Parioglossus raoi

Rui Wang & Richard Winterbottom, 2006, Osteology and phylogeny of Parioglossus (Teleostei, Gobioidei), with a revised key to the species., Zootaxa 1131, pp. 1-32 : 4-14

Osteology of Parioglossus raoi

The following osteological description is based almost exclusively on a 16.5 mm SL male of Parioglossus raoi from Negros, Philippines (ROM 1657CS), although the prootic region of the skull represents a composite derived from several specimens from that lot. Both the statements made in the descriptions, and the illustrations, were checked against these additional specimens.

The Cranium (Figs. 2-4)

Vomer (medial) toothless; anterior portion enlarged and broader ventrally than dorsally; narrow posterior process of vomer inserts into groove on anteroventral surface of parasphenoid (medial). Ventral portion of mesethmoid (medial) joined with anterodorsal surface of parasphenoid; posterodorsal aspect of mesethmoid overlapped by frontal bones and joined to parasphenoid through cartilage at its posteroventral margin; anterolaterally, mesethmoid joined to lateral ethmoids (which are separated by ethmoid cartilage). Lateral ethmoid forms most of anterior wall of orbit, and has a cartilage-tipped ventrolateral process to which the thin, poorly ossified lacrimal (not figured) attaches; foramen for olfactory nerve lies between lateral ethmoid and mesethmoid. Frontal large, narrowing anteriorly where it bifurcates around posterior portion of mesethmoid; in post orbital region, frontal bears a descending lateral wing, which joins sphenotic and prootic; in supraorbital region, frontal bears a groove for supraorbital canal (Springer, 1983); posterior end of frontal forms a large portion of roof of braincase; it joins pterosphenoid (Fig. 4) ventrally to form dorsoposterior wall of orbit; laterally, it overlaps sphenotic and partially overlaps supraoccipital posterolaterally. Sphenotic joins pterotic and supraoccipital posteriorly and prootic ventromedially; sphenotic smaller than pterotic, and articulates with anteriormost dorsal condyle of hyomandibular. Pterotic joins epioccipital posterolaterally and exoccipital posterodorsally; anteroventrally, pterotic articulates with posterodorsal condyle of hyomandibular, and is partially overlapped by epioccipital dorsolaterally.

Epioccipital occupies posterolateral corner of cranial roof and bears a process for attachment to dorsal arm of posttemporal; it is overlapped by supraoccipital dorsally, partially overlaps pterotic anterolaterally, joins its antimere beneath overlapping supraoccipital (medial) posteromedially, and is synchondrally joined with exoccipital posteriorly. Laterally on pterotic and exoccipital a long, deep trough contains the lateral sensory canal. Supraoccipital situated posteromedially on cranial roof, forked anterolaterally with a rounded median anterior projection; small portion of its anterior process overlapped by frontal; extreme posterolateral aspect of supraoccipital slightly overlaps exoccipitals; posterior portion with prominent median posterodorsal flange. Exoccipital forms most of posterior surface of cranium, forming lateral and dorsal margins of foramen magnum; exoccipital possesses condyle which articulates with first vertebra; exoccipitals synchondrally united along dorsal midline; epioccipital meets its antimere anterodorsally and slightly overlaps supraoccipital, joins pterotic laterally and partly ventrolaterally; exoccipital may or may not join intercalar ventrolaterally; thin projections of exoccipital join with similar projections of basioccipital ventromedially. Exoccipital has two foramina, a vagal foramen (Springer, 1983) anteriorly; posterior foramen is possibly a passage for first spinal nerve. Basioccipital (medial) is posteroventral terminus of cranium, articulating with first vertebra; forked anteriorly with most of this portion overlapped by parasphenoid medially, joining with posterior portion of prootic anteriorly; anterolaterally, basioccipital is overlapped by intercalar; posterolaterally, thin projections of basioccipital interdigitate with similar projections of exoccipitals. Intercalar small, overlaps basioccipital, and may meet with exoccipital in some specimens.

Prootic (with large trigemino-facial foramen) makes up lateral region of posterior orbit and side of braincase posterior to this; joins with sphenotic anterolaterally, basioccipital posteriorly, pterotic posterolaterally, and is overlapped by parasphenoid ventromedially. Pterosphenoid small, occupies portions of posterolateral wall of orbit, synchondrally joining frontal dorsally and meets prootic and parasphenoid ventrally (Fig. 4). Parasphenoid (medial) constitutes large portion of ventromedial aspect of cranium; anteriorly, groove in parasphenoid receives posterior process of vomer; overlaps prootics laterally and basioccipital posteriorly. Foramen present at base of each parasphenoid dorsal wing, near area of overlap with prootic.

