Accepted by M. de Carvalho: 1 Nov. 2006; published: 18 Jan. 2007 1
ISSN 1175-5326 (print edition)
ISSN 1175-5334 (online edition)
Copyright © 2007 · Magnolia Press
Zootaxa 1393: 1–18 (2007)
Descriptions of skate egg cases (Chondrichthyes: Rajiformes: Rajoidei) from the
eastern North Pacific
DAVID A. EBERT & CHANTE D. DAVIS
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA. 95039, U.S.A.; ph.
831-771-4427; fax 831-632-4403. E-mail: email@example.com
Egg cases for 10 of 11 valid skate species known to occur in the eastern North Pacific (ENP) were identified and are here
described. In addition, egg cases of two unidentified skate species were collected from very deep water off central and
southern California, USA. Examples of egg cases for all species, except for two, were removed in utero in order to con-
firm their species specific identification. The egg cases of seven skate species, including egg cases from the two uniden-
tified species, have not previously been described or illustrated from this region. Previous attempts to identify skate egg
cases with their associated species have been inadequate. The ENP skate egg cases can broadly be classified into two
main groups: those with broad lateral keels (> 10% maximum egg case width) and those with narrow lateral keels (<
10% maximum egg case width). Egg cases in the former group (with broad lateral keels) generally have a finely striated
surface texture that is smooth to the touch. Those in the latter group (with narrow lateral keels), with one exception, tend
to have a coarse surface texture, often with prickles, and are rough to the touch. A revised key to the skate egg cases from
the ENP is provided.
Key words: Amblyraja, Bathyraja, Raja, skate egg cases, eastern North Pacific
Skates are the most diverse elasmobranch group, comprising over 20% of the known species for this group of
fishes (Compagno, 2005). These flatsharks, as they are sometimes called, occur from nearshore to the outer
continental shelf in cool temperate to polar waters and in the deepsea. The number of species within this elas-
mobranch group is likely to increase as taxonomic issues are resolved and new species are identified. One
method by which skate species may be distinguished from each other is by their egg case morphology. The
egg case morphology of each skate species, like the claspers on males, is unique to that species and can be
used in its identification (Ishiyama, 1958a).
The use of skate egg cases as a taxonomic tool for species identification and to study their phylogenetic
relationships is well known (Ishiyama, 1958a, b; Hubbs & Ishiyama, 1968; Ishiyama & Hubbs, 1968). How-
ever, identification of species specific egg cases is often wanting as researchers often assume, incorrectly, that
an egg case came from a certain species since the species in question is known to occur in a particular area.
Often this assumption does not account for the possibility of non-resident species migrating into an area,
depositing their egg cases, and then leaving. Therefore, proper identification of egg cases associated with the
correct species can be erroneous if they are not removed from the adult female in utero.
Since 2002, researchers from the Pacific Shark Research Center (PSRC), Moss Landing Marine Laborato-
ries (MLML), have been studying the life history and systematics of eastern North Pacific (ENP) skates,
including those found in the Bering Sea (Ebert, 2005) and Gulf of Alaska. As part of this research program we
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have been removing egg cases in utero from females that have been necropsied. Cox (1963) described the egg
cases of several elasmobranchs, including those of six skates, from California waters and provided a key to
their identification. However, Cox (1963) did not indicate how he was able to identify the species he associ-
ated with each egg case. Upon examination of the photographs figured by Cox (1963) it appears that some of
these egg cases were collected in situ and were not removed from the female. Thus, creating some uncertainty
as to whether the egg cases he figured actually came from the species he associated them with. In fact, upon
review we have determined that several of the egg cases depicted by Cox (1963) were incorrectly identified
and or inadequately described. Furthermore, since this work was published five additional skate species have
been recorded from ENP waters. Therefore, given the improved state of knowledge on skate distribution and
occurrence in ENP waters (Ebert, 2003), and the usefulness of skate egg cases as a taxonomic identification
tool we present a new and revised description, and key, to the egg cases of ENP skates.
