Holocentricola coronatus, Cutmore & Cribb, 2021

Cutmore, Scott C. & Cribb, Thomas H., 2021, A new order of fishes as hosts of blood flukes (Aporocotylidae); description of a new genus and three new species infecting squirrelfishes (Holocentriformes, Holocentridae) on the Great Barrier Reef, Parasite (Paris, France) 28 (76), pp. 1-17 : 10-11

Holocentricola coronatus n. sp. ( Figs. 2C , 3C )

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Type host: Sargocentron diadema (Lacepède) , Crown squirrelfish ( Holocentriformes : Holocentridae ).

Type locality: Off Lizard Island (14 ° 40 0 S, 145 ° 27 0 E), northern Great Barrier Reef, Australia .

Site in host: Ventricle, branchial arteries, vessels of liver, wash of head split.

Prevalence: 2 of 9 (adults in one).

Intensity: 4 worms in single fish from which adult worms were recovered.

Type material: Holotype ( QM G239125 ) and 3 paratypes ( QM G239126–28 ).

Representative DNA sequences: Partial cox 1 mtDNA, one sequence (submitted to GenBank, OK421320); ITS2 rDNA, one sequence (submitted to GenBank, OK422498).

Etymology: This species is named from the Latin coronatus (crowned) for the type and only host, the Crown squirrelfish.

Description [based on four specimens]: Body lanceolate, ventrally concave, broadest at level of testis or caeca, 839– 937 × 111–141 (890 × 124), 6.16–8.44 (7.25) times longer than wide; subtle notch at level of male genital pore; distinct terminal notch at posterior end; distinct bulge sometimes present at level of uterus. Tegumental spines arranged in ventro-marginal transverse rows for entire body length, 6 long, straight for most of body length, those in final 5–10 rows slightly curved with small hook on tip, 8–9 long. First spine row with 4 spines, increasing in number after first few rows, 5–6 spines per row for most of body length, decreasing in number posterior to ovary, 3 spines in final row; spine rows 8–9 wide, spaced 3 apart in anterior third of body, 4–5 apart in middle and posterior thirds of body. Dorsal nerve commissure 25– 37 (30) across, 80–90 (86) from anterior extremity. Nerve cords well-defined, 5–8 (7) in diameter, run length of body, 22–30 (25) from body margin at midbody. Oral sucker poorly delineated, weakly muscularised, 14–18 × 16–23 (16 × 19), bearing concentric rows of fine spines, number of rows undetermined. Mouth a simple pore, ventrally subterminal, 5–8 (7) from anterior extremity. Oesophagus gently sinuous, thick-walled, 311–349 (337) long. Oesophageal glands enveloping oesophagus posterior to dorsal nerve commissure, thickening and forming glandular bulb distinctly anterior to anterior caeca. Caeca form X-shape; intestinal bifurcation in middle third of body, 311–355 (339), or 37.1–39.5% of total body length, from anterior extremity. Anterior caeca equal to subequal in length, much shorter than posterior caeca; left anterior caecum 28–48 (34); right anterior caecum 30–41 (34); longer anterior caecum occupying 3.5–5.1% of total body length. Posterior caeca equal to subequal in length, 2.9–5.5 (4.2) times longer than anterior; left posterior caecum 131–153 (141); right posterior caecum 127–142 (134); longer posterior caecum occupying 14.6–17.6% of total body length. Total caecal length 178–192 (183), occupying 20.0–21.2% of body length.

Testis single, roughly rectangular, with margins irregularly lobed, immediately posterior to posterior ends of posterior caeca, extends laterally beyond lateral nerve cords and posteriorly to anterior margin of ovary, 127–153 × 77–95 (138 × 84), occupying 14.3–16.7% of total body length; post-testicular space 264–310 (287), or 31.3–33.1% of body length. Vas deferens originates medially from posterior margin of testis, passing ovary and uterus ventrally, widening posteriorly in one specimen, entering cirrus-sac dorso-anteriorly. External seminal vesicle absent. Cirrus-sac retort-shaped, rounded anteriorly, dramatically narrowed posteriorly; anterior rounded portion 42–63 × 24–37 (51 × 31), contains seminal vesicle and pars prostatica; posterior narrow portion 80–98 (86) long, notably thickened at marginal genital pore, contains ejaculatory duct (un-everted cirrus; everted cirrus not observed), 4–7 (5) wide at midpoint, 6–9 (7) wide at marginal thickening. Seminal vesicle round to ovoid, 23–43 × 25–30 (35 × 28), restricted to anterior, rounded portion of cirrus-sac, joining coiled pars prostatica; prostatic cells not observed. Ejaculatory duct long. Male genital pore on sinistral margin at subtle marginal notch, 70–79 (74), or 8.1–8.7% of body length, from posterior extremity.

