Both specimens of Chiloscyllium punctatum Müller & Henle, 1838 are of a nut-brown colour dorsally, with little to no patterning, while the ventral side is distinctly lighter in colour and creamy white in vivo (Figs 1, 2). The head is spatulate and rather stout, with the male’s head being clearly more acute (Fig. 1A). The female’s head has a much flatter angle anteriorly, which is more arch-like (Fig. 2A). It also is noticeable that, in dorsal view, the head of the male is distinctly broader in the area of the gill openings than that of the female (Fig. 1A). The snout is not very prominent, as is typical for orectolobiform sharks. The width of the snout corresponds approximately to the width of the rest of the head and tapers anteriorly (Figs 1A, 2A). In ventral view, the mouth opening with distinct labial folds, the paired barbels and the nostrils are clearly visible (Figs 1C, 2C). When the mouth is closed, no teeth are visible externally.

In dorsal view, the two spiracles, which are at the same level as the posterior eyelids, are discernible (Figs 1A, 2A). Especially dorsally and ventrally, but also laterally, rows of pores of different sizes are present. They extend from the dorsal side of the rostrum to the lateral side of the head, and from the ventral side to the lateral side ventral to the eyes. The eyes are relatively small in relation to the body and are positioned slightly dorsally on the head (Figs 1A–B and 2A–B). The gill openings are located laterally at the level of the pectoral fins. Four of these gill openings are rather large while the fifth one is noticeably smaller and very closely placed to the fourth one, rendering its identification difficult (Figs 1B, 2B).

After removing the skin during manual dissection, the ampullae of Lorenzini were exposed, particularly in the rostral region (Figs 3, 4). Several individual groups of ampullae can generally be distinguished such as the superficial ophthalmic, the deep ophthalmic, the buccal, the hyoid, and the mandibular ampullae (Goto 2001). The majority of these are located along the dorsal and lateral area of the rostrum. The ducts of the ampullae extend in general from the rostral process to the branchial region as far as the first gill slit with few exceptions that extend posteriorly over the pectoral girdle (Figs 3A–C, 4A–B). Only few ampullae occur ventrally. However, many pores open onto the surface in this area, which correspond to openings of the ampullae, which however not only include those located directly in this area but also those that run laterally along the rostrum. Some ampullae of Lorenzini also are observable dorsally, which run along the chondrocranium between the Musculi levator labii and extend caudally to about the level of the eyes (Figs 3A, 4A).

In general, the chondocranium represents a single large element that encloses and protects both the brain and the sensory organs in this area. This makes it a very distinctive and prominent structure (Figs 5, 6, 7, 8). The nasal capsules are situated relatively distant from the preorbital wall and thus the orbit results in a fairly wide distance between them. The two nasal capsules are separated by a relatively narrow internasal septum, which tapers gradually towards the rostral process (Figs 5D, 6D, 7D, 8C). The subnasal fenestrae are prominent, elliptical (Figs 5D–E, 7D–E) and are directed dorso-ventrally approximately in the middle of the nasal capsules. Ventrally they extend between the preorbital wall and the nasal capsules. The prefrontal fontanel is clearly visible in the scans of both specimens, as well as in both manual dissections (Figs 5C, 6C, E 7C, 8D). The orbital region contains a relatively small eyeball but occupies about one third of the entire skull (Figs 5A, 6A, 7A, 8A).

In lateral view, the first perforation of the skull is that of the orbito-nasal vein. It lies at about the same level (dorso-ventral axis) as the foramen for the optic nerve (CN II), but further anteriorly on the outer edge of the preorbital wall (Figs 5A, 6A, 7A, 8A). Slightly further dorsally are the foramina for both branches of the trigeminal nerve (CN V), the ramus profundus and the ramus superficialis (Fig. 5A, 6A, 7A, 8A). Somewhat more posteriorly, the prominent and very large foramen for the optic nerve (CN II) stands out. This is located at the lower anterior border of the orbita (Figs 5A, 6A, 7A, 8A). Posterior to the optic foramen, the foramen for the pseudobranchial artery and the pituitary vein are located close to each other (Figs 5A, 6A, 7A, 8A). Directly adjacent to this, in the basal area of the orbita, is the prominent foramen for the major branch of the Nervus trigeminalis (CN V) and the Nervus fascialis (CN VII). Directly dorsal to this is another rather large foramen, which is the opening for the ramus superficialis of the Nervus trigeminalis (CN V). Further posteriorly, just anterior to the hyomandibular fossa, the foramen for the fascial nerve is located (CN VII) (Figs 5A, 6A, 7A, 8A).

