Rockacestus blasi, García Facal & Ivanov & Menoret, 2024

Garcia Facal, Guillermina, Ivanov, Veronica A. & Menoret, Adriana, 2024, New species of Rockacestus (Cestoda, Phyllobothriidea) from skates of the genus Bathyraja (Rajiformes, Arhynchobatidae) in the Southwestern Atlantic Ocean with comments on the distribution of the genus, Zoosystematics and Evolution 100 (2), pp. 357-372 : 357

Rockacestus blasi sp. nov.

Figs 1A , 2 , 3 , 7A-C , 8

Type material.

Holotype whole mature worm, off Villa Gesell, Buenos Aires Province, Argentina (37°33.10'S, 55°19.20'W), 98.7 m, 06 Aug. 2012, A. Menoret leg., MACN-Pa No. 783.

Paratypes 1 whole mature worm, 1 whole gravid worm, 1 detached gravid proglottid, same data as holotype, MACN-Pa Nos. 784/1-3. One detached gravid proglottid, same data as for preceding, MLP-He No. 8097. One whole mature worm, 1 detached gravid proglottid, off Río Grande, Tierra del Fuego Province, Argentina (54°29.50'S, 65°3.16'W), 133 m, 16 Mar. 2011, V. A. Ivanov & A. Menoret leg., MACN-Pa Nos. 786/1-2. Nine whole gravid worms, cross-section of 2 attached mature proglottid, off Necochea, Buenos Aires Province, Argentina (39°52.64'S, 56°38.72'W), 91.3 m, 27 Mar. 2011, V. A. Ivanov & A. Menoret leg., MACN-Pa Nos. 785/1-9, 785/11-24. Three whole gravid worms, same data as for preceding, MLP-He No. 8096. One whole gravid worm, off Necochea, Buenos Aires Province, Argentina (39°53.99'S, 57°0.64'W), 94 m, same data as for preceding, MACN-Pa No. 785/10. One whole immature worm, off the Marine Protected Area Namuncurá /Burdwood Bank, Argentina (53°55.92'S, 61°31.93'W), 184 m, 19 Apr. 2016, A. Menoret leg., MACN-Pa No. 787.

Description.

Based on 18 specimens (14 whole gravid worms, 3 whole mature worms, 1 immature worm), 3 detached gravid proglottids, cross-sections of 1 mature proglottid, and 3 scoleces examined with SEM. Worms apolytic, proglottids craspedote. Specimens possessing mature proglottids, 26.8-45.2 (35.7 ± 9.2, n = 3) mm long, 140-204 (163 ± 36, n = 3) proglottids per worm. Specimens possessing gravid proglottids, 22.3-50.9 (36.1 ± 7.6, n = 14) mm long, 106-162 (128 ± 18, n = 14) proglottids per worm (Fig. 1A ). Maximum width at level of scolex or immature proglottid. Scolex composed of 4 bothridia, 400-830 (621 ± 127, n = 17) long, 580-1,220 (891 ± 193, n = 17) wide. Bothridia folded, 375-685 (506 ± 100, n = 8) long, 425-750 (571 ± 113, n = 8) wide when folded, sessile anteriorly, free posteriorly; with apical sucker and marginal loculi (Figs 2A , 3A , 8B ). Posterior part of each bothridium with weak depression surrounded by circular band of muscle (Fig. 2A ). Apical sucker, 80-123 (107 ± 14, n = 13) long, 85-135 (113 ± 13, n = 13) wide (Figs 2A , 3A, B ). Cephalic peduncle, absent. Neck 8.8-18.5 (14.0 ± 3.0, n = 17) mm long.

Apex of scolex proper covered with acicular filitriches. Proximal bothridial surface covered with acicular filitriches (Fig. 3I ). Distal bothridial surface covered with acicular filitriches interspersed with lingulate spinitriches, lingulate spinitriches increasing in density posteriorly (Fig. 3F, J ). Distal surface of apical sucker covered with acicular filitriches interspersed with lingulate spinitriches; posterior half of external rim of apical sucker with small lanceolate spinitriches (Fig. 3B-E ). Distal surface of marginal loculi covered with papilliform to acicular filitriches interspersed with short coniform spinitriches (Fig. 3G, H ). Capilliform filitriches on neck and strobila arranged in scutes (Fig. 3K ). Cilia not observed.

