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Schroederichthys tenuis Springer ZBK , 1966

(Figs. 1-38, Tables 1-5)

Diagnosis. A differential diagnosis of S. tenuis ZBK is provided by Springer (1966, 1979; see also Compagno, 1984; Compagno et al, 2005). The genus Schroederichthys ZBK is effectively diagnosed in Springer (1966, 1979) and Compagno (1984, 1988).

FIGURES 1, 2. Adult female of Schroederichthys tenuis ZBK (CEPNOR uncat, 440 mm TL) in dorsal (1) and lateral (2) views.

Coloration. As in most scyliorhinids, Schroederichthys tenuis ZBK presents both spots and saddles dorsally, and a mostly white, pale ventral surface (Figs. 1-11). The spots are smaller than eye diameter, dark, rounded, with regular diameters, and distributed both inside and around the saddles. In adults, there are numerous spots within the saddles and surrounding them from head to first dorsal fin. Juveniles have a reduced number of spots inside the saddles and fused spots around them forming continuous lines. White spots are absent in juveniles. There are three types of saddles, primary (1), secondary (2) and subsaddles (S) (Figs. 1-4, 6-11). Primary saddles are dark, conspicuous, and without major differences between mature and immature specimens. Secondary saddles are found posterior to the first dorsal fin, and are not as dark and as well defined as primary saddles; the pre-interdorsal secondary saddle was not found in juveniles. Subsaddles are located on the paired fins below the lateral line in both adults and juveniles. The color pattern of S. tenuis ZBK becomes more faded with growth. The saddles have a strong and bold outline containing few rounded spots in younger specimens, but this outline seems to break with growth, becoming very weak or disappearing completely. The spots inside the saddles become more numerous and may eventually surround or outline the saddle.

FIGURES 3, 4, 5. Illustration of an adult male Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL) in lateral (3), dorsal (4), and ventral (5) views. Primary saddles are designated nasal (1N), supraorbital (1SO), prebranchial (1PB), branchial (1BR), pectoral (1P), postpectoral (1PP), pre first dorsal (1PD 1), first dorsal (1D 1), interdorsal (1ID), second dorsal (1D 2), precaudal (1PC), and caudal (1C). Secondary saddles are designated first postdorsal (2PD 1), pre-interdorsal (2PID), second dorsal (2PD 2), second postdorsal (2POD 2), and caudal (2C). Subsaddles are termed branchial (SBR), pectoral (SP), pelvic (SPV), anterior caudal (SCA), intermediate caudal (SCI), and posterior caudal (SCP).

FIGURES 6, 7. Holotype of Schroederichthys tenuis ZBK (USNM 188052, 230 mm TL, immature male) in lateral (6) and dorsal (7) views.

FIGURES 8, 9. Color pattern of Schroederichthys tenuis ZBK (holotype, USNM 188052, 230 mm TL, immature male) in dorsal (8) and lateral (9) views.

Size and sexual maturity. According to our material, male specimens of S. tenuis ZBK display the first signs of sexual maturity between 335-407 mm TL, as evidenced by the gradual calcification of internal clasper components, and probably reach full maturity at or before 473 mm TL. Based on material examined, the onset of sexual maturity in females seems to be between 217-373 mm TL (Gomes and de Carvalho, 1995). Sexual dimorphism is apparent in mature specimens in the shape of the mouth, which is more angular in females (Figs. 12, 13, respectively).

FIGURES 10, 11. Side-by-side comparison of immature (10) and mature (11) male specimens of Schroederichthys tenuis ZBK in dorsal view, showing ontogenetic changes in color pattern (based on CEPNOR specimens).

FIGURES 12, 13. Side-by-side comparison of ventral head region of adult male (12) (CEPNOR uncat., 473 mm TL) and adult female (13) (CEPNOR uncat., 440 mm TL) specimens of Schroederichthys tenuis ZBK showing sexual dimorphism; note inverted “U”-shaped mouth in 12, and “V”-shaped mouth in 13. Anterior to top.

TABLE 1. Measurements for specimens of Schroederichthys tenuis ZBK (in mm and % of TL). Mature and immature specimens refer to material from UERJ, UFPB, and CEPNOR (see material examined). Mean (x) and standard deviation (SD) are expressed as % of TL.

