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A New Record of the Heart Urchin Rhynobrissus cuneus (Spatangoida: Brissidae) from Buxton Beach, Dare County, North Carolina
Patricia G. Weaver, Bronwyn W. Williams, and Eric M. Sadorf

Southeastern Naturalist, Volume 17, Issue 3 (2018): N34–N39

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2018 Southeastern Naturalist Notes Vol. 17, No. 3 N34 P.G. Weaver, B.W. Williams, and E.M. Sadorf A New Record of the Heart Urchin Rhynobrissus cuneus (Spatangoida: Brissidae) from Buxton Beach, Dare County, North Carolina Patricia G. Weaver1,*, Bronwyn W. Williams2, and Eric M. Sadorf3 Abstract - Rhynobrissus cuneus, a small, irregular sea urchin, was originally described from 5 tests washed onto the beach at Fort Macon, NC, and it has been reported only once since, from 7 specimens collected from Playa Jicacal, Los Tuxtlas, Veracruz, Mexico. Here we record R. cuneus from Buxton Beach, Dare County, NC, ~124 km (77 mi) directly northeast of the 1957 record. This is only the third report of R. cuneus and represents the northernmost record of the species. Specimens were found as empty tests washed ashore, most likely a result of recent beach-restoration activities. Rhynobrissus is an infrequently encountered genus of small, irregular sea urchins placed in the family Brissidae within the order Spatangoida (heart urchins). Rhynobrissus has a wide, yet disparate distribution, occurring patchily throughout the Indo-Western Pacific, the eastern Pacific, and the northern mid-latitudes of the western Atlantic. Despite this broad geographic range, the genus is not highly diverse; it contains 6 currently accepted species, 2 of which are fossil taxa. Fossil Rhynobrissus species are limited to a narrow temporal distribution spanning the early Miocene through the Plio/Pleistocene. Rhynobrissus daviesi (Jain), known from the early to middle Miocene Gaj Formation of Kathiawar, Gujarat, India, was originally described as Brissus daviesi by Jain (2002) and reassigned to Rhynobrissus by Kroh et al. (2011). Rhynobrissus rostratus Cooke was named from specimens recovered from the late Miocene La Vela Formation, Punta Gavilan, Falcon, Venezuela. Rhynobrissus sp. was reported from the Plio/Pleistocene of Punta Banco, Punta Burica, Costa Rica (Alvarado et al. 2006). Kroh et al. (2011) remarked that a specimen from the early Miocene Gaj Formation of Pakistan, listed as Brissus sp. by Duncan and Sladen (1885), is likely also a Rhynobrissus. The 4 accepted extant species of Rhynobrissus include R. pyramidalis A. Agassiz, R. hemiasteroides A. Agassiz, R. cuneus Cooke, and R. tumulus McNamara. Three of these species occur in the Indo-Pacific. Rhynobrissus pyramidalis was described from the China Sea (Agassiz 1872), and was later recovered from the Gulf of Thailand, Singapore, and off Madras, India (Mortensen 1951); near Darwin, Australia (Clark 1946); and off the coast of Sri Lanka (Jayakody 2012). Agassiz (1879) described R. hemiasteroides from Tahiti Harbor from specimens recovered at a depth of 37 m. This species has also been reported from several localities in Western Australia (Clark 1946, McNamara 1982) and a few sites along the east coast of Australia (McNamara 1982). McNamara (1982) described R. tumulus from dried tests washed up on the beach east of Cape Dupuy along the northern coast of Barrow Island, Western Australia. Rhynobrissus cuneus, described by Cooke (1957) from specimens washed onto the beach at Fort Macon, NC, USA, is the sole species attributed to Rhynobrissus known from the Atlantic Ocean. This species was known only from the type locality for 1Geology/Paleontology, North Carolina Museum of Natural Sciences, 11 West Jones Street, Raleigh, NC 27601-1029. 2Non-Molluscan Invertebrates, North Carolina Museum of Natural Sciences, Research Laboratory, 1671 Gold Star Drive, Raleigh, NC 27699. 3315 Hemlock Street, Cary, NC 27513. *Corresponding author - Manuscript Editor: Matthew Heard Notes of the Southeastern Naturalist, Issue 17/3, 2018 N35 2018 Southeastern Naturalist Notes Vol. 17, No. 3 P.G. Weaver, B.W. Williams, and E.M. Sadorf more than 55 years, until Martinez-Melo et al. (2014) found 7 individuals along the coast of Playa Jicacal, Los Tuxtlas, Veracruz, Mexico. Three additional extant Rhynobrissus species have been described, namely R. micrasteroides (A. Agassiz) from the Yucatan Channel, R. macropetalus H.L. Clark from Western Australia, and R. placopetalus A. Agassiz and H.L. Clark from the vicinity of Modu Manu, Hawaiian Islands. However, neither R. macropetalus nor R. placopetalus is currently considered valid, yet are erroneously listed as such in the World Echinoidea Database (Kroh and Mooi 2018). The type specimen of R. placopetalus was deemed to represent a juvenile of