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343 results for “Brittle stars”
Figure 4 in Brittle stars (Echinodermata: Ophiuroidea) from La Réunion and the systematic position of Ophiocanops Koehler, 1922
Figure 4. Digital images of Amphioplus sp.; A, ventral view; B, dorsal view; C, arm in dorsal view; SEM images of Amphipholis squamata; D, dorsal view; E, ventral view. Abbreviations: AS, adoral shield; DAP, dorsal arm plate; GP, genital plates; LAP, lateral arm plate; OP, oral papillae; OS, oral shield; RS, radial shield; VAP, ventral arm plate. Scale bars in millimetres.
Fig. 4. Oral papillae sensu lato. A in Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions
Fig. 4. Oral papillae sensu lato. A. Ventral side of a schematic brittle star. B. One angle of the oral frame includes a dental plate (DP), two oral plates (= half-jaws) (OP), two adoral shields (AdSh), and one oral shield (OSh), positioned from proximal towards distal. The typical position of teeth, tooth papillae, secondary infradental papillae (2IPa), infradental papillae (IPa), buccal scale, secondary adoral shield spine (2AdShSp), adoral shield spine (AdShSp) on DP, OP and AdSh are illustrated, respectively. The presence / absence, number and shape of each papilla vary among different taxa.
Fig. 6 in Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions
Fig. 6. DELTA interactive key workspace. The software window shows: available characters (blue box), used characters (grey), remaining taxa (green) and eliminated taxa (red).
Fig. 2 in Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions
Fig. 2. SEM images of various brittle star ossicles. A–E. Disc structures. A. Dorsal disc, radial shield with tubercles (Ophiomusa lymani (Wyville-Thomson, 1873)). B. Dorsal disc (Ophiolimna bairdi (Lyman, 1883)). C. Ventral disc (Ophionereis porrecta Lyman, 1860), the interradius is assumed as a triangle and H gives its height. D. Dorsal disc, triangular radial shield (Ophiactis savignyi (Müller & Troschel, 1842)). E. Ventral disc, mouth (Ophioderma sp.). – F–H. Atypical arm spines. F. Umbrella-shaped arm spine (Ophiotholia spathifer (Lyman, 1879)). G. Hook-shaped arm spine (Asteronyx loveni Müller & Troschel, 1842). H. Bristle spines (Ophiernus vallincola Lyman, 1878). – I–L. Lateral arm plates (LAP). I. LAP with constriction (Ophioscolex glacialis Müller & Troschel, 1842). J. Dorsal and ventral part of LAP without constriction (Ophiura ophiura (Linneaus, 1758)). K. Ventral part of LAP projecting ventro-proximalwards (Ophiopallas paradoxa Koehler, 1904). L. Ventral part of LAP not projecting ventro-proximalwards (Ophiosphalma fimbriatum (Koehler, 1922)).
Fig. 5. Typical arm spine shape. A in Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions
Fig. 5. Typical arm spine shape. A. Tapering (conical): distally ⅓ as thick as proximal diameter with a round cross-section; Pointed: distally half as thick as proximal diameter with a round cross-section; Cylindrical: same thickness at both ends with flat/round tip. B. Flat: distally half as thick as proximal diameter with oval cross-section. Red dashed lines show the ⅓ distal cross-section. The letters ʻaʼ and ʻbʼ illustrate the diameter of ⅓ distal and basal cross-sections, respectively. ʻa/bʼ shows the approximate ratio of these diameters.
Fig. 3 in Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions
Fig. 3. SEM images of various ossicle structures in brittle stars. A. Muscle and nerve opening on LAP separated by small ridge if at all (Amphiura chiajei Forbes, 1843). B. Muscle and nerve opening on LAP separated by large, prominent ridge or regular stereom (Ophiolycus purpureus (Düben & Koren, 1846)). C. Non-keeled vertebra (Amphiura chiajei). D. Keeled vertebra (Ophiothrix fragilis Abildgaard, 1789). E. Vertebra with oral bridge (Euryale aspera Lamarck, 1816). F. Sockets indicate teeth and tooth papillae on dental plate as single row (Amphilepis norvegica (Ljungman, 1865)). G. ½ single row of teeth and ½ tooth papillae (Ophiothrix fragilis). H. ⅔ single row of teeth and ⅓ tooth papillae (Ophiocamax vitrea Lyman, 1878). I. Sockets on dental plate covering evenly (Asteronyx loveni Müller & Troschel, 1842). J–K. LAP not arched = position lateral. L. LAP arched = wrapped around the arm.