USNM 188052 holotype USNM 188053 paratype immature specimens (n = 12) mature specimens (n = 12) X SD
mm % of TL mm % of TL mm % of TL mm % of TL
total length 230.0 180.0 157.0-335.0 372.0-473.0 - -
orbit length 8.0 3.5 5.0 2.8 4.0-12.0 2.5-3.6 13.0-18.0 3.4-4.0 3.4 0.4
dist. between eye and spiracle 3.0 1.3 2.0 1.1 2.0-3.0 0.9-1.3 3.0-4.0 0.7-1.0 0.9 0.2
spiracle diameter - - - - 2.0-3.0 0.9-1.3 3.0-5.0 0.7-1.1 0.9 0.2
internasal distance 6.0 2.6 5.0 2.8 4.0-9.0 2.3-3.2 9.0-14.0 2.4-3.8 2.8 0.4
mouth width 14.0 6.1 10.0 5.6 8.0-18.0 3.7-6.4 22.0-28.0 5.3-6.5 5.6 0.7
mouth length 6.0 2.6 4.0 2.2 3.0-13.0 1.9-3.9 12.0-23.0 3.2-4.9 3.6 1.0
length upper labial fold 4.0 1.7 - - 2.0-7.0 1.3-2.1 6.0-11.0 1.6-2.3 1.9 0.3
length lower labial fold 5.0 2.2 3.0 1.7 2.0-5.5 1.2-1.8 5.0-9.5 1.3-2.0 1.6 0.3
1st gill slit width 4.0 1.7 2.0 1.1 2.0-5.0 1.3-1.8 6.0-10.0 1.6-2.1 1.7 0.3
5th gill slit width 2.0 0.9 1.0 0.6 2.0-4.0 1.2-1.4 3.0-6.0 0.7-1.6 1.1 0.3
pelvic fin length - - - - 11.0-28.0 7.0-9.7 40.0-43.0 8.7-9.5 8.6 0.9
clasper inner margin length 4.0 1.7 3.0 1.7 3.0-17.0 1.7-5.1 44.0-52.0 9.9-11.0 6.4 4.3
dist. between dorsal fins 44.0 19.1 33.0 18.3 31.0-68.0 18.9-20.3 73.0-96.0 17.5-20.7 19.7 0.9
length upper lobe caudal fin 50.0 21.7 37.0 20.6 31.0-60.0 17.9-19.7 61.0-78.0 15.5-18.4 17.9 1.8
pelvic fin to tip of tail 167.0 72.6 123.0 68.3 113.0-225.0 67.2-72.0 237.0-311.0 63.7-67.9 67.7 2.3
TIP OF SNOUT TO:
anterior nasal aperture 4.0 1.7 3.0 1.7 3.0-9.0 1.9-2.8 8.0-13.0 2.0-2.7 2.3 0.4
posterior nasal aperture 6.0 2.6 5.0 2.8 5.0-12.0 2.9-3.6 10.0-15.0 2.5-3.2 3.0 0.3
mouth 9.0 3.9 8.0 4.4 6.0-14.0 3.8-4.7 12.0-20.0 2.9-4.3 4.0 0.4
eye 11.0 4.8 9.0 5.0 6.0-15.0 3.8-5.2 17.0-23.0 4.4-5.1 4.8 0.4
spiracle 21.0 9.1 16.0 8.9 13.0-30.0 8.3-9.7 32.0-42.0 8.6-9.3 8.9 0.4
1st gill slit 28.0 12.2 23.0 12.8 15.0-38.0 9.6-12.9 42.0-63.0 11.3-13.3 12.0 1.0
5th gill slit 34.0 14.8 26.0 14.4 20.0-51.0 12.7-16.6 58.0-82.0 15.5-17.3 15.6 1.1
origin pectoral 36.0 15.7 24.0 13.3 22.0-48.0 14.0-15.7 55.0-76.0 14.1-16.1 14.8 0.9
origin of 1st dorsal fin 81.0 35.2 62.0 34.4 54.0-127.0 34.4-37.9 145.0-193.0 38.3-41.0 37.7 2.1
origin of pelvic fins 63.0 27.4 57.0 31.7 44.0-110.0 28.0-32.8 125.0-163.0 32.1-36.3 32.3 2.3
origin of anal fin 112.0 48.7 89.0 49.4 77.0-185.0 49.0-55.2 206.0-265.0 53.2-56.1 53.6 2.9
anus 68.0 29.6 53.0 29.4 48.0-114.0 30.6-35.5 127.0-171.0 32.3-36.3 33.3 2.3
origin of 2nd dorsal fin 133.0 57.8 100.0 55.6 91.0-210.0 56.7-62.7 197.0-299.0 41.8-63.2 59.3 5.7
lower lobe of caudal fin 181.0 78.7 134.0 74.4 120.0-274.0 76.4-81.8 303.0-390.0 79.4-83.6 80.4 2.5
upper lobe of caudal fin 186.0 80.9 146.0 81.1 125.0-276.0 79.6-83.7 303.0-403.0 81.2-85.6 82.3 1.6

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TABLE 1 (continued)

