Taxonomy and morphology of the skate genus Atlantoraja (Rajiformes: Arhynchobatidae)

Soares, Karla D. A.; Moreira, Renan A.; Silva, Rafael F. L. da; Gomes, Ulisses L.

doi:10.1590/1982-0224-2021-0096

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Original Article • Neotrop. ichthyol. 19 (04) • 2021 • https://doi.org/10.1590/1982-0224-2021-0096 copy

Taxonomy and morphology of the skate genus Atlantoraja (Rajiformes: Arhynchobatidae)

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The skate genus Atlantoraja is composed of three species (A. castelnaui, A. cyclophora, and A. platana) which differ from the other Riorajini species, Rioraja agassizii, in regards to their clasper features, squamation and presence of a caudal fin. Despite of being distributed along Southwestern Atlantic and commonly captured by fisheries in Brazil, Uruguay and Argentina, detailed accounts on external and internal morphology are scarce and the taxonomic status of Atlantoraja species was not revised so far. The aim of this study, therefore, is to review the taxonomy of the genus Atlantoraja, updating information on type specimens and clarifying misidentifications among species, and to describe in detail anatomical structures such as neurocranium, visceral arches, pelvic girdle, dermal denticles and teeth. Lectotypes and paralectotypes are designated for Atlantoraja castelnaui and A. cyclophora. Notes on intraspecific variation within species are also provided. Atlantoraja cyclophora and A. platana are more similar to each other than to A. castelnaui in regards to the squamation (body dorsal surface smooth vs. densely covered by prickles) and color pattern of body dorsal surface, position of orbital foramina, overall shape of neucrocranium and body measurements. Lastly, we discuss the morphological differences among species of Atlantoraja and recommend the inclusion of characters presented here in future cladistic analyses.

Keywords:
Anatomy; Atlantoraja castelnaui; Atlantoraja cyclophora; Atlantoraja platana; Taxonomic review

Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá., Av. Colombo, 5790, 87020-900, Phone number: +55 44-3011-4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br

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Jennifer Wyffels

Measurements	MNRJ 608 (mm)	Range (mm)	Range (%)	Mean (mm)	Mean (%)
Total length (TL)	318.2	675–828	100	747.5	100
Disc width	180.3	468–559	67.5–69.3	513.5	68.7
Caudal length	167.2	298–334	40.3–44.0	316.0	42.3
Disc length	142.5	350–444	51.8–53.6	397.0	53.1
Preorbital length	34.9	92–118	13.6–14.2	105.0	14.0
Prenasal length	20.4	54–78	8.0–9.4	66.0	8.8
Internasal distance	21.6	53–62	7.5–7.8	57.5	7.7
Eye diameter	11.9	8–14	1.2–1.7	11.0	1.5
Interorbital distance	14.5	35–48	5.2–5.8	4.5	5.5
Preoral length	35.7	72–99	10.7–11.9	85.9	11.5
Snout-vent length	–	321–397	47.5–47.9	359.0	48.0
Mouth width	24.8	51–68	7.5–8.2	59.5	7.9
Distance from first dorsal fin origin to posterior end of caudal fin	–	110–131	15.8–16.3	120.5	16.1
Distance from posterior margin of pelvic fin to first dorsal fin origin	–	165–195	23.5–24.4	180.0	24.1
First gill slit width	3.9	12–13	1.6–1.8	12.0	1.6
Third gill slit width	–	11–12	1.6–1.8	11.5	1.5
Fifth gill slit width	1.2	7–10	1.0–1.2	8.5	11.4
Distance between first gill slits	36.8	102–118	14.2–15.1	110.0	14.7
Distance between fifth gill slits	28.1	71–74	8.9–10.2	72.5	9.7

Counts	A. castelnaui	A. cyclophora	A. platana
Rostral thorns	5–6	none	none
Preorbital thorns	3–4	none	none
Interorbital thorns	3–4	none	none
Midorbital thorns	3–4	none	none
Postorbital thorns	3–4	none	none
Spiracular thorns	3–4	none	none
Interspiracular thorns	3–4	none	none
Nuchal thorns	6–7	none	none
Scapular thorns	5–6	none	none
Mediocaudal thorns	12–20	4–13	9–15
Interdorsal thorns	2–3	1–3	1–3
Alar thorns	*	88–93	58–76
Alar thorns (rows)	–	6	4