Jaws, Suspensorium, Superficial Bones of Head (Fig. 5)

Premaxilla with two rows of caninoid teeth, outer row larger than inner row; a short medial ascending process adjoins large, rounded, externally concave articular process; posterior process is lateral to, but much smaller in size than, articular process. Rostral cartilage (medial) replaced at least partially by bone, flattened laterally and attached to upper tip of ascending process of the premaxilla as well as to anterodorsal end of maxilla, overlies vomer. Maxilla with long, flat posterior portion and convoluted anterior head, which articulates with articular process of premaxilla posteromedially and maxillary process of palatine anterolaterally. Dentary with two rows of caninoid teeth, outer row enlarged. Adjacent to last tooth is large coronoid process. Posteriorly on its internal surface, dentary receives dorsal ramus of anguloarticular. Meckels cartilage long, rod-like, extending anteriorly from endosteal process on medial surface of anguloarticular to a point in hollow end of dentary, just anterior to level of a foramen that completely perforates dentary. Posterodorsally, anguloarticular articulates with quadrate. There is no coronomeckelian (sesamoid articular). Retroarticular a small bone joined to ventroposterior end of anguloarticular, and is connected by a ligament to anterior end of interopercle.

Hyomandibular with three articular condyles. Anterodorsally, hyomandibular articulates with sphenotic, posterodorsally with pterotic, and posteriorly with opercle. Groove in anterior surface of hyomandibular receives metapterygoid; ventral projecting surface synchondrally joins with posterior head of symplectic. Most of posterolateral surface of hyomandibular overlain by preopercle, which fits into large groove formed by wide, thin posterolateral projection of hyomandibular. At approximate centre of medial surface of hyomandibular lies large foramen, which leads to canal exiting anteroventrally on lateral surface, canal carries the hyomandibular branch of facial nerve (Birdsong, 1975; Freihofer, 1978). Metapterygoid slender and elongate, not reaching quadrate; broadly overlaps, and tightly joined to, posterolateral surface of symplectic ventrally, and anterodorsal surface of hyomandibular posteriorly. No mesopterygoid. Anterior portion of symplectic attaches to the groove on medial surface of quadrate and is overlapped by metapterygoid dorsally; posterior portion delicately joined by cartilage to hyomandibular.

Posterodorsal surface of quadrate rimmed with cartilage; anterior portion overlapped by ectopterygoid, a broad groove in the medial surface of quadrate receives anterior portion of symplectic. Short anteroventral condyle unites quadrate with anguloarticular, and very long, blade-like ventroposterior extension joins preopercle in shallow ventral groove. Ectopterygoid very well ossified, plate-like, overlaps quadrate posteriorly and synchondrally joins palatine along its anterior surface. Palatine toothless, “T” shaped, ventroposterior portion joins ectopterygoid; anterior portion of palatine bears two arms: anterior-most tipped with cartilage and articulating with maxilla and ligamentously joins ascending process of premaxilla; posterior process articulates with lateral ethmoid and ligamentously joins mesethmoid. Lacrimal (not figured) thin, poorly ossified, attaches to ventrolateral process of lateral ethmaoind posterior to palatine. Opercle with a strong, concave condyle that articulates with posterior condyle of hyomandibular, overlaps subopercle ventrolaterally. Preopercle gently curved, fits into broad shelf of hyomandibular dorsally and into narrow shelf of quadrate anterodorsally; posterior portion of preopercle with trough (not shown) which carries preopercular portion of laterosensory canal system; interhyal attaches firmly to medial surface of preopercle; a medial triangular process meets symplectic and hyomandibular to form a large foramen. Preopercle overlies thin, blade-like interopercle; anteriorly, long and flat interopercle attaches ligamentously to anguloarticular; posteriorly, attaches ligamentously to posterior tip of posterior ceratohyal.

Hyoid Arch (Fig. 6)

Interhyal ventrally ligamentously bound to, and articulates with, the posterior ceratohyal. Dorsolateral surface of interhyal strongly attached to medial face of preopercle; dorsal tip cartilaginous. Posterior ceratohyal articulated with interhyal posterodorsally; anterior ceratohyal overlapped anteriorly by hypohyals.

