Rockacestus magellanicus, 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 magellanicus sp. nov.

Figs 1B , 4A-C , 5 , 7D-F

Type material.

Holotype whole mature worm; off Río Grande, Tierra del Fuego Province, Argentina (53°51.36'S, 67°03.84'W), 58 m, 31 Mar. 2014, A. Menoret leg., MACN-Pa No. 789.

Paratypes 1 whole mature worm, 1 mature strobila, 2 detached mature proglottid, cross-section of 1 detached mature proglottid, off Río Grande, Tierra del Fuego Province, Argentina (54°19.91'S, 64°14.26'W), 122 m, 22 Apr. 2016, A. Menoret leg., MACN-Pa Nos. 790/1-14. One strobila, 1 detached mature proglottid, same data as preceding, MLP-He No. 8098. One whole mature worm, off Río Grande, Tierra del Fuego Province, Argentina (53°26.35'S, 64°58.56'W), 130 m, 1 Apr. 2012, A. Menoret leg., MACN-Pa No. 792. One whole mature worm, off the Marine Protected Area Namuncurá /Burdwood Bank (54°32.60'S, 60°1.28'W), 98 m, 30 Mar. 2016, A. Menoret leg., MACN-Pa No. 791. One whole mature worm, same data as preceding, MLP-He No. 8099.

Description.

Based on 7 specimens (5 whole mature worms and 2 strobilae without scoleces), 5 detached mature proglottids, 3 detached gravid proglottids, cross-sections of 1 detached mature proglottid, and 3 scoleces examined with SEM. Worms euapolytic, 9.9-19.5 (14.4 ± 4.0, n = 5) mm long, 61-115 (90.3 ± 23, n = 7) craspedote proglottids per worm (Fig. 1B ). Maximum width at level of scolex or immature proglottids. Scolex composed of 4 bothridia, 520-810 (631 ± 113, n = 5) long, 779-1,050 (944 ± 116, n = 5) wide (Figs 4A , 5A ). Bothridia folded, 450-471 (n = 2) long, 411-550 (n = 2) wide when folded, sessile anteriorly, free posteriorly, with apical sucker and marginal loculi. Posterior part of each bothridium with weak depression surrounded by circular band of muscle (Figs 4A , 5A ). Apical sucker, 70-105 (84 ± 17, n = 4) long, 70-100 (85 ± 17, n = 4) wide (Figs 4A , 5A, B ). Cephalic peduncle, absent. Neck, 3.6-8.3 (5.4 ± 2.0, n = 5) mm long.

Apex of scolex proper covered with acicular filitriches (Fig. 5H ). Proximal bothridial surface covered with acicular filitriches (Fig. 5G ). Distal bothridial surface covered with acicular filitriches interspersed with lingulate spinitriches, lingulate spinitriches increasing in density posteriorly (Fig. 5E, F ). Distal surface of apical sucker covered with acicular filitriches interspersed with lingulate spinitriches; posterior half of external rim of apical sucker with lanceolate spinitriches (Fig. 5B-D ). Distal marginal loculi surface covered with papilliform to acicular filitriches interspersed with short coniform spinitriches (Fig. 5I, L ). Capilliform filitriches on neck and strobila arranged in scutes (Fig. 5J, K ). Cilia observed in proximal and distal bothridial surfaces, including apical sucker and marginal loculi (Fig. 5G, L ).

Immature proglottids wider than long, 59-109 (84 ± 23, n = 7) in number. Mature proglottids wider than long, becoming longer than wide with maturity, 2-7 (4 ± 2, n = 7) in number (Fig. 1B ). Terminal mature proglottid longer than wide, 925-1,430 (1,115 ± 201) long, 376-680 (502 ± 111) wide, length-to-width ratio, 1.4-2.7 (2.3 ± 0.4, n = 6): 1 (Fig. 4C ).

Testes oblong, 67-89 (76 ± 8, n = 6) in total number, 51-67 (62 ± 6, n = 6) long, 44-57 (49 ± 5, n = 6) wide, extending from anterior margin of proglottid to anterior quarter of ovary; arranged in 5-6 columns anteroposteriorly and 2 layers deep in cross-section observed in anterior portion of proglottid (Figs 4C , 7D ). Cirrus sac oval, curved anteriorly, 200-340 (269 ± 58, n = 6) long, 95-140 (118 ± 18, n = 6) wide. Cirrus coiled, armed with minute spinitriches. Vas deferens highly coiled, extending anteriorly to vagina bend, overlapping medial margin of cirrus sac, entering cirrus sac through ventral margin (Figs 4C , 7E ).