Measurements	Females (n = 5)		Male (n = 1)
Measurements	Range	Mean
Neurocranium length	145.8–175.0	156.3	123
Rostral cartilage length	56.3–70.8	61.9	–
Neurocranium width	85.0–104.2	95.0	–
Interorbital distance	33.3–38.5	35.0	34.4
Rostral base width	16.7–23.8	20.3	22.9
Anterior fontanelle length	40.0–44.0	41.8	–
Anterior fontanelle width	16.3–17.5	16.8	16.4
Epihyseal bridge length	22.5–26.4	24.2	–
Posterior fontanelle length	18.7–18.8	18.8	–
Posterior fontanelle width	7.5–8.0	8.0	9.8
Width across otic capsules	42.5–50.0	47.0	42.6
Basal plate width	23.8–37.5	33.0	23.0
Nasal aperture width	38.8–45.8	41.9	41.0
Internasal distance	13.8–16.7	15.5	13.1

Measurements	Range (mm)	Range (%)	Mean (mm)	Mean (%)
Total length (TL)	504–576	100	551	100
Disc width	371–435	73.6–75.5	410.8	74.5
Caudal length	223–256	44.2–44.4	240.9	43.7
Disc length	259–319	51.4–55.3	296.1	53.6
Preorbital length	72–84	14.3–14.6	77.6	14.1
Prenasal length	52–64	10.3–11.1	56.9	10.3
Internasal distance	32–39	6.3–6.8	36.3	6.6
Eye diameter	15–21	3.0–3.6	17.2	3.1
Interorbital distance	18–23	3.6–4.0	20.2	3.7
Preoral distance	61–75	12.1–13.0	69.3	12.6
Snout-vent length	238–285	47.2–49.5	268.4	48.7
Mouth width	38–45	7.5–7.88	41.0	7.4
Distance from first dorsal fin origin to posterior end of caudal fin	96–114	19.0–19.8	107.2	19.4
Distance from posterior margin of pelvic fin to first dorsal fin origin	94–114	18.6–19.8	106.6	19.3
First gill slit width	8–10	1.6–1.7	9.0	1.6
Third gill slit width	7–11	1.4–1.9	9.2	1.7
Fifth gill slit width	4–9	0.8–1.6	5.6	1.0
Distance between first gill slits	63–78	12.5–13.5	72.8	13.2
Distance between fifth gill slits	32–50	6.3–8.4	42.4	7.7

Measurements	Females (n = 20)		Males (n = 10)
Measurements	Range	Mean	Range	Mean
Neurocranium length	144.9–200.0	180.6	170.0–191.7	182.0
Rostral cartilage length	68.2–98.4	84.0	70.0–92.0	83.5
Neurocranium width	82.8–100	92.6	82.0–97.2	88.2
Interorbital distance	25.8–35.3	28.8	26.0–33.3	29.8
Rostral base width	17.2–28.6	21.3	11.9–22.2	17.5
Anterior fontanelle length	41.5-49.0	45.1	38.0–45.7	42.7
Anterior fontanelle width	9.0–16.7	12.6	10.0–14.0	11.3
Epiphysial bridge length	20.0–31.7	23.2	22.0–26.1	24.0
Posterior fontanelle length	16.7–25.5	20.0	17.4–22.0	17.9
Posterior fontanelle width	5.8–14.2	8.6	6.0–9.5	8.1
Width across otic capsules	42.4–49.0	45.9	44.0–48.0	45.3
Basal plate width	18.0–28.6	21.8	17.2–21.7	19.6
Nasal aperture width	38.0–45.5	42.2	36.0–45.7	40.5
Internasal distance	10.8–19.0	12.3	10.0–12.0	11.1