At the posterior base of the sphenopterotic ridge is the foramen for the glossopharyngial nerve (CN IX) (Figs 5A, 6A, 7A, 8A). This ridge is forming the insertion for the Musculus epaxialis. Following the sphenopterotic ridge anteriorly (and slightly dorsally), the postorbital process, which merges into the supraorbital crest, is situated (Figs 5A, 6A, 7A, 8A). In this crest the superficial ophtalmic foramina opens, a single series of fine perforations running in an arc along the dorsal roof of the orbit (Figs 5A, 6A, 7A, 8A).

In anteriad view, the prominent foramen magnum can be seen and laterally the two foramina for the Nervus vagus (CN X) (Figs 5B, 6B, 7B, 8B). In posteriad view, the foramina for the ramus profundus are well visible and slightly more dorsally those for the ramus superficialis of the Nervus trigeminalis (CN V), both of which perforate at the base of the supraorbital crest (Figs 5B, 6B, 7B).

In dorsal view, the well-developed endolymphatic and perilymphatic fenestrae are exposed. They are located at the level of the posterior end of the orbita (Figs 5E, 6E, 7E, 8D). The antorbital and postorbital processes also are clearly visible (Figs 5E, 6E, 7E, 8D). Ventrally, the palatobasal ridge is at the same level as the antorbital process (Figs 5D, 6D, 7D, 8C). Further posteriorly is the paired foramen for the orbital artery (Figs 5D, 6D, 7D, 8C).

Comparing the micro-CT models of male and female specimens, it is noticeable that the chondrocranium of the female is generally more robustly shaped. The skull of the male, conversely, is proportionally narrower dorso-ventrally. In dorsal view, the male’s chondrocranium is clearly broader, especially when comparing the nasal capsules of both specimens. The distance between the nasal capsule and the orbit is shorter in the female compared to the male. On the other hand, the occipital region, i.e., the area posterior to the orbit, appears to be longer in the female. In the micro-CT model as well as in the dissected skulls, the postorbital processes of the female specimen are more protruding and more angular.

The nasal capsules are located anterior to the orbits but are slightly smaller than the orbits. They contain the actual sensory epithelium, which is responsible for olphactoric sensory perception (Figs 9, 10). This epithelium, called the olphactoric sacs, is roughly shaped like a sphere, with the inner cavity being connected to the nostrils (Goto 2001). Inside, the epithelium is folded up several times, with these folds in turn having creases to increase the surface area. These individual folds can be seen in the micro-CT images in Figure 9 and 10 (Figs 9G, 10G, arrows point to the folds). These folds are called lamellae, on the surface of which the sensory receptors are located. The olphactoric sacs are directly connected caudally to the olfactory bulbs, which are responsible for transmitting stimuli from the sensory receptors to the olfactory lobes in the brain. The nasal capsules have no connection to the oral cavity. In order to optimise the flow of water through the sensory epithelium, there is an inflow and outflow opening (Figs 9D–E, 10D–E, arrows mark the direction of flow). The nasal capsules of the female generally appear to be slightly smaller, but this could also be an artefact due to fixation.

The inner ear is very prominent in both sexes. However, creating accurate models based on the micro-CT scans is not an easy task, as the transitions to the cerebral cavity are almost fluent, as is the transition to the outer area via the endolymphatic duct. Nevertheless, most of the essential components are clearly visible in both models (Figs 10 and 11). In posterior view, the endolymphatic duct stands out proximally (Figs 10C, 11C). At its base two ducts are situated representing the anterior and the posterior semicircular ducts, respectively. Between these two ducts, the horizontal semicircular duct runs in a semi-curve from anterio-posteriorly. At the base of each duct is a thickening, which has been representatively labelled on the horizontal semicircular duct in Figs 10C, 11C. In lateral view, the sacculus of the inner ear can be seen at the distal side at the base (Figs 10D, 11D). In the micro-CT scan, no otoliths were visible in either specimen, which might have been dissolved, as otoliths should have been present (Schnetz et al. 2019).

The visceral- or splanchnocranium of Chiloscyllium punctatum consists of seven visceral arches, which represent the mandibular arch with associated labial cartilages, the hyoid arch and five branchial arches. Each arch consists of different cartilaginous elements.

3.2.6.1. Mandibular arch

The mandibular arch is composed of a ventral element, the Meckel’s cartilage and a dorsal element, the palatoquadratum (Figs 13, 14, 15, 16). The palatoquadratum represents a rather prominent cartilaginous structure (Figs 13A,C, 14A–B, E, 15A,C, 16A–B). Both antimeres of this cartilage are connected medially by soft tissue along the symphysis (Figs 13A–B, 14B–C, 15A–B, 16C). In lateral view, the palatoquadratum roughly describes a semicircular arch and tapers anteriorly. Centrally, there is a raised process pointing laterally the so called adductor mandibular process (Figs 13C, 14E, 15C, 16B). This serves as the attachment point of the Musculus adductor mandibulae. Dorsally, there is another process, which is directed dorsally. This is the so-called ascending process of the palatoquadratum (Figs 13, 14B–C, E, 15, 16A–C). On the median side of this process there is another protrusion pointing proximally, which serves as the attachment point for the inner quadrato-mandibular ligament.