Ovary lobulated, H-shaped in frontal view, X-shaped in cross-section at level of isthmus, 255-615 (418 ± 135, n = 6) long, 163-375 (246 ± 75, n = 6) wide (Figs 4B, C , 7F ). Vagina thick-walled, extending anteriorly from ootype region forming a seminal receptacle to bulk of vas deferens, then descending laterally along anterior margin of cirrus sac to enter genital atrium anterior to cirrus (Figs 4C , 7F ). Vagina and cirrus sac join into genital atrium, 40-60 (53 ± 12, n = 3) deep. Genital pores alternate irregularly, 62-75% (68 ± 5, n = 6) of proglottid length from posterior margin of proglottid.

Vitellarium follicular, follicles irregular in shape, 15-34 (26 ± 7, n = 6) long, 38-55 (47 ± 6, n = 6) wide, arranged in 2 lateral bands almost reaching midline in anterior third of proglottid, each band consisting of multiple columns (4 columns of follicles anterior to cirrus sac), extending throughout proglottid length, uninterrupted by ovary, partially interrupted by genital atrium (Figs 4C , 7D-F ). Uterus saccate, restricted to region between ovary and cirrus sac, running anteriorly up to genital pore level; uterine duct observed (Figs 4C , 7F ). Mehlis´ gland, 55-110 (77 ± 20, n = 5) long, 55-75 (71 ± 9, n = 5) wide, posterior to ovarian isthmus (Fig. 4B, C ).

Detached mature proglottids, 1,650-2,075 (1,875 ± 207, n = 5) long, 550-770 (654 ± 99, n = 5) wide, length-to-width ratio, 2.7-3.2 (2.9 ± 0.2, n = 5): 1. 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 magellanica (Philippi, 1902), Magellan skate ( Rajiformes , Arhynchobatidae ) (type host). Prevalence of infection, 40% in B. magellanica (4 hosts infected out of 10 examined).

Etymology.

The specific name refers to the species distribution along the Magellanic Province in the Argentine Sea, SWA.

Distribution.

This species is known from southern waters off Tierra del Fuego Province, Argentina including the Marine Protected Area Namuncurá /Burdwood Bank, Argentina (Fig. 9 ).

Remarks.

Rockacestus magellanicus sp. nov. is shorter than R. blasi sp. nov., R. brittanicus , R. georgiensis , R. piriei , R. radioductus , R. rakusai , R. siedleckii , and R. williamsi (9.9-19.5 vs. 22.3-250 mm in total length, respectively). Specimens of R. magellanicus sp. nov. have fewer testes than those of R. carvajali (67-89 vs. 46-55, respectively). Moreover, R. magellanicus sp. nov. has lingulate spinitriches and acicular filitriches on the distal surface of the bothridia whereas R. carvajali has only papilliform filitriches. Rockacestus magellanicus sp. nov. differs from R. conchai in the scolex width (779-1,050 vs. 1,122-1,775, respectively), size of bothridia (450-471 long by 411-550 wide vs. 478-624 long by 600-830 wide, respectively). Additionally, R. magellanicus sp. nov. has acicular filitriches and small lingulate spinitriches on the distal surface of apical sucker whereas R. conchai only has acicular filitriches. Rockacestus magellanicus sp. nov. is different from R. arctowskii in the size of the cirrus sac (200-340 long by 95-140 wide vs. 370-480 long by 154-215 wide, respectively) and in the size of the apical sucker (70-105 long by 70-100 wide vs. 212-250 in diameter, respectively).

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 4. Line drawings of species of Rockacestus from the Southwestern Atlantic. A-C. Rockacestus magellanicus sp. nov. from Bathyraja magellanica; A. Bothridium (paratype MLP-He No. 8099); B. Detail of ootype region, mature proglottid (paratype MACN-Pa No. 790 / 4); C. Terminal mature proglottid (paratype MLP-He No. 8098); D-E. Rockacestus ottavianoi sp. nov. from Bathyraja magellanica; D. Bothridium (paratype MACN-Pa No. 794 / 1); E. Terminal mature proglottid (holotype MACN-Pa No. 793).

Figure 5. Rockacestus magellanicus sp. nov. from Bathyraja magellanica, scanning electron micrographs. A. Scolex, small letters indicate the location of details shown in Fig. 5 B, 5 E-I; B. Apical sucker, small letters indicate the location of details shown in Fig. 5 C-D; C. Surface of the external apical sucker rim, acicular filitriches and lanceolate spinitriches; D. Distal apical sucker surface, acicular filitriches and lingulate spinitriches; E-F. Distal bothridial surface, acicular filitriches and lingulate spinitriches; G. Proximal bothridial surface, acicular filitriches, and cilium (white arrow); H. Apex of scolex, acicular filitriches; I. Distal surface of marginal loculi, acicular filitriches and coniform spinitriches; J. Scutes on surface of neck; K. Detail of scutes, capilliform filitriches; L. Detail of microtriches in marginal loculi and cilium (white arrow).

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 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.