R. pyramidalis by Mortensen (1951) and McNamara (1982), the type of R. macropetalus was so severely damaged prior to publication that the name of this species is considered nomen dubium (McNamara 1982, Mortensen 1951), and Rhynobrissus micrasteroides was designated the type species of Neopneustes (Duncan 1889). Here we report R. cuneus from Buxton Beach, Dare County, NC, ~124 km (77 mi) northeast of Cooke’s 1957 record. This is only the third known occurrence of R. cuneus. Our observations provide additional insight into the distribution and habitat of this littleknown species. Between 21 November 2017 and 23 November 2017, E.M. Sadorf collected several empty tests of R. cuneus that had washed ashore along Buxton Beach in an area between N35.264809°, W75.518322° and N35.258521°, W75.519464°. During those 3 days, active dredging was occurring ~0.8 km (½ mi) offshore as part of ongoing beach-restoration activity. The dredge was situated at approximately N35.261655°, W75.509629° and the outflow pipe was located at N35.265387°, W75.518434°. While walking his dog, E.M. Sadorf first noticed and collected echinoid specimens around 7:30 am on 21 November from the washline of the highest waves, approximately an hour before high tide. Not knowing these particular echinoids were considered rare, he only collected a few specimens that were of good quality. After a while several people had started beachcombing for shells, probably picked up a few echinoids, and likely trampled quite a few, as E.M. Sadorf observed many broken echinoid pieces along the strandline. Later that afternoon, while surf fishing in the area where he originally found the echinoids, E.M. Sadorf noticed broken echinoid pieces washing back and forth with each wave. At sunrise on 22 November, ~2 h before high tide, E.M. Sadorf collected numerous specimens, almost all of which were found on the strandline of the highest wave. Later in the day, he searched south of the coordinates given above, but found no echinoids. He also searched north of the active dredging area, where dredging had been completed, but found no sign of echinoids. On the afternoon of 23 November, he collected 4 echinoid specimens from the southern part of the collection area, during a falling tide, approximately halfway between high and low tide. On this day, waves were a little higher and echinoid tests were found in the depression of truck-tire tracks. All of the echinoid tests collected showed some degree of mechanical damage (i.e., small holes, missing or broken spines) or were partial tests. E.M. Sadorf donated 12 specimens to the Non-Molluscan Invertebrates Collection at the North Carolina Museum of Natural Sciences, Raleigh, NC (NCSM 29771- 29782) and 7 specimens to the Mississippi Museum of Natural Science, Jackson, MS (MMNS IZ-163.1-163.4 and MMNS IZ 164.1- 164.3). We identified the echinoids as Rhynobrissus cuneus based on descriptions given in Cooke (1957, 1959) and Martinez-Melo et al. (2014) (Fig. 1). Figure 1 (following page). Rhynobrissus cuneus: (A–D) with spines intact, (E–H) without spines. (A) aboral surface of NCSM 29771, (B) oral surface of NCSM 29772, (C) posterior view of NCSM 29771, (D) left side of NCSM 29771, (E) aboral surface of NCSM 29773, (F) oral surface of NCSM 29774, (G) posterior view of NCSM 29773, and (H) left side of NCSM 29773. 2018 Southeastern Naturalist Notes Vol. 17, No. 3 N36 P.G. Weaver, B.W. Williams, and E.M. Sadorf N37 2018 Southeastern Naturalist Notes Vol. 17, No. 3 P.G. Weaver, B.W. Williams, and E.M. Sadorf Rhynobrissus cuneus has a thin test and is rounded anteriorly and widest at the apical system, resulting in a diamond-shaped horizontal outline and wedge-shaped longitudinal outline. The oral surface is flat and the aboral surface is slightly convex. The apical system is nearly central, with the madreporite extending beyond and between the posterior ocular plates. Adults have 4 genital pores. The ambulacrum on the anterior aboral surface is inconspicuous, not petaloid, with small pores. Paired ambulacra, extending to the peripetalous fasciole, are long, straight, and slightly sunken with oval conjugate pores. The oval, anal fasciole, on the posterior surface, adjoins the heart-shaped subanal fasciole. The peristome is strongly reniform and is surrounded by conspicuous phyllodes. The periproct is oval with sharp ends. Tubercles on the aboral surface are generally homogeneous; however, they are almost twice as large at the adapical end of ambulacrum III. Tubercles are noticeably larger on the oral surface. The phyllodes and posterior ambulacra are bare. The aboral surface is covered with curved, hair-like spines, whereas the oral surface is covered by spatulate spines approximately twice the length of aboral spines. Rhynobrissus cuneus is distinguished