The dentition of the upper jaw extends medially from the symphysis laterally at about the level of the adductor mandibular process. At this point, the ventral edge of the palatoquadratum describes a dorsal curve and, together with the corresponding ventrally directed Meckel’s cartilage, creates an ellipsoidal gap between the two jaws (Figs 13C, 14E, 15C, 16B). The teeth in the upper jaw are arranged in rows and files. The individual files run from labial to lingual (Figs 14B,G, 16C,G). A file of symphyseal teeth is present medially but does not differ morphologically from the adjacent rows of teeth. Each tooth consists of a pointed, triangular main cusp, which is laterally accompanied at the base by two cusplets (Figs 14G, 16G). The two functional rows of teeth are located along the outer margin of the upper jaw. The replacement teeth develop close to the cartilage with the tip pointing dorsally and turn ventrally over time when the previous tooth reaches the outer edge of the jaw cartilage and is pushed outwards (Figs 14G, 16G). The degree of abrasion, especially of the cusplets, is striking in older teeth compared to younger ones (Figs 14G, 16G). From anterior to posterior the teeth become noticeably smaller. The rear-most four files of teeth are distinctly different in that they have significantly lower crowns than the anterior ones. The cusplets also are distinctively smaller or even absent. The tooth crowns in the last two files are very reduced forming small hump-like structures.

The Meckel’s cartilage is a distinctly more planar and slender cartilage element than the palatoquadrate (Figs 13, 14A,E, 15, 16A–B). It is also composed of two single elements, which are connected medially along the symphysis by soft tissue (Figs 13A–B, 14D, 15A–B, 16D). In lateral view, the Meckel’s cartilage has an approximately triangular outline. On the dorsal edge, the recess for the ellipsoid shaped gap formed with the upper jaw, as already mentioned for the palatoquadrate, is noticeable. The caudal end of Meckel’s cartilage describes an arc and forms a fold, causing the distal end to face forward. This fold is called the sustentaculum and represents a mechanical reinforcement of the jaw (Figs 13C, 14E, 15C, 16B). At the ventral base of the sustentaculum is a large, circular foramen (Figs 13A–B, 14A, 15A–B, 16A). This is clearly visible in the micro-CT images, but barely noticeable during dissection. The opening appears to be covered by fibrous connective tissue, which is why it is barely visible, if at all. At the posterior edge of the sustentaculum lies the lateral quadrato-mandibular joint, at which the palatoquadrate articulates with the Meckel’s cartilage and thus forms the primary jaw articulation. Functionally, this articulation represents a hinge joint. Posterior to this, at the caudo-lateral end of the Meckel’s cartilage, a process, the mandibular knob, is directed posteriorly. It is a rather flat socket distally, on which the hyomandibula articulates (Figs 13B–C, 14E, 15B–C, 16B) forming the hyomandibulo-mandibular joint.

The teeth of the lower jaw are morphologically very similar to those of the upper jaw, just a little bit sturdier (Figs 14B,F, 16C,E–F). However, there are noticeably more tooth rows in the lower jaw, of which the two labial-most rows represent functional teeth. The apices of the teeth of the other series are directed lingually and represent replacement teeth (Figs 14F, 16E–F). As in the upper jaw, the morphology of the teeth in the distal-most files changes noticeably. Mesio-distally, the teeth decrease noticeably in size along the rows. Especially the teeth in the posterior-most six files are distinctly different. Their apices are considerably lower than those of the anterior teeth. Thus, the teeth are clearly broader than high. The cusplets are also much less distinct and less pronounced. The last few teeth are merely small cusps (Fig. 16E).

In the upper jaw there is a pair of labial cartilages on each side, which supports the upper lip (Figs 17, 18). The first labial cartilage starts very anteriorly, initially runs parallel to the palatoquadratum and then describes an arc ventrally. The second labial cartilage starts slightly more posteriorly, but is morphologically similar to the first one. The lower jaw displays only one labial cartilage (Figs 17, 18). It starts at the same level as the second labial cartilage of the upper jaw. Analogous to the upper jaw, the labial cartilage of the lower jaw runs in an arc dorsally. There, both labial cartilages are almost contacting each other and are connected by soft tissue (Figs 17, 18).

