Petrarca morula, GRYGIER, 1985

Kolbasov, Gregory A., Savchenko, Alexandra S., Yu, Meng-Chen, Tsao, Yao-Feng, Ganmanee, Monthon & Chan, Benny K. K., 2023, Integrative taxonomy, larval biology and functional morphology of the little known gall-forming coral endoparasite Petrarca (Thecostraca: Ascothoracida), Zoological Journal of the Linnean Society 198, pp. 767-801 : 777-780

PETRARCA MORULA GRYGIER, 1985

( FIGS 1G , 8–13 )

Petrarca morula Grygier, 1985: 1036–1038 , fig. 6, Grygier & Nojima, 1995: 93–96, fig. 18 (probably another species).

Material examined: Four specimens in Turbinaria bifrons Brüggemann, 1877 , 22 ° 40 ʹ 39.2 ″ N, 121°28 ʹ 57.2 ″ E, Green Island (L ǜ d ǎ o), Taiwan, 24.04.2015, at a depth of 4–20 m.

Here we provide additional descriptions based on SEM analysis that supplements Grygier’s (1985) original description.

Diagnosis: Carapace spherical, with large lumpy inflations, without radial ridges; carapace margin not crenulated; ventral side of carapace with large conical papillae, lateral surface with small papillae. Mandibles with 10–14 sharp, simple teeth; maxillules with small denticles; six pairs of thoracopods, first thoracopod setiform; penis with relatively small, rounded rami.

Description: Living specimens pink, with dark inclusions at the anterior part of carapace ( Fig. 1G ); tip of penis often extending out of carapace ( Fig. 8 ). Adult (mature) specimens 2.13–2.42 mm long (1.2– 3.8 mm from the Grygier material), 1.85–1.96 mm high (0.9–4.0 mm from the Grygier material), 2.00– 2.24 mm wide (1.0– 4.6 mm from the Grygier material) ( Figs 8 , 11A ). Carapace ( Figs 8 , 11A ) spherical; valves with conspicuous rounded lumpy inflations (8–14), without radial ridges, dorsal and posterior margins not crenulated; long, conical papillae with a tiny terminal pore on anterior half of ventral margin ( Fig. 11A, D ). Cuticle on the lateral external and posteriodorsal internal surfaces of carapace with dense, polygonal, small swellings or bumps ( Fig. 11B, H ). Small volcano-shaped papillae with tiny a terminal pore and microscopic pores inserted between bumps on external surface of carapace ( Fig. 11B, C, E ). Thin cuticular lining (mantle) of inner surface of carapace with rows of dense ctenoid scales in central part ( Fig. 11F, G, I ).

Body inflated, curved, enclosed between carapace valves, tip of penis almost adjoins oral cone ( Figs 8 , 12A ). Cephalon with large adductor muscle lying above big oral cone flanked by five-segmented antennules. Thorax with sinusoid arched dorsal margin, without distinct segmentation, with clusters of rudimentary uniramous thoracopods ( Fig. 12A ). Abdomen with massive first segment bearing long penis and vestigial rear part ( Fig. 12A ).

scales on lateral surface enlarged in circle outline). F, medial languette, lateral view (groups of denticles on anterior margin enlarged in oval outline, basal ‘pore-field’ enlarged in circle outline). G, distal part of mandible (lower part of cutting edge enlarged in oval outline). H, maxillule (lower half of cutting edge enlarged in oval outline). Abbreviations: ae, aesthetasc; cl, claw; clg, claw guard. Scale bars in µm.

Antennules W-shaped, with little armament (external sculpture) on two distal segments ( Figs 9A–C , 12B–H ). First segment irregularly rectangular, narrowing somewhat distally; second segment rectangular; third segment triangular, narrowing toward lower/ventral margin; fourth segment trapezoid, with slightly curved ventral margin, short distal seta inserted at anteriodorsal corner ( Fig. 12C ). Fifth segment narrow, rectangular, slightly shorter than fourth and armed with sensory and grasping structures ( Figs 9B, C , 12D–H ). Short massive curved claw with smooth concave margin. Three rudimentary setae at base of claw and to each side ( Figs 9B, C , 12F ); tiny pores (five to seven) on inner and outer lateral sides ( Figs 9B, C , 12D, E ). Claw sheathed by large, oval claw guard ( Fig. 12F ); claw guard with three vestigial, distal setae with a terminal pore ( Fig. 12H ); developed subdistal aesthetasc almost half as long as claw guard, terminates with two outgrowths, rudimentary seta with a terminal pore at base of aesthetasc ( Fig. 12F, H ). Ventral (postaxial) margin of fifth segment and claw guard with wrinkled cuticle bearing tiny pores ( Fig. 12G ).

