Archinotodelphys nudus, Kim & Boxshall, 2020

Kim, Il-Hoi & Boxshall, Geoff A., 2020, A revision of the family Archinotodelphyidae Lang, 1949 (Copepoda: Cyclopoida Oithonida), with the recognition of 15 new species, Zootaxa 4801 (1), pp. 1-56 : 48-53

Archinotodelphys nudus sp. nov.

(Figs. 29-31)

Type material. Holotype (♀, MNHN-IU-2014-21208), allotype (♂, MNHN-IU-2014-21209) and paratypes (14 ♀♀ plus 3 ♂♂, MNHN-IU-2014-21210, intact). Dissected paratypes (2 ♀♀ and 1 ♂) in the collection of IHK.

Type host. Polycarpa sp. (MNHN-IT-2008-6805 = MNHN S1 / Pol.B /326) .

Type locality. N. Sulawesi, Indonesia, OCDN A5 , Stn Manado 12, CRRF coll., 15 May 1993 .

Etymology. The name of the new species refers to the loss of the outer margin spines on the second exopodal segment of legs 2 to 4 in this species.

Female. Body (Fig. 29A) small, flattened, with thin exoskeleton; mean body length 658 μm (range 604 to 695 μm, based on 7 specimens); length of dissected specimen 667 μm: prosome 376 μm long, greatest width 306 μm across cephalosome; fourth pedigerous somite markedly narrower than other prosomites. Urosome (Fig. 29B) 5- segmented; fifth pedigerous somite 86 μm wide; genital double-somite 83×75 μm, bearing paired genital apertures dorsolaterally at 37% of double-somite length. Three free abdominal somites 54×48, 56×42, and 34×38 μm, respec- tively; articulations between urosomites incompletely defined. Caudal ramus (Fig. 29C) as long as wide (17×17 μm), armed with 6 naked setae; all setae located distally or subdistally.

Rostrum (Fig. 29D) broad with rounded distal margin. Antennule (Fig. 29E) 137 μm long and 15-segmented; armature formula 3, 5, 8, 2, 2, 6, 4+aesthetasc, 1, 2, 1, 2, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna (Fig. 29F) with unarmed coxa; basis with 2 equal, outer distal setae representing exopod; endopod 3-segmented with armature 1, 3, and 6+claw on first to third segments, respectively.

Labrum (Fig. 29G) simple (without posteromedian lobe), unornamented. Mandible (Fig. 29H) with coxal gnathobase narrowing towards reduced biting edge, bearing minute denticles; basis with robust medial seta; exopod 4-segmented; each segment with 1 seta; endopod with 4 and 9 setae on first and second segments, respectively. Paragnath not observed. Maxillule (Fig. 29I) with 4 setae on precoxal arthrite; coxa with 1 seta each on endite and epipodite; basis with 5 setae on medial margin; exopod with 4 large setae; endopod with 8 setae (4 on medial margin and 4 distally). Maxilla (Fig. 30A) 5-segmented; syncoxa with 1, 2, and 2 setae on first to third endites; basis with 1 claw plus 1 seta; endopod 3-segmented with 1, 1, and 4 setae on first to third segments. Maxilliped (Fig. 30B) 3- segmented with 4 (2+2), 1, and 3 setae on first to third segments.

Legs 1–4 with 3-segmented rami. Third endopodal segment with well-developed, spiniform outer distal process in legs 1-4 (Fig. 30C–E): outer seta on basis of legs 1–3 large. Second exopodal segment of legs 2–4 laterally expanded, lacking outer spine. Legs 3 and 4 lacking inner coxal seta. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

Leg 1: 0-1 1-I I-1; I-1; II, 5 0-1; 0-1; 2, 4

Leg 2: 0-1 1-0 I-1; 0-1; 2, 1, 3 0-1; 0-2; 2, 4

Leg 3: 0-0 1-0 I-1; 0-1; 2, 1, 3 0-1; 0-2; 2, 4

Leg 4: 0-0 1-0 I-1; 0-1; 3, 1, 3 0-1; 0-2; 2, 3

Leg 5 (Fig. 30F) protopodal segment broader than long, armed with outer seta; exopodal segment about 1.9 times longer than wide (28×17 μm) and armed with 4 setae. Leg 6 (Fig. 30G) represented by 1 spine, 1 seta and 1 denti- form process on genital operculum.

Male. Body (Fig. 31A) similar to that of female. Length 384 μm. Urosome (Fig. 31B) 6-segmented: fifth pedi- gerous somite 42 μm wide: genital somite and 4 abdominal somites 32×47, 27×35, 33×32, 33×28, and 19×26 μm. Caudal ramus 11×12 μm.

FIG. 29. Archinotodelphys nudus sp. nov. paratype female. A, habitus, dorsal; B, urosome, dorsal; C, left caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, 0.1 mm; B, 0.05 mm; C, 0.01 mm; D–I, 0.02 mm.

FIG. 30. Archinotodelphys nudus sp. nov. paratype female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5; G, right genital aperture, dorsal. Scale bars: 0.02 mm.

FIG. 31. Archinotodelphys nudus sp. nov. paratype male. A, habitus, dorsal; B, urosome, ventral; C, antennule. Scale bars: A, 0.05 mm; B, C, 0.02 mm.

Rostrum as in female. Antennule (Fig. 31C) 113 μm long and 12-segmented; geniculation weakly expressed be- tween segments 10 and 11; armature formula 3, 5, 8, 2, 2, 2, 4+aesthetasc, 1, 1, 2, 1+2 aesthetascs, and 7+aesthetasc. Antenna, labrum, maxilla and maxilliped as in female. Mandible with 2 and 7 setae on first and second endopodal segments, respectively. Maxillule with 7 setae on endopod, 3 (not 4 as in female) medial and 4 distal.

Legs 1–5 as in female. Leg 6 (Fig. 31B) represented by 2 setae on genital operculum.

Remarks. This is the smallest species known in the genus Archinotodelphys : the mean body length of the adult female of A. nudus sp. nov. is only 658 μm while females of other species range in size from about 1.0 mm ( A. profundus ) up to 3.32 mm (in A. antarcticus sp. nov.). Archinotodelphys unisetosus sp. nov. (described below) is also small, with a female body length of 815 μm. The caudal ramus of the new species is as long as wide whereas all other species have caudal rami that are longer than wide, ranging from 2.3 times longer than wide in A. curtus sp. nov. and 2.6 times longer in A. unisetosus sp. nov., up to about 9.4 times in A. longicaudatus sp. nov. The tapering shape of the narrow coxal gnathobase of the mandible of A. nudus sp. nov. is unique within the genus; all other species have a broad biting edge. There are major differences also in the armature formula of the swimming legs: the second exopodal segment of legs 2–4 lacks an outer margin spine (which is present in all other species), the third exopodal segment of legs 2–4 carries a reduced number of armature elements (6 in legs 2 and 3 and 7 in leg 4, compared with 9 and 8 elements respectively, in all other species), and legs 3 and 4 lack the inner coxal seta (present in all other species).

FIG. 32. Archinotodelphys unisetosus sp. nov. holotype female. A, habitus, dorsal; B, urosome, dorsal; C, right caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilliped. Scale bars: A, B, 0.1 mm; C–J, 0.02 mm.

FIG. 33. Archinotodelphys unisetosus sp. nov. holotype female. A, maxilla; B, leg 1; C, leg 2; D, leg 4; E, leg 5; F, right genital aperture, dorsal. Scale bars: 0.02 mm.