When comparing both sexes, it is noticeable that the jaw of the female seems to be much more robust. In general, the palatoquadrate and Meckel’s cartilage are more compressed along the anterior-posterior axis compared to the male. Thus, both cartilage elements are clearly higher and therefore more planar than those of the male. The palatoquadrate of the male is relatively narrow, has a rather straight labial edge and curves at the end ventrally, terminating in a hook-like shape. The palatoquadrate of the female remains almost straight and terminates in a rounded edge. The adductor mandibular process of the female palatoquadrate starts slightly more anteriorly but does not differ in relative size from that of the male. The ascending process of the palatoquadrate of the female is more pronounced and dorsally higher. Due to the different shape of the two jaw elements between the sexes, there is also a different shape of the lateral gap formed by the palatoquadrate and Meckel’s cartilage, which is relatively narrow and elongated in the male specimen, whereas it is much broader in the female specimen (Figs 13C, 14E, 15C, 16B).

3.2.6.2. Hyoid arch

The hyoid arch essentially consists of five elements: One median unpaired basihyal, paired ceratohyales and attached to it, paired hyomandibulae (Figs 14, 16, 19, 20). The ceratohyals and the hyomandibulae are located medial to the jaw elements. The posterior part of the hyomandibula contacts the ceratohyal, which is about one third longer than the hyomandibula. The anterior tips are articulating with the posterior edge of the basihyal (Figs 14B–D, 19C–D, 16C,E, 20C,E).

The basihyal is an unpaired element located at the base of the oral cavity (Figs 14B–D, 19C–D, 16C–E, 20C–E). It is roughly crescent-shaped and curves posteriorly. There are two postero-lateral socket-like facets for articulation with the two ceratohyal. The areas dorsal of these articulation facets are elongated and form rather pointed processes that are pointing backwards. The anterior part of the basihyal is semi-circular as previously described and rests on the coraco-hyoideus muscle (Figs 36B and 38B).

The hyoid arch of the female generally tends to be somewhat more robustly. Other than that, there are no significant differences in the structure of the hyoid arch between the sexes.

3.2.6.3. Branchial arches

Posterior to the hyoid arch are the branchial arches (Figs 21, 22, 23, 24,) consisting of five pairs of arches (Shirai 1992), which is also the case in C. punctatum. Each individual arch comprises a sequence of characteristic single elements, i.e., the pharyngobranchialia, epibranchialia, ceratobranchialia, hypobranchialia, and basibranchialia (Figs 21A, 23A). The pharyngobranchial is the dorsal-most cartilage of the branchial arches, which is connected dorsally to the vertebral column via connective tissues. Cranially, the very flat element extends into a triangular shape. In the middle, the cartilaginous element runs in a relatively straight line postero-anteriad. Antero-laterally, the pharyngobranchial articulates with the epibranchial. The epibranchial is rather stout and has a large central foramen for the branches of the branchial nerve. The pharyngobranchial of the posterior-most two gill arches and the epibranchial of the last gill arch are fused into a single large element, the gill pickax. This is medially elongated with a spatulate extension on the outer lateral side. The ceratobranchial is elongated and has a median extension on half of its length. The distal end articulates with the epibranchial element. With the anterior end, the ceratobranchial articulates from the second to fourth arch with the hypobranchial, in arch five with the basibranchial and in arch one with the basihyal. The hypobranchial is only present in arches 2–4. This element is elongated and rather narrow. It extends roughly in a cranio-caudal direction and articulates anteriorly with the ceratobranchial and posteriorly with the basibranchial. The length of the hypobranchial decreases continuously from arch two to four.

The basibranchial generally consists of a single unpaired element. It lies medial on the ventral side of the branchial arches. This element is diamond shaped. Caudally, there is an articulation with the accessory cartilage, which is small and narrow.

The gill rays are not visible in the micro-CT scan, but are distinct in the dissection (Figs 22B–C, 24B–C). There are no significant differences in the structure or morphology of the branchial apparatus between the two sexes.

3.2.7.1. Mandibular muscles

3.2.7.1.1. Musculus levator labii. At the posterior end of the nasal capsules, the Musculus levator labii superioris is attached dorsally to the chondrocranium (Figs 25, 26, 28A, C–D, 30,A,C). The fact that the muscle attaches directly to the neurocranium, and not through a tendon as in squaliform sharks, identifies C. punctatum as a representative of galeomorph sharks, a criterion used for establishing the monophyly of galeomorphs; Soares and Carvalho (2013). In dorsal view, it originates anteriorly at the same level as the subnasal fenestrae and extends dorsally to the endolymphatic and perilymphatic foramina (Figs 25B, 26B, 28A, 33A), where it meets the Musculus epaxialis without merging with it. Laterally, the Musculus levator labii reaches around the palatoquadratum both anteriorly and posteriorly, while the posterior strand inserts on the anterior wall of the orbit (Figs 25A,C, 26A,C). The anterior cord does not extend as far ventrally in the female as in the male specimen, in which it extends slightly beyond the lower edge of the palatoquadratum (Figs 25A,C).