Oral cone prominent ( Figs 9D , 12A, I ); labrum prow-shaped, exterior with dense ctenoid scales ( Fig. 12I, J ); mandibles elongated, cutting edge straight, with 14 sharp, simple teeth (ten in Grygier specimen) ( Fig. 9E ); maxillules with sclerotized, triangular distal parts, inner margin with small denticles ( Fig. 9F, G ); fused maxillae ending in a pair of short, rounded lobes, with dense ctenoid scales on lateral surfaces ( Figs 9H , 12I ).

Studied specimens with six pairs of thoracopods; thoracopod 1 setiform ( Fig. 10A ); thoracopods 2–6 ( Fig. 10B ) uniramous, unsegmented, grouped in cluster and arranged in an unorderly sequence in lateral view; thoracopods 2–4 longer and wider than thoracopods 5 and 6. Cuticle of thoracopods 2–6 with rows of dense and long ctenoid scales ( Fig. 13A, B ). Batteries of ampuliform seminal receptacles ( Fig. 10B ) associated with thoracopods 2–5 (~11, 6, 8 and 7 receptacles, respectively).

Long, terminally bifid penis originates from large first abdominal segment ( Figs 10D , 12A , 13C ). Shaft of penis supports two small, rounded rami about 125 µm long; distal part of penis, including rami, bearing numerous short but wide conical setae. Rest of abdomen vestigial, consisting of two segments bearing rare ctenoid scales and tiny pores; posterior end of abdomen with cleavage with few terminal denticles ( Figs 10C , 13D–F ).

Remarks: Grygier & Nojima (1995) indicated that both P. morula and P. goanna may represent ‘the extremes of morphological variability in a single species’. However, along with molecular evidence provided here, there are a number of morphological features that can be used to distinguish these species. Thus, P. morula differs from P. goanna in having numerous long conical papillae on the anterioventral part of carapace vs. only a few inconspicuous ventral papillae in P. goanna ; exterior of carapace with small volcano-shaped papillae (absent in P. goanna ) but without radial ribs and crenulated margin (present in P. goanna ); teeth of the mandible are simple and fewer (simple and bifid teeth present in P. goanna ); inner margin of maxillules with small denticles (bigger teeth in P. goanna ); subterminal aesthetasc of claw guard terminates with two outgrowths (four in P. goanna ).

Figures

Figure 1. Species of the genus Petrarca (Thecostraca: Ascothoracida) endoparasitic in Turbinaria corals in Taiwan. A, globular galls (circled) formed by Petrarca on the surface of Turbinaria coral (modified after Kolbasov et al., 2021). B, gall formed by Petrarca on the coral surface. C, underneath the gall chipped off from coral shows two individuals of Petrarca goana (indicated by

Figure 8. Petrarca morula, general view, light microscopy.A, B, lateral view, right and left sides. C, dorsal view, anterior end on the left. D, ventral view, anterior end on the right. Abbreviations: pe, penis. Scale bar in µm.

Figure 9. Petrarcamorula, antennules and mouthparts.A,right antennule,segmentsnumbered.B,C, terminal(fifth) segmentsofright and left antennules respectively,lateral view.D, labrum, lateral view.E, mandible.F, maxillule.G, cutting edge of maxillule.H, maxillae. Abbreviations:ae, aesthetasc;cl, claw;clg, claw guard;ml, medial languette; mo, mouth opening;oe, oesophagus.Scale bars in µm.

Figure 10. Petrarca morula, thoracopods, penis and abdomen. A, rudimentary setiform thoracopod 1. B, left thoracopods 2–6 (numbered) with groups of seminal receptacles. C, rudimentary abdomen, segments numbered. D, distal part of penis. Abbreviations: sr, seminal receptacles. Scale bars in µm.

Figure 11. Petrarcamorula, general view and mantle (carapace)structures, SEM.A, habitus, lateral view,right side.B, external surface of mantle, central part (papillae coloured in magenta, micropores between bumps coloured in green). C, micropore enlarged from (B). D, external surface of mantle with conspicuous papillae, ventral side. E, tip of papilla with micropore (indicated by arrowhead). F, left valve of carapace, lateral view of internal surface. G, I, ctenoid scales in anteriodorsal and central parts of internal side of carapace respectively. H, cuticle in posterior part of internal side of carapace. Scale bars in µm.

Figure 12. Petrarca morula, body proper, antennules and oral cone, SEM. A, body proper, lateral view, right side. B, right antennule, segments numbered, lateral view. C, rudimentary seta on fourth antennular segment. D, micropores (encircled) on lateral side in proximal half of fifth antennular segment. E, micropore of fifth antennular segment enlarged from (D). F, distal part of fifth antennular segment with claw and claw guard, reduced setae indicated by arrowheads. G, wrinkled

Figure 13. Petrarca morula, rudimentary thoracopods, abdomen and penis, SEM. A, thoracopod 2. B, ctenoid scales on thoracopod 2 enlarged from (A). C, distal part of penis. D, rudimentary abdomen, segments numbered. E, F, tiny pores and ctenoid scales on abdominal segment 3, respectively. Scale bars in µm.