USNM 188052 holotype USNM 188053 paratype immature specimens (n = 12) mature specimens (n = 12) X SD
mm % of TL mm % of TL mm % of TL mm % of TL
FIRST DORSAL FIN:
base 10.0 4.3 8.0 4.4 6.0-13.0 3.8-5.1 14.0-22.0 3.8-5.0 4.4 0.4
length free inner margin 7.0 3.0 5.0 2.8 4.0-10.0 2.5-4.1 9.0-13.0 2.0-3.0 2.8 0.5
height 8.0 3.5 7.0 3.9 4.0-14.0 2.3-4.2 14.0-25.0 3.4-6.7 4.0 1.1
length anterior margin 9.0 3.9 14.0 7.8 13.0-28.0 6.9-8.4 31.0-36.0 7.4-8.8 7.6 1.2
SECOND DORSAL FIN:
base 15.0 6.5 13.0 7.2 10.0-20.0 6.0-7.0 20.0-26.0 4.5-6.7 6.0 0.7
length free inner margin 7.0 3.0 6.0 3.3 6.0-10.0 2.8-4.7 10.0-18.0 2.3-3.8 3.1 0.6
height 11.0 4.8 7.0 3.9 4.0-17.0 2.5-5.1 14.0-24.0 3.8-5.4 4.3 0.8
length anterior margin 21.0 9.1 16.0 8.9 15.0-29.0 8.7-10.1 21.0-44.0 4.8-9.4 8.8 1.3
ANAL FIN:
base 21.0 9.1 15.0 8.3 11.0-24.0 7.0-8.7 30.0-35.0 6.8-8.0 7.8 0.7
length free inner margin 6.0 2.6 7.0 3.9 4.0-9.0 2.3-3.2 9.0-11.0 2.0-2.3 2.6 0.5
height 6.0 2.6 5.0 2.8 3.0-10.0 1.7-3.8 13.0-15.0 2.8-3.4 3.0 0.6
length anterior margin 15.0 6.5 13.0 7.2 9.0-19.0 5.4-8.8 18.0-25.0 4.8-5.7 6.0 1.1
PECTORAL FIN:
anterior margin 24.0 10.4 17.0 9.4 17.0-37.0 10.5-12.0 40.0-54.0 10.4-11.5 10.9 0.6
width at base 19.0 8.3 6.0 3.3 5.0-13.0 3.2-4.1 12.0-17.0 3.2-3.7 3.9 1.3
greatest width 14.0 6.1 11.0 6.1 8.0-23.0 5.1-6.9 30.0-34.0 6.6-8.6 6.6 1.0
DIST. BETWEEN BASES:
pectoral and pelvic fins - - - - 24.0-50.0 13.8-15.3 58.0-75.0 14.1-15.9 14.6 0.6
pelvic and anal fin - - - - 27.0-62.0 16.6-18.5 74.0-90.0 17.0-19.5 18.0 0.9
anal and lower caudal lobe - - - - 33.0-61.0 18.2-22.3 77.0-88.0 17.4-19.3 18.9 1.4
2nd dorsal and upper caudal lobe - - - - 25.0-53.0 15.8-16.6 58.0-77.0 13.3-16.4 15.4 1.1

Dermal denticles. Dermal denticles are divided into three regions, the denticle crown (DCR), pedicel (PED) and base (BAS) (Figs. 14, 15). In adult specimens, the crown presents an acute medial cusp (MCU). On the opposite side there are mostly four (sometimes three) medial ridges (MRI), with central ridges longer than lateral ones. On the external sides of the base of the medial ridges there are reticulated depressions (RED). The lateral expansions (LEX) are rounded (Figs. 14, 15, 18). In juveniles, the crowns present a very acute medial cusp with superficial medial ridges. Small specimens (to about 200 mm TL) present no lateral expansions, which are present in larger specimens of about 470 mm TL (Figs. 16, 17). Both adults and juveniles present short denticle pedicels and radiate denticle bases. Dermal denticles are imbricated in adults, with the medial cusp of an anterior denticle partially covering the medial ridge of a posterior one. However, in juveniles the denticles are scattered with no superposition (Fig. 16). As shown by Springer (1966, 1979), dermal denticles change shape during ontogeny in many species of scyliorhinids, which is confirmed for S. tenuis ZBK .

FIGURES 14, 15, 16, 17, 18. Dermal denticles of Schroederichthys tenuis ZBK (denticles from region just above pectoral fin, left side). (14) mature male (CEPNOR uncat, 473 mm TL) in dorsal view. (15) same specimen in lateral view. (16) juvenile female (CEPNOR uncat., 157 mm TL) in dorsal view. (17) juvenile male (CEPNOR uncat., 217 mm TL) in dorsal view. (18) mature male (CE PNOR uncat., 473 mm TL) in dorsal view.

Dentition. The dentition is typically scyliorhinid, with a well-developed primary cusp (PC) flanked by two or three cusplets (PMC) on each side. There is a basal groove (BG) between the root (RT) and the crown (CR) (Figs. 19-25). The transverse ridges (TR) or striae are present on both inner and outer aspects of the cusp and cusplets. The root is secondarily anaulacorhizid, with a fully closed groove, and has two root lobes with a central foramen (CF). Monognathic heterodonty is present, as teeth near the symphisis present well developed primary cusps (Figs. 19-21) while posterior or commissural teeth present a low primary cusp (posteriormost teeth with a very small central cusp; Fig. 25). Gynandric heterodonty was also found - the principal cusp is more slender and developed in males (Fig. 21) than in females, when corresponding teeth are compared (Fig. 22; the same condition was reported for S. bivius by Goztonyi, 1973). The dental formula of the three first adults captured in 1991 could not be determined due to poor preservation. The dental formula of the holotype is 44/34. Variation was detected in tooth numbers between antimeres in both upper and lower jaws; the dental formula for the nine additional specimens is 28-34 (left), 26-36 (right) / 24-28 (left), 23-28 (right) (Table 2).