3.2.7.1.2. Musculus adductor mandibulae. The Musculi adductor mandibulae are the primary jaw closing muscles in sharks. They generally consist of four subgroups labelled I to IV (Figs 27, 28B–C, 29A–C, 30B–C). Although superficially separated, the internal fibres of all subgroups intersect.

The M. adductor mandibulae I is the most anterior part (Figs 27, 28B–C, 29A–C, 30B–C). Its fibres have a dorso-ventral orientation. It is posteriorly positioned to the M. adductor mandibulae II in the dorsal region and to the M. adductor mandibulae III in the ventral region (Figs 27, 28B–C, 29A–C, 30B–C). There is a blending of the fibres at the ventral border of M. adductor mandibulae I and III. The M. adductor mandibulea II extends diagonally at 45° from antero-dorsal to postero-ventral. Typically for Chiloscyllium, this muscle strand is situated dorsal to the M. adductor mandibulae III (Soares and Carvalho 2013). It inserts at the palatoquadratum and extends towards the Meckel’s cartilage where only a small part of the muscle is attached to it. The M. adductor mandibulae III, on the other hand, is connected to both elements of the mandibular arch to approximately the same extent. The postero-ventral portion of the mandibular muscle is the M. adductor mandibulae IV. This is fused with the upper and lower jaws and covers the area of the quadrato-mandibular joint. In both sexes the jaw muscles are developed to the same extent and do not differ in direction or arrangement.

3.2.7.2. Hyoidal muscles

3.2.7.2.1. Musculus intermandibularis. The Musculus intermandibularis is a paired, very slender muscle whose fibres run transversely to the longitudinal axis of the body. Both muscles attach to almost the entire length of the ventral edge of the Meckel’s cartilage from the distal end of the Meckel’s cartilage, at the level of the sustentaculum, almost to the symphysis (Figs 28B, 30B, 31C–D). This is where both parts of the muscle join. Typically for Chiloscyllium, this muscle is strongly connected to the Musculus constrictor hyoideus ventralis. Since the muscle forms a very slender and thin muscle bundle, it is hardly visible in the CT-Images. It could only be reconstructed in the male, but it is clearly visible in both sexes in the dissection (Figs 28B, 30B).

3.2.7.2.2. Musculus constrictor dorsalis. The Musculus constrictor dorsalis runs along the lower edge of the orbit, which appears to split into several individual bundles anteriorly (Figs 33E–F, 34E–F, 22D, 24D). It attaches to the ventral side of the postorbital process and is slightly antero-ventrally oriented. The Musculus levator palatoquadrati represents the innermost part of the M. constrictor dorsalis (Figs 33E and 34E). It inserts postero-ventral on the postorbital process and anteriorly slightly below the Ligamentum mandibulo-palatoquadrati. The constrictor dorsalis I muscle, which attaches centrally to the dorsal edge of the palatoquadrate, runs further distally parallel to the Musculus levator palatoquadrati. It is slightly longer than the M. levator palatoquadrati (Figs 3E–F, 34E–F, 22D, 24D). In Chiloscyllium and Hemiscyllium the muscle is divided into two individual bundles according to Goto (2001), one with a proximal and the other with a distal tendon. The bipartition is clearly visible in both sexes in the micro-CT models (Figs 33E and 34E). The most distal of the three muscles is the Musculus spiracularis (Figs 33E–F, 34E–F, 22D, 24D). It originates near the hyomandibular fossa and inserts on the distal end of the palatoquadratum. Typical for Chiloscyllium is the small subdivision of the spiracularis, which branches off at about two-thirds of its length (Figs 33F and 34F). This strand inserts on the mandibular knob of the lower jaw. The Musculus constrictor dorsalis forms the anterior wall of the spiracle in Chiloscyllium. In the male specimen, parts of the suborbitalis muscle were reconstructed.

3.2.7.2.3. Musculus constrictor hyoideus. This muscle is divided into dorsal and ventral parts. The dorsal part in turn is divided into the Musculus levator hyomandibulae and Musculus constrictor hyoideus dorsalis (Figs 27 and 29). The former inserts in the otic region on the chondrocranium and extends lateroventrally to the hyomandibula, to which it is firmly attached. Dorsally, the levator hyomandibulae muscle borders the M. epaxialis. The Musculus constrictor hyoideus dorsalis arises at the lateral edge of the M. epaxialis and extends ventrally (Figs 27A–B and 29A–B).