Materials and methods
The study area ranged between Cape Flattery, Washington (47°20’ N, 125°25’ W) and southern California
(32°40’ N 117°33’ W). Skates collected during survey cruises conducted by the NOAA Fisheries Southwest
Fisheries Science Center (SWFSC), Santa Cruz, California laboratory and the Northwest Fisheries Science
Center (NWFSC), Newport, Oregon laboratory were subsequently returned to MLML and necropsied. Egg
cases found in utero during necropsies were removed and fixed in 10% buffered formalin, and subsequently
preserved in 70% ethanol. Egg cases were also collected, after deposition, from specimens maintained in
holding tanks at the Monterey Bay Aquarium (MBA). Additionally, a near-term embryo removed from one
egg case (CAS 25617) and six unidentified egg cases collected in situ from very deepwater by a remote oper-
ated vehicle (ROV) were also examined. Egg cases from each species examined were subsequently deposited
in collections at the California Academy of Sciences (CAS), MLML, or Scripps Institute of Oceanography
Egg cases were described and measured following Ishiyama and Ishihara (1977) with some modifications
and additions. The skate egg case or capsule is usually rectangular in shape with a horny process at each cor-
ner with a more or less loosely closed, concave, anterior margin through which the embryo emerges at hatch-
ing in most cases and a more or less flattened posterior margin that is tightly fused. The dorsal and ventral
surfaces are more or less convex, with the dorsal surface being more domed than the ventral. Lengthwise the
sides are generally keeled, or flanged, from very narrow to very broad. Lateral keels on some species may
extend onto anterior and or posterior horns. The horns vary from very short, less than the case length, to very
long, more than two times case length, with the horns tapering, becoming filamentous, thread-like, or flatten-
ing towards the tips. Some egg cases may have fibrous sheets of byssus-like material present on the surface of
the egg case structure. This fibrous covering may be variably thin and loose to rather thick and tight fitting.
The lateral margins of some cases, depending on the species, may have attachment fibers. The location of
attachment fibers, if present, varies between species. The dorsal and or ventral surfaces of the case can be
smooth and glossy or covered by longitudinal ridges or striations that can be straight or undulated and smooth
or papillose and can give the surface a rough to velvety texture or matte appearance.
Egg case measurements and abbreviations include (Figure 1): Egg case length (ECL), used as an indepen-
dent variable for proportional dimensions of other egg case structures and measured longitudinally between
the anterior and posterior apron borders; anterior border width (ABW) is the distance between the bases of the
anterior horns; anterior horn length (AHL) is the distance from the horn base to the tips; posterior border
width (PBW) is the distance between the bases of the posterior horns; posterior horn length (PHL) is the dis-
tance from the posterior horn base to the tips; maximum case width (MAW), the transverse width of the case
in its lateral plane at its widest part of the case; minimum case width (MIW), the transverse width of the case
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DESCRIPTIONS OF SKATE EGG CASES
in its lateral plane at its narrowest part of the case; lateral keel width (LKW) is the distance from the capsule
keel junction to the keel edge.
FIGURE 1. Skate egg case terminology and measurements.
Egg case descriptions
Amblyraja badia (Garman, 1899)
Remarks: Originally described from off Panama, this species has subsequently been reported from the ENP,
north to the Bering Sea and westward to Japanese waters (Ebert, 2003). This is the only ENP species for
which we have been unable to positively identify egg cases. Garman (1899) noted two egg cases that were
dredged up during the Albatross expedition of 1891, the same expedition in which the holotype of A. badia
was collected. However, the egg cases were collected at a different, although nearby, location from where the
A. badia was caught. Therefore, it is uncertain whether these egg cases belong to that species. The egg cases
were described by Garman (1899) as “covered with fine villi or pile, in longitudinal series, though harsh to the
touch gives the appearance of a soft rich black velvet”. We attempted to locate these egg cases that were
accessioned at the Museum of Comparative Zoology (MCZ 1009 and 1010), Harvard University for further
examination, but they appear to have been lost (Ann Holmes, curator, MCZ, pers. comm.).
Bathyraja abyssicola (Gilbert, 1896)
Description: The egg cases of Bathyraja abyssicola (Figure 2) are large, 108 to 111 mm in length, with MAW
about 67–69% of ECL. Egg case surface texture coarse and very rough to the touch, striated, the surface is
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irregular and with rasp-like denticles. LKW is very narrow, < 5% of MAW and with a distinct groove between
the lateral keel and case proper. This groove is not present in any other ENP skate egg case. Lateral keels
extend onto horns and are also present on inner horns. Anterior apron border of egg case broad and concave,
anterior horns more robust than posteriors at base, becoming flattened and thread-like at tips. Posterior apron
is nearly straight, broad, and transverse, about 10 mm wider than anterior apron. Posterior horns long, about
two times length of anteriors and about 1.2 times ECL, curved inwards, each tapering to a thread-like tip.
Attachment fibers present, originating on lateral keel near the junction of exterior base of posterior horns and
case. Egg cases removed from a single specimen was a light golden brown in color.
Remarks: Bathyraja abyssicola is a large, deepwater species usually found on the continental slope
between 362 and 2906 m, although most records of its capture have come from > 1,000 m deep (Zorzi &
Anderson, 1988). It is considered to be a rare species, but recent deepwater surveys along the ENP continen-
tal slope have revealed this skate to be more common than previously thought (unpublished data). To the best
of our knowledge this is the first confirmed record and description of the egg case of this species.
