Notodelphys allmani Thorell, 1859

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 : 20-23

Notodelphys allmani Thorell, 1859

( Fig. 8 , 9 )

Material examined. 1 ♀, 1 ♂ (MNHN-IU-2018-1753) from Cystodytes senegalense Monniot F., 1969 , Dakar, Senegal; 9 ♀♀ (MNHN-IU-2018-1754) from unknown host, Bizerte, North coast of Tunisia; 7 ♀♀, 1 ♂ (MNHN-IU-2018-1755) and 1 dissected ♀ (figured)from Ascidiella aspersa (Müller, 1776) , Israel; 3 ♀♀, 3 ♂♂ (MNHN-IU- 2018-1756) from A. aspersa , Porto Munzio, Italy; 1 ♀ (MNHN-IU-2018-1757)from A. aspersa, Roscoff , France, 1878; 1 ♀ (MNHN-IU-2018-1758) from Ascidia mentula (Müller, 1776) , Roscoff 1878; 3 ♀♀ (MNHN-IU-2018- 1759) and 1 dissected ♀ from A. mentula, Dinard , France; 2 ♀♀, 2 ♂♂ (MNHN-IU-2018-1760) and 1 dissected ♀ from Ascidia conchilega M̹ller, 1776, Sanit-Vaast-La-Hougue, France, 30 August 1996; 1 ♀ (MNHN-IU- 2017-2163) from A. aspersa, MEDITS 2016 , Stn M16-6 (43°25.64 Ń, 4°04.01 É), depth 32 m, 31 May 2016; 8 ♀♀ (MNHN-IU-2017-2166) from A. aspersa, MEDITS 2016 , Stn M16-2 (43°20.98 Ń, 4°19.64 É), depth 32–33 m, 31 May 2016.

Supplementary description of female. Body ( Fig. 8A ) slightly dorsoventrally depressed. Body length of dissected specimen 2.90 mm (largest observed specimen 4.35 mm). First pedigerous somite narrower than other pedigerous somites, lacking dorsal tergite. Tergites of second and third pedigerous somites well defined. Fourth pedigerous somite forming brood pouch, longer than wide with rounded corners; fifth pedigerous somite largely incorporated into brood pouch. Free urosome ( Fig. 8B ) 5-segmented, consisting of genital and 4 abdominal somites: genitalsomite 182×240 μm; 4 freeabdominal somites 222×211, 218×200, 171×185, and 153×185 μm, respectively.Anal somite ornamented with transverse row of fine spinules posteroventrally, near base of caudal rami ( Fig. 8C ). Caudal ramus ( Fig. 8C ) about 3.9 times as long as wide (200×51 μm) and about 1.3 times as long as anal somite, ornamented with setules along parallel inner and outer margins 2 ventral rows of minute spinules at inner distal corner; armed with 6 setae, outer lateral seta naked and positioned at 67% of ramus length; dorsal seta (seta VII) naked, other 4 distalsetae pinnate.

Rostrum ( Fig. 8E ) about 1.5 timeslongerthan wide, tapering distally with nipple-shaped median process at apex. Antennule ( Fig. 8D ) 15-segmented; armature formula 3, 5, 12, 6, 4+aesthetasc, 2, 2, 2, 1, 1+aesthetasc, 1, 1, 1, 2+aesthetasc, and 7+aesthetasc; most of setae pinnate (as figured); distalsetaon ninth ( XX) and twelfth ( XXIII) segments annulated at base. Antenna ( Fig. 8F ) 4- segmented; short coxa unarmed; basiswith 2 large pinnate setae representing exopod, shorter seta about 0.7 times length of longer; first endopodal segment with 1 inner seta; compound distal endopodal segment about 3.6 times longerthan wide (129×36 μm), ornamented with 2 rows of fine spinules on outer margin; armed with terminal claw plus 10 setae (arranged as 1, 1, 3, 2, and 3).

