Agnathia chuki, Staples, 2021

Staples, D. A., 2021, Diagnosis ofthe new genusAgnathia (Pycnogonida, Callipallenidae) and description of two new species from southern Australia, Zootaxa 4950 (3), pp. 487-500 : 493-497

Agnathia chuki sp. nov.

Figures 2A–J , 3A–H ; Plate 2A–F

Material examined. Holotype, female ( NMV J62430 ), Tasmania. Bass Strait, Kent Group , Erith I., Bulli Cove. SCUBA, 4 m, D.A. Staples, 11 May 1975.

Paratypes. Victoria. One male carrying eggs, protonymphon and juveniles ( NMV J62431 ), Port Phillip , Point Lonsdale kelp beds, 7.6 m, D.A. Staples, 10 December 1972 . One female, gravid ( NMV J62432 ), off Point Nepean, Port Phillip Survey 1957–1963, area 66, stn 292, dive 1, 18 m, 15 May 1963 . One ovigerous male ( NMV J62433 ), Lawrence Rocks, Portland , on hydroid Haloptris campanula (Busk), D.A. Staples, November 1981 . One female, gravid ( NMV J62434 ), Cliffy I., Wilsons Promontory , 20 m, D.A. Staples, 12 August 1983 .

Other material. South Australia. One juvenile ( NMV J62435 ), Investigator Group, Stn 62, ‘ The Hotspot’ reef, 9.3 km west of north end Flinders I. (33º 40.50’S, 134º 22.00’E), 17 m, G.C.B Poore & H. Lew Ton. 19 April 1985 . Victoria. One juvenile ( NMV J62436 ), Port Phillip, Stn 3B1 (38º 17.0’S, 144º37.7’E –38º 16.8’S, 144º 38.3’E), SCUBA, Marine Research Group, March 1986 . One juvenile ( NMV J62437 ), Waterloo Bay , Wilsons Promontory, J.E. Watson, January 1978 . One female ( NMV J62438 ), 1.5 km off Barwon Heads , on reef, 21 m, J.E. Watson, 14 April 2012 .

Description. Female holotype. Trunk moderately elongate ( Fig. 2A ), gently arched, fully segmented in dorsal and ventral views, midline smooth, ventral and dorsal surface segments 1 to 3 lowly inflated distally ( Fig. 2B ); lateral processes slightly inflated, narrowest at bases, separated from the trunk by faint suture line that also straddles the trunk behind the ocular tubercle, length of lateral processes about equal to basal width (but slightly variable), first three lateral processes separated by 60 to 75% of basal diameter, processes 3 and 4 much closer but distinctly separated ( Plate 2A ), spines on lateral processes tiny, in order 2:2;2;2, those on inner margins of lateral process 1 and 4 inconspicuous, obscure. Neck region of cephalon short, narrowing from anterior margin to bases of ovigers, width at narrowest point greater than trunk width, strong lobes at bases of chelifore implants, each with one to three spinules, small conical mound present between the lobes. Ocular tubercle width at base greater than height, two well-defined apical papillae, four eyes pigmented ( Plate 2C ).

Proboscis angled downwards, consisting of a swollen basal part and distal tubiform part, ( Fig. 2B ; Plate 2B, E ), tubiform part represents about 40% overall length, distally hirsute, setae simple, three petal-shaped lips, flared when open; basal part narrowing in mid-region, widest proximally, ventral surface vaguely uneven.

Anal tubercle short, inflated, inclined at about forty-five degrees ( Plate 2E ), anal slit gaping.

Chelifore scape ( Plate 2B ) directed ventrally, reaching about level with the merger of the proximal and distal parts of proboscis, with deep ventral recess near base, single, strong spine on inner distal margin, variably accompanied by one or two smaller dorsal spines; chela mostly carried anaxially, with the moveable finger inner-most or upper-most, fingers of about equal length to each other, about 70% palm length, fingers off-set at tip, not meeting, fixed finger rounded at tip and in cross-section, digit-like, single stout tooth present at about one-fifth length, outer distal surface covered with tiny, blunt, granules, moveable finger smooth, curved, slightly widened and hooked at tip; chela palm with prominent protuberance on ventrodistal surface near base of fixed finger ( Figs 2I, J ), protuberance shaped much like the fixed finger but about half length and broader, surface with about six strong spines distally and several lesser proximal spines.

Oviger ( Fig. 2E ) ten-segmented, bases in contact with anterior margin of first lateral processes, barely evident in dorsal view, segment four longest, with swelling on the posterior surface presumably representing the site of a pore opening, segment 5 strongly curved, strigilis well-developed, terminal claw about 1.4 times length of segment 10, seven or more rake-like teeth spread around distal surface; spines on segments 7–10 simple, strong, curved forward, spine formula estimated 4:2:3:3 with additional straight spines on distal ventral and dorsal surfaces.