FIGURES 19, 20, 21, 22, 23, 24, 25. Teeth of Schroederichthys tenuis ZBK . (19) inferior (3rd) tooth from right ramus in lateral view (CEPNOR uncat., 473 mm TL mature male). (20) same tooth, lingual view. (21) same tooth, labial view. (22) inferior (3rd) tooth from right ramus in labial view (CEPNOR uncat., 440 mm TL mature female). (23) inferior (8th) tooth from right ramus, labial view (CEPNOR uncat., 473 mm TL adult male). (24) inferior (21st) tooth from right ramus, labial view (same specimen). (25) inferior (31st) tooth from right ramus, labial view (same specimen).

TABLE 2. Dental formula for specimens of Schroederichthys tenuis ZBK . Values indicate variation in tooth number between antimeres of both jaws. All specimens from CEPNOR (uncatalogued).

mature male mature female mature female mature male mature female mature male immature female immature female immature female
total length (mm) 473 471 455 442 440 355 217 172 157
upper jaw 30-31 32-30 31-30 28-26 29-28 30-31 29-30 34-32 29-26
lower jaw 24-23 29-28 28-27 25-26 25-23 24-26 24-27 28-28 25-23

Vertebral counts. Vertebral counts range from 139-150 total centra, with 32-36 monospondylous and 107-114 diplospondylous centra (Table 3). Stutter zones of alternating long and short centra were not found. No significant differences in counts were found between males and females.

TABLE 3. Vertebral counts of Schroederichthys ZBK spp.; mono = monospondylous; diplo = diplospondylous; n = number of specimens.

Species mono diplo total source
S. tenuis ZBK (UERJ 1196.1) 36 114 150 present study
S. tenuis ZBK (UERJ 1196.2) 32 113 145 present study
S. tenuis ZBK (USNM 188052; holotype)1 32 107 139 present study
S. tenuis ZBK (USNM 188053; paratype) 34 107 141 present study
S. bivius (n = 1) - - 153 present study
S. chilensis (n = 2) - - 135-139 Compagno (1988)
S. maculatus ZBK (n = 32) - - 132-145 Springer (1979)

Springer (1979) reports 138 total vertebrae for the holotype.

Head skeleton. The head skeleton is formed by the neurocranium and visceral skeleton (jaws, labial cartilages, hyomandibulae, and branchial arches) (Figs. 26-28). The palatoquadrate (PQ) and the Meckel's cartilage (MC) are somewhat slender. The palatine process (PP) is low and positioned behind the nasal capsule (NC). Two small and slender labial cartilages (LC) are present laterally at midjaw, and contact each other on lower jaw. The branchial arches are slightly inclined posteriorly.

Cranial morphology. The neurocranium is widest at nasal capsules (NC), and most narrow between orbits (OR) (Figs. 29-31; cranial measurements are presented in Table 4). Rostral cartilages are slender and not hypercalcified in adults. Lateral rostral cartilages (LR) and medial rostral cartilage (MR) are fused at their tips, forming the rostral node (RN). These three cartilages form a relatively short rostrum, with its length about onefourth of nasobasal length. Bases of lateral rostral cartilages are fused to the dorsal aspect of nasal capsules (NC) (Figs. 29-31). The nasal capsules are relatively large and somewhat oval, with broadly expanded nasal apertures (NA), and extend posteriorly from the rostral cartilages to the preorbital process (PR) dorsally and orbital notch (ON) ventrally. The anterior (precerebral) fontanelle (AF) is longer than wide, with well-defined margins, and extends anteriorly in between the nasal capsules (Fig. 29). Two small foramina are dorsolaterally situated on each nasal capsule, anterior to the preorbital process (Fig. 29). The nasal fontanelles (NF) are visible ventrally (Fig. 30).

The cranial roof extends posteriorly from the anterior fontanelle, at the level of the external foramen for the preorbital canal (FOE), to the parietal fossa (PRF) (Fig. 29). The dorsally situated external profundus nerve foramina (FPE) are smaller than the external foramen for the preorbital canal (FOE). The cranial roof is broadly arched between orbits, forming the supraorbital crests which are perfurated anteriorly by the large external foramina for the preorbital canal and the external profundus nerve foramina, and by numerous small supraorbital foramina (SOF) along the supraorbital groove (SG) (Fig. 29). The basal plate is flat, and lacks both the ectethmoid condyle and subethmoid fossa (Fig. 30), and is very narrow across the prominent orbital notches (ON). The basal plate originates behind the nasal apertures anteriorly, and extends posteriorly to the level of the stapedial foramen. The greatest width across suborbital shelves (SS), at the level of the postorbital processes (PT), is about two-thirds of nasobasal length. Two pairs of arterial foramina are present posteriorlly on the basal plate, one pair for the internal carotids (ICF) and one for the stapedial arteries (SF). The suborbital shelf is laterally straight.

