Psalidichelia concinna, Bird, 2020

Bird, Graham J., 2020, Additions to the Tanaidacea (Crustacea: Peracarida) of Rangitâhua, the Kermadec Islands, from the Southwest Pacific Expedition 2017, Zootaxa 4860 (2), pp. 151-178 : 163-165

Psalidichelia concinna n. sp.

Figs 6– 10 , 12E

Material examined. Holotype — prep. ♀, 1.48 mm, AIM MA73608 , SWP2017-135 -2, South end of Denham Bay , Raoul Island, Rangitâhua Kermadecs, 4–18 m, coral rubble (see Table 1 ).

Allotype —cop. ♂, 1.3 mm ( AIM MA73614 ); details as for holotype.

Paratypes — 1 manca-II, 4 manca-III, 8 juveniles (=immature ♀♀), 15 non-ov. ♀♀, 15 prep-ov. ♀♀ (1 dissected on 2 microslides, AIM MA73612 ), 8 ov. ♀♀, 1 post-ov. ♀, 31 copulatory (cop.) ♂♂ (1 dissected on 2 microslides, AIM MA73613 ), AMS P.105581, SWP2017-135-2; 1 ov. ♀, AMS P.105589, SWP2017-135-3; 1 prep. ♀, AMS P.105595, SWP2017-137-3; 2 non-ov. ♀♀, 5 cop. ♂♂, AMS P.105588, SWP2017-143-2 .

Diagnosis. See genus diagnosis.

Etymology. Use of the Latin adjective concinnus / concinna , ‘ neat’, ‘pleasing’, ‘elegant’, etc. An appreciation of this species’ appearance, both males and females.

Type locality. Raoul Island, Rangitâhua-Kermadecs, 4–18 m, coral rubble.

Description Holotype preparatory female (AIM MA73608). Habitus ( Fig. 6A , 12E ) slender, 7.7 times ltb. Cephalothorax as long as pereonites 1–2 combined, 18% of body length, flask-shaped, 1.4 times ltb; carapace plates not clearly delineated. lateral margins with seta just posterior to eye-lobe, and cheliped sclerite seta also visible in dorsal view; rostrum pointed, weakly produced; eyes conical, multifaceted, with dark pigment. Pereon 64% of body length, with weakly convex margins of pereonites 1–6, all but pereonite-5 as long as or shorter than broad, pereonite-1 shortest, 0.4, 0.8, 0.8, 1.0, 1.1, and 0.7 times ltb respectively; pereonite-1 with two anterodorsal setae, pereonite-6 with posterolateral seta, all with anterolateral seta (coxal seta visible in dorsal view on pereonites 1–3). Pleon 12.6% of body length, about as long as broad, epimera with two lateral setae, pleonite-1 also with anterolateral seta. Pleotelson ( Fig. 6B ) 6% of body length, length of pleonites 4–5 together, rounded with weakly produced posterior margin, and deflexed apex bearing pair of long setae; other setation as figured.

Paratype preparatory females (mostly based on AIM MA73612 ), all following. Antennule ( Fig. 6C ) ‘four-articled’ (three peduncular articles, one discrete flagellar segment), 0.8 times length of cephalothorax (holotype), six times ltb; article-1 0.6 times total length, 3.3 times ltb, lateral margin with three proximal PSS , one long seta with three associated PSS at midlength, and distal seta longer than article-2, with two or three associated PSS, mesial margin with two proximal setae and one distal seta; article-2 twice as long as broad, with one distomesial and one distolateral distal setae, and one mesial PSS; article- 31 1.25 times length of article-2, 4.3 times ltb, with two distal seta, one PSS and one aesthetasc; terminal segment narrower than article-3, twice as long as broad, with two setae and PSS.

Antenna ( Fig. 6D ) 0.8 times length of antennule; article-1 as long as broad, naked; article-2 1.7 times ltb, with dorso- and ventrodistal spines, the former on slight apophysis; article-3 0.7 times length of article-2, as long as broad, with dorsodistal thorn-like spine; article-4 longer than articles 2 and 3 combined, four times ltb, at least one PSS and two simple distal setae (longer than article-5); article-5 longer than article-3, three times ltb, with one seta; article-6 small, as long as broad, with four setae and one PSS.

Mouthparts. Labrum ( Fig. 7A ) typical, hood-shaped, setulate. Mandibles ( Fig. 7 B–C) with left mandible ( Fig.