Leg ( Fig. 2F ) surface irregular, thickened cuticular line extends laterally from coxa 1 to base of tarsus; coxa 1 with few tiny distal spines; coxa 2 about 1.5 times length coxa 3, with several dorsal and ventral spines, strongly swollen ventrodistally in region of genital pore; coxa 3 with several strong ventral spines; femur marginally longer than tibia 2, ventral surface greatly swollen in region between two prominent, spine-tipped, peaks occurring at about one-third and two-thirds length, each peak sits atop base with many irregular spinous lateral protuberances, dorsal surface with few strong spines evenly-spaced along its length and with 4 to 5 closely-spaced spines distally, spines without prominent bases, the distal margin is fringed with stronger spines; second tibia about one-fifth longer than first tibia, both tibiae with three pair of conical dorsolateral swellings, each with one or two apical spines and several much smaller lateral spines ( Fig. 2G ), third swelling on tibia 1 placed on distal margin, third swelling on tibia 2 subterminal; tarsus with several ventrodistal spines and single spine-tipped dorsodistal process; propodus variably curved, dorsal surface with four to eight spines, distal margin over-reaching base of main claw ( Fig. 2H ), sole with dense field of spines, heel well-defined, mostly with four spines but 5 and 6 also sometimes present, heel spines of about equal size, terminal claw strong, reaching to base of heel when folded. All leg spines sit on a small tubercle or socle. Genital pore large, round, conspicuously present on ventrodistal surface, slightly posterior to median line, of second coxae all legs ( Plate 2F ).

Male smaller than female. Spination of trunk and legs more prominent and abundant ( Fig. 3A , Plate 2D ), basal tubercle or socle on which many spines sit is taller. Oviger ( Fig. 3B ) ten-segmented, segment five longest, curved, almost twice length segment four, several small, curved spines along outer dorsal margin, prominent distal apophysis digitiform, bearing two, perhaps three, short terminal spines, apophysis slightly curved inwards and backwards, segments 7 to10 seemingly without spines, segment ten short, terminal claw simple, equal to, or much shorter than tenth segment, margins irregular ( Fig. 3C ). Scape narrows proximally but lacks distinct ventral constriction found in females. Cephalic lobes at bases of chelifores bulbous, inflated more-so than female. Coxa 2 relatively longer than female, close to twice the length of coxa 3, with prominent spine-tipped tubercle at about one-third length of dorsal surface. Femur as for female but more slender, and slightly inflated distally, dorsodistal spinous fringe more-pronounced, corona-like. Propodal sole spines more robust and fewer in number. Cement glands not evident. Genital pores not sighted.

Measurements of holotype (mm). Trunk, length (frontal margin of cephalic segment to tip of 4 th lateral processes), 2.25; cephalon length, 1.10; width (across 2 nd lateral processes), 1.15; proboscis length (dorsal) 1.11, proboscis diameter (measured across distal-most inflated part) 0.40; third leg; coxa 1, 0.28; coxa 2, 0.64; coxa 3, 0.45; femur, 1.98; tibia 1, 1.45; tibia 2, 1.76; tarsus, 0.08; propodus, 0.82; main claw, 0.55. Oviger, seg.1, 0.14; seg. 2, 0.22; seg. 3, 0.24; seg. 4, 0.32; seg. 5, 0.20; seg 6, 0.22; seg. 7, 0.24; seg. 8, 0.22; seg. 9, 0.16; seg. 10, 0.16; claw 0.23.

Etymology. Named for Dr John Chuk the collector and photographer of many specimens.

Distribution. The Investigator Group, South Australia; western, central (including Port Phillip) and eastern regions of the Victorian coast and east Bass Strait Islands, Tasmania. Depth 4 to 21 m.

Remarks. Superficially, the differences between this species and A. aria appear to be subtle but on close examination they are distinctive. These differences are: a much larger overall size, the presence of a digitiform process on the chela palm, the distinct separation of trunk segment 3 and 4 accompanied by a ventral segmentation line, a more defined propodal heel and ten-segmented male ovigers. The larger size of A. chuki is evident at the most advanced juvenile stage.

The chelae are mostly carried anaxially, transverse to the oral surface but a wide arthrodial membrane at the base of the chela permits considerable lateral movement. The chela moveable finger is inner-most or upper-most ( Plate 2B ). In lateral view, the fixed finger and the ventrodistal process can form a confusing chelate appearance.

The orientation of the proboscis ranges from almost horizontal to near vertical downwards. Movement is made possible by a wide arthrodial membrane at the base of the proboscis.

General comments relating to variability in the spination of A. aria apply equally to this species. The number of propodal heel spines is mostly four, but this varies from three to six.

The number of female oviger strigilis spines is difficult to determine with some being concealed by the orientation of the tiny oviger. Only curved spines are recorded as part of the spine formula. The apparent absence of male strigilis spines is puzzling but perhaps the complete absence of a strigilis in male specimens of A. aria indicates that the settlement of epizoites in the genus is discouraged by chemical means rather than physical contact.

Figures

FIGURE 2. Agnathia chuki. sp. nov., holotype, female. A, trunk, dorsal view; B, trunk lateral view; C, trunk ventral view; D, trunk anterior view; E, left oviger; F, leg 3; G, first tibia, dorsal, leg 2; H, propodus, leg 3; I, right chela, ventral; J, left chelifore.

PLATE 2. Agnathia chuki. sp. nov., holotype, female.A, trunk, ventral view; B, trunk, anterior view; C, ocular tubercle, dorsal view. Paratype, male (NMV J62431). D, trunk, dorsal view; E, trunk, lateral view; Paratype, female (NMV J62434). F, trunk, anteroventral view.

FIGURE 3. Agnathia chuki. sp. nov., paratype, male (NMV J62431). A, trunk, dorsal. B, right oviger; C, right oviger, distal segments (200x); paratype, male (NMV J62433). D, leg 3. Protonymphon (NMV J62431). E, body, lateral (400x). Juvenile (NMV J62431). F, anterior view (100x); G, propodus (400x); H, fixed finger (400x).