The paired Musculus constrictor hyoideus ventralis has transversal fibres. Ventrally, the muscle attaches to the distal end of the Meckel’s cartilage (Figs 27A,C and 29A,C). According to Soares and Carvalho (2013), a thin cord attaches superficially to the distal tip of the ceratohyal. However, this was neither observed in the 3D models nor in the dissected specimens. Posteriorly, the M. constrictor hyoideus ventralis is connected to the M. constrictor hyoideus dorsalis in the branchial region by interconnecting muscle fibres.

3.2.7.3. Hypobranchial muscles

In Orectolobiformes, the hypobranchial musculature typically consists of the Musculus genio-coracoideus, the Musculus rectus-cervicis and the Musculus coraco-branchialis (Goto 2001). The M. genio-coracoideus extends from a fascia of the M. rectus cervicis ventrally to the symphysis of the lower jaw (Figs 28B, 30B, 35, 37). There it inserts on the ventral surface of the Meckel’s cartilage. It is relatively narrow, long and tapers both anteriorly and posteriorly into a rounded end (Figs 35B and 37B). The M. rectus-cervicis consists of the M. coraco-arcualis and the M. coraco-hyoideus, which are both clearly separated by a septum (Figs 35A–C and 37A–C). The M. rectus-cervicis runs parallel dorsal to the M. genio-coracoideus. It consists of a pair of parallel muscle bundles. On about one third of the anterior part of the M. rectus-cervicis, the muscle bundles are separated from the posterior part by a septum. The anterior part, called the M. coraco-hyoideus, attaches to the ventral side of the basihyale (Figs 36B and 38B). The posterior part, the M. coraco-arcualis, originates on the ventral side of the coracoid and further dorsally on the anterior tip of the Muscoli hypaxialis (Figs 35D and 37D).

The M. coraco-hyoideus and the M. genio-coracoideus originate from a fascia of the M. rectus-cervicis. The M. coraco-hyoideus inserts anteriorly on the caudal end and the ventral surface of the basihyal. The five Muscoli coraco-branchialis posteriorly or dorsally of the M. rectus-cervicis vary only slightly in size (Figs 35C, 36A,C, 37C, 38A,C). The posteriormost strand appears clearly separated from the four anterior ones (Figs 35C, 36A, 37C, 38A). It points caudally in a semi-arch. The four posterior strands of the M. coraco-branchialis originate in the anterior part of the coracoid and attach to the Muscoli hypobranchialis and Muscoli ceratobranchialis (Shirai, 1992).

In Chiloscyllium punctatum the eyes are relatively small. They are located slightly posterior to the mouth opening and slightly anterior to the spiracles (Figs 1A–B and 2A–B). The pupils are more or less slit-shaped, depending on the amount of incoming radiation, and slope from posterior to anterior at an angle of 45°. In the micro-CT images, the lens is particularly bright, as it seems to have absorbed a considerable amount of iodine. Around the eyeball, a series of narrow muscle bands are visible representing the oculomotor muscles.

In Chiloscyllium punctatum there are six oculomotor muscles, two pairs of muscles and two single muscles (Figs 33A–D and 34A–D). Anteriorly, there is the Musculus obliquus superioris and the Musculus obliquus inferioris (Figs 33A–D and 34A–D). Both are clearly separated from each other, and both originate on the anterior part of the orbit at the interorbital wall. The main function of the obliquus superioris muscle is to roll the eye anteriorly, whereas the obliquus inferioris muscle is mainly responsible for rolling the eye caudally (Goto 2001). Further posteriorly, the Musculus rectus internus is located centrally between the other five oculomotor muscles. It originates further posteriorly on the interorbital wall, close to but clearly separated from the other three rectus muscles. At its base, there is an extra muscle bundle, which originates ventrally and joins the extra bundle of the inferior rectus muscle (not visible in the micro-CT scans) at the same point, the ocular pedicle (Goto 2001). The main bundle runs almost horizontal in an anterior direction and attaches to the eye between the two oblique muscles. It is significantly involved in adduction, i.e., the anterior movement of the eye.

As is typical of Orectolobiformes, the rectus muscles originate individually on the interorbital wall (Goto 2001) (Figs 33A and 34A). The Musculus rectus superioris and the Musculus rectus inferioris arise as a pair between the M. rectus externus and M. rectus internus muscles. The M. rectus superioris attaches dorsally, the rectus inferioris ventrally to the posterior third of the eye (Figs 33D and 34D).

