Notodelphys agilis 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 : 19-20

Notodelphys agilis Thorell, 1859

( Fig. 7 )

Material examined. 6 ♀♀ (MNHN-IU-2018-1749) from Molgula socialis Alder, 1863 , Wimereux, Atlantic coast of France; 1 ♀ (MNHN-IU-2018-1750) from Molgula bleizi (Lacaze-Duthiers, 1877) , Morgat, Atlantic coast of France; 8 ♀♀, 9 ♂♂ (MNHN-IU-2018-1751) and 1 dissected ♀ from Molgula scutata Millar, 1955 , WALDA CM 1; 9 ♀♀ (MNHN-IU-2018-1752) and 1 dissected ♀ (figured) from Corella parallelogramma (M̹ller, 1776), Kristineberg, Sweden.

Diagnostic characters of female. Body ( Fig. 7A ) of dissected specimen 2.96 mm long. Caudal ramus ( Fig. 7B ) 242×52 μm, about 4.7 times as long as wide and about 1.7 times as long as anal somite; ornamented with hair-like setules on both inner and outer margins, setules on inner margin very fine, almost invisible; outer lateral seta located in middle of ramus. Rostrum longer than wide, with pair of nipple-shaped tubercles apically. Antennule 14-segmented. Antenna ( Fig. 7C ) with exopod represented by 1 large pinnate seta and 1 vestigial seta on basis; compound distal endopodal segment about 3.8 times as long as wide. Mandibular endopod ( Fig. 7D ) 2- segmented, armed with 3 setaeon first segment and 9 setae on second; largest distalmost setaon first segment and 3 mediodistal setae on second segment naked, other setae pinnate. Maxillulary endopod incompletely 2-segmented, armed with 1 and 4 setae on first and second segments, respectively. Maxilliped 3-segmented, armedwith 10, 1, and 3 setae on first to third segments, respectively. Leg 5 ( Fig. 7E ) protopod broad, unornamented, with outer distal process not longer than exopod, tipped with 1 naked seta; free exopodal segment about 1.1 times longer than wide (32×30 μm), sub-quadrate and without basal constriction, inner and outer margins parallel, armed with 1 small and 1 longer seta, both naked.

Remarks. Notodelphys agilis was first described by Thorell (1859) based on material associated with four different hosts ( Ascidia mentula M̹ller, 1776, Ciona intestinalis (Linnaeus, 1758) (as Ascidia canina ), Ascidiella aspersa (M̹ller, 1776), and Corella parallelogramma ) collected off the coast of Sweden. These samefour ascidianspecies apparently serve as hosts to a total of seven different species of Notodelphys , all of which are still regarded as valid ( N. agilis , N. allmani , N. caerulea Thorell, 1859 , N. elegans Thorell, 1859 , N. prasina Thorell, 1859 , N. rufescens Thorell, 1859 , and N. tenera Thorell, 1859 ). Given the co-occurrence of these congeneric species both geographically and in terms of host associations, it is not surprising that there has been historic confusion over the identities of some of them. The original descriptions lacked detail and the morphological concepts of some of Thorell’s species have gradually been fixed by subsequent accounts. The most important contribution was that of G.O. Sars (1921) who redescribed all seven species. His redescription of N. agilis established the modern concept of this species, as recognized by Illg (1958) in his overview of the family Notodelphyidae .

The character states exhibited by our specimens conform to the illustrations of Sars (1921). In his original description, Thorell (1859) characterised N. agilis by two major features: the caudal rami are twice as long as the anal somite and the outer lateral seta on the caudal ramus is positioned at the mid-length. In contrast to his text, Thorell’s illustration ( Thorell, 1859: Fig. 6F 3 ) shows a caudal ramus at most 1.7 times as long as the anal somite, a similar proportion to our specimen (1.67:1) and also similar to the specimen illustrated by Sars (1921: Pl. XVII, fig. 3F), which has caudal rami measuring 1.5:1.

Confusingly, the exopod of the antenna is illustrated as comprising 2 subequal large setae in Thorell’s original description, whereastheantennalexopod of ourspecimens and that illustrated by Sars is represented by a large and a small seta. However, according to Monniot (1981) the small exopodal seta on the antenna in N. agilis is variable in length, ranging between 15 and 37% of the length of the large seta, but still showing a clear length difference between the two setae. One possible explanation for this discrepancy is that Thorell (1859) illustrated the antenna of a different specimen belonging to another coassociated species of Notodelphys , given that the four type hosts of N. agilis also served as hosts to another six congeneric species. We have followed Sars (1921) in our morphological concept of N. agilis .

The ascidians Molgula bleizei and M. scutata are reported here as new host records of N. agilis .

Figures

FIGURE 3. Bathynotodelphys defayeae gen. et sp. nov., male. A, habitus, dorsal; B, urosome, ventral; C, antennule. Scale bars: A, 0.5 mm; B, C, 0.1 mm.

FIGURE 6. Pronotodelphys caledonica gen. et sp. nov., male. A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, ventral; D, antennule; E, legs 5 and 6. Scale bars: A, 0.2 mm; B, 0.1 mm; C–E, 0.05 mm.

FIGURE 7. Notodelphys agilis Thorell, 1859, female. A, habitus, lateral; B, left caudal ramus, ventral; C, antenna; D, endopod of mandible; E, leg 5. Scale bars: A, 0.5 mm; B–E, 0.05 mm.