Anterior ceratohyal has a cartilaginous margin ventrolaterally and posteriorly; posterior ceratohyal has a cartilaginous margin anteriorly, and together forming a synchondral joint.

Four branchiostegal rays extend ventrally from anterior ceratohyal, one from posterior ceratohyal; anteriormost branchiostegal arises from slender portion of anterior ceratohyal, is thin, rib-like and smallest; other branchiostegals all blade-like, with one on posterior ceratohyal being largest. Hypohyals overlap anterior ceratohyal laterally, and ligamentously join dorsal head of urohyal (medial) and posterior portion of basihyal (medial). Dorsal hypohyal has long ligamentous connection to hypobranchial 1, and is bound to its antimere via a long medial ligament. Ventral hypohyal ligamentously connected to blade of urohyal posteroventrally, and to base of urohyal and posterior basihyal posterodorsally. Urohyal (medial) consists of dorsal head and posteroventrally projecting broad blade. Dorsal part forked; situated within this concavity of the urohyal base is small cartilaginous basibranchial 1.

Branchial Apparatus (Fig. 7)

Basihyal (medial) long, broader anteriorly than posteriorly; anterior tipped with cartilage, ligamentously joins hypohyals and urohyal posteriorly. Posterior to basihyal, in straight line, lie basibranchials 1-4 (medial). Basibranchials 2 and 3 relatively well ossified with only tips cartilaginous, whereas basibranchials 1 and 5 (see below) entirely cartilaginous.

Basibranchial 2 articulates with medial surface of hypobranchial 1. Basibranchial 3 synchondrally joins basibranchial 2 anteriorly; articulates laterally with hypobranchial 2; anterolaterally tipped with cartilage; and joined by long ligament to hypobranchial 3 posteriorly. Basibranchial 4 ligamentously bound to third hypobranchial; lies above anterior cartilaginous tip of ceratobranchial 4. A tiny, rounded, medial, unstained nubbin of cartilage lies on anterodorsal surfaces of cartilaginous anteroventral tips of fifth ceratobranchials (not shown in Fig. 7), which may represent basibranchial 5 (Gill, pers.comm.). Hypobranchials (1-3) ligamentously and sequentially joined to each other and articulate with their respective ceratobranchial posterolaterally. Each hypobranchial is cartilaginously tipped. Five pairs of ceratobranchials present. Ceratobranchials 1-3 join their respective hypobranchials anteroventromedially; ceratobranchial 4 joins hypobranchial 3 by a ligament and basibranchial 4; ceratobranchial 5 ligamentously bound to ceratobranchial 4 and basibranchial 4. Ceratobranchial 1 with 13 to 15 outer gill rakers; ceratobranchials 2-4 with long, bifid-tipped gill rakers suspended in connective tissue; ceratobranchial 5 with large triangular tooth plate. Each of four epibranchials (1-4) articulating with posterodorsal tip of its respective ceratobranchial. Epibranchial 1 has 4-5 gill rakers; epibranchials 1 and 3 have cartilaginous-tipped uncinate processes. Uncinate process of epibranchial 1 articulates with interarcual cartilage. Interarcual cartilage and epibranchials 2-4 articulate with infrapharyngobranchials 2-3 (epibranchial 4 posteriorly and a little laterally displaced in Fig. 7). Infrapharyngobranchial 1 absent. Infrapharyngobranchials 2-3 have tooth plates fused to bone, which bear cartilaginous processes for articulation with respective epibranchial. Fourth infrapharyngobranchials either fused to third or been lost (the latter is more likely, Gill, pers.comm.); however, fourth toothplate remains as a separate entity.

Pectoral and Pelvic Fins and Girdles (Figs 8-9)

Posttemporal composed of central body, with longer dorsal arm connected to epioccipital and shorter ventral arm joined to intercalar. Supracleithrum extends posteriorly from medial surface of central body of posttemporal; ventromedial surface joins dorsolateral portion of cleithrum ligamentously. Cleithrum forked dorsally. Posteroventromedially, cleithrum with an indentation to receive ventral intercleithral cartilage (medial), which in turn articulates with pelvis through pelvic intercleithral cartilage (medial). Central portion of cleithrum anteriorly flattened with posterior surface bearing groove. Scapulocoracoid cartilage well developed with large scapular foramen dorsally and synchondrally joins cleithrum anteriorly and dorsally, four pectoral radials posteriorly, and merges with coracoid ventrally. Coracoid well-ossified, joins cleithrum. Margin of proximal radials cartilaginous; 16-18 fin rays articulate with 15 cartilagenous distal radials, dorsalmost and sometimes ventralmost fin rays articulate directly on posterior faces of proximal radials. Single, sickle-like ventral postcleithrum present (not figured). No dorsal postcleithrum.