Material examined: CAS 224336, 141.0 cm TL, west of Alexander Island, Washington (47.4935 N, -
125.5185 W), 1428 m, 24 August 2004.
FIGURE 2. Egg case of Bathyraja abyssicola. Scale bar 20 mm.
Bathyraja aleutica (Gilbert, 1896)
Description: The egg cases of Bathyraja aleutica (Figure 3) are very large, >120 mm in length, with MAW
about 73–76% of ECL. Egg case surface very coarse, striated, and with long anteriorly directed prickles giv-
ing it a velvety texture. Lateral keels very narrow, about 6–7% of MAW. Attachment fibers present, originat-
ing near base of posterior horns. Anterior apron border broad and concave, similar in width to the posterior.
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DESCRIPTIONS OF SKATE EGG CASES
Anterior horns relatively short, about 60–80% of ECL, curved inwards, tapering towards tips, becoming thin
and filamentous. Posterior apron straight, broad, transverse, posterior horns longer than anteriors and about
90% or more length of egg case, tapering towards tips with tendrils coiling towards filamentous tips. Color
after preservation a golden brown, lighter along lateral keels.
Remarks: A common species in the Bering Sea and Gulf of Alaska its southern range is now known to
extend into northern California (Hoff, 2002; Ebert, 2003).
Material examined: CAS 224337, 138.0 cm TL, eastern Bering Sea (56.1972 N, 169.7457 W), 242 m, 17
June 2002; MLML uncatalogued, 136.0 cm TL, eastern Bering Sea (60.3806 N, -178.6524 W), 295 m, 29
June 2002; MLML uncatalogued, 134.9.0 cm TL, eastern Bering Sea (60.3806 N, -178.6524 W), 295 m, 29
FIGURE 3. Egg case of Bathyraja aleutica. Scale bar 20 mm.
Bathyraja kincaidii (Garman, 1908)
Description: The egg cases of Bathyraja kincaidii (Figure 4) are very small, 50 to 66 mm in length, with
MAW about 76–91% of ECL. Egg case dorsal surface covered with thin layer of fine fibers, ventral surface
with either a very thin fibrous layer or without. Surface of egg case beneath fibrous layer finely striated with
longitudinal rows and smooth to the touch. LKW very broad, about 14–19% of MAW, and extending length of
case including outer edge of horns; a keel is present along inner edge of the posterior horns, but absent on
anterior horns. Attachment fibers present along entire edge of lateral keels. Anterior apron border broad, con-
cave; anterior horns about 50–80% ECL, and flattening towards tips becoming thread-like. Anterior horns
curve perpendicular to dorsal aspect of egg case and hooking rearward. Posterior apron border broad, nearly
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straight, transverse, about 3–9 mm wider than anterior apron. Posterior horns moderately long, length similar
to ECL, curved inward to median aspect of egg case, flattening toward tips, and becoming thread-like. Egg
cases from preserved specimens range from a light to dark brown except for lateral keels which are usually
lighter brown to gold colored.
Remarks: The egg case described and depicted by Cox (1963) for this species appears to be consistent
with our findings in that it is a small egg case, nearly as wide as long, has attachment fibers present, and prom-
inent lateral keels. Our description differs in that we found the egg cases of B. kincaidii to be smooth to the
touch while Cox (1963) described the surface texture as moderately rough. Since we do not know the location
of where those egg cases were collected or their eventual deposition we are unable to directly compare our
egg cases with those of Cox (1963). It may be that the slight differences we observed in our samples are
within the normal range of variability. Bathyraja kincaidii, however, may represent a species complex of two
or more distinct, sympatrically occurring species ranging between the Gulf of Alaska and California. There-
fore, careful examination of egg cases from throughout this region may help elucidate this question.
Material examined: CAS 224339, 48.2 cm TL, off Davenport, California (ca 36.5368 N, -122.1445 W),
170 m, 3 August 2002; MLML BK0209-6, 50.1 cm TL, off Davenport, California, (ca 36.5368 N, -122.1445
W), 181 m, 21 September 2002; MLML BK0210-7: 50.0 cm TL, off Davenport, California (ca 36.5596 N, -
122.2220 W), 311 m, 24 October 2003; MLML BK121503-4-1, 53.5 cm TL, off central Oregon (45.7385 N,
-124.3820 W), 153 m, 13 September 2003; MLML BK102403-02-3, 56.9 cm TL, off northern California
(40.2276 N, -124.5422 W), 360 m, 5 October 2003.
FIGURE 4. Egg case of Bathyraja kincaidii. Scale bar 20 mm.
Bathyraja microtrachys (Osburn & Nichols, 1916)
Description: The egg cases of Bathyraja microtrachys (Figure 5) are small, 79 to 81 mm in length, with
MAW about 63–64% of ECL. The egg case surface is coarsely striated, with irregular rasp-like denticles,
making its texture very rough to the touch. LKW is very narrow, < 5% of MAW and not extending onto horns.