Also typical for Orectolobiformes is the additional muscle bundle on the M. rectus inferioris (not visible in micro-CT models). It arises from the interorbital wall at the base of the inferior rectus. As previously mentioned, this strand joins the extra bundle of the internal rectus at the disc of the eyestalk (Goto 2001). The main function of the superior rectus is to elevate the eye. The M. rectus inferioris, on the other hand, is mainly responsible for lowering (depressing) the eyeball (Goto 2001).

The Musculus rectus externus attaches most posteriorly and, typically for Chiloscyllium and Hemiscyllium, arises from its own fossa posterior to the foramen for the superior branch of cranial nerve V (Figs 33A,C and 34A,C). Its main purpose is to move the eye backwards (Goto 2001).

As these are very fine muscle bundles, an exact reconstruction of the individual muscles is not easy given the resolution of the micro-CT scans. Some components, such as the extra bundles of the rectus inferioris and parts of the extra bundles of the M. rectii internus, are not visible in the reconstructions. A probable artefact, which could also be caused by the resolution, is the fusion of the M. rectus inferioris and the M. obliquus inferioris and the clearly shortened M. rectus externus in the male specimen.

The shoulder girdle is U-shaped, which is typical for Orectolobiformes (Figs 39A–B,D–E, 41A–B,D–E). Several individual cartilaginous elements are seamlessly fused. These are the scapula and the coracoid. The scapula is a cylindrical, vertical element that is slightly tilted caudally in lateral view (Figs 39C, 40C, 41C, 42C–D). Dorsally on the scapula is the rudimentary suprascapula, which is very small and oval, and which is connected to the scapula by soft tissue (Figs 39A–E, 40D, 41A–E, 42D). A suprascapula only is present in the genera Chiloscyllium, Hemiscyllium, Ginglymostoma, Stegostoma and Rhincodon within Orectolobiformes (Goto 2001). Ventrally, the coracoid is adjacent to the scapula. The coracoid appears flat and runs horizontally (Figs 39A–B,D–E and 41A–B,D–E). The median area where the coracoids meet is widened forming a trough-like basin representing the so-called apron. This apron supports the ventral wall of the pericardial cavity. The process for the Musculus levator pectoralis is located posteriorly below the foramen for the pectoral nerves and artery (Figs 39B,E and 41B,E). The foramen for the brachial artery penetrates the fossa for the pectoral depressor muscle longitudinally, which is typical for Chiloscyllium and Hemiscyllium within Orectolobiformes (Goto 2001).

The pectoral fins, which articulate laterally with the shoulder girdle, consist of three cartilages at their base, with several radialia attached distally (Figs 40B and 42B). The basal cartilages are from anterior to posterior the propterygium, mesopterygium and metapterygium (Figs 41F, 42B, 43F, 44B). The propterygium is rather small and flat. In the micro-CT scan, the protopterygium is indistinguishable from the mesopterygium and both appear fused (Figs 39F and 41F). In the dissected specimens, however, the protopterygium can be distinguished as a separate (very fine) cartilage (Figs 40B and 42B). Only one radialia attaches to the protopterygium. The mesopterygium is positioned between the protopterygium and the metapterygium. It is sickle-shaped and curved caudally (Figs 39F, 40B, 41F, 42B). The metapterygium is about the same length as the mesopterygium, but broadens distinctly distally, ending in a spatulate widening. The radialia are generally tripartite and comprise a longer proximal, a shorter median and a shorter distal component.

All components of the shoulder girdle are very similar in both sexes and hardly or not at all different. In the male specimen, only the foramina for the pectoral nerves and artery are not identifiable in the micro-CT models, but this is due to the resolution of the scans, as it is clearly visible in the dissected shoulder girdle.

3.2.10.1. Musculus cucullaris

The Musculus cucullaris is positioned between the M. epaxialis and the Musculus constrictor branchiales superficialis (Figs 28, 30, 43, 44). It is a relatively thin but planar muscle. The M. cucullaris originates from the fascia of the M. epaxialis and attaches to the dorsolateral surface of the posterior two epibranchialia and to the scapular process of the pectoral girdle.

3.2.10.2. Pectoral fin musculature

The dorsal musculature of the pectoral fin consists essentially of the Musculus levator pectoralis, which comprises one superficial and two inferior layers (Figs 45A,C–D and 46A,C–D). The M. levator pectoralis superficialis is relatively thick and covers the proximal half of the dorsal side of the fin in a fan shape (Goto 2001). This muscle originates from the lateral side of the scapula. The Musculus levator pectoralis inferioris is short and lies below the M. levator pectoralis superficialis on the base of the dorsal side of the pectoral fin (Goto 2001). Its origin is at the Processus levator pectoralis and inserts at the basal cartilages of the pectoral fin. The Musculus levator pectoralis distalis is relatively narrow, also fan-shaped and starts distal to the M. levator pectoralis inferioris at the distal edges of the basal cartilages of the pectorals and ends at the base of the proximal radialia (Goto 2001). The ventral component of the pectoral musculature is the Musculus depressor pectoralis (Figs 45 and 46). This is relatively massive and also fan-shaped. It originates from a fossa lateral to the coracoid and attaches to the ventral surface of the fin.