Large, pelvic intercleithral cartilage (medial) joins medial surface of posteriorly directed processes of cleithrum. Posteriorly, this cartilage continuous with pelvic girdle. Anterior margins of pelvic bone join pelvic intercleithral cartilage anteriorly. Medial portion of pelvic bone dorsally convex; pockmarked with small, irregular openings and not as well ossified nor as substantial as dorsally concave and well-ossified lateral margins. Posterolateral edge of pelvic bone with a cartilaginous margin (often interpreted as a fused pelvic radial) which is straddled by four segmented pelvic fin rays. Single pelvic fin spine attaches to pelvic bone anteroventrolaterally to lateralmost pelvic ray. An antenna-like sub-pelvic process arises posteriorly on ventromedial surface of pelvic bone. Posterior process of pelvis very long, slightly more than 10% length of entire pelvis.

Vertebrae and Unpaired Fins (Fig. 10)

Vertebral column made up of 26 vertebrae divided into 10 precaudal and 16 caudal vertebrae; vertebrae 3-10 bear ribs; epineurals present on vertebrae 1-10; no epicentrals or epipleurals. First precaudal vertebra (first vertebra) bears condyles for articulation with exoccipitals anteriorly. All vertebrae, except compound ural centrum, with neural spines, and at least one foramen. Vertebrae 24 (= PU3) and 25 (= PU2) with modified haemal and neural spines continuous with centra. Spines of vertebra 24 are more distally broadened and flattened than those of preceding vertebrae, reach anteromedial margins of procurrent cartilages, and the tips are sometimes bifurcate or trifurcate. Vertebra 25 with a short and broad neural spine, whereas the haemal spine is elongate with broad, flat anterior margin distally articulating with posteromedial margin of ventral procurrent cartilage, and cylindrical posterior margin which articulates with two of ventral caudal rays. Posteriormost vertebral centrum (representing fusion of preural centra 1, and ural centra 1 and 2), and hypurals 3-4 fused together; hypural 5 about half the length of hypurals 1+2, well separated from ural centrum. Anterior to hypural 5 a single, large epural with a cylindrical core near posterior margin; anterodorsal to epural is dorsal procurrent cartilage. Large, triangular, plate-like element representing fused hypurals 1-2 inserting in groove on ventral side of ural centrum. Parhypural ventral to hypurals 1-2, well separated from vertebral centrum proximally, with a slender cylindrical core. Anteroventral to parhypural lies enlarged haemal spine of vertebra 25.

Typically seven or eight dorsal and seven or eight ventral procurrent rays (unsegmented); one simple, segmented ray inserting on epural and another on hypural 5; 7 branched rays on hypurals 3-4; 5 branched rays on hypurals 1-2; one branched ray on parhypural; and one simple, segmented ray on last hemal spine (sometimes branched at tip). First dorsal fin with six spines. Pterygiophores of dorsal spines I and II insert in third interneural space, those of III and IV in fourth, V in fifth, and VI in sixth; pterygiophore formula (as defined by Birdsong, 1975) 3 (22110). Second dorsal fin normally consists of one spine and 14-17 rays, each element supported by its own pterygiophore except for last two rays, which are counted as one because they are close together and arise from same pterygiophore. Two anteriormost pterygiophores with proximal and medial radials undifferentiated and distal radials absent, remaining elements separate. Posteriormost medial radial with posteromedially directed flange attached to wedge-shaped piece of cartilage straddled by last ray. All other rays straddle distal radials. Interneural space 8 receives first pterygiophore of spine of second dorsal; space 9 second pterygiophore; space 10 third; 11 fourth; 12 fifth and sixth; 13 seventh; 14 eighth and ninth; 15 tenth; position of posterior part of pterygiophore may vary. First pterygiophore of anal fin inserts anterior to first hemal arch; second pterygiophore in first interhemal space posterior to first hemal arch; third and fourth in space between hemal spines 2 and 3; fifth in third; sixth and seventh in fourth; proximal tips of all pterygiophores of medial fins cartilaginous.