Dendromonocotyle bradsmithi, Chisholm, Leslie A., Glennon, Vanessa & Whittington, Ian D., 2005

Chisholm, Leslie A., Glennon, Vanessa & Whittington, Ian D., 2005, Dendromonocotyle bradsmithi n. sp. (Monogenea: Monocotylidae) from the skin of Myliobatis australis (Elasmobranchii: Myliobatidae) off Adelaide and Perth, Australia: description of adult and larva, Zootaxa 951, pp. 1-15 : 3-10

Dendromonocotyle bradsmithi n. sp.

Type­host: Myliobatis australis Macleay, 1881 (Myliobatidae) .

Type­locality: Port Adelaide River (34°48’00’’S, 138°31’00’’E), off Torrens Island. Outer Harbour, Adelaide, South Australia, Australia.

Other localities: Comet Bay (32°25'68"S, 115°43'83"E) off Mandurah, Western Australia and The Aquarium of Western Australia (AQWA), Perth, Western Australia, Australia.

Site: Dorsal skin surface.

Infection details: Seven rays infected with numerous parasite specimens. Prevalence 100%.

Etymology: The species is named after Mr Brad Smith, a keen angler, who caught the rays in South Australia.

Material deposited: Holotype SAMA AHC 28776, 24 paratypes SAMA AHC 28777­ 28800; 18 paratypes USNPC 95896 and 95897.

Adult description (Figs 1–3)

Dendromonocotyle (sensu Chisholm & Whittington 1995). Description and measurements based on 2 live and 25 fixed and mounted sexually mature specimens. Live adult worms with distinct pigmentation. Body 3,088 (2,061–4,720, n = 25) long, 2,230 (1,277– 3,013, n = 24) wide at level of posterior portion of testis (Fig. 1). Haptor 1,656 (1,142– 2,629, n = 25) in diameter, divided into 1 central and 8 peripheral loculi. Hamuli absent. Fourteen hooklets distributed symmetrically in thicker portion of marginal valve between every 4 papillae (Fig. 1). Haptoral rim with 56 marginal papillae; 8 papillae associated with each posterior loculus; 7 papillae associated with each posterolateral and anterolateral loculus; and 6 papillae associated with each anterior loculus (Fig. 1). Marginal papillae with 6–8 sclerites (Fig. 1); terminal papillar sclerite distinct from other papillar sclerites ( Fig. 2 A). Sclerites on radial, inner and outer ring septa similar ( Fig. 2 B); tripartite sclerites sometimes present at junction of radial septum with inner or outer ring septum ( Fig. 2 C).

Mouth ventral, subterminal. One anterolateral gland duct opening on either side of head (Fig. 1), contains needle­like secretion. Subterminal groove present at anterior end (Fig. 1). Two pairs of eyespots anterodorsal to pharynx; crystalline lenses still present. Pharynx 311 (223–395, n = 25) long, 310 (225–423, n = 25) wide. Intestinal diverticula extend from anterior margin to posterior margin of body proper (Fig. 1). Pigment present, associated with lining of intestinal diverticula, in all specimens collected, including juveniles.

Testis 758 (559–946, n = 17) wide. Vas deferens arises from left side of testis, and runs anteriorly dorsal to vagina, narrows and curves to right side of body ventral to ejaculatory bulb, inflates to form looping seminal vesicle then narrows, entering ejaculatory bulb posteriorly (Fig. 1). Ejaculatory bulb 279 (199–356, n = 25) long, 260 (192–318, n = 25) wide. Male copulatory organ long, sclerotised tube 973 (866–1,105, n = 22) long; distal end distinct with criss­crossed sperm duct and coiled accessory filament ( Figs 2 D, 3D). Muscular sheath surrounds entire length of male copulatory organ (Fig. 1). Proximal end of male copulatory organ looped in juvenile specimens; straightens as worm matures ( Fig. 3 A–C).

Ovary bilobed with one lobe on either side of testis (Fig. 1); fusing medially; single branch loops right intestinal caecum dorsoventrally and forms oviduct. Oviduct receives common vitelline duct and duct from seminal receptacle and forms ovovitelline duct which enters oötype posteriorly. Oötype 330 (180–421, n = 23) long. Mehlis’ gland not seen. Vaginal pore on left side of body at level of anterior portion of ejaculatory bulb (Fig. 1). Proximal part of vagina sclerotised then narrows and enters seminal receptacle. Seminal receptacle 256 (167–410, n = 15) long, 136 (85–200, n = 15) wide (Fig. 1). Sclerotised spermatophore ( Fig. 2 E) present in vagina of 4 specimens; spermatophore 504 (398–614, n = 4) long, bulb diameter 211 (192–229, n = 3).

