Integrative taxonomy, larval biology and functional morphology of the little known gall-forming coral endoparasite Petrarca (Thecostraca: Ascothoracida) Author Kolbasov, Gregory A. Author Savchenko, Alexandra S. Author Yu, Meng-Chen Author Tsao, Yao-Feng Author Ganmanee, Monthon Author Chan, Benny K. K. text Zoological Journal of the Linnean Society 2023 2023-07-31 198 767 801 journal article 54779 10.1093/zoolinnean/zlad009 4c065cc9-0f2c-4e04-9141-c36bf101c3d5 0024-4082 8152364 A2863AB5-855B-4549-89EC-A57C46140CD9 Petrarca goanna Grygier, 1991: 35–38 , figs 18, 19. Material examined: Four specimens in Astreopora sp. , two specimens in Turbinaria mesenterina ( Lamarck, 1816 ) and 12 specimens in Turbinaria sp. , 22°40 ʹ 39.2 ″ N , 121°28 ʹ 57.2 ″ E , Green Island (L ǜ d ǎ o), Taiwan , 24.04.2015 , at 4–20 m depth. Fifteen specimens in Turbinaria frondens ( Dana, 1846 ) and four specimens in Turbinaria sp. , 10°41 ʹ 56.5˝N , 99°24 ʹ 28.4 ″ E , Koh Khai Island, Chumphon , Thailand , 06– 07.07.2019 , at 3–4 m depth. Grygier (1991a) provided a detailed description of this species. We provide additional observations obtained mainly with SEM. Diagnosis: Carapace valves of adults with crenulated margins formed by protruding outer ends of five to eight radially directed dorsal and posterior irregular ridges; ridge exterior with irregular lumpy inflations; ventral side of carapace with few papillae; lateral surface of carapace without small papillae. Labrum with short lateral extensions; maxillae mostly exposed; mandibles with 15–25 sharp, simple or bifid teeth; teeth of the maxillules in lower half with spiniform tips and tending to form two rows; six pairs of thoracopods, first thoracopod setiform; penis with relatively small, squarish rami. Description: Living specimens pink or crimson-coloured ( Fig. 1F ); tip of penis often extending out of carapace ( Fig. 2C, E, F ). Adult (mature) specimens 5.26–6.08 mm long, 4.32–6.15 mm high ( Figs 2A–D , 5A ); young (juvenile) specimens ( Fig. 2E–G ) 2.80–3.83 mm long and 2.40–3.33 mm high. Carapace ( Figs 2 , 5A ) roughly ovoid (spherical), valves with short anteriodorsal hinge line, lateral surfaces with five to eight radial ridges with irregular lumpy inflations. These inflations are less developed in the anterior part of adults and in young specimens. Dorsal and posterior margins of valve crenulated due to carapace ridges ( Figs 2 , 5F ). Ventral margin with few inconspicuous papillae ( Fig. 5C, D ) with central micropore on tip ( Fig. 5E ).Cuticle on lateral, external and internal surfaces of carapace with dense, polygonal, small swellings or bumps but without papillae, teeth or ctenes ( Fig. 5B, G ). Body inflated, crescent-like, enclosed between carapace valves ( Fig. 5F ). Cephalon with large adductor muscle lying above big oral cone ( Fig. 5F ) flanked by five-segmented antennules. Thorax with arched dorsal margin but without distinct segmentation, with clusters of rudimentary uniramous thoracopods; cuticle of thorax with ctenoid scales in dorsal part ( Fig. 5H ). Abdomen with massive first segment bearing long penis and vestigial rear part ( Figs 5F , 7D ). Figure 2. Petrarca goanna , general view, light microscopy. A, B, specimen dissected for body parts’ examination on Figures 3, 4, lateral view from right (A) and left (B) sides. C, D, mature specimen, lateral view from right (C) and left (D) sides. E–G, young specimens, lateral view from right (E, G) and left (F) sides. Scale bars in µm. Antennules somewhat prehensile, with little armament or external sculpture on two distal segments ( Figs 3A–D , 6A–D ). First segment irregularly rectangular, narrowing somewhat distally; second segment trapezoidal; third segment almost triangular, narrowing toward lower/ ventral margin; fourth segment slightly longer than wide, with slightly curved ventral margin, short distal seta inserted at anteriodorsal corner ( Figs 3A, D , 6A, B ). Fifth segment rectangular, slightly shorter and narrower than fourth and armed with sensory and grasping structures ( Figs 