Subphylum Crinozoa
 
                 
                                             
 

CRINOIDEA- Descriptions by J. C. Brower

   
     

Click here for more images of Echinoderms

 

                                             
                                             
   

-Species Descriptions-

   
CRINOIDEA – Descriptions by J. C. Brower

Calceocrinus barrandii Walcott, 1884

Calceocrinus barrandii Walcott, 1883, p. 6, Pl. 17, figs. 1-2 (adv. pub.); Walcott, 1884, p. 212, Pl. 17, figs. 1-2; Miller, S. A., 1889, p. 230; Bassler and Moodey, 1943, p. 469; Moore, 1962a, p. 21, figs. 7, no. D, fig. 11, no. C; Webster, 1973, p. 73; Brower, 1982, p. 92, fig. 32, no. I, figs. 33-38; Webster, 1988, p. 46.
Eucheirocrinus barrandii (Walcott, 1883). Bassler and Moodey, 1943, p. 469.

Description and Occurence: Disparida Calceocrinidae. Rare in the Trenton Group. The three known specimens have been found at Walcott-Rust Quarry where they are associated with Cincinnaticrinus varibrachialus and Ectenocrinus simplex. Cup and arms are unusual in having bilateral symmetry. Cup relatively slender; cup and arms with smooth plates. Arms nonpinnulate, uniserial; E ray arm long and unbranched; A and D ray arms have four slender axil arms with wide spaced branches; one or two nonaxillary plates present in each part of the main axil series. Column round, long and recumbent.

Ecology: Calceocrinids are unique crinoids because the stem is recumbent and runs along the seafloor. The cup is hinged between the basal and radial plates. To begin feeding, closing the hinge elevates the crown up roughly at a right angle to the stem and the arms are spread into a semicircular and somewhat curved filtration net with the food grooves facing down current. Calceocrinid crowns are located close to the seafloor, which minimizes the amount of competition with other crinoid species as well as with other stalked echinoderms. When not feeding, the hinge opens and the crown lies along the stem in the resting orientation, which is largely out of the zone of current flow. When resting the crinoid appears to be dead which is probably a defense mechanism to avoid predation. Although the food grooves are unknown, the thin arms are consistent with feeding on small food particles, which could consist of plankton and/or resuspended organic detritus.

 

Calceocrinus barrandii, MCZ 106419   Calceocