Notopygus unispinatus, 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 : 391-395

Notopygus unispinatus gen. et sp. nov.

( Figs. 259–261 )

Type material. Holotype (intact ♀, MNHN-IU-2014-21330 ), allotype (♂, MNHN-IU-2014-21331), paratypes (35 intact ♀♀, MNHN-IU-2014-21332), and dissected paratypes (2 ♀♀, 1 ♂, figured) from Ascidia multitentaculata (Hartmeyer,1912) , Saldana Bay Harbour, South Africa, SAA 67, Griffiths coll., 28 August 1994.

Etymology. The specific name is from the Latin uni (=single) and spin (=spine), referring to the presence of a single spine on the caudal ramus.

Descriptionoffemale. Body ( Fig. 259A ) compressed, 4.21 mmlong: prosome 2.53 mmlong. Dorsalcephalic shield well-defined; metasomeindistinctly segmented, bulbous,distinctlybroadeningposteriorly,retainingvestiges of 3 tergites. Globular brood pouch formed by markedly inflated third and fourth pedigerous somites, much longer than anterior part of prosome. Free urosome ( Fig. 259B ) slender, cylindrical, 5-segmented: genitalsomite 260×385 μm; 4 abdominalsomites 262×335, 262×302, 225×280, and 210×247 μm, respectively. Anal somite with nearly parallellateralmarginsandshallow posteromedian incision. Caudalramus ( Fig. 259C ) slender, 5.9 timeslongerthan wide (377×64 μm) but gradually narrowing distally, with 1 small tubercle distally: armedwith 5 setae; outer proximal and dorsal setae positioned at 31 and 65% of ramus length, respectively; 3 distal setae unequal in length; distal spine 40 μm long, articulated at base.

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

Rostrum ( Fig. 259D ) 129×127 μm, well-sclerotized, narrowing distally towards rounded apical margin bearing several sensillae. Antennule ( Fig. 259E ) slender, 405 μm long, 10-segmented; first and second segments distinctly broader than other segments; armature formula 3, 17, 5, 4+aesthetasc, 1, 3, 2+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; all setae naked; aesthetascs thin, difficult to distinguish from setae. Antenna ( Fig. 259F ) 4-segmented; coxashortand unarmed;basis 109×60 μm, withsmallknob at outer distal corner (exopod) tipped with 2 minute setal vestiges; first endopodal segment 90×59 μm, with 1 small setaonsubdistalinnermargin; compounddistalendopodal segment about 2.8 times longer than wide (105×38 μm) and about 1.2 times longerthan firstendopodal segment; armed with 9 setae (including 3 unequal, bluntly tipped distal setae) and 2 groups of spinules; terminal claw 68 μm long, strongly curved, 0.65 times as long as segment.

Labrum ( Fig. 259G ) with paired rows of setules running from ventral surface toposterior margin; posterior margin protruding in middle. Mandible ( Fig. 259H ) with 5 teeth, 1 small subsidiary tooth on distal margin, and 1 smallproximal setaon coxal gnathobase: basis with 1 seta on medial margin; exopod 4-segmented; 3 distal segments much narrower than first, each segment with 1 seta, distalmost seta shorter than other setae: endopod with 4 and 10 setae on first and second segments, respectively; outermost distal seta less than half length of adjacent seta. Paragnath ( Fig. 259I ) with setules and 1 denticle apically, and setules and row of minute spinules on medial surface. Maxillule ( Fig. 259J ) consistingof precoxa, coxa, basis, exopod and endopod; precoxa with 9 setae on arthrite, row of minute spinules on dorsal surface near base of coxal endite; coxa with endite bearing 1 seta and several minute spinules at tip and epipodite bearing 2 unequal setae; basis with 1 small proximal seta and 2 long distal setae on medial margin; exopod with 3 setae and 1 pointed process between outer and middle setae; endopod with 3 equal setae. Maxilla ( Fig. 260A ) 5-segmented; syncoxawith 3, 1, 2, and 3 setae on first to fourth endites, respectively; basis with claw ornamented with setules along concave margin plus 2 unequal setae; endopod with 1, 1, and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 260B ) unsegmented but with short indentation subdistally onmedial side; armed with 9 setaeon medial marginand 2 unequalapicalsetae.

