Notopygus trispinatus, 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 : 395-399

Notopygus trispinatus gen. et sp. nov.

( Figs. 262–264 )

Typematerial. Holotype (intact ♂, MNHN-IU-2014- 21333 ) , paratypes (4 intact ♂♂, MNHN-IU-2014-22334), and dissected paratypes (1 ♀, 1 ♂, figured) from Ascidia incrassata Heller, 1878 , Saldana Bay, South Africa, SAA 67, Griffiths coll., 28 August 1994.

Etymology. The specific name is a combination of tri (=three) and spin (=spine), referring to the presence of the three spines on the caudal ramus.

Descriptionoffemale. Body ( Fig. 262A ) slightly compressed; length 3.50 mm. Prosome consistingof welldefined cephalosome and inflated metasome, broadening posteriorly, with vestiges of 3 dorsal tergites plus large, thin-walled, balloon-like swelling on posterodorsal surface. Fifth pedigerous somite fused with fourth. Free urosome ( Fig. 262B ) 5-segmented, graduallynarrowing posteriorly:genitalsomite160×509μm, slightlynarrowing posteriorly; 4 abdominalsomites 290×393, 298×338, 218×309, and 233×269 μm, respectively. Anal somite with shallow posteromedial incision. Caudal rami slender, widely separated from each other; each ramus ( Fig. 262C ) about 5.3 times longer than wide, slightly constricted at proximal fifth: armed with 3 spines distally and 3 setae (including distal seta); outer proximal and dorsal setae located at 29 and 67% of ramus length, respectively; 3 distal spines unequal, largest apical seta 38 μm, smaller spines 23 and 18 μm long; all 3 setae thin, shorter than width of ramus.

Rostrum ( Fig. 262D ) small, 145×197 μm, tapering strongly in proximal third and tapering weakly in distal two-thirds towards rounded apex; surface ornamented with minute sensillae. Antennule ( Fig. 262E ) slender, 410 μm long, 10-segmented; 3 proximal segmentsbroaderthan distal segments; armatureformula 3, 17, 6, 4+aesthetasc, 1, 3,2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; setae generally short and thin, all naked. Antenna ( Fig. 262F ) moderately stout, 4-segmented; coxashortand unarmed; basis 113×64 μm, bearing small innerdistal seta plus 2 outer distal setae (representing exopod); first endopodal segment 89×64 μm, with 1 small subdistal seta on medial margin; compound distal endopodal segment about 2.7 timeslongerthan wide (109×40 μm) and ornamented with 2 patches of minute spinules on outer margin: armed with 9 setae (outer distal seta distinctly larger) plus large terminal claw, 82 μm, 0.75 times as long as segment.

Labrum ( Fig. 263A ) densely setulose along posterior margin and on small posteromedial lobe. Mandible ( Fig. 262G ) with coxal gnathobase bearing 5 teeth, 1 small proximal seta, and 1 minute subsidiary tooth on distal margin at base of distalmost tooth: basis with 1 seta on medial margin; exopod obscurely 4-segmented, armed with 4 large, subequal setae; endopod 2-segmented; first segment incompletely articulated from basis, armed with 4 setae on medial margin and ornamented with minute spinules on outer distal corner and mediodistal region, secondsegment distinctly narrowerthan first, armedwith 10 setae. Maxillule ( Fig. 262H ) bearing 9 setaeon arthrite; coxal endite tipped with 1 seta, epipodite with 2 unequal setae: basis with short proximal seta and 2 distal setae (equal in length and about 3 times longerthan proximal seta): exopod with 3 setae distally (2 equal medial and 1 larger outer) plus 1 minute lobe (representing setal vestige) tipped with setule between outer and middle setae: endopodwith 3 subequal setae. Maxilla ( Fig. 263B ) 5-segmented; syncoxa with 9 setae arranged as 3, 1, 2, and 3; basis with strong claw bearing setules along concave margin plus 2 setae; endopod with 1, 1, and 3 setae on firsttothird segments, respectively. Maxilliped ( Fig. 263C ) unsegmented but with partial suture subdistally on medial side, and armed with 9 medial and 2 apical setae.

Legs 1–4 biramous with 3-segmented exopods and 2-segmented endopods ( Fig. 263 D-F); exopods longer than endopods in all legs. Inner coxal seta well-developed and pinnate; outersetaonbasis minute. Innerdistal spine on basis of leg 1 extending slightly beyond distal border of first endopodal segment, ornamented with few marginal spinules. Distal tip of third exopodal segment terminating in pointed process inlegs 2 and 3, but in 2 slender processes in leg 4. Distal endopodal segment of leg 4 elongate, about 4 times longer than first; outer and distalsetae on exopod of legs 2–4 bluntly tipped.Armature formula for legs 1–4 as in N. unispinatus gen. et sp. nov.