Dendromonocotyle bradsmithi n. sp. Whole adult parasite, composite drawing, ventral view. NB: For clarity, the intestinal diverticula surrounding and overlying the reproductive organs are not drawn. Abbreviations: alg, anterolateral gland duct opening with needle­like secretion; e, eyespot; eb, ejaculatory bulb; h, hooklet; i, intestinal diverticulum; m, mouth; mco, male copulatory organ; mp, marginal papilla; ms, muscular sheath surrounding male copulatory organ; mv, marginal valve; oot, oötype; o, ovary; p, pharynx; sg, subterminal groove; sr, seminal receptacle; sv, seminal vesicle; t, testis; tps, terminal papillar sclerite; tvd, transverse vitelline duct; v, vagina; vd, vas deferens; vs, sclerotised portion of vagina. Scale bar: 500 m.

Vitellarium inconspicuous, largely obscured by extensive pigmented intestinal diverticula, extends from level of mouth to posterior portion of body proper. Transverse vitelline duct at level of anterior portion of seminal receptacle; common vitelline duct joins oviduct. Egg dimensions below.

Remarks

Live specimens attached to the bottom of Petri dishes and exhibited characteristic undulating movements. The undulating movements observed in live D. bradsmithi have also been reported in other skin­parasitic monogeneans. Kearn (1962) demonstrated that this characteristic movement in the capsalid Entobdella soleae (van Beneden & Hesse, 1864) Johnston, 1929 increases when oxygen levels in the water decrease and therefore probably aids respiration. Monocotylid larvae usually have a prominent crystalline lens associated with each of the 4 eyespots (e.g. Figs 4 A, 5A). This is the first time the crystalline lenses have been reported to persist in adult monocotylids.

Egg development and hatching

Egg tetrahedral ( Fig. 2 F); side length 113 (106–120, n = 10); measured from freshly laid eggs. Eyespots developed after 5 days and larvae hatched spontaneously after 7 days at 22°C. Batch A: total of 106 eggs, 99 hatched (93% success), 7 embryonated but not hatched. Batch B: total of 411 eggs, 385 hatched (94% success), 21 embryonated but not hatched, 5 unembryonated.

Description of larva ( Figs 4 , 5 A–C)

Observations based on 17 living larvae. Larva 187 (168–225, n = 11) long and 74 (60–105, n = 11) wide. Ciliated cells in 3 zones; one anterior band, 2 median patches and ciliated cone on haptor ( Fig. 4 A). Refringent droplets present in epidermal cells bearing cilia ( Figs 4 A, 5A). Group of about 20 non­motile cilia observed at anterior end of larva. Refringent droplets, probably lipid, observed throughout body ( Fig. 4 A).

Four pigmented eyes with crystalline lenses arranged as illustrated ( Figs 4 A, 5A, 5B). Pigment distributed throughout body of larva ( Fig. 5 B). Pharynx 24 (19–28, n = 11) in diameter. Small bifurcate gut present. Two anteromedian gland cells containing granular secretion; single duct from each gland cell runs anteriorly and opens at anterior margin of head ( Fig. 4 A). Group of 3 gland cells containing needle­like secretion on either side of pharynx ( Fig. 4 A), sometimes obscured by body pigment. One duct from each of these gland cells runs anteriorly and opens at slightly swollen endings on lateral borders of head ( Fig. 4 A). Two posterior gland cells, 1 on each side of body, near haptor containing granular secretion ( Figs 4 A, 5C). Pores or ducts associated with these gland cells not seen.

Five pairs of flame bulbs observed: 1 pair anterior to eyes; 1 pair anterolateral to pharynx; 1 pair posterior to gut; 1 pair in posterior body near posterior gland cells; 1 pair extending into haptor ( Fig. 4 A). Path of ducts connecting flame bulbs as shown ( Fig. 4 A). Excretory bladders distinct, lateral to pharynx.

Haptor with 14 hooklets, each of similar shape and size 14 (13–15, n = 14) long with distinct domus ( Figs 4 A, 4B, 5A, 5C). Hamuli not seen in freshly hatched larvae.