3A–C , 6A, C, D ). Short but massive curved claw with smooth concave margin arising from distal end of segment. Three rudimentary setae at base of claw and to each side; tiny pores (three to four) on inner and outer lateral sides. Claw sheathed by large, oval claw guard on posteriodistal corner; claw guard with three vestigial, distal setae with a terminal pore; developed aesthetasc almost half as long as claw guard, inserted closer to its distal end and terminating with four outgrowths, rudimentary seta at base of aesthetasc ( Fig. 6A, D ). Ventral (postaxial) margin of fifth segment and claw guard with wrinkled cuticle bearing tiny pores ( Fig. 6C ). Figure 3. Petrarca goanna , antennules and mouthparts. A, left antennule, segments numbered. B, C, terminal (fifth) segments of left and right antennules, respectively. D, rudimentary seta on fourth antennular segment. E, labrum, anterior view. F, mandible. G, cutting edge of mandible. H, maxillule. I, cutting edge of maxillule. J, maxillae. Abbreviations: ae , aesthetasc; cl , claw; clg , claw guard; oe , oesophagus. Scale bars in µm. Figure 4. Petrarca goanna , thoracopods, penis and abdomen. A, rudimentary setiform thoracopod 1. B, right thoracopods 2–6 (numbered) with clusters of seminal receptacles. C, rudimentary abdomen, segments numbered. D, distal part of penis. Scale bars in µm. Oral cone prominent, consisting of massive labrum underlaid posteriorly with massive, fused maxillae, unpaired medial languette and paired mandibles and maxillules ( Figs 3E–J , 5F , 6E–H ). Labrum prow-shaped, with short posteriolateral extensions leaving maxillae largely exposed, exterior with dense ctenoid scales ( Figs 3E , 6E ). Medial languette with groups of sharp denticles (two to five) along anterior margin and dense basal pores forming ‘pore-field’ ( Fig. 6F ). Mandibles ( Figs 3F, G , 6G ) elongated, outer/upper margin with hillock and clusters of dense, thin setae in middle part, cutting edge straight, with 15–21 sharp, simple or rarely bifid teeth and one to two small spinules in middle part. Maxillules ( Figs 3H, I , 6H ) with sclerotized, triangular distal parts, inner margin with 17–20 teeth, teeth in upper half with often blunt tips, while those in lower half smaller, irregular, with spiniform tips and tending to form two irregular rows. Fused maxillae ( Fig. 3J ) ending in a pair of short, rounded lobes, with dense ctenoid scales on lateral surfaces ( Fig. 7B ), distal ends covered with sclerotized, thick and wrinkled cuticle without denticles, pores or setules ( Fig. 7A ). Thoracopods 2–6 ( Figs 4B , 5F ) are present in all examined specimens, uniramous, unsegmented, grouped in cluster and arranged in an unorderly sequence in lateral view. Thoracopods 2–4 are conical with wide bases, while thoracopods 5 and 6 are shorter and narrower. Cuticle of thoracopods 2–6 has dense and long ctenoid scales ( Fig. 7C ). Batteries of numerous ampuliform seminal receptacles ( Fig. 4B ) associated with thoracopods 2–5 (~7, 20, 20 and 11 receptacles, respectively). Setiform thoracopod 1 ( Fig. 4A ) present in all studied specimens. Long, thick, terminally bifid penis originates from large first abdominal segment ( Figs 4D , 5F , 7E ). Long shaft of penis supports two small, squarish rami about 190–200 µm long ( Figs 4D , 7E ). Distal half of penis, including rami, bearing numerous short but wide conical setae. Rest of abdomen vestigial, apparently consisting of two segments ( Figs 4C , 5F , 7D ). Posterior end of abdomen with cleavage that may represent rudimentary furcal rami ( Fig. 7D ). Remarks: The morphology of our specimens generally corresponds to that of the individuals described by Grygier (1991a) , but differs in having rare ventral papillae on the carapace (absent in Grygier’s specimens) and presence of all six pairs of thoracopods (inconsistent number of thoracopods in Grygier’s material). However, these details could have been overlooked in the type material. This is the first finding of Petrarca in scleractinian corals of the genus Astreopora .