Anterior apron border of egg case broad, deeply concave, anterior horns robust at base, but flattening towards
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DESCRIPTIONS OF SKATE EGG CASES
tips and becoming thread-like, tips curving dorsally and back towards egg case. Posterior apron is nearly
straight, broad, and transverse, width similar to anterior. Posterior horns robust at base, very long, about 66%
length of anteriors and about 1.1 times ECL, curved inwards, each tapering to a thread-like tip. Attachment
fibers present, extending length of lateral keel. Egg cases removed from a single preserved specimen were a
dark golden brown.
Remarks: This is the first confirmed record, and description, of the egg case of this species. The egg
cases described here were removed in utero from a 62.8 cm TL specimen (SIO 8780). Cox (1963: Figure 7)
suggested that the egg case he described and illustrated as B. trachura may eventually prove to be this species.
However, the term embryo that was removed from that egg case (CAS 25617), and described below, appear to
be that of B. spinossisima (Ebert, 2005).
Until recently this species had been considered a synonym of B. trachura (Ebert, 2003). However, exami-
nation of the holotypes of B. microtrachys and B. trachura by the senior author, plus additional material con-
firm that these species are distinct. To further separate these two species their egg cases can be used to
distinguish them from each other. The egg case of B. microtrachys differs from that of B. trachura in that the
former has very narrow lateral keels and a coarsely striated surface texture that is rough to the touch, while the
latter has very broad lateral keels and is smooth to the touch.
Bathyraja microtrachys is one of the deepest occurring skate species, known to occur down to at least
3,100 m (unpublished data). The shallowest record of this species is the holotype known from 1,995 m. All
other records of it have come from depths greater than 2,000 m.
Material examined: SIO 8780, 62.8 cm TL, off Waldport, Oregon (44.4130 N, -125.3410 W), 2850 m, 6
FIGURE 5. Egg case of Bathyraja microtrachys. Scale bar 20 mm.
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Bathyraja spinossisima (Beebe & Tee-Van, 1941)
Description: The egg case of Bathyraja spinossisima (Figure 6) is large, about 92 mm in length excluding
horns, with MAW of 73% ECL. The surface is weakly striated, with both dorsal and ventral surfaces being
plush to the touch. LKW is very narrow, about 3% of ECL, and extending onto horns. Attachment fibers are
absent. Anterior apron broadly concaved, curving perpendicular from horizontal plane of egg case, and nar-
rowing at tips. Posterior apron about 7 mm wider than anterior, nearly straight, broad, and transverse. Poste-
rior horns about two-thirds ECL, curved inwards, and narrowing to tips. Egg case color after preservation is a
uniform plum brown.
FIGURE 6. Egg case of Bathyraja spinossisima. Scale bar 20 mm.
Remarks: A single egg case originally identified by Follett (1952: Figure 1) as that of Bathyraja trachura
based on a near term embryo found inside was subsequently described by Cox (1963). This egg case has also
been inaccurately illustrated in the literature as being that of B. trachura (Eschmeyer et al., 1983; Mecklen-
berg et al., 2002; Ebert, 2003). However, Ebert (2005) examined this egg case and embryo (CAS 25617), and
compared it with egg cases removed in utero from B. trachura, and concluded that the embryo fit that of the
holotype of B. spinossisima. Miller and Lea (1972) first reported the occurrence of B. spinossisma from the
ENP based on this specimen, but without explanation, only giving the museum catalogue number where it is
deposited. At the time Follett (1952) and Cox (1963) identified this egg case as B. trachura, B. spinossisima
had not been reported from the ENP.
The holotype of B. spinossisima is an embryo that had been removed from an egg case collected in very
deepwater off Panama. Interestingly, a pair of egg cases also collected off Panama, in very deepwater, by Gar-
man (1899) in some aspects appears to fit the description of this species. Unfortunately, the egg case for the
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DESCRIPTIONS OF SKATE EGG CASES
holotype of B. spinossisima and Garman’s egg cases have been lost.
Material examined: CAS 25617, egg case with embryo present, Mulberry Seamount, 78 km west of
Point Montara, central California (37.2630 N, -123.2842 W), 1400 to 2000 m, 8 February 1950.
Bathyraja trachura (Gilbert, 1892)
Description: The egg cases of Bathyraja trachura (Figure 7) are small, 62 to 78 mm in length, with MAW
about 77–97% of ECL. Egg case surfaces with prominent longitudinal striations and smooth to the touch.