from other species of Rhynobrissus in the shape of the test and having adjoined anal and subanal fascioles. Measurements of specimens now housed in collections at NCSM and MMNS are given in Table 1 and fall within the ranges for R. cuneus given in Cooke (1957) and Martinez- Melo et al. (2014). It is likely that the range of sizes reflects different ages. All specimens are dry and extremely fragile. These new specimens more than double the number known from previous collections of the species [i.e., 5 specimens at the US National Museum, Washington, DC (USNM E8032, USNM E8033, USNM E8234, USNM E8235 and USNM E36599) and 7 specimens in the Colección Nacional de Equinodermos, Instituto de Ciencias del Mar y Limnologia, Unversidad Nacional Autónoma de México, Mexico City, Mexico (ICML-UNAM 4.78.0). Table 1. Maximum length, width, and height of dried tests of Rhynobrissus cuneus collected at Buxton Beach, NC. Although all specimens were damaged to some degree, only 2 had damage in areas that affected standard measurements. Catalog Number Length (mm) Width (mm) Height (mm) NCSM 29773 29.8 29.0 18.6 NCSM 29775 26.9 26.5 17.2 NCSM 29778 32.3 30.8 19.3 NCSM 29774 27.9 26.6 16.9 NCSM 29777 24.5 24.5 14.9 NCSM 29776 25.4 24.3 14.5 NCSM 29779 33.4 32.5 20.1 NCSM 29780 27.5 27.3 16.9 NCSM 29781 - 28.7 17.6 NCSM 29771 24.7 25.7 15.1 NCSM 29782 27.1 27.4 16.0 NCSM 29772 25.0 24.2 - MMNS IZ-163.1 27.0 25.6 17.0 MMNS IZ-163.2 29.9 27.5 17.3 MMNS IZ-163.3 27.4 26.6 16.1 MMNS IZ-163.4 27.6 27.5 17.5 MMNS IZ-164.1 18.3 17.8 11.3 MMNS IZ-164.2 19.4 19.4 12.4 MMNS IZ-164.3 18.0 18.5 10.6 2018 Southeastern Naturalist Notes Vol. 17, No. 3 N38 P.G. Weaver, B.W. Williams, and E.M. Sadorf Rarity of observations of R. cuneus is likely an artifact resulting from lack of targeted sampling efforts rather than representative of true occurrence. Indeed, our record, similar to that of Cooke (1957), is opportunistic, based on specimens that had washed up on shore, and therefore provide little information about the habitat of the species. However, it is likely that the appearance of R. cuneus on Buxton Beach is related to beach-restoration activities, where sand is dredged from an offshore location and deposited onshore to counteract erosion. Sediment deposition along the shoreline may have disturbed resident R. cuneus, causing a large die-off. Tests of deceased individuals would then wash ashore via waveinduced movement along the sea bottom. This scenario suggests that R. cuneus occupies shallow nearshore waters, just far enough offshore to escape detection by beach goers and not far enough offshore to come up in trawls, which is consistent with the findings of Martinez- Melo et al. (2014), who recovered specimens of R. cuneus on the coast of Veracruz, Mexico at a 1-m water depth. It is possible that R. cuneus may occur further offshore, in or near habitats directly impacted by the dredge itself. However, it is unlikely that the tests of R. cuneus discovered on the beach were translocated by the dredging process; the thin and fragile tests of specimens would be completely demolished passing through the dredge during the sediment relocation process. Yet, habitat destruction, or changes in sedimentation, caused by the dredge could result in large-scale die-off of offshore populations, and specimens would wash ashore as above, via wave-induced movement. Our record, together with those of Cooke (1957) and Martinez-Melo et al. (2014), suggest that R. cuneus likely inhabits shallow waters ranging from the Mid-Atlantic region of the US to the Gulf of Mexico. Cape Hatteras, on which Buxton is located, represents a major marine biogeographic boundary along the western Atlantic coast (e.g., Cerame-Vivas and Gray 1966, Grothues and Cowen 1999). Targeted surveys are needed to determine if the distribution of the species extends north, across this faunal transition zone, or if Cape Hatteras marks its northernmost extent. Likewise, research is needed to determine if the distribution of R. cuneus is continuous between its northernmost and southernmost known occurrences, and if it extends farther south along the Gulf Coast. Interestingly, Cooke (1961) posited that morphological differences observed between his fossil species R. rostratus from Venezuela and R. cuneus might be due to distortion or individual variation. If further investigation reveals these taxa to be synonymous, then R. cuneus occupies a far broader geographic and temporal distribution than currently perceived. Acknowledgments. We thank Janet Edgerton for assistance in obtaining bibliographic references and George Phillips for providing measurements of specimens deposited at the Mississippi Museum of Natural Sciences. Literature Cited Agassiz, A. 1872. 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