1 Article-3 is a composite (fused) flagellar segment (aesthetasc-bearing). 7B) weakly bifid, lacinia broad and distally crenulate, molar broad with apex blunt and relatively smooth; incisor of right mandible ( Fig. 7C ) with crenulate distal margin, molar as in left mandible. Labium ( Fig. 7D ) typical, outer lobes broader and just longer than inner, both distally setulate. Maxillule ( Fig. 7E ) endite sparsely setulate, with at nine relatively stout and crowded terminal spines, and outer corona of finer setae and setules; palp with two setae. Maxilla not observed.

Maxilliped ( Fig. 7 F–H) combined bases about as long as wide, basis with two setae long, overreaching endite; endite distal margin with large blunt lateral seta, blunt, incisor-like tubercles (“gustatory cusps” sensu Segadilha et al 2018) and with two medial coupling hooks; palp article-1 longer than broad, naked, article-2 with lateral seta and three mesial setae, article-3 with seven setae (in two rows); article-4 with superodistal seta and five apical setae. Epignath not observed.

Cheliped ( Figs 6E , 7 I–K) coxal sclerite triangular, reaching posterior of cephalothorax, with long seta; basis 1.6 times ltb, posterior lobe reaching pereonite-1 ( Fig. 6E ), 0.7 times length of anterior mass, latter with dorsolateral seta; merus ventral margin as long as that of carpus, with two setae; carpus 2.2 times ltb, with (two) dorsal setae at midlength and distal; ventral margin with three setae. Chela just shorter and distinctly narrower than carpus; propodus palm not flared, 2.8 times ltb, with slender spine near articulation with dactylus, two mesial combs of two spines and several setules respectively ( Fig. 7J ); fixed finger ( Fig. 7K ) 0.4 times length of palm, with five distal setae, incisive margin raised, with three low teeth; dactylus with proximomesial seta.

Pereopod-1 ( Fig. 8A ) coxa with long seta [and oostegite bud]; basis arcuate, 4.2 times ltb, with two proximal superior seta; ischium with short seta; merus twice as long as broad, distal margin strongly oblique with carpus; carpus as long as merus, twice as long as broad, with four distal seta, superodistal seta about as long as carpus; propodus about as long as merus and carpus combined, 3.5 times ltb, with four unequal superodistal setae, and one inferodistal seta; dactylus slightly shorter than unguis, with proximal accessory seta; unguis with distal pore, together with dactylus 0,8 times as long as propodus.

Pereopod-2 ( Fig. 8B ) coxa with seta (and oostegite bud in preparatory female)—not figured; basis not arcuate, as broad as that of pereopod-1, 2.8 times ltb, with two proximal superior two PSS; merus just longer than broad, with inferodistal crotchet; carpus as long as merus, 1.1 times longer than broad, with superodistal seta, two unequal inferodistal setae and inferodistal crotchet; propodus 2.6 times ltb, about as long as merus and carpus combined`, with two superodistal setae and inferodistal crotchet; dactylus as long as unguis, together claw-like and half as long as propodus.

Pereopod-3 ( Fig. 8C ) as pereopod-2 but basis without PSS [not observed]; propodus with one superodistal seta.

Pereopod-4 ( Fig. 8D ) coxa naked (and with oostegite bud in preparatory female, as figured); basis broader than in pereopods 2–3, 2.5 times as ltb, with two inferior PSS; ischium with one seta; merus geniculate, about twice length of broad, with two stout inferodistal crotchets; carpus about length of merus, twice as long as broad, subrectangular, with three unequal distal crotchets (one longer than rest, one short and blunt); propodus 1.1 times longer than carpus, 2.8 times ltb, with three slender superodistal spines and two inferodistal crotchets; dactylus and minute unguis not fused, claw-like, half as long as of propodus.

Pereopod-5 ( Fig. 8E ) as pereopod-4.

Pereopod-6 ( Fig. 8F ) as pereopod-5 but basis only with superior PSS and propodus with five slender superodistal spines.

Pleopod ( Fig. 8 G–J) peduncle just shorter than broad, with mesial seta; rami sub-ovate, endopod shorter than exopod, endopod and exopod about 2.0–2.3 times ltb respectively; endopod mesial margin with plumose seta at mid-length, lateral margin with fringe of 6–7 plumose setae, distalmost with whip-like tip; exopod lateral margin with proximal circumplumose seta separated by small gap from fringe of eight or nine plumose setae.