LKW very broad, striated, about 15–20% of MAW, and extending length of case including outer edge of
horns; an inner keel is present along edge of both anterior and posterior horns. Attachment fibers present
along lateral keels, originating about outer base of posterior horns. Anterior apron border broad and concave,
anterior horns about one-half ECL, horns curved inwards toward median plane of egg case, tips curling
towards ventral aspect of egg case, and flattening towards tips. Posterior apron nearly straight, broad, trans-
verse, and up to 7 mm wider than posterior apron. Posterior horn length variable, 0.8 to 1.4 times ECL, horns
curved inwards to median plane of egg case, and flattening towards tips. A distinct crossbar originating mid-
way along posterior horns was present on six of nine egg case pairs. One pair had evidence of an incompletely
formed crossbar and two had no evidence. This crossbar is unique among ENP skates. Color after preserva-
tion a dark brown becoming a light golden brown on keels.
FIGURE 7. Egg case of Bathyraja trachura. Arrow denotes crossbar (broken). Scale bar 20 mm.
Remarks: Ebert (2005) described the egg case of this species, based on material from the eastern Bering
Sea, and commented that the egg case described and figured by Cox (1963) as B. trachura was not that spe-
cies. The egg case figured by Cox (1963: Figure 5), and captioned as Raja stellulata, is actually that of B. tra-
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The posterior horns on some B. trachura egg cases, 75% in this study, have a unique crossbar that is not
present on any of the other skate egg cases that we have examined from this region (Figure 7). In some
instances the crossbar was broken or missing. Whether the crossbar remains intact, or for how long, once the
egg case is deposited on the seafloor is unknown as we did not obtain any egg cases of this species in situ.
Material examined: CAS 224340, 79.1 cm TL, off central Oregon (45.3862 N, -125.5707 W) 924 m, 3
September 2004; MLML BT 100804-1-6, 86.5 cm TL, off central Oregon (45.3862 N, -125.5771 W), 929 m,
3 September 2004; MLML BT 110504-2-3, 66.3 cm TL, off northern California (37.0453 N, -120.3272 W),
1101 m, 12 October 2004; MLML BT 031105-04, 789 mm TL, off northern California (38.5142 N, -122.6890
W), 320 m, 17 February 2005; MLML BT 011205-19, 78.7 cm TL, off central California (36.2502 N, -
122.0718 W), 366 m, 6 January 2005.
FIGURE 8. Egg case of Raja binoculata. Scale bar 20 mm.
Raja binoculata Girard, 1854
Description: The egg cases of Raja binoculata (Figure 8) are perhaps the most distinctive skate egg case
found in the ENP. The dorsal surface is convex with two prominent ridges; no other known ENP skate egg
case has these ridges. These are very large egg cases, 210 to 280 mm in length from anterior to posterior apron
borders, with a MAW about 52% of ECL. Egg case surface very smooth, without striations or fibrous cover-
ing. Under magnification the surface appears smooth and without striations. LKW very broad, about 30–33%
of MAW, narrowing to about 4–6% at MIW, and extending length of egg case including outer edge of horns;
keels also along inner edge of horns. Attachment fibers not present. Anterior apron border broad, slightly
concave, fraying along edge, anterior horns about 28–30% of ECL, curving dorsally, with tips flattening and
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DESCRIPTIONS OF SKATE EGG CASES
curling toward egg case. Posterior apron broad, transverse, and fraying at edge, its width less than that of
anterior. Posterior horns short, stout, about 32–38% ECL, horn base width about 24% of horn length; horns
curved, and flattening towards tips. Lateral keels extend beyond horn length. Color of egg case after preserva-
tion a dark brown to greenish brown.
Remarks: The egg case of R. binoculata is perhaps the largest egg case of any known skate species, with
a maximum known length, excluding horns, exceeding 300 mm (Hitz, 1964). Raja binoculata is the only
skate species, except for R. pulchra Liu, 1932, known to have multiple embryos per egg case. These skates
may have 2–7 embryos, with an average of 3–4 per egg case (Hitz, 1964). The Japanese endemic R. pulchra
is known to have 1–5 embryos per egg case (Ishiyama, 1958b). Although it has not been studied in detail,
increased fecundity, due to multiple oviparity, in these species may have significant conservation implica-
tions. Raja binoculata is known to produce up to 360 egg cases per year in captivity (Kevin Lewand,
Monterey Bay Aquarium, pers. comm.). Assuming an average of 3.5 embryos per egg case the annual fecun-
dity may reach 1,260 neonates, or more, making it one of the most fecund of all elasmobranchs.
Material examined: CAS 224341, northern California (38.033 N, -123.1237 W), 78 m, 24 September
2004; MLML RB 102403-4-06, 146.7 cm TL, central California (36.4076 N, -121.5276 W), 69 m, 22 October
2003; MLML EX 58, southern Oregon (44.311 N,
-124.257 W), 71 m, 4 September 2004.
FIGURE 9. Egg case of Raja inornata. Scale bar 20 mm.