Appendix 2 in Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea)
Appendix 2. Matrix for phylogenetic analysis
Fig. 1 in A New Record of Brittle Star Ophiopsila cf. polyacantha (Echinodermata: Ophiuroidea) from Southwestern Japan, with Notes on its Bioluminescence
Fig. 1. Sampling location of Ophiopsila cf. polyacantha (star symbol).
Brittle Stars (Paleocoma egertoni)
Jurassic Middle Lias Formation Dorset County, Englend Thanks to the Houston Museum of Natural Science HMNS.org Taken by austinbeaulier.com Source: Objaverse 1.0 / Sketchfab
Functional characterization of luciferase in a brittle star indicates parallel evolution influenced by genomic availability of haloalkane dehalogenase
Open the record for dataset details and reuse information.
FIGURE 3. Ophiocoma cynthiae, a-d in New records of brittle stars (Echinodermata: Ophiuroidea) from the Lakshadweep atolls, northern Indian Ocean, with notes on Indophioderma ganapatii Sastry Marimuthu & Rajan, 2019
FIGURE 3. Ophiocoma cynthiae, a-d: IO/SS/ECD/00229, e-f: IO/SS/ECD/00230. (a) live specimen, ex situ, (b) disc, dorsal view, (c) proximal arm, dorsal view, (d) disc and proximal arm, ventral view, (e, f) dental plate, external and internal view, respectively. Scale bar: 2mm.
FIGURE 1 in A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean
FIGURE 1. Map showing the position of the Punta Mazza section at Capo Milazzo, NE Sicily, Italy, marked by a star. Maps redrawn from publicly available material by Sémhur/Wikimedia Commons.
FIGURE 4 in A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean
FIGURE 4. Lateral arm plates of various extant species of Ophiacanthidae (black-rimmed area) and Ophiotomidae, all shown with dorsal edges upwards, and with external view (left), internal view (middle) and the same internal view with the vertebral articular structures marked in red (right) for every species. Colours of background correspond to clade colours in Fig. 5. White background means the species are not included in the tree on Fig. 5. Scale bars equal 0.25 mm.
FIGURE 5 in A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean
FIGURE 5. Phylogenetic tree of the Ophiacanthidae modified from O'Hara et al. (2017), with clades informally designated and colour-coded as in Figs. 3–4. Species represented in Figs. 3–4 in bold.
FIGURE 3 in A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean
FIGURE 3. Lateral arm plates of various extant species of Ophiacanthidae, all shown with dorsal edges upwards, and with external view (left), internal view (middle) and the same internal view with the vertebral articular structures marked in red (right) for every species. Colours of background correspond to clade colours in Fig. 5. White background means the species are not included in the tree on Fig. 5. Scale bars equal 0.25 mm.
FIGURE 2 in A new bathyal ophiacanthid brittle star (Ophiuroidea: Ophiacanthidae) with Caribbean affinities from the Plio-Pleistocene of the Mediterranean
FIGURE 2. Ophiacantha oceani sp. nov. (A–F) from the Piacenzian to Gelasian, latest Pliocene to earliest Pleistocene (approximately 2.6 mya) of Punta Mazza, Capo Milazzo, NE Sicily, Italy, A–B: MnhnL OPH074, holotype, proximal lateral arm plate in external (A) and internal (B) views; C–D: MnhnL OPH075, paratype, proximal lateral arm plate in external (C) and internal (D) views; E–F: MnhnL OPH076, paratype, distal lateral arm plate in external (E) and internal (F) views. Recent Ophiacantha stellata (G–J) from the tropical NW-Atlantic as closest living relative of Ophiacantha oceani sp. nov., G: complete skeleton in ventral view; H: detail of arm in lateral view; I–J: lateral arm plate in external (I) and internal (J) views. Abbreviations: ckv: central knob of the vertebral articular structures; di: distal; do: dorsal; pr: proximal; prv: proximal ridge of the vertebral articular structures; sa: spine articulation; sp: spur; ve: ventral.