The orbits are broadly oval in lateral view (Fig. 31). The orbital (or prootic) fissure (ORF) is the largest orbital foramen, located posteroventrally anterior to the otic capsule. The small orbital artery foramen (OF) is ventral to the orbital fissure, and the interorbital canal for posterior cerebral vein (IOC) is anterior to it. The foramen for the efferent spiracular artery (FES) is near the suborbital shelf, anterior to the interorbital canal. Almost directly dorsal to the efferent spiracular artery is the oculomotor nerve foramen (III). The orbitonasal foramen (ONF) is just posterior to the nasal capsule and close to the suborbital shelf. Posterior to the orbitonasal foramen is the well developed optic nerve foramen (II), and directly above it is the foramen for the anterior cerebral vein (FCV). The orbital foramen for the deep ophthalmic nerve (FPI) is located ventrally within the orbit, just dorsal to the orbitonasal foramen. The orbital foramen for the preorbital canal (FOI) is positioned more dorsally near the preorbital process. Posteriorly there are two small foramina, the trochlear nerve foramen (IV) and posterior to it the orbitocerebral foramen for the deep ophthalmic nerve (FPC). The foramen for the superficial ophthalmic nerve (FOC) is located near the postorbital process (PT).

FIGURES 26, 27, 28. Head skeleton of Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL, mature male) in lateral (26), dorsal (27), and ventral (28) views. Anterior to left.

FIGURES 29, 30, 31, 32. Neurocranium of Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL, mature male) in dorsal (29), ventral (30), lateral (31), and posterior (32) views. Anterior to top in 29 and 30; anterior to left in 31.

TABLE 4. Cranial measurements of Schroederichthys tenuis ZBK , based on UERJ 1106.2, a 373 mm TL mature female. Measurements in mm and % of nasobasal length.

Measurements mm %
nasobasal length 24
rostral length 6 25.0
basal plate at suborbital notch level 10 45.8
basal plate at occipital level 16 66.6
least width across supraorbital crest 8 33.3
greatest width at nasal capsule level 21 87.5
width of anterior fontanelle 5 20.8
length of anterior fontanelle 9 37.5
otic capsule length 13 54.1

The otic capsules are relatively short, located in between postorbital processes (PT) and occipital region (Figs. 29-31). The otic capsules are not greatly expanded or inflated, their greatest width just greater than one-half of nasobasal length. Dorsally on the otic capsules are the pterotic process (FTP) posterior to the postorbital process, and the sphenopterotic ridge (SR) posterior to the pterotic process. In the center of the otic capsule, the parietal fossa (PRF) bears anteriorly a pair of endolymphatic foramina (FEN) and posteriorly a pair of perilymphatic foramina (FPN). Lateral to these foramina are the anterior semicircular canals (ASC), followed by the posterior semicircular canals (PSC). Laterally, the hyomandibular facet (HF) is well defined, small and horizontally elongate. The opisthotic ridge (ORI) forms the superior margin of the hyomandibular facet. The occipital region presents low and short occiptal condyles (OCC) that do not project posteriorly, with the occipital centrum located in between (OCN). The foramen magnum (FM) is subtriangular. The vagus (X) and glossopharyngeal (IX) nerve foramina are ventrally positioned (Figs. 29, 30, 32).

Hyomandibular and branchial skeleton. The hyomandibular arch is formed by the hyomandibula (HMB), ceratohyal (CH), and basihyal (BH). The hyomandibula is short, about one-half as long as the ceratohyal cartilage. Its ventral extremity articulates with the ceratohyal, and its dorsal aspect articulates with the hyomandibular facet (HF) of the neurocranium (Fig. 31). The ventral portion of the ceratohyal is slightly wider than its dorsal segment, and articulates with the lateral aspect of the basyhial. The basihyal (BH) is a flat plate, widest at its posterior two-thirds, and tapers posteriorly where it contacts the ceratohyals.

The branchial arches are composed of pharyngobranchials (PB), epibranchials (EB), ceratobranchials (CB), hypobranchials (HB), and the basibranchial copula (BBC). There are four independent pharyngobranchials (PB 1-4), all directed posteriorly (Figs. 26, 27, 33). The first and second pharyngobranchials are the longest, and the fourth is the shortest.