Remarks

In addition to the anteromedian gland cells and the posterior pair of gland cells ( Figs 4 A, 5C), monocotylid larvae described so far generally have 2 other sets of gland cells on either side of the body posterolateral to the pharynx. The first set comprise 3 to 4 gland cells containing needle­like secretion located on either side of the body just posterolateral to the pharynx (see Chisholm & Whittington 1996). The second set comprises a pair of gland cells containing granular secretion located on either side of the body just posterior to the cells containing needle­like secretion (see Chisholm & Whittington 1996). A single duct runs from each of these gland cells and opens at the anterior end of the larva. In contrast to this standard arrangement, we did not detect the pair of lateral granular glands and associated ducts in D. bradsmithi larvae; only 3 gland cells containing needle­like secretion were seen on either side of the pharynx ( Fig. 4 A). Chisholm & Whittington (1995) also only observed 3 gland cells on either side of the body just posterolateral to the pharynx in D. ardea , but these were believed to contain granular secretion. The secretion type in the lateral gland cells should be verified in D. ardea because with this single exception, the arrangement of gland cells is otherwise identical in D. bradsmithi and D. ardea . No gland cells were described or illustrated lateral to the pharynx in D. kuhlii (see Young 1967).

Distribution of oncomiracidial ciliated epidermal cells and sensilla ( Figs 5 D,E, 6)

Thirty­three larvae stained with AgNO3; description based on 18 stained larvae. Anterior zone with 25 ciliated cells distributed over dorsal and ventral surfaces as illustrated ( Fig. 6 ). Two smaller ciliated cells (probably support non­motile cilia shown in Fig. 4 A) also present at anterior­most tip of larva on dorsal surface ( Fig. 6 A). Small spaces present between some ciliated cells in anterior zone as illustrated ( Figs 5 E, 6A, 6B). Median zone with 11 ciliated cells on either side of larva; most median zone cells located ventrally ( Fig. 6 A, 6B). Spaces not seen between cilated cells of median zone. Haptoral zone with 13 ciliated cells (but see Discussion) ( Fig. 6 A, 6B). No spaces seen between any ciliated cells in haptoral zone. Dorsal and ventral sensilla distributed as shown ( Figs 5 D, 6A, 6B); some sensilla probably obscured by body pigment.

Figures

FIGURE 2. Dendromonocotyle bradsmithi n. sp. A. Haptoral terminal papillar sclerite. B. Other haptoral papillar sclerite. C. Tripartite sclerite. D. Distal end of male copulatory organ showing accessory filament (af) and terminal criss­crossed sperm duct (sd). E. Spermatophore with proximal (p) bulb and distal (d) tapered region. F. Egg with appendage (a). Scale bars: A – C = 20 µm; D = 50 µm; E, F = 100 µm.

FIGURE 3. Male copulatory organ (MCO) development of Dendromonocotyle bradsmithi n. sp. A. Juvenile specimen (900 µm long), MCO (400 µm long) looped (arrowhead) twice. B. Juvenile specimen (1180 µm long), MCO (460 µm long) looped once. C. Adult worm (2030 µm long), MCO (1015 µm long) not looped; box delineates distal end of organ enlarged in Fig. 3 D. D. Enlargement of distal end of adult MCO showing terminal criss­crossed sperm duct and accessory filament. Scale­bars: 50 µm.

FIGURE 4. Dendromonocotyle bradsmithi n. sp. oncomiracidium. A. Larva. B. Hooklet. Note for clarity the body pigment in the larva (see Fig. 5 B) has not been drawn. Abbreviations: agc, anteromedian gland cell containing granular secretion; c, cilium; cl, crystalline lens of eyespot; d, domus; e, eyespot; ebl, excretory bladder; f, flame bulb; h, hooklet; lnc, lateral gland cell containing needle­like secretion; m, mouth; nm, non­motile cilium; p, pharynx; pgc, posterior gland cell containing granular secretion. Scale bars: A = 50 µm; B = 10 µm.

FIGURE 5. Dendromonocotyle bradsmithi n. sp. oncomiracidium. A. Dark field photomicrograph of whole larva showing refringent droplets associated with ciliated epidermal cells. B. Bright field photomicrograph of anterior half of larva showing strands of pigment extending throughout body. C. Phase contrast photomicrograph of posterior end showing 14 hooklets each with domus and showing posterior gland cells (arrowheads) containing granular secretion. D. Dorsal view of silver stained specimen showing distribution of dorsomedian sensilla (arrowhead). E. Ventral view of silver stained specimen showing distribution of anteroventral ciliated epidermal cells. Scale bars: A = 50 m; B – E = 20 m.

FIGURE 6. Diagram of distribution of ciliated epidermal cells in anterior zone (az), median zone (mz) and posterior zone (pz) and sensilla on larva of Dendromonocotyle bradsmithi n. sp. as revealed by silver staining. A. Dorsal view. B. Ventral view; note: complement of ciliated cells in posterior region may not be complete (see Discussion).