Ovary roughly rectangular or wedge-shaped, medial, with margins irregularly lobed, immediately posterior to testis, extending laterally beyond lateral nerve cords, 32–40 × 85–102 (37 × 94); post-ovarian space 241–284 (264), or 28.7–30.3% of total body length. Oviduct originates from posterior margin of ovary, passes posterio-dorsally to vitelline duct and dextro-lateral to ascending portion of uterus, posteriorly curving sinistrally to meet oötype, heavily distended with sperm. Oötype posterior to rest of genitalia, medial, surrounded by Mehlis’ gland, 75–94 (86) from posterior extremity. Uterus weakly convoluted, passing anteriorly between oviduct and dextral side of cirrus-sac, ventrally overlapping posterior margin of ovary, then passing posteriorly, sinistral to cirrus-sac, to female genital pore; distal portion of uterus often forming egg reservoir, creating distinct marginal bulge; egg reservoir sometimes distorting position of cirrus-sac. Female genital pore dorsal, sinistro-submedial, separate from and anterior to male pore, just posterior to level of constriction dividing anterior and posterior portions of cirrus-sac, 23–30 (26) from sinistral margin, 127–146 (138) from posterior extremity. Eggs in utero ovoid to subspherical, very thin-shelled, anoperculate, 25–28 × 16–22 (27 × 19). Vitellarium follicular, distributed from just posterior to dorsal nerve commissure to anterior margin of ovary, laterally exceeding nerve cords, largely confluent anterior to testis, interrupted partially by ends of caeca and oesophageal gland dorsally, interrupted partially by testis ventrally and dorsally. Vitelline duct passes ovary ventrally, passing posterio-dextrally to oötype, ventrally overlaps oviduct, posteriorly curving sinistrally to meet oötype.

Excretory vesicle small, pyriform; paired collecting ducts not traceable. Excretory pore at apex of terminal notch.

Remarks

Infections of H. coronatus were found in two of nine S. diadema ; eggs were lodged in the gills of both infected hosts, and four adult worms (one worm in each of the four infected body sites) in one of the two. Sequence data for this species were derived from eggs in gill tissue.

Figures

Figure 2. Species of Holocentricola from Great Barrier Reef Holocentridae, whole worms, ventral views. (A) Holocentricola rufus n. sp. ex Sargocentron rubrum from off Heron Island (holotype, QM G239429); (B) Holocentricola exilis n. sp. ex Neoniphon sammara from off Lizard Island (paratype, QM G239111); (C) Holocentricola coronatus n. sp. ex Sargocentron diadema from off Lizard Island (holotype, QM G239125). Scale-bars: A–C, 200 µm.

Figure 3. Species of Holocentricola from Great Barrier Reef Holocentridae, terminal genitalia, dorsal views; spines illustrated are ventral. (A) Holocentricola rufus n. sp. ex Sargocentron rubrum from off Heron Island (paratype, QM G239440); (B) Holocentricola exilis n. sp. ex Neoniphon sammara from off Lizard Island (paratype, QM G239119); (C) Holocentricola coronatus n. sp. ex Sargocentron diadema from off Lizard Island (paratype, QM G239126). Abbreviations: CS, cirrus-sac; ER, egg reservoir; FGP, female genital pore; MGP, male genital pore; Od, oviduct; Oö, oötype; Ov, ovary; PP, pars prostatica; SV, seminal vesicle; Ut, uterus; VD, vas deferens; VitD, vitelline duct. Scale-bars: A–C, 100 µm.