Calanopia thompsoni A. Scott, 1909

Al-Aidaroos, Ali M., Salama, Adnan J. & El-Sherbiny, Mohsen M., 2016, New record and redescription of Calanopiathompsoni A. Scott, 1909 (Copepoda, Calanoida, Pontellidae) from the Red Sea, with notes on the taxonomic status of C. parathompsoni Gaudy, 1969 and a key to species, ZooKeys 552, pp. 17-32 : 18-22

Taxon classification Animalia Calanoida Pontellidae

Calanopia thompsoni A. Scott, 1909 Figs 1, 2, 3, 4, 5, 6, 7

Material examined.

Twelve adult females and ten adult males collected at Al-Wajh waters of the east coast of Saudi Arabian Red Sea.

Body length.

Female 1.92-1.98 mm (mean ± SD = 1.95 ± 0.02 mm, n = 12), male 1.79-1.83 mm (1.81 ± 0.01 mm, n = 10).

Female.

Body robust (Fig. 1A), 1.94 mm in length. Prosome elliptical comprising cephalosome and four pedigerous somites, prosome approximately 2.5 times as long as urosome; cephalosome distinctly separated from first pediger with one median eye and lateral hooks; fourth and fifth pedigerous somites fused, symmetrical with posterolateral corners pointed in dorsal aspect reaching nearly one-third of way along genital compound somite (Fig. 2A). Rostrum bearing pair of pointed processes with very small medial subterminal notch (Figs 1B, C, 2B). Urosome (Figs 1A, B, 2A) of two free somites; genital compound somite symmetrical and ventral surface without any processes (Figs 1B, 2A). Second urosomite symmetrical and slightly shorter than genital compound somite. Caudal rami symmetrical and approximately 2.3 times as long as wide, each ramus carrying five plumose setae along distal margin and reduced seta (seta VII) located on dorsal surface near medial distal angle.

Antennules (Fig. 1D, E) 19-segmented, when extended reaching almost anterior border of second urosomite. Armature formula as follows: ancestral segment I (segment 1) = 1 setae + aesthetasc (ae), II-VI (2) = 5 + 2 ae, VII (3) = 1 + ae, VIII-X (4) = 4 (1 spiniform) + ae, XI-XII (5) = 2 + ae, XIII (6) = 2 (1 spiniform) +ae, XIV (7) = 1 + ae, XV (8) = 1 + ae, XVI (9) = 2 + ae, XVII (10) = 2 + ae, XVIII (11) = 2 + ae, XIX (12) = 2 + ae, XX (13) = 2 + ae, XXI (14) = 2 +ae, XXII (15) = 1, XXIII (16) = 1, XXIV (17) = 1 + 1, XXV (18) = 1 + 1, XXVI-XXVIII (19) = 6 + ae.

Antenna (Fig. 1F) biramous with short coxa bearing plumose seta at distomedial angle; basis with two subequal setae distomedially; exopod 5-segmented with setal formula of 0, 4, 1, 2, 3. Endopod 2-segmented, proximal segment with two unequal subterminal setae, distal segment bilobed, with medial (proximal) lobe bearing eight setae, and with lateral (distal) lobe crowned with six setae and transverse row of fine setules.

Mandibular gnathobase (Fig. 3A) carrying eight teeth on coxal cutting edge, third to seventh teeth ornamented with row of short spinules anterodistally at base. Palp biramous; basis with four unequal setae on medial margin. Exopod 5-segmented with setal formula of 1, 1, 1, 1, 4. Endopod 2-segmented, proximal segment with two setae at distomedial corner, distal segment with seven long and one short setae.

Maxillule (Fig. 3B) with praecoxal arthrite bearing nine marginal strong spines and four setae on posterior surface. Coxal epipodite with nine setae; coxal endite with three setae, basal exite with one seta. Proximal and distal basal endites with three and one setae, respectively. Exopod carrying a total of nine setae; endopod incorporated into basis with three setae laterally and seven setae terminally.