Uropod ( Fig. 6F ) longer than pleotelson; peduncle about twice as long as broad, naked; endopod segment-1 naked, segment-2 with or without distal seta, segment-3 with seta and one PSS, segment-4 with seta, segment-5 with four simple setae and a two PSS; exopod about 0.75 times length of endopod segment-1, with one subdistal and two distal setae.

Allotype copulatory male (AIM MA73614). Habitus ( Fig. 9A ) slender, 8.2 times ltb. Cephalothorax flaskshaped, as long as pereonites 1–2 combined, 1.5 times ltb, rostrum ( Fig. 9B ) slightly produced, carapace with seta posterior to each eyelobe, and sclerite setae visible from above; eyes proportionately larger than in female. Pereonites all shorter than, or as long as broad; pereonite-1 shortest, together with pereonites 2–3 longer than broad; pereonites 1–6 0.53, 0.73, 0.78, 1.0, 0.97 and 0.84 times ltb respectively (excluding posterior sheath in the relaxed specimen); setation as in female. Pleon ( Fig. 9C ) 24% of body length, just longer than broad; setation as in female. Pleotelson as in female.

Paratype copulatory males, 1.24 and 1.28 mm (AIM MA73613). Antennule ( Fig. 9D ) about 1.4 times longer than cephalothorax; peduncle three-articled, article-1 twice as long as broad, just longer than article-2; article-2 1.6 times ltb; article-3 0.7 times length of article-2, simple; flagellum five-segmented (occasionally six-segmented), longer than peduncle article-1; terminal segment much smaller than preceding segments, all except terminal with bundle of aesthetascs (3–4), segment-1 with two bundles—proximal and distal; other setation as figured. Antenna ( Fig. 9E ) like that in female but article-4 more slender than in female; article-5 more slender, 4.4 times ltb.

Mouthparts atrophied, fused solid mass.

Cheliped ( Fig. 9 F–G) gracile, about 1.5 times longer than cephalothorax, setation similar to that of female;; sclerite triangular, with seta; basis 1.6 times ltb, posterior lobe smaller than anterior mass, with dorsolateral seta; merus shorter than inferior margin of carpus, with two setae; carpus 2.4 times ltb, with two dorsal and three ventral setae; propodus shorter but as wide as carpus, 2.3 times ltb; palm 1.6 times longer than fixed finger, with weakly divergent dorsal and ventral margins; mesial comb vertical, with 13 simple spines ( Fig. 9G ); fixed finger incisive margin convex, without apophyses, finely crenulate; dactylus strongly arcuate, incisive margin finely crenulate.

Pereopod-1 ( Fig. 10A ) like that of female but basis with one proximal superior seta, merus with inferodistal seta. Pereopod-2 ( Fig. 10B ) like that of female but basis without PSS, slightly more elongate, 4.1 times ltb; merus, carpus and propodus more slender. Pereopod-3 ( Fig. 10C ) like pereopod-2 but slightly shorter, propodus with one superodistal seta, dactylus without proximal accessory seta.

Pereopod-4 ( Fig. 10D ) like that of female, but basis without PSS (not observed), ischium with two setae; meral and carpal spines more slender; propodus and claw combined proportionately longer. Pereopod-5 ( Fig. 10E ) like pereopod-4. Pereopod-6 ( Fig. 10F ) like pereopods 4–5 but propodus with five superodistal spines.

Pleopod ( Fig. 10G ) like that of female but with one or two additional setae on distal fringe of exopod and endopod.

Uropod ( Fig. 10H ) as in female but peduncle with distal seta.

Intraspecific variation. Manca-II: Habitus similar to immature female (see below), but stouter, 5.6 times ltb (n=1), body length 0.68 mm (n=1). Pereonite-6 short (without pereopods). Pleon without pleopods, 11.9% of body length (n=1). Uropod endopod four-segmented, segments short.

Manca-III: Habitus similar to immature female, but stouter, 6.3 times ltb (n=1), body length 0.81–0.93 mm (n=4). Pereonite-6 short (with rudimentary pereopods). Pleon ( Fig. 10I , AMS P.105581) with rudimentary pleopods, 12.9–13.7% of body length (n=4). Uropod ( Fig. 10J , AMS P.105581) endopod four-segmented, segments longer than in manca-II, as in immature female.