Raja inornata Jordan & Gilbert, 1881
Description: The egg cases of Raja inornata (Figure 9) are very small, 68 to 73 mm in length from anterior to
posterior apron borders, with MAW about 73–77% of ECL. Egg case surfaces finely striated, without fibrous
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covering, and very smooth to the touch. LKW is very broad, about 17–25% of MAW, and extending length of
case including outer edge of horns; keels absent or very minute along inner horn edge. Attachment fibers not
present. Anterior apron border broad, concave, anterior horns about 34–52% of ECL, curling ventrally, and
flattening and hook-like towards tips. Posterior apron nearly straight, broad, transverse, and about 4–6 mm
wider than anterior apron width. Posterior horns relatively short, about one-half ECL, curved, and flattening
towards tips. Preserved egg case color dark brown becoming lighter on keels.
Remarks: The present description of this egg case differs from the original description by Cox (1963) in
that we did not observe attachment fibers to be present in any of the specimens examined. Also, Cox (1963)
did not comment on the broad lateral keels of these egg cases which we found to be a good characteristic for
separating between similar looking egg cases, but from different species.
Material examined: Ten egg cases all deposited between July and August 2005 by R. inornata specimens
held at the Monterey Bay Aquarium. Two of these egg cases accessioned as CAS 224342.
FIGURE 10. Egg case of Raja rhina. Scale bar 20 mm.
Raja rhina Jordan & Gilbert, 1880
Description: The egg cases of Raja rhina (Figure 10) are large, 93 to 102 mm in length, with MAW about 62–
70% of ECL. Egg case dorsal surface covered with dense woven-like fibers, ventral surface with either a thin
fibrous layer or without. Surface of egg case beneath fibrous layer is finely striated and smooth to the touch.
LKW broad, about 13–19% of MAW, and extending length of case including outer edge of horns; an inner
keel is present along edge of both anterior and posterior horns. Attachment fibers present along lateral keels,
originating about midway along egg case. Anterior apron border broad and concave, anterior horns also about
one-half ECL, and flattening towards tips, becoming thread-like. Posterior apron nearly straight, broad, trans-
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DESCRIPTIONS OF SKATE EGG CASES
verse, and about 1–7 mm wider than anterior apron width. Posterior horns relatively short, about one-half
ECL, curved, flattening towards tips, and becoming thread-like. Color from fresh specimens a uniform golden
Remarks: DeLacy and Chapman (1935), who first described these egg cases, found that they may range
up to 130 mm in length, making it one of the larger skate egg cases found in the ENP. Although Cox (1963)
stated that these egg cases were very similar to that of R. inornata we found them to be quite distinct. The egg
case of R. inornata is much smaller, lacks a fibrous covering, and has a broader lateral keel, without attach-
ment fibers, relative to the maximum egg case width.
Material examined: CAS 224343, 74.8 cm TL, off central California (36.4701 N, -121.5312 W), 488 m,
10 December 2002; MLML RR121602-3-11, 85.6 cm TL, off central California (36.4574 N, -121.5469 W),
186 m, 16 December 2002; MLML RR121602-1-04, 73.1 cm TL, off central California (36.4536 N, -
121.5382 W), 91 m, 16 December 2002.
Raja stellulata Jordan & Gilbert, 1880
Description: The egg cases of Raja stellulata (Figure 11) are large, 91 to 92 mm in length, with MAW about
66–70 % of ECL. The egg case is covered with dense fibers on the dorsal surface, thinner on the ventral. The
outer fibrous covering appears as an intricately woven sheath with a wool-like texture. Beneath these fibers
the egg case is smooth, with very fine longitudinal striations. The LKW is narrow, < 10% of ECL, and not
extending onto horns. Attachment fibers are present along lateral keels. Anterior apron border broad and con-
cave, anterior horns become flattened towards the tips and hook inwards. Posterior apron nearly straight,
broad, transverse, and about 1–2 mm wider than anterior apron width. The posterior horns are about 5 to 6 mm
longer than anteriors, curved, conical and tapering, becoming flattened, but without filamentous tips. The tips
are hook-shaped at the ends. Color after preservation a uniform brown.
FIGURE 11. Egg case of Raja stellulata. Scale bar 20 mm.
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14 · Zootaxa 1393 © 2007 Magnolia Press
Remarks: The egg case of R. stellulata has not been previously described. The egg case figured by Cox
(1963: figure 5) as this species is actually that of B. trachura. The egg case of R. rhina and R. stellulata are
somewhat similar, but can be easily distinguished by the narrower lateral keels present on the latter. Also, the
attachment fibers on R. stellulata extend the length of the lateral keels, while the fibers on R. rhina egg cases
originate midway along lateral keel of egg case.
Material examined: CAS 224344, 73.2 cm TL, off Davenport, California (36.9235 N, -122.2275 W), 88
m, 16 April 2004.