Specimens possessing mature proglottids with 133-202 (158 ± 38, n = 3) immature proglottids and 2-7 (5 ± 3, n = 3) mature proglottid per worm. Mature proglottids becoming longer than wide posteriorly (Fig. 1A ). Terminal mature proglottid, 940-1,360 (1,180 ± 216, n = 3) long, 600-800 (727 ± 110, n = 3) wide, length-to-width ratio, 1.6-1.7 (1.6 ± 0.1): 1. Specimens possessing gravid proglottids with 99-146 (120 ± 17, n = 14) immature proglottids, 4-8 (7 ± 1.5, n = 14) mature proglottids, and 1-2 (1 ± 0.4, n = 14) gravid proglottids per worm. Gravid proglottids longer than wide. Terminal gravid proglottid, 1,180-1,820 (1,591 ± 203, n = 14) long, 620-970 (783 ± 97, n = 14) wide, length-to-width ratio, 1.4-2.9 (2.1 ± 0.4): 1 (Fig. 2B ).

Testes spherical to slightly oblong, 75-96 (86 ± 9, n = 4) in total number, 55-88 (78 ± 10, n = 17) long, 54-93 (77 ± 10, n = 17) wide, extending from anterior margin of proglottid to anterior quarter of the ovary; arranged in 6-8 columns anteroposteriorly and 3-4 layers deep in cross-section observed in anterior portion of proglottid (Figs 2B , 7A ). Postvaginal testes present. Cirrus sac oval, curved anteriorly, 276-450 (379 ± 42, n = 16) long, 115-175 (148 ± 19, n = 16) wide. Cirrus coiled, armed with minute spinitriches. Vas deferens highly coiled, anterior and adjacent to medial margin of cirrus sac, entering cirrus sac through anterior margin (Figs 2B, C , 7B ).

Ovary lobulated, H-shaped in frontal view, X-shaped in cross-section at level of isthmus, 230-580 (350 ± 79, n = 17) long, 250-610 (456 ± 83, n = 17) wide (Figs 2B , 7C ). Vagina thick-walled, extending anteriorly from ootype region forming a seminal receptacle, then running laterally along vas deferens bulk to anterior quarter of proglottid, recurving posteriorly to enter genital atrium anterior to cirrus sac (Figs 2B, C , 7C ). Vagina and cirrus open into a small common genital atrium, 40-85 (66 ± 14, n = 16) deep. Genital pores alternate irregularly, 54-73% (61 ± 5, n = 17) of proglottid length from posterior margin of proglottid. Vitellarium follicular, follicles irregular in shape, 31-52 (41 ± 9, n = 17) long, 50-80 (70 ± 10, n = 17) wide, arranged in 2 lateral bands almost reaching midline in anterior third of proglottid, each band consisting of multiple columns (5 columns of follicles anterior to cirrus sac), extending throughout the length of proglottid, uninterrupted by ovary, partially interrupted by genital atrium (Figs 2B , 7A-C ). Uterus saccate, restricted to region between ovary and cirrus sac, running anteriorly up to genital pore level; uterine duct not observed (Fig. 2B ). Mehlis´ gland, 80-115 (101 ± 8, n = 15) long, 60-110 (94 ± 13, n = 15) wide, posterior to the ovarian isthmus (Fig. 2B ).

Detached gravid proglottids, 2,300-2,525 (2,392 ± 118, n = 3) long, 725-775 (758 ± 29, n = 3) wide, length-to-width ratio, 3.0-3.3 (3.2 ± 0.1): 1.

Host.

Bathyraja macloviana (Norman, 1937), Patagonian skate ( Rajiformes , Arhynchobatidae ) (type host). Prevalence of infection, 83% in B. macloviana (5 hosts infected out of 6 examined).

Etymology.

This species is named in memory of the first author’s father, Blas García Mallarine for his invaluable love, support, and encouragement over the years.

Distribution.

This species is widespread along the continental shelf of Argentina occurring from waters off Buenos Aires Province to southeast Patagonia including the Marine Protected Area Namuncurá /Burdwood Bank, Argentina (Fig. 9 ).

Remarks.