The third pharyngobranchial is bifurcated at its base (probably because it incorporates the fourth epibranchial). The fourth and fifth pharyngobranchials may be fused, forming a compound posterior pharyngobranchial element. There are five epibranchials (EB 1-5); the longest are the first and second, while the shortest are the third and fifth. The fourth epibranchial is probably fused to the posterior branch of the third pharyngobranchial (Fig. 33). The five ceratobranchials (CB 1-5) are directed backwards and are about equal in length (Fig. 33). Ceratobranchials 2-3 are widest ventrally where they articulate with the hypobranchials; their ventral segments overlap the anterior portion of the subsequent ceratobranchial. Ceratobranchials 2-4 articulate with hypobranchials ventrally, but ceratobranchial 5 articulates directly with the basibranchial copula (BBC) (Fig. 33). Hypobranchials 2-4 are directed posteriorly towards the basibranchial copula. The first hypobranchial element is lacking, as is an isolated fifth hypobranchial (which is probably incorporated into the basibranchial copula). The second and third hypobranchials are longer and about equal in size, and do not touch the basibranchial copula (their posterior extremities meet each other medially); the fourth hypobranchial is the smallest and its posterior extremity articulates with the anterior portion of the basbranchial copula (Fig. 33). The basibranchial copula is flat, rounded anteriorly, and pointed posteriorly. It articulates laterally with the fourth hypobranchial and the fifth ceratobranchial (Fig. 33).

FIGURE 33. Branchial skeleton of Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL, mature male) in dorsal view, with dorsal elements laterally expanded. Anterior to left.

FIGURES 34, 35. External morphology of right clasper of Schroederichthys tenuis ZBK (CEPNOR uncat, 455 mm TL) in dorsal view (34), with detail of expanded glans (35). Anterior to top.

Claspers . Externally, the claspers are tubular with the glans ending in a pointed extremity. On the clasper shaft, the medial wall (MW, new term) covers the dorsal marginal cartilage (RD) while the lateral wall (LW, new term) covers the ventral marginal cartilage (RV). The clasper groove (CG) is located between the medial and lateral walls (Fig. 34). Anterodorsally, the clasper groove originates at the apopyle (AP), the receiving port of the clasper. Some structures of the external clasper glans are directly supported by skeletal components (Figs. 34, 35). The apex is formed laterally by the lateral terminal margin (LT, new term), which is supported internally by the ventral terminal cartilage, and medially by the medial terminal margin (MT, new term), which is supported by the dorsal terminal cartilage. The rhipidion (RH), situated between the lateral and ventral terminal margins, is an anteroposteriorly elongated flap on the floor of the glans, supported internally by the dorsal terminal 2 cartilage (Fig. 34). The envelope (EN), a medial extension of the lateral wall that covers part of the clasper groove, is a rounded, fleshy and soft flap with no internal support. The exorhipidion (ERH) is a longitudinally elongated and fleshy blade that covers the ventral terminal 2 cartilage and part of the ventral terminal cartilage. It is located laterally between the envelope and the lateral terminal margin (Fig. 34). The cover rhipidion (CRH) is located opposite the exorhipidion, and is an extension of the dorsomedial margin, internally supported by the accessory dorsal marginal cartilage. The pseudosiphon (PSS) is a dorsally opening, blind pocket in the posterior edge of the cover rhipidion, along the medial edge of the clasper. The hypopyle (HP) is the posterior opening of the clasper groove between the cover rhipidion and exorhipidion, anterior to the rhipidion. Dermal denticles (DD) are present on the internal side of the medial wall, envelope, and medial and lateral terminal margins, respectively (Figs. 34, 35).

A single intermediate segment (B1) and beta cartilage (β) are present dorsally in the clasper skeleton, both articulating with the basipterygium (Figs. 36, 37). In dorsal view, the preglans clasper is composed of a pair of semicylindrical marginal cartilages, the dorsal marginal (RD) and the ventral marginal (RV) (Fig. 36). The clasper groove (CG) is located in between the marginal cartilages. In ventral view, the pre-glans clasper is formed by three cartilages, with the axial cartilage (AX), an elongated and flattened rod, fused on both sides to the marginal cartilages (Fig. 37).

Five main cartilages are present in the clasper glans: ventral terminal (TV), ventral terminal 2 (TV 2), dorsal terminal (TD), dorsal terminal 2 (TD 2), and acessory dorsal marginal (RD 2) (Figs. 36, 37). The ventral terminal, the dorsal terminal and the ventral terminal 2 cartilages are lanceolate with pointed apices. The ventral terminal dorsally (Fig. 36), and the ventral terminal 2 ventrally (Fig. 37), are attached to the ventral marginal cartilage. In dorsal view, the subtriangular accessory dorsal marginal cartilage is attached to the dorsal marginal, as is the dorsal terminal cartilage ventrally. The dorsal terminal 2 cartilage lies between the accessory dorsal marginal and the ventral terminal 2, is poorly calcified, and is attached to the floor of the glans. Attached to the dorsal terminal is the small dorsal terminal acessory cartilage (TDA) (Figs. 36, 37). Four small cartilages are visible dorsally (Fig. 37). On the dorsal surface of the accessory dorsal cartilage there are two small elements. The anterior and smallest piece is here termed the accessory marginal cartilage 2 (RD 3). The largest element is here termed the accessory marginal cartilage 3 (RD 4), and is about three times the size of the accessory marginal cartilage 2. Both structures were found also in S. saurisqualus ZBK . Dorsally, between the ventral marginal and the ventral terminal 2 cartilages, are two small cartilages here designated the ventral terminal 3 (TV 3) for the internal piece, and the ventral terminal 4 (TV 4) for the external element.