The heart is located in the pericardium. This in turn is supported by the apron of the shoulder girdle (Figs 47, 48A, 49A). Only in the male it was possible to reconstruct the heart from the micro-CT scan. As could be seen during the dissection, the iodine had attacked the heart tissue in the female quite severely, which is why it appeared very diffuse and unclear in the micro-CT data. In the micro-CT model of the male heart, however, relatively little detail can be seen. Atrium and ventricle appear as a fused unit (Fig. 47) and the boundaries cannot be determined. The only other element that stands out is the conus arteriosus. Much more detail is seen in the dissection of the heart (Figs 48 and 49). Due to the lack of internal pressure, caused by the blood flow, the individual blood vessels are collapsed and are not easy to observe. In ventral view, the ventricle is the most prominent structure (Figs 48 B and 49 B). It is a large, slightly pyramidal, muscular chamber. It rests on top of the atrium, which is only indistinctly visible in ventral view. Cranially, adjacent to the ventricle is the conus arteriosus, which is the fourth chamber of the shark’s heart and contains several rows of conus valves. Descending from the conus arteriosus are the individual branchial arteries (Fig. 48B). Gills III–V have their own artery, while gills I and II have a shared inflow through the anterior (afferent) branchial artery. The left lateral view nicely shows the position and size relationship of the atrium to the ventricle. The atrium is supplied by the two lateral common cardinal and the two caudal suprahepatic veins, which flow into the first ventricle that is the sinus venosus (Tota 1999). The sinus venosus lies mostly dorsal and its apex points towards the atrium, into which it flows via the sinoatrial junction. The sinus venosus is located on the right dorsal side and is clearly visible in Figure 48C and 49C in the longitudinal section of the heart. The atrium is connected to the ventricle via the atrioventricular valve. The compartmentation of the ventricle is clearly visible in the dissection (Figs 48C and 49C). It has three basic areas. In the centre is the so-called spongiosa, which has a sponge-like appearance as it is built up of countless very thin muscle bundles (trabeculae). Surrounding the spongiosa is the compacta (especially ventrally). This is built up by dense, ordered muscle bundles, which give the tissue a much denser structure. According to Tota (1999) it is only found in a few teleosteans with high metabolic or locomotor activity, but in many chondrichthyans from various groups. Just anterior to the transition to the conus arteriosus is the so-called lumen. To get from the lumen to the conus arteriosus, the blood passes through several pairs of conal valves (Figs 48C). From there, the bloodstream divides into the individual afferent branchial arteries, where it is oxygenated by flowing through the gills. The structure of the heart is equivalent in both sexes and differs only in the suboptimal condition of heart tissue preservation in the female.

The vertebral column is the central supporting structure or cartilage staff in all vertebrates. In Chiloscyllium as in all chondrichthyans, the notochord is persistent and runs through a central canal of the vertebral centra (Figs 50D and 51D). The vertebral column also provides a protective cover for the spinal cord, which runs through the spinal canal formed by the neural arches. The structure of the vertebrae can be seen very clearly in the micro-CT scans (Figs 50 and 51). The neural arches continue dorsally into the neural spine, which serves as attachment points for the epaxial muscles. In the micro-CT scans, it was only possible to reconstruct the vertebral centra, as the neural spine or the neural arch hardly shows any calcification (Figs 50A–C and 51A–C). Several longitudinal ribs run around the centre. These are terminated cranially and caudally of each vertebra by a flat plate. Both sexes have a similar vertebral morphology.

Lateral to the vertebral column are the two epaxial muscles, which are massive muscle strands that extend dorsally over a large part of the body length (Figs 28A, 30A, 43A,D, 44A,D). They insert anteriorly on the chrondrocranium at the sphenopterotic ridge (Figs 28A, 30A, 43A, 44A). Caudally, each lateral muscle cord splits into dorsal and lateral components (Goto 2001). Further anteriorly these components are indistinct from each other. The ventral separation from the hypaxial musculature is quite clear due to the horizontal myoseptum. The Musculus hypaxialis consists of only one muscle strand, which forms a very thin muscle layer, especially ventrally (Figs 28A–C, 30A–C, 45A–C, 46A–C). This muscle envelops the abdominal cavity from the shoulder girdle to the pelvic girdle. Posteriorly, the muscle becomes again a longitudinal strand extending caudally (Goto 2001).