FIGURE 12. a. Egg case of unidentified deepsea skate species “A”. Scale bar 20 mm; b. Egg case of unidentified deep-
sea skate species “A” collected in situ by the MBARI ROV Tiburon; c. Egg case of unidentified deepsea skate species
“A” nested among other egg cases in situ.
Unidentified deepsea skate egg case “A”
Description: The egg cases of this unidentified species (Figure 12a) are very large, 188 to 198 mm in length,
with MAW about 58–62% of ECL. The surface is finely striated, smooth to the touch, and without a fibrous
outer layer. Surface under magnification appear as shallow, wavy, concave striations. The LKW is very broad,
about 14% of MAW, and folds over itself. Attachment fibers are absent. Anterior apron border broad and con-
cave, anterior horns more robust than posterior, inner and out keels present, horn length 53–57% ECL, curv-
ing dorsally relative to aspect of egg case, and flattening to tips and curling. Posterior apron border almost
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DESCRIPTIONS OF SKATE EGG CASES
straight, transverse, thinning along edge, and slightly less than width of anterior apron. Posterior horns 58–
67% of ECL, curving medially and ventrally, slightly longer than anterior, flattening to tips, and with outer
and inner keels present along edges. Color in situ a light yellowish, but becoming a bronze to greenish brown
after preservation (Figure 12b).
Remarks: Three examples of these large unidentified skate egg cases were collected by the Monterey Bay
Aquarium Research Institute (MBARI) remote operated vehicle (ROV) Tiburon off San Diego, California at a
depth of 1,820 m (Figure 12b). These three egg cases were nested among some rocks in what appears to be a
nursery area as numerous egg cases were observed on this rough rocky relief substrate (Figure 12c). An adult
male and adult female B. spinossisima were observed to swim past the ROV and it is possible that these egg
cases may be of that species. However, these egg cases are unlike the egg case that we have tentatively identi-
fied as B. spinossisima in that these are not plush to the touch. The only known species that we do not have an
example of its egg case is A. badia. Given the high degree of endemism found in skates and the remote off-
shore location of where these egg cases were observed they may represent an otherwise unknown species.
Additional examples of these egg cases, perhaps some with developing embryos, will shed light on their
Material examined: CAS 224345, three egg cases, collected by MBARI remote operated vehicle Tiburon
in situ, off San Diego, California (32.9635 N, -121.0484 W), 1820 m, 29 April 2004.
FIGURE 13. a. Egg case of unidentified deepsea skate species “B”. Scale bar 20 mm; b. Egg case of unidentified deep-
sea skate species “B” collected in situ by the MBARI ROV Tiburon; c. Egg case of unidentified deepsea skate species
“B” in situ on the Davidson Seamount.
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16 · Zootaxa 1393 © 2007 Magnolia Press
Unidentified deepsea skate egg case “B”
Description: The egg cases of this unidentified species (Figure 13a) are large, 96 to 103 mm in length, with
MAW about 79–82% of ECL. The surface is finely striated, smooth to the touch, and without a fibrous outer
layer. The LKW is very broad, about 12–14% of MAW, and extending length of case, tapering off along outer
edge of horns. Attachment fibers are absent. Anterior apron border broad and concave, anterior horns curling
ventrally, becoming flattened and hook-like towards tips, horn length about 47–54% of ECL. Posterior apron
border nearly straight, broad, transverse, thinning along edge, and about similar in width to anterior apron.
Posterior horns relatively long, 87–96% of ECL, flattening to a filamentous tip. Color in situ is a dark brown
on the egg case proper, but becoming lighter along lateral keel and aprons (Figure 13b).
Remarks: Three examples of these large unidentified skate egg cases were collected by MBARI ROV
Tiburon on the Davidson Seamount, an inactive submarine volcano located approximately 120 km southwest
of Monterey, California at a depth of between 1,310 and 1,319 m (Figure 13b). These three egg cases, col-
lected on two separate dives, were on each occasion found to be nested near deepsea corals and gorgonians in
apparent nursery areas as numerous additional egg cases were observed on each dive where they were col-
lected (Figure 13c). One of the egg cases, upon dissection, was found to contain a small developing embryo of
an unknown species of skate. A female A. badia was observed swimming in the vicinity of where these egg
cases were collected.
Material examined: Three egg cases collected by MBARI remote operated vehicle Tiburon in situ; CAS
224346, Davidson Seamount, California (35.7211360 N, -122.7235850 W), 1312 m, 27 January 2006. CAS
224347, Davidson Seamount, California (35.721340 N, -122.7234670 W), 1310 m, 27 January 2006. CAS
224348, Davidson Seamount, California (350 43.5688 N, 1220 43.6120 W), 1319 m, bottom temperature 2.9
0C, 18 May 2002.