Immature female: Habitus similar to preparatory female, but stouter, 6.9 times ltb (n=1), body length 0.98–1.22 mm (n=8). Pleon 13.5–15.4% of body length (n=34; mean 14.4%). Uropod endopod four-segmented, or four- and five-segmented on same individual.

Non-ovigerous female: Habitus similar to preparatory female but generally stouter, 7.1–8.1 times ltb (n=6; mean 7.6), body length 1.14–1.55 mm (n=15). Pleon 11.4–14.4% of body length (n=15; mean 13.5%). Uropod endopod five-segmented.

Preparatory female: Habitus length: width 7.5–8.5 times ltb (n=7; mean 8.0), primarily from proportionately longer pereonites 3–5, body length 1.31–1.59 mm (n=16). Pleon 9.7–14.2% of body length (n=16; mean 13.3%).

Ovigerous female: Habitus as preparatory female, sometimes more slender, 7.5–8.9 times ltb (n=7; mean 7.9), body length 1.32–1.57 mm (n=9). Pleon 10.7–13.8% of body length (n=9; mean 12.3%).

Copulatory male: body length 1.13–1.4 mm (n=34). Pleon 12.2–14.4% of body length (n=34; mean 13.2%).

Distribution. Raoul and Macauley islands, coral rubble, encrusting coral on rocks, and red algae, 4– 18 m.

Remarks. This small leptocheliid is possibly representative of many species that may be overlooked in sampling and collection regimes. Discovery of similar taxa from neighbouring regions (Fiji-Tonga, New Caledonia, Northeastern Australia) would facilitate proper subfamilial classification and phylogenetic relationships.

Figures

FIGURE 1. Rangitâhua-Kermadec Islands sector of the SWP2017 survey indicating location of sampling sites yielding Tanaidacea (red arrows). Map based on chart NZ222 from Land Information New Zealand and Figure 1 in Trnski & de Lange (2015), courtesy of Hamish MacDonald.

FIGURE 6. Psalidichelia concinna n. g. n. sp. non-ovigerous female holotype (AIM MA73608).A, habitus, dorsal; B, pleotelson. Non-ovigerous female paratype (AIM MA73612). C, antennule; D, antenna; E, cephalothorax-cheliped, lateral; F, uropod. Scale bars: 0.5 mm for A; 0.25 mm for B–F.

FIGURE 7. Psalidichelia concinna n. g. n. sp. non-ovigerous female paratype (AIM MA73612). A, labrum; B, left mandible and molar process; C, right mandible (molar obscured) and apex of molar process; D, labium; E, maxillule endite and obscured setation; F, maxilliped bases; G, maxilliped basis and endite, H, maxilliped palp; I, right cheliped, lateral, J, fixed finger, distal; K, left cheliped dactylus and dorsomesial palm. Scale bars: 0.125 mm for all.

FIGURE 8. Psalidichelia concinna n. g. n. sp. non-ovigerous female paratype (AIM MA73612). A–F, pereopods 1–6 respectively; G, pleopod peduncle; H, pleopod endopod; I, pleopod exopod. Scale bars: 0.125 mm for all.

FIGURE 9. Psalidichelia concinna n. g. n. sp. male allotype (AIM MA73614).A, habitus (antennule flagellum setation simplified), dorsal; B, cephalothorax anterior, rostrum, C, pleon, dorsal. Male paratype (AIM MA73613).D, right antennule, numbers indicate aesthetascs not figured for clarity; E, antenna; F right cheliped, lateral; G, left chela, mesial. Scale bars: 1 mm for A; 0.125 mm for B–G.

FIGURE 10. Psalidichelia concinna n. g. n. sp. male paratype (AIM MA73613).A–F, pereopods 1–6 respectively; G, pleopod; H, uropod. Manca-III (AMS P.105581). I, pleon lateral; J, uropod. Scale bars: 0.125 mm.

FIGURE 12. Comparative size of Rangitâhua-Kermadecs shallow-water tanaids based on holotype or representative specimens. A, Chondrochelia acrolophus; B, Aparatanais tetradonta; C, Zeuxo kermadecensis; D, Paradoxapseudes floppae; E, Psalidichelia concinna; F, Metatanais progenitor; G, Tanais sp.; H, Collettea coralensis; I, leptocheliid LK#1. Scale bars: 1 mm for all.