Pygodelphys antarctica ( Schellenberg, 1922 )

Kim, Il-Hoi & Boxshall, Geoff A., 2020, Untold diversity: the astonishing species richness of the Notodelphyidae (Copepoda: Cyclopoida), a family of symbiotic copepods associated with ascidians (Tunicata), Megataxa 4 (1), pp. 1-6 : 93-96

Pygodelphys antarctica ( Schellenberg, 1922)

( Figs. 60 , 61 )

Material examined. 53 ♀♀, 40 ♂♂ (MNHN-IU-2018- 1779) and dissected 1 ♀, 1 ♂from Paramolgula gregaria (Lesson, 1830) , Magellan Strait; 4 ♀♀ (MNHN-IU-2018- 1780) and 1 dissected ♀ from P. gregaria , Tierra del Fuego, Argentina.

Supplementary description of female. Body ( Fig. 60A ) Doropygus -like in form, relatively slim. Body length 5.15 mm. First to third pedigerous somites each with well developed dorsal tergite. Brood pouch of fully grown adults shorter than anterior part of prosome; fifth pedigerous somite incorporated into brood pouch. Freeurosome ( Fig. 60B ) slender, clearly 5-segmented; comprising short genital somite, 160×516 μm and 4 free abdominalsomitesgraduallyshorterand narrowertowards posterior, 501×480, 436×400, 349×356, and 255×313 μm, respectively. First and second abdominal somites ornamented with scattered rows of minute spinules on ventral surface ( Fig. 60B ). Caudal ramus ( Fig. 60C ) slender, about 6.2 times as long as wide (590×95 μm) but variable in length (in other dissected specimen 4.6 times as long as wide, 391×85 μm); armed with 6 setae, distal setae stiff, not flexible, longest seta 263 μm long, 0.45 times as long as ramus; outer lateral seta invariably located at 35% of ramus length.

Rostrum ( Fig. 60D ) tapering, shield-shaped, longer than wide, with angular apex. Antennule 10-segmented ( Fig. 30 ); firstandsecondsegments broadened; armature formula 3, 17, 6, 3+aesthetasc, 1, 3, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; one of distalsetae on second segment pinnate, all other setae naked. Antenna ( Fig. 60F ) 3-segmented, consistingof coxa, allobasis, and 1-segmented free endopod; basiswith 2 large setae of subequal length (1 pinnate and 1 naked, wrinkled) subdistally on outer margin representing exopod, and 1 seta (derived from first endopodal segment) on inner margin; free compound endopodal segment about 3.6 times as long as wide, slightly shorter than basis, and armed with 11 setae plus terminal claw, half as long as segment.

Labrum ( Fig. 60G ) strongly tapering, concave along posterior margin, ornamented withsetules posterolaterally and with spinules and setules on weak median lobe. Mandible ( Fig. 60H ) with 6 teeth (2 proximal teeth spinule-like) and 2 small setae on coxal gnathobase; basis with 1 setaonmedial margin; exopod 2-segmented, with 1 and 4 setae on first and second segments, respectively; endopod with 4 and 10 setae on first and second segments, respectively. Paragnath ( Fig. 60I ) as simple lobe bearing setules on medial margin. Maxillule ( Fig. 60J ) with 9 setae on arthrite, 1 on coxal endite, 2 on epipodite, 3 unequal setae on medial margin of basis, and 4 on exopod; endopod 2-segmented with 2 setae on first segment and 4 on second. Maxilla ( Fig. 61A ) 5-segmented; armed with 10 setaeonsyncoxa (4, 1, 2, and 3), clawplus 2 setae on basis, and 1, 1, and 3 setae on first to third endopodal segments, respectively. Maxilliped ( Fig. 61B ) 2-segmented; first segment with 9 setae; secondsegment with 2 setae distally and ornamented with curved row of long setules.

Legs 1–4 with 3-segmented rami ( Fig. 61 C–E) but articulation between second and third endopodal segments indistinct in legs 2–4. Inner distal spine on basis of leg 1 shorter than first endopodal segment. Legs 2–4 armed with setiform outer margin elements on exopods. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod
Leg 1	0-1	1-I	I-1; I-1; III, 1, 4 0-1; 0-1; 1, 2, 3
Legs 2 & 30-1		1-0	1-1: 1-1; 3, 1, 5	0-1; 0-2; 1, 2, 3
Leg 4	0-1	1-0	1-1; 1-1; 2, 1, 4	0-1; 0-2; 1, 2, 2

Leg 5 ( Fig. 61F ) consistingof 2 small lobes, each tipped with 1 naked seta.

Descriptionofmale. Body ( Fig. 61G ) 2.27 mm long. Urosome 6-segmented, comprising fifth pedigerous somite, genitalsomite 159×255 μm, and 4 freeabdominal somites 205×210, 218×193, 190×173, and 105×150 μm, respectively. Caudal ramus about 6.1 times as long as wide (273×45 μm); outer lateral seta positioned at 30% of ramus length; all caudal setae thin and flexible.

Rostrum as in female. Antennule with one seta (indicated by dark seta in Fig. 60E ) on anterior margin of second segment enlarged and spiniform, otherwise antennule as in female. Antenna, mouthparts, and legs 1–4 asin female.

Leg 5 ( Fig. 61H ) represented by ventrolateral lobe tipped with 1 seta, and small trapezoidal exopodal segment tipped with 1 seta. Leg 6 ( Fig. 61H ) represented by 2 setae on genital operculum.

Remarks. The original description of this species was inadequate. Our material exhibits a very similar morphology to the type material, with the slender, tapering caudal rami bearing stiff distalsetae (“sabershaped” according to Schellenberg (1922)), and it occurs in association with the type host species in the same geographic region as the type. On this basis we attribute our material to Pygodelphys antarctica with confidence and provide a full modern description of this species.

Schellenberg (1922) recorded the ascidian Paramolgula gregaria collected at the Falkland Islands and at Ushuaia, Tierra del Fuego ( Chile), as host to two different species of copepod associates, P. antarctica (as Doropygus antarctica ) and Campopera michaelseni Schellenberg, 1922 .

Figures

FIGURE 30. Schematic comparison of antennular segmentation patterns in selected notodelphyid taxa. Roman numerals mark ancestral segments, Arabic numerals indicate number of setae on each segment/compound segment. ae = aesthetasc. Supernumerary setae are identified by reference to the observed maximum setal number known within the Copepoda (see Boxshall & Huys, 1998). Supernumerary setae are present on segments III–XI, XII–XIV, XV–XVI, XXIV and XXV of Paranotodelphys polycarpae, on segments III–XI, XII, XV–XVI, XXI–XXIII, XXIV, XXV and XXVI–XXVIII of P. saccata, and on segments XVII–XX, XXI–XXIII, XXIV, and XXV of Doropygopsis novemsetifera.

FIGURE 60. Pygodelphys antarctica (Schellenberg, 1922), female. A, habitus, right; B, urosome, ventral; C, right caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, paragnath; J, maxillule. Scale bars: A, 1 mm; B, 0.2 mm; C–F, H, 0.1 mm; G, I, J, 0.05 mm.

FIGURE 61. Pygodelphys antarctica (Schellenberg, 1922). Female: A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Male: G, habitus, right; H, anterior part of urosome showing legs 5 and 6, ventral. Scale bars: A–E, H, 0.1 mm; F, 0.05 mm; G, 0.2 mm.