Labrum ( Fig. 8G ) slightlynarrowing distally; posterolateral protuberances ornamented with denticles and setules; median posterior margin convex and ornamented with several spinules in middle and setules on both sides. Mandible ( Fig. 8H ) consisting of coxa and biramous palp; coxalgnathobase with 5 major teeth and 2 setae, second distal tooth acutely pointed; basis with 1 seta on medial margin and patch of minute spinules on proximal outer surface; exopod with 5 setae, terminal seta about twice as long as other 4 setae; 2-segmented endopod armed with 4 setae on first segment and 9 setae on second. Paragnath ( Fig. 8J ) as small lobe, hirsute on medial surface, with dentiform process medio-distally. Maxillule ( Fig. 8I ) armedwith 10 setae (including 2 small ones) on precoxal arthrite, 1 seta on coxal endite, 2 setae on epipodite; basis with 3 setae on medial margin, proximal seta much smaller than distal 2; exopod with 4 setae distally; endopod incompletely 2-segmented with 1 setaon first segment and 4 setaeon second. Maxilla ( Fig. 9A ) 5-segmented; syncoxa (first segment) with 10 enditic setae (arranged as 4, 1, 2, and 3); basis with strong claw bearing minute spinules along concave margin, plus 2 unequal setae; 3-segmented endopodwith 1, 1, and 3 setae on first to third segments, respectively. Maxilliped ( Fig. 9B ) 3-segmented and armedwith 10, 1, and 3 setae on first to third segments; larger setaon third segment spiniform and fused to segment at base.

Legs 1–4 biramous with 3-segmented rami ( Fig. 9 C–E); first exopodal segment with spinules on outer surface, those on leg 1 larger than in other 3 legs; inner coxal seta pinnate in legs 1–3, but naked in leg 4; outer seta on basis pinnate in leg 1, but naked in legs 2–4. Minute bifurcate spinules present at junction between basis and endopod of leg 1 and on distal border of first and second endopodal segments of legs 2 and 3. Leg 1 with innerdistal spine on basis 60 μm long and spinulose along margins. First endopodal segment of leg 1 about 1.4 times longerthan wide (95×67 μm). Outer spines on exopods of legs 1–4 with membranous fringes. Armature formula for legs 1–4 as in generic diagnosis.

Leg 5 ( Fig. 9F ) consistingof broad protopod and free exopod. Protopod indistinctly delimited from brood pouch at base, with digitiform outer distal process about 45 μm long bearing pinnate seta at tip; ornamented with dentiform process subdistally on inner margin, and 6 to 9 spinules proximally on inner margin. Exopodal segment 36×31 μm, outer distalmargin expanded, strongly convex; armed with 1 smooth inner subdistal spine and 1 weakly pinnate distal seta; ornamented with 2 to 4 small spinules on inner margin near base of spine.

Remarks. Notodelphys allmani is the most common species of Notodelphys and has been found in association with more than ten species of solitary ascidians ( Gotto, 1993). It is difficult to distinguish from its closely related congener, N. rufescens . In his original description Thorell (1859) differentiated between the two species by the ornamentation on the outer surface of the first exopodal segment of leg 1: spinulose in N. allmani versus smooth in N. rufescens . However, subsequent authors seemed unable to confirm this difference between the two species. Sars (1921) stated that the caudal rami were twice as long as the anal somite in N. allmani but less than twice in N. rufescens and that the outer lateral seta on the caudal ramus is located further from the apex in N. rufescens . These and other minor differences mentioned by Sars (1921) could not, however, be confirmed by reference to his illustrations of the two species. Stock (1951) considered that the position of the outer lateral seta on the caudal ramus is a reliable character for distinguishing the two species, but he did not clarify the correct position of the seta in these species. Bocquet & Stock (1960) used the armature of leg 5 exopod to distinguish the two species: the exopod bearing 2 long setae in N. allmani against 1 long seta and 1 short, strong seta in N. rufescens .

In our specimens examined above: (1) the caudal ramus is about 4 times as long as wide and about 1.3 to 1.4 times as long as anal somite; (2) the outer lateral seta of the caudal ramus is positioned at 67% of ramus length; (3) the first exopodal segment of leg 1 is ornamented with spinules on the outer surface (and this is visible as a patch of spinules when the leg is viewed from lateral aspect); and (4) the exopod of leg 5 is slightly longer than wide and armed with 1 inner spine and 1 distal seta and the seta is only slightly longer than the spine. No significant variability in these four characters was exhibited by our material and all of these characters can be observed without dissection of the specimens. All of these specimens were identified as N. allmani because the first exopodal segment of leg 1 is ornamented with spinules on outer surface, as defined by Thorell (1859). We consider that N. rufescens is probably a variant of N. allmani but we do not propose a formal synonymy.

Figures

FIGURE 8. Notodelphys allmani Thorell, 1859, female. A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, ventral; D, antennule; E, rostrum; F, antenna; G, labrum; H, mandible; I, maxillule; J, paragnath. Scale bars: A, 0.5 mm; B, 0.2 mm; C–J, 0.05 mm.

FIGURE 9. Notodelphys allmani Thorell, 1859, female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: 0.05 mm.