Maxilla (Fig. 3C) praecoxal and coxal endites carrying 3 and 2, 2, 3 bilaterally spinulate setae respectively; basal endite with two setae, one longer than other; endopod 3-segmented, carrying six bilaterally spinulate setae.

Maxilliped (Fig. 3D) syncoxal lobes with 1, 3, 3 setae on their medial margins. Basis carrying two setae distally; endopod 4-segmented with setal formula of 2, 2, 1, 3.

Swimming legs 1-4 (Fig. 4 A–D) biramous, with 3-segmented exopods and 2-segmented endopods. On leg 1 to leg 3, coxa with one medial seta and patch of fine hairs. All lateral spines on exopods of legs 1-4 with serrated hyaline margins. Leg 5 (Figs 2C, 4E) symmetrical, basis with short seta posteriorly; exopod 2-segmented, first segment with two strong bilaterally serrated processes laterally (distal one longer and pointed slightly mediad). Second exopod segment nearly as long as first one, bearing two bilaterally serrated, lateral spines, one small medial process fused to segment and bilaterally serrated long, distal spine fused to segment (Figs 2C, D, 4E). Armature of legs as follows:

Male. Body (Fig. 5A, B) with plump prosome approximately 2.2 times as long as urosome comprising cephalosome and four pedigerous somites. Cephalosome distinctly separated from first pediger; fourth and fifth pedigerous fused and produced posterolaterally into symmetrical and slightly pointed corners reaching end of first urosomite (Figs 5A, 6A). Rostrum bearing pair of pointed processes directed posteroventrally (Fig. 5B). Urosome (Fig. 5A, B) comprising five free symmetrical urosomites, second urosomite longest; anal somite shorter preceding somite. Caudal rami symmetrical, 2.2 times longer than wide; caudal setae as in female. Some male specimens from Red Sea revealed the presence of one and/or two fine spinules, ventrally on the right side in the first and second urosomite respectively (Fig. 6A).

Right antennule (Fig. 5 C–E) 17-segmented, geniculate between segments XX (13) and XXI-XXIII (14). Armature as follows: ancestral segment I (segment 1) = 1 setae + aesthetasc (ae), II-V (2) = 6 + ae, VI-VII (3) = 5 + 3 ae, VIII (4) = 1 + ae, IX (5) = 2 + ae, X (6) = 1 + ae, XI (7) = 1 + ae, XII (8) = 2 + ae, XIII-XIV (9) = 3 + 2 ae, XV (10) = naked, XVI-XVII (11) = 3 (1 spiniform) + 2 ae, XVIII-XIX (12) = 2+ process + 2 ae, XX (13) = 1+ ae, XXI-XXIII (14) = 2 + 2 processes, XXIV (15) = 1 + 1, XXV (16) = 1+ ae + 1, XXVI-XXVIII (17) = 5 + ae.

Left antennule, antenna, mouthparts and swimming legs 1-4 as in female. Leg 5 uniramous and asymmetrical. Left leg (Fig. 7A) with short coxa; basis 1.8 times longer than coxa with plumose seta located posteriorly near proximal end. Exopod 2-segmented, first (proximal) segment slightly shorter than basis with pointed attenuation near distolateral corner, second (distal) segment short, hirsute on posteromedial surface, with curved relatively long spine laterally, short spine with triangular base medially and one rounded and serrated process distally (Figs 6B, C, 7B, C). Right leg (Fig. 7D) longer than left, coxa with one blunt process on posterior surface distally; basis with plumose seta laterally. Exopod 2-segmented, forming a stout subchela, first exopodal segment without thumb and nearly 4 times as long as wide, distal part of subchela with elongate depression medially and one seta on proximal border of the depression (Figs 6D, 7D). Second exopodal segment (finger) elongate, curved at one-third its length, not acutely tapering with one medial seta proximally and two setae laterally nearly at midlength, distal part of finger with shallow depression medially.