FIGURES 36, 37. Skeletal components of right clasper of Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL, mature male) in dorsal (36) and ventral (37) view. Anterior to top.

Pectoral skeleton. The pectoral fin skeleton is aplesodic (Fig. 38) with elongated ceratotrichia, which are longer than the fin endoskeleton. The propterygium (PRO) is short with one proximal (PRA), one intermediate (IRA), and one distal (DRA) radial segment. The mesopterygium (MES) is subtriangular, and bears three proximal radial segments fused at their bases. Distally, each proximal radial articulates with one intermediate and one distal radial. The metapterygium (MET) is the largest basal cartilage, articulating with eight proximal radial segments, each with one intermediate and one distal radial segment. The metapterygial axis (MTS) is composed of shorter elements with two segments contacting the metapterygium and two distal segments. There are 12 total radial pieces (pro + meso + metapterygium) (Table 5).

FIGURE 38. Right pectoral fin skeleton of Schroederichthys tenuis ZBK (UERJ 1106.1, 407 mm TL, mature male) in dorsal view. Anterior to top.

TABLE 5. Pectoral radial counts of Schroederichthys ZBK spp.; n = number of specimens.

Species counts source
S. bivius (n = 1) 15 Nakaya (1975)
S. chilensis (n = 1) 13 Compagno (1988)
S. maculatus ZBK (n = 1) 14 Compagno (1988)
S. tenuis ZBK (n = 1) 12 present study

Results and Discussion

Morphological comparisons. Compagno’s (1984) estimate that adults of S. tenuis ZBK reach 700 mm TL was based on the Schroederichthys ZBK specimen from southeastern Brazil deposited in Hamburg and mistakenly identified as S. tenuis ZBK by G. Krefft (see “Introduction” above; Springer, 1979). Specimens of this species ( S. saurisqualus ZBK ) that we examined, including the Hamburg individual, measured 578-590 mm TL, and are all sexually mature. Our observations indicate that S. tenuis ZBK reaches a maximum total length of probably under 500 mm, and that adults definitely have a strongly attenuated body. Species of Schroederichthys ZBK fall within two size classes, one for the small-sized species S. tenuis ZBK and S. maculatus ZBK (with maximum known total lengths 473 mm and 340 mm, respectively), and one including the large-sized species S. bivius , S. chilensis , and S. saurisqualus ZBK (reaching 700 mm TL, 620 mm TL, and 600 mm TL, respectively); we believe, however, that S. saurisqualus ZBK is more closely related to S. tenuis ZBK and S. maculatus ZBK , as detailed below.

According to Springer (1966, 1979) and Compagno (1988), S. chilensis has the highest tooth count (62/56) among congeners, with S. maculatus ZBK intermediate (48-53/36-42) and S. tenuis ZBK with the lowest number of rows (44/34 in the holotype and 26-34/23-29 in the additional specimens examined; no data were available for S. bivius ). Gosztonyi (1973) described for S. bivius from Argentina the same secondary sexual dimorfism in jaw shape reported here for S. tenuis ZBK , which is common among scyliorhinids (Brough, 1937; Nakaya, 1975; Springer, 1979; Gomes and Tomás , 1991; Ellis and Scharley, 1995).

Vertebral counts are less reliable to separate species of Schroederichthys ZBK . Vertebral numbers are higher in adults of S. tenuis ZBK than in the type specimens (both juveniles), but this is probably artificial as counts in juveniles may be negatively affected by weaker calcification (the types of S. tenuis ZBK have 139-141 centra while in adults counts range from 145-150). Compared to S. chilensis (135-139) and S. maculatus ZBK (133-145), Table 3 shows no significant differences between them (data also from Springer, 1979; Compagno, 1988). A specimen of S. bivius (MNHN 1990-1020, a mature female) has slightly higher counts at 153 centra (33 monospondylic and 120 diplospondylic).

Neurocranial morphology is fairly distinct between S. chilensis and S. maculatus ZBK , as shown by Compagno (1988: fig. 13.6). The cranial topography of S. tenuis ZBK is very similar toS. maculatus ZBK and S. saurisqualus ZBK in being relatively straight between the supraorbital crests, in the shape of the nasal capsules and nasal apertures, size and shape of the anterior fontanelle, width of the basal plate, and in the presence of a longitudinal groove between the anterior fontanelle and the base of the rostral cartilages between the nasal capsules (the neurocranium of S. bivius was not seen). Laterally, the cranial roof as well as the supraorbital crests of S. tenuis ZBK are both arched, but in S. chilensis these are straight as described by Leible et al. (1982).

The only description of branchial elements in other species of Schroederichthys ZBK is that of Leible et al. (1982) for S. chilensis , which is generally similar to S. tenuis ZBK . There are differences mainly in the shape and position of the basihyal (longer than wide and articulating posterolaterally with the ceratohyal in S. tenuis ZBK , but wider than long and overlapping the ceratohyal in S. chilensis ). The base of the third pharyngobranchial is not bifurcated in S. chilensis as it is in S. tenuis ZBK . The basibranchial cartilage is unsegmented in S. tenuis ZBK , and does not articulate with the second and third hypobranchials, whereas in S. chilensis the basibranchial is longer, segmented, and articulates with the second to the fourth hypobranchials.