Specimens of R. blasi sp. nov. can easily be distinguished from five valid species in the genus by the total length. Rockacestus blasi sp. nov. is longer than R. carvajali and R. conchai (22.3-50.9 mm vs. 13.1-14.5 mm and 9.9-16.9 mm, respectively), and is shorter than R. brittanicus , R. georgiensis and R. williamsi (22.3-50.9 mm vs. 170-250 mm, 60-170 mm, and 90 mm, respectively). Rockacestus blasi sp. nov. differs from R. piriei , R. radioductus , and R. rakusai in possessing fewer testes (75-96 vs. 137-165, ≥100, and 120-165, respectively). Rockacestus blasi sp. nov. can also be distinguished from R. radioductus in the distribution of testes (arranged in 6-8 columns in anteroposterior view vs. more than 15), the distribution of the vitelline follicles in the anterior third of the proglottid (reaching almost the midline of the proglottid vs. restricted to lateral bands), and in the position of the genital pore (54-73% from the posterior margin of the proglottid vs. equidistant from the anterior and posterior margin of the proglottid). Rockacestus blasi sp. nov. can be distinguished from R. arctowskii by the number of proglottids (140-204 vs. 24-98, respectively). Rockacestus blasi sp. nov. is different than R. siedleckii in the length of the scolex (400-830 vs. 840-960, respectively) and in the size of the apical sucker (80-135 vs. 185-220, respectively). Finally, R. blasi sp. nov. can be distinguished from 9 members in the genus by being apolytic instead of euapolytic.

Figures

Figure 1. Light micrographs of whole worms of Rockacestus from the Southwestern Atlantic Ocean. A. Rockacestus blasi sp. nov. (holotype MACN-Pa No. 783) from Bathyraja macloviana; B. Rockacestus magellanicus sp. nov. (holotype MACN-Pa No. 789) from Bathyraja magellanica; C. Rockacestus ottavianoi sp. nov. (holotype MACN-Pa 793) from Bathyraja magellanica.

Figure 2. Line drawings of Rockacestus blasi sp. nov. from Bathyraja macloviana. A. Scolex (holotype MACN-Pa No. 783); B. Terminal mature proglottid (holotype MACN-Pa No. 783); C. Detail of terminal genitalia, terminal mature proglottid (holotype MACN-Pa No. 783).

Figure 3. Rockacestus blasi sp. nov. from Bathyraja macloviana, scanning electron micrographs. A. Scolex, small letters indicate the location of details shown in Fig. 3 B, 3 F-G, 3 I, 3 K; B. Apical sucker, small letters indicate location of detail shown in Fig. 3 C-D; C. Distal surface of apical sucker, acicular filitriches and lingulate spinitriches; D. Surface of the external apical sucker rim, lanceolate spinitriches; E. Detail of distal surface of the apical sucker, acicular filitriches; F. Distal bothridial surface, lingulate spinitriches; G. Distal surface of marginal loculi, acicular filitriches and short coniform spinitriches; H. Detail of distal surface of marginal loculi; I. Proximal bothridial surface, acicular filitriches; J. Distal bothridial surface, detail of lingulate spinitriches; K. Scutes on surface of neck.

Figure 7. Light micrographs of cross-sections of mature proglottids of species of Rockacestus off Argentina. A-C. Rockacestus blasi sp. nov.; A. At the level of the testes, anterior to the cirrus sac; B. At the level of the cirrus sac; C. At the level of ovarian isthmus; D-F. Rockacestus magellanicus sp. nov.; D. At the level of the testes, anterior to the cirrus sac; E. At the level of the cirrus sac; F. At the level of ovarian isthmus; G-I. Rockacestus ottavianoi sp. nov; G. At the level of the testes, anterior to the cirrus sac; H. At the level of the cirrus sac; I. At the level of ovarian isthmus; cs - cirrus sac; oc - ovicapt; ov - ovary; sr - seminal receptacle; t - testes; u - uterus; ut - uteroduct; vd - vas deferens; vf - vitelline follicle; vg - vagina; vod - ventral osmoregulatory duct.

Figure 8. Light micrographs of scoleces of Rockacestus blasi sp. nov. A. Bothridia fixed while still attached to the host tissue (paratype MACN-Pa No. 787); B. Bothridia properly relaxed and fixed (paratype MACN-Pa No. 784 / 2).

Figure 9. Geographic distribution of the valid species of Rockacestus from the Southern Hemisphere. Symbols: red dot: new records; blue dot: previous records; Rar - Rockacestus arctowskii; Rbl - Rockacestus blasi sp. nov.; Rca - Rockacestus carvajali; Rco - Rockacestus conchai; Rge - Rockacestus georgiensis; Rma - Rockacestus magellanicus sp. nov.; Rot - Rockacestus ottavianoi sp. nov.; Rra - Rockacestus rakusai; Rsi - Rockacestus siedleckii.