Measurements	Range (mm)	Range (%)	Mean (mm)	Mean (%)
Total length (TL)	533–755	100	681.7	100
Disc width	484–620	82.1–90.8	555.9	82.5
Caudal length	227–303	40.1–42.6	279.1	40.9
Disc length	336–492	63.0–65.1	408.0	640
Preorbital length	77–140	14.4–18.5	101.4	14.8
Prenasal length	55–78	8.2–10.3	65.9	9.7
Internasal distance	44–63	8.2–8.3	50.7	8.2
Eye diameter	15–24	2.8–3.2	19.9	2.9
Interorbital distance	24–40	4.5–5.3	31.6	4.7
Preoral distance	62–95	11.6–12.6	82.1	12.0
Snout-vent length	277–397	52.0–52.6	344.0	52.4
Mouth width	50–63	8.3–9.4	57.3	8.5
Distance from first dorsal fin origin to posterior end of caudal fin	75–159	14.1–21.0	135.7	18.6
Distance from posterior margin of pelvic fin to first dorsal fin origin	94–128	16.9–17.6	114.0	17.2
First gill slit width	9–13	1.7	11.0	1.7
Third gill slit width	8–13	1.5–1.7	11.1	1.6
Fifth gill slit width	5–9	0.9–1.2	7.2	1.1
Distance between first gill slits	81–112	14.8–15.2	101.0	15.0
Distance between fifth gill slits	43–68	8.1–9.0	55.6	8.6

Measurements	Females (n = 7)		Males (n = 3)
Measurements	Range	Mean	Range	Mean
Neurocranial length	114.0–180.2	147.5	149.4–169.6	161.2
Rostral cartilage length	53.6–80.2	70.8	49.4–69.6	61.2
Neurocranium width	84.9–92.8	88.9	83.5–84.8	84.0
Interorbital distance	26.7–36.1	32.3	30.4–32.9	32.1
Rostral base width	22.0–27.0	23.9	21.5–24.0	22.8
Anterior fontanelle length	38.9–47.6	43.6	44.3–49.4	46.4
Anterior fontanelle width	11.6–19.4	14.3	7.6–12.7	11.0
Epiphysial bridge length	21.4–27.8	23.4	22.8–28.0	25.4
Posterior fontanelle length	16.3–20.2	18.0	17.7–20.3	18.6
Posterior fontanelle width	5.6–9.3	7.5	7.6	7.6
Width across otic capsules	20.0–44.9	39.1	41.7–43.0	42.2
Basal plate width	19.8–25.0	23.2	20.2–21.5	21.1
Nasal aperture width	36.0–47.2	39.2	35.4–36.7	36.3
Internasal distance	11.6–16.7	14.1	11.4–12.7	11.8

Characters	*A. castelnaui*	*A. cyclophora*	*A. platana*
Body dorsal surface	Densely covered by prickles and thorns	Smooth	Smooth
Nasal capsule	Strongly oblique to the anteroposterior axis	Slightly oblique to the anteroposterior axis	Perpendicular to the anteroposterior axis
Anterior region of cranial roof	Broad	Slender	Slender
Anterior extension of anterior fontanelle	Half-length of rostral cartilage	Posterior fourth of rostral cartilage	Posterior fourth of rostral cartilage
Posterior fontanelle	Subrectangular	Teardrop-shaped	Teardrop-shaped
Preorbital process	Inconspicuous	Conspicuous	Conspicuous
Foramen for the trochlear nerve (IV)	Dorsal to the foramen for the optic nerve (II)	On the same line of foramen for the optic nerve (II)	Dorsal to the foramen for the optic nerve (II)
Foramen of the optic nerve (II)	Posterior to half-length of orbital wall	Anterior to half-length of orbital wall	Anterior to half-length of orbital wall
Optic pedicel	Between the foramina for oculomotor and the abducens nerves	Ventral to the foramen for the abducens nerve (VI)	Ventral to the foramen for the abducens nerve (VI)
Foramen for the abducens nerve (VI)	Closer to the posterior margin of orbital wall	Closer to the half-length of orbital wall	Closer to the half-length of orbital wall