Legs 1–4 biramous with 3-segmented exopods and 2-segmented endopods ( Fig. 260 C-E); endopods shorter than exopods in all legs. Innercoxal setaof leg 1 extending to distal margin of basis, but that of legs 2–4 much longer, extending beyond middle of second endopodal segment. Outer setaon basis of legs 1–4 rudimentary and naked. Innerdistalspineonbasisofleg 1extending todistalborder of first endopodal segment, 60 μm long. Outer margin of first exopodal segment with spinules in leg 1, but smooth in legs 2–4. Outer setae on exopods of legs 2–4 spiniform, bluntly tipped. Distal setae on third exopodal segment of legs 2–4 shortened and bluntly tipped. Third exopodal segment of legs 2 and 3 terminating in spiniform process. Third exopodal segment of leg 4 armed with 9 armature elements (setae). Second endopodal segment of legs 2–4 slender. 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; 1, 2, 4
Legs 2 & 3	0-1	1-0	1-1; 1-1; 3, 1, 5	0-1; 1, 2, 5
Leg 4	0-1	1-0	1-1; 1-1; 3, 1, 5	0-1; 1, 2, 4

Leg 5 ( Fig. 260F ) consisting of broad protopod not articulated at base, armed with small seta at outer distal corner and ornamented with row of spinules near base of exopod, plus elongate free exopodal segment, extending beyond posterior border of genital somite, about 5.5 times longerthan wide (218×40 μm), with parallel lateral margins; armed distally with slender spine (48 μm long) and small seta (subequal in length to spine), ornamented with 5 rows of minute spinules on dorsomedial surface.

Description of male. Body ( Fig. 261A ) curved ventrally, slender, not expanded: bodylength 1.78 mm. Prosome 5-segmented with broad cephalosome and 4 well-defined pedigerous somites. Urosome ( Fig. 261B ) 6-segmented, but with fifth pedigerous somite indistinctly articulated from prosome. Genital somite 131×218 μm, narrowing posteriorly, with well-developed paired genital opercula ventrally ( Fig. 261C ). Four free abdominal somites 153×167, 135×164, 109×145, and 73×127 μm, respectively. Anal somite with slightly concave lateral margins and small paired papillae on distal margin. Caudalramus ( Fig. 261D ) slender, slightly curved, about 5.8 times longerthan wide (174×30 μm): armed with 5 setae and 1 spine, plus 1 distal tubercle; one of distal setae much longer than others ( Fig. 261E ).

Antennule segmented and armed as in female, but aesthetasc on penultimate segment short (length about 0.3 of segment width). Rostrum, antenna, mouthparts, and legs 1–4 asin female.

Leg 5 ( Fig. 261C ) similartothatof female; exopodal segment about 6.9 timeslongerthan wide (94×14 μm), armed distally with 2 subequal setae. Leg 6 ( Fig. 261C ) represented by 3 small setae (2 distal and 1 on outer margin) on genital operculum.

Remarks. The sexual dimorphism exhibited by the type species is on an unusually small scale. Apart from the basic body form, sexual dimorphism was observed in the length of an antennulary aesthetasc, in the slightly more elongate exopodal segment on leg 5 and in the form of leg 6.

Figures

FIGURE 259. Notopygus unispinatus gen. et sp. nov., 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, 0.5 mm; B, 0.2 mm; C, H, 0.1 mm; D–G, I, J, 0.05 mm.

FIGURE 260. Notopygus unispinatus gen. et sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: 0.1 mm.

FIGURE 261. Notopygus unispinatus gen. et sp. nov., male. A, habitus, right; B, urosome, ventral; C, anterior part of urosome, ventral; D, caudal ramus; E, distal part of caudal ramus. Scale bars: A, 0.2 mm; B, 0.1 mm; C, D, 0.05 mm; E, 0.02 mm.