Pachypygus stomozoae, Kim & Boxshall, 2020

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 : 129-132

Pachypygus stomozoae sp. nov.

( Figs. 84 , 85 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21242 ) from the compound ascidian Stomozoa roseola (Millar, 1955) (MNHN-IT-2008-8049 = MNHN A3/STO/4), CRRFOCDN 1218-J, Manado Is., Sulawesi, Indonesia (01°23.74’N– 124°32.41’E), depth 20 m, 06 May 1993.

Etymology. The species name is derived from the generic name of the ascidian host.

Descriptionoffemale. Body ( Fig. 84A ) bilaterally compressed, flexed ventrally. Bodylength 3.06 mm. Dorsal shield of cephalosome with prominent, nipplelike posterolateral processes. Brood pouch in lateral view slightly longer than wide, tapering in posterior third, with rounded posterior margin; fifth pedigerous somite largely incorporated into brood pouch. Free urosome ( Fig. 84B ) 5-segmented: genital somite much wider than long, 173×318 μm, with convex lateral margins; 4 free abdominalsomites 286×259, 273×223, 182×173, and 68×132 μm, respectively. First to third abdominal somites each distinctly longer than wide. Anal somite ( Fig. 84C ) with rounded expansion ventrally, with sclerotized ventral surface. Caudal ramus ( Fig. 84D ) inserted dorsolaterally on anal somite, curved ventrally, tapering, about twice as long as wide (114×56 μm), and armed with 4 claws and 2 setae; claws 26, 17, 15, and 15 μm long; 2 setae shorter than width of ramus at base, positioned at 60% and 75% of ramus length.

Rostrum ( Fig. 84E ) conical, slightly longer than wide (170×159 μm), with slightly angular apex.Antennule ( Fig. 84F ) 9-segmented, graduallynarrowing from second to apical segments; armatureformula 3, 16, 5, 4+aesthetasc, 4, 3, 2, 2+aesthetasc, and 7+aesthetasc; secondsegment broadest and longest, about 1.5 times longer than wide; all setae thin and naked. Antenna ( Fig. 84G ) slender, 4-segmented; coxa, basis and first endopodal segment unarmed; basis only slightly longer than first endopodal segment; compound distal endopodal segment about 3.5 timeslongerthan wide (131×38 μm) and about 1.2 times longerthan first; armedwith 9 setae (arranged as 1, 3, 2, and 3) plus terminal claw, nearly as long as segment.

Labrum ( Fig. 84H ) setulose along lateral margins; with paired spinulose, semicircular posterolateral lobes and weak mid-posterior lobes. Mandible ( Fig. 84I ) with 5 teeth and 2 setaeon coxal gnathobase; basis with 1 setaon medial margin; exopod unsegmented, armedwith 5 setae, innermost shorter than others, outer 2 setae distinctly longerthan other 3; endopod with 4 and 10 setaeon first and second segments, respectively; second and third inner distalsetae on second segment about half as long as first and fourth innerdistal setae. Paragnath ( Fig. 84J ) with distal and subdistal dentiform processes and ornamented with setules on medial margin. Maxillule ( Fig. 84K ) and maxilla ( Fig. 85A ) armedas in P. exilis sp. nov. Maxilliped ( Fig. 85B ) 3-segmented and armed with 9, 1, and 3 setae on first to third segments, respectively; articulation between first and second segments incomplete.

Legs 1–4 ( Fig. 85 C–F) with 3-segmented rami. Inner seta on coxa well-developed in legs 1 and 2, but absent in legs 3 and 4. Outer setaon basis large and pinnate in leg 1, but small and naked in legs 2–4. Inner distal spine on basis of leg 1 longerthan first endopodal segment, 73 μm long, ornamented with minute spinules along margins. Basis and first to third endopodal segments of leg 1 with 3, 7, 3, and 3 hair-like sensillae, respectively on anterior surface. First exopodal segments of legs 2–4 each about 2.5 times longer than wide. Third exopodal segment of legs 2–4 about 2.0, 2.6, and 2.6 timeslongerthan wide, respectively. Armature formula for legs 1–4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-1	1-I	I-1; I-1; III, I, 4	0-1; 0-1; 1, 2, 3
Leg 2	0-1	1-0	I-1; I-0; II, II, 0	0-1; 0-2; 1, 2, 3
Leg 3	0-0	1-0	I-1; I-0; II, II, 0	0-1; 0-2; 1, 2, 3
Leg 4	0-0	1-0	I-0; I-0; II, II, 0	0-1; 0-2; 1, 2, 2

Leg 5 ( Fig. 85G ) 2-segmented: protopod about as long as wide, not articulated basally, with 1 outer distal seta and minute spinules on posteroventral border; free exopodal segment about 2.9 times longer than wide (144×49 μm), armedwith small, claw-like spineand naked seta on oblique distal margin, and ornamented with 4 rows of minute spinules on medial surface.

Male. Unknown.

Remarks. In possessing paired posterolateral processes on the dorsal shield of the cephalosome and 3 setae on the third segment of the maxilliped, Pachypygus stomozoae sp. nov. is similar to P. papillosus sp. nov. and P. exilis sp. nov. Itcan be differentiated from P. papillosus sp. nov. by its smooth body surface, lacking the numerous papillae so characteristic of P. papillosus sp. nov., and by the smaller posterolateral processes on the cephalosome and the possession of 10 setae on the second endopodal segment of the mandible (vs. 9 in P. papillosus sp. nov.). Pachypygus stomozoae sp. nov. is more similar to P. exilis sp. nov. The differences between the new species and P. exilis sp. nov. are as follows: (1) the body is almost twice as long, 3.06 mm long (vs. 1.55 mm in P. exilis sp. nov.); (2) the first and second abdominal somites are distinctly longer than wide (vs. wider than long in P. exilis sp. nov.); (3) the second antennular segment is about 1.5 times longer than wide (vs. about twice as long as wide in P. exilis sp. nov.); (4) the 2 outer setae on the mandibular exopod are longerthan the other 3 setae (vs. the outermost seta is longer than the other 4 in P. exilis sp. nov.); and (5) the first exopodal segment of leg 3 bears an inner seta (vs. this seta lacking in P. exilis sp. nov.). This comprehensive set of differences justifies the establishment of the new species.

Figures

FIGURE 84. Pachypygus stomozoae sp. nov., female.A, habitus, right; B, urosome, ventral; C, distal part of abdomen, right; D, left caudal ramus, outer; E, rostrum; F, antennule; G, antenna; H, labrum; I, mandible; J, paragnath; K, maxillule. Scale bars: A, 0.5 mm; B, 0.2 mm; C, F, H, J, K, 0.05 mm; D, 0.02 mm; F, G, I, 0.1 mm.

FIGURE 85. Pachypygus stomozoae sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, leg 5. Scale bars: A, B, G, 0.05 mm; C–F, 0.1 mm.