Leg 5 ( Fig. 263G ) consistingof short protopod not articulated at base, armed with 1 naked seta at outer distal corner and row of spinules near base of exopod plus free exopodal segment elongate, 6.0 times longer than wide (264×44 μm); armed distally with 1 spine and 1 naked seta, ornamented with 6 rows of spinules on dorsomedial surface.

Descriptionofmale. Body ( Fig. 264A, B ) slender, cylindrical; length 1.67 mm. Prosome clearly segmented: dorsal cephalic shield distinctly broader than metasome; with posterolateral corners extended posteriorly. Urosome ( Fig.264C ) 6-segmented: fifthpedigeroussomitefree from metasome. Genital somite 136×227 μm; first and second abdominal somites equal in length, each slightly longer than wide. Anal somite bearing pair of small papillae on posterior margin, just medial to bases of caudal rami. Caudalramus ( Fig. 264D ) about 5.8 timeslongerthan wide (191×33 μm) and 1.9 times longer than anal somite, curved ventrally with pointed ventrodistal corner: armed with 1 spine (distal) and 5 setae (3 distal, 1 proximal, and 1 middle), 1 distal seta much longer than others.

Rostrum as in female. First and second segments of antennule less expanded than in female, but with same setation pattern. Antenna, labrum, mandible, maxillule, and maxilla all as in female. Maxilliped ( Fig. 264E ) unsegmented and armed with 9 medial and 2 apical setae as in female, but 2 apical setae very unequal, medial seta half length of outer.

Legs 1–4 as in female. Leg 5 ( Fig. 264F ) with broad free exopodal segment about 7.3 times longer than wide (132×18 μm); distal seta about twice length of spine. Leg 6 ( Fig. 264G ) represented by 3 small setae on genital operculum (medial seta smaller than other 2).

Remarks. It is probable that the balloon-like dorsal structure on the fourth pedigerous somite in the female of this species is simply a swelling of the epidermis, and should probably be considered to be an artefact. In other respects, Notopygus trispinatus gen. et sp. nov. is very similar to the type species, N. unispinatus gen. et sp. nov. The form of the antennule, antenna, mouthparts and legs 1–5 are all similar, and both species were discovered from the same genus of ascidian hosts in South African waters. One significant difference between them is the possession of 3 spines and 3 setae on the caudal ramus in female N. trispinatus gen. et sp. nov., compared to only 1 spine and 5 setaein N. unispinatus gen. etsp. nov. Another notable difference is that the female genital somite of N. trispinatus gen. et sp. nov. is about 3 times wider than long compared to about 1.5 times wider than long in the typespecies.

The free exopodal segment of leg 5 of N. trispinatus gen. et sp. nov. is 264 μm long in the female and 132 μm in the male, whereas these dimensions are 218 μm in the female and 94 μm in the male of N. unispinatus gen. et sp. nov. So the segment is larger in N. trispinatus gen. et sp. nov., even though itis the smaller of the two species, with a body length of only 3.50 mm in female and 1.67 mm in male compared to 4.21 mm in the female and 1.78 μm in the male of N. unispinatus gen. et sp. nov.

The number of spinule rows on the free exopodal segment of leg 5 appears to be consistent within each of these species, 6 rows are present in N. trispinatus gen. et sp. nov. but only 5 in N. unispinatus gen. etsp. nov. These differences are sufficient to justify the establishment of a separate species.

Figures

FIGURE 262. Notopygus trispinatus gen. et sp. nov., female. A, habitus, right; B, urosome, ventral; C, right caudal ramus, ventral with inset showing detail of armature at tip; D, rostrum; E, antennule; F, antenna; G, mandible; H, maxillule. Scale bars: A, 0.5 mm; B, 0.2 mm; C, D, G, 0.1 mm; E, F, H, 0.05 mm.

FIGURE 263. Notopygus trispinatus gen. et sp. nov., female. A, labrum; B, maxilla; C, maxilliped; D, leg 1; E, leg 2; F, leg 4; G, leg 5. Scale bars: A–C, G, 0.05 mm; D–F, 0.1 mm.

FIGURE 264. Notopygus trispinatus gen. et sp. nov., male. A, habitus, dorsal; B, habitus, right; C, urosome, ventral; D, caudal ramus; E, maxilliped; F, leg 5; G, leg 6. Scale bars: A–C, 0.2 mm; D, F, G, 0.05 mm; E, 0.02 mm.