Data from: Crossing the divide: admixture across the Antarctic Polar Front revealed by the brittle star Astrotoma agassizii
The Antarctic Polar Front (APF) is one of the most well-defined and persistent oceanographic features on the planet and serves as a barrier to dispersal between the Southern Ocean and lower latitudes. High levels of endemism in the Southern Ocean have been attributed to this barrier, whereas the accompanying Antarctic Circumpolar Current (ACC) likely promotes west-to-east dispersal. Previous phylogeographic work on the brittle star Astrotoma agassizii Lyman, 1875 based on mitochondrial genes suggested isolation across the APF, even though populations in both South American waters and the Southern Ocean are morphologically indistinguishable. Here, we revisit this finding using a high-resolution 2b-RAD (restriction-site-associated DNA) single-nucleotide polymorphism (SNP)-based approach, in addition to enlarged mitochondrial DNA data sets (16S rDNA, COI, and COII), for comparison to previous work. In total, 955 biallelic SNP loci confirmed the existence of strongly divergent populations on either side of the Drake Passage. Interestingly, genetic admixture was detected between South America and the Southern Ocean in five individuals on both sides of the APF, revealing evidence of recent or ongoing genetic contact. We also identified two differentiated populations on the Patagonian Shelf with six admixed individuals from these two populations. These findings suggest that the APF is a strong but imperfect barrier. Fluctuations in location and strength of the APF and ACC due to climate shifts may have profound consequences for levels of admixture or endemism in this region of the world.
Data from: Dwarf brooder versus giant broadcaster: combining genetic and reproductive data to unravel cryptic diversity in an Antarctic brittle star
Poecilogony, or multiple developmental modes in a single species, is exceedingly rare. Several species described as poecilogenous were later demonstrated to be multiple (cryptic) species with a single developmental mode. The Southern Ocean is known to harbor a high proportion of brooders (Thorson's Rule) but with an increasing number of counter examples over recent years. Here we evaluated poecilogony versus crypticism in the brittle star Astrotoma agassizii across the Southern Ocean. This species was initially described from South America as a brooder before some pelagic stages were identified in Antarctica. Reproductive and mitochondrial data were combined to unravel geographic and genetic variation of developmental modes. Our results indicate that A. agassizii is composed of seven well supported and deeply divergent clades (I: Antarctica and South Georgia; II: South Georgia and Subantarctic locations including Kerguelen, Patagonian shelf, and New Zealand; III-VI-VII: Patagonian shelf, IV-V: South Georgia). Two of these clades demonstrated strong size dimorphism when in sympatry and can be linked to differing developmental modes (Clade V: dwarf brooder versus Clade I: giant broadcaster). Based on their restricted geographic distributions and on previous studies, it is likely that Clades III-VI-VII are brooders. Clade II is composed of different morphological species, A. agassizii and A. drachi, the latter originally used as the outgroup. By integrating morphology, reproductive and molecular data we conclude that the variation identified in A. agassizii is best described as crypticism rather than poecilogony.
Data from: Geographic structure in the Southern Ocean circumpolar brittle star Ophionotus victoriae (Ophiuridae) revealed from mtDNA and single nucleotide polymorphism data
Marine systems have traditionally been thought of as "open" with few barriers to gene flow. In particular, many marine organisms in the Southern Ocean purportedly possess circumpolar distributions that have rarely been well verified. Here, we use the highly abundant and endemic Southern Ocean brittle star Ophionotus victoriae to examine genetic structure and determine whether barriers to gene flow have existed around the Antarctic continent. Ophionotus victoriae possesses feeding planktotrophic larvae with presumed high dispersal capability, but a previous study revealed genetic structure along the Antarctic Peninsula. To test the extent of genetic differentiation within O. victoriae, we sampled from the Ross Sea through the eastern Weddell Sea. Whereas two mitochondrial DNA markers (16S rDNA and COI) were employed to allow comparison to earlier work, a 2b-RAD single-nucleotide polymorphism (SNP) approach allowed sampling of loci across the genome. Mitochondrial data from 414 individuals suggested three major lineages, but 2b-RAD data generated 1,999 biallelic loci that identified four geographically distinct groups from 89 samples. Given the greater resolution by SNP data, O. victoriae can be divided into geographically distinct populations likely representing multiple species. Specific historical scenarios that explain current population structure were examined with approximate Bayesian computation (ABC) analyses. Although the Bransfield Strait region shows high diversity possibly due to mixing, our results suggest that within the recent past, dispersal processes due to strong currents such as the Antarctic Circumpolar Current have not overcome genetic subdivision presumably due to historical isolation, questioning the idea of large open circumpolar populations in the Southern Ocean.
FIGURE 4 in New brittlestars (Echinodermata: Ophiuroidea) from New Zealand waters
FIGURE 4: Ophiophycis richardi n.sp. holotype, disc diameter 4 mm. A: dorsal, B: ventral, E: armbase (SEM). Ophiophycis johni n.sp. holotype, disc diameter 5.5 mm. C: dorsal, D: ventral, F: armbase (SEM).
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