Stn 2349; (B) Chauliopleona sp.AM#1, BIOICE Stn 2257; (C) Chauliopleona amdrupi (Hansen), BIOICE Stn 3282; (D) Cryptocopoides arcticus (Hansen), BIOICE Stn 2912; (E) Insociabilitanais sp.AM#1, BIOICE Stn 2337; (F) Leptognathia breviremis agg., BIOICE Stn 2772; (G) Paranarthrurella arctophylax (Norman and Stebbing), BIOICE Stn 2860. Not to scale; pleopods omitted from (A–D) and (F, G).