Key to the Eastern North Pacific Skate Egg Cases
The ENP skate egg cases can be broadly classified into two main groups: those with broad lateral keels (> 10% MAW)
and those with narrow lateral keels (< 10% MAW). Egg cases in the former group (with broad lateral keels) generally
have a surface texture that is finely striated and smooth to the touch. Those in the latter group (with narrow lateral keels)
tend to have an egg case surface that is coarse in texture, often with prickles, and is rough to the touch. The only excep-
tion in this group is the egg case of R. stellulata that differs in having a finely striated surface beneath a thick fibrous cov-
The key below includes all of the known valid skate species, plus two unidentified species, known to occur from the
eastern Gulf of Alaska (ca 590 N, 1380 W) southwards to the California Mexico border (ca 320 N 1170 W). The validity of
two species, B. obtusa (Gill & Townsend, 1897) and B. rosispina (Gill & Townsend, 1897) is questionable and the occur-
rence of the Alaska Skate, B. parmifera (Bean, 1881), in the eastern Gulf of Alaska has not been confirmed from this
region. The egg cases of B. parmifera, if found to occur in this area, are quite distinct. A description and illustration of
the egg case of B. parmifera can be found in Ebert (2005).
1a. Lateral keel width broad, > 10% of maximum egg case width...................................................................2
1b. Lateral keel width narrow, < 10% of maximum egg case width.................................................................8
2a. Egg case very large, > 180 mm....................................................................................................................3
2b. Egg case usually smaller, < 100 mm........................................................................................................... 4
3a. Dorsal surface distinct with two convex ridges; horns < 50% ECL; keel width very broad > 30% of MAW
3b. Dorsal surface without convex ridges; horns > 50% ECL; keel width broad about 15 % of MAW.............
........................................................................................................Unidentified deepsea skate species “A”
4a. Attachment fibers absent.............................................................................................................................5
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DESCRIPTIONS OF SKATE EGG CASES
4b. Attachment fibers present............................................................................................................................ 6
5a. Lateral keel width very broad, 17–25% of maximum egg case width; posterior horns about one-half egg
case length...............................................................................................................................Raja inornata
5b. Lateral keel width broad, 12–14% of maximum egg case width; posterior horns about equal to egg case
length .............................................................................................. Unidentified deepsea skate species “B”
6a. Fibrous covering absent..................................................................................................Bathyraja trachura
6b. Fibrous covering present..............................................................................................................................7
7a. Fibrous covering thick, woven-like..............................................................................................Raja rhina
7b. Fibrous covering thin......................................................................................................Bathyraja kincaidii
8a. Attachment fibers present............................................................................................................................9
8b. Attachment fibers absent ..........................................................................................Bathyraja spinossisima
9a. Egg case with fibrous covering...............................................................................................Raja stellulata
9b. Egg case without fibrous covering............................................................................................................. 10
10a. Egg case very large, > 100 mm................................................................................................................ 11
10b. Egg case smaller, < 100 mm ..................................................................................Bathyraja mircotrachys
11a. Surface coarse, striated, with long anteriorly directed prickles giving it a velvety texture, and without a
distinct groove demarcating lateral keel and egg case.....................................................Bathyraja aleutica
11b. Surface very coarse, without anteriorly directed prickles, with a distinct groove demarcating lateral keel
and egg case................................................................................................................. Bathyraja abyssicola
We thank the following people for assistance on various aspects of this project: Lewis Barnett, Joe Bizzarro,
Greg Cailliet, Brooke Flammang, Diane Haas, Colleena Perez, Heather Robinson, and Wade Smith (Pacific
Shark Research Center, Moss Landing Marine Laboratories), Kelly Clendenning (Menlo High School), Don
Pearson, John Fields, and E.J. Dick (NOAA Fisheries SWFSC, Santa Cruz Lab), Keith Bosley, Erica Fruh,
Dan Kamakawa, Aimee Keller, and Victor Simon (NOAA Fisheries NWFSC), Manny Ezcurra, Scott Green-
wald, and Ed Seidel (Monterey Bay Aquarium), Andrew DeVogelaere (Monterey Bay National Marine Sanc-
tuary) and Lori Chaney, David Clague, and Linda Kuhnz (Monterey Bay Aquarium Research Institute). Haul
station location data provided by Beth Horness (NOAA NWFSC West Coast Groundfish Survey Database).
Funding for this research was provided by NOAA/NMFS to the National Shark Research Consortium and
Pacific Shark Research Center, and in part by the National Sea Grant College Program of the U.S. Department
of Commerce’s National Oceanic and Atmospheric Administration under NOAA Grant no.
NA04OAR4170038, project number R/F-199, through the California Sea Grant College Program and in part
by the California State Resources Agency.
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