Compagno (1988) described the accessory dorsal terminal 2 cartilage in carcharhinoid sharks as being present in Rhizoprionodon acutus , Halaelurus buergeri , and Halaelurus natalensis . Cunha and Gomes (1994) described this structure also for Rhizoprionodon lalandii and R. porosus . In the present study the accessory dorsal terminal 2 cartilage, as well as a structure herein termed the accessory dorsal terminal 3 cartilage, were found in Schroederichthys tenuis ZBK and S. saurisqualus ZBK . Compagno (1988) affirms that the ventral terminal 2 cartilage is absent in S. chilensis and present in S. maculatus ZBK ; this cartilage is present in S. tenuis ZBK and S. saurisqualus ZBK according to our observations. According to Compagno (1988), the ventral terminal 3 is present in several scyliorhinids and Leptocharias ZBK , and the ventral terminal 4 cartilage occurs in some Galeus spp. and Halaelurus ZBK spp. (both scyliorhinid genera). Both cartilages occur in S. tenuis ZBK . Compagno (1988) verified that the exorhipidion is supported internally by the ventral terminal 2 cartilage; however, both S. tenuis ZBK and S. saurisqualus ZBK have a fleshy exorhipidion without a specific endoskeletal support, and which overlies the ventral terminal and part of the ventral terminal 2 cartilages.

The arrangement of the pectoral skeleton of S. tenuis ZBK is similar to S. chilensis as described by Leible et. al (1982) (undescribed for S. maculatus ZBK and S. bivius ). The number of radial cartilages increases from pro- to metapterygium in species of Schroederichthys ZBK , with S. bivius reaching the highest number and S. tenuis ZBK the lowest (Table 5). More data are required to establish if pectoral radial counts are useful to separate species of Schroederichthys ZBK .

Phylogenetic relationships within Schroederichthys ZBK . According to Melendez et al. (1993), Compagno (1999a) and Compagno et al. (2005), five species of Schroederichthys ZBK are presently recognized: S. bivius (Smith, 1838), S. chilensis (Guichenot, 1848), S. maculatus ZBK Springer, 1966, S. tenuis ZBK Springer, 1966, and S. saurisqualus ZBK Soto, 2003. Our study supports preliminary results that S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK form a monophyletic group, and that S. bivius (Smith, 1838) and S. chilensis (Guichenot, 1848) should be removed from the genus (de Carvalho and Gomes, in prep.). S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK , as mentioned above, share anteroposteriorly elongated nasal apertures and nasal capsules, bulging nasal capsules that abruptly meet at their dorsal midline leaving a dorsal longitudinal groove, anteriorly oval anterior (precerebral) fontanelle with well-defined margins, presence of a small median protuberance at posterior border of anterior fontanelle, slender and laterally compressed neurocranium, slender basal plate, strongly tapered and elongated postpelvic trunk region, among other characters. These features are considered to be derived within the Scyliorhinidae, even though a posterior median protuberance is present in the anterior fontanelle of some species of Poroderma , Halaelurus ZBK , Holohalaelurus ZBK , and Haploblepharus ZBK (probably independently), and Asymbolus analis also has somewhat bulging and elongated nasal capsules, even though these are distinct from S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK (Compagno, 1988). The distribution of the ventral terminal 2 cartilage, present in S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK , is presently unknown within the Scyliorhinidae, as is the accessory dorsal terminal 3 cartilage, reported here in S. tenuis ZBK and S. saurisqualus ZBK (unknown for S. maculatus ZBK ). There are also significant distinctions in the gill arch skeleton of S. tenuis ZBK and S. chilensis , but the branchial skeleton of other species of Schroederichthys ZBK needs to be described to reveal if it supports the monophyly of S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK . The nasal flap of S. saurisqualus ZBK is broad and more similar to that of S. maculatus ZBK than to the elongated nasal flap of S. tenuis ZBK , but the phylogenetic significance of nasal flap morphology is questionable, as S. bivius has nasal flaps resembling S. tenuis ZBK and S. chilensis has nasal flaps more similar to S. maculatus ZBK . Gomes and de Carvalho (1995) reported that the suedelike texture, opacity and color of the egg-capsules of S. maculatus ZBK and S. tenuis ZBK was derived, a condition later found in S. saurisqualus ZBK but not in S. bivius and S. chilensis (Soto, 2003), further corroborating the monophyly of S. maculatus ZBK , S. tenuis ZBK and S. saurisqualus ZBK . Historically, S. bivius and S. chilensis have been placed either in Halaelurus ZBK , Scyliorhinus ZBK or Schroederichthys ZBK (for a review of their classification, see Springer, 1979; Compagno, 1988), but in our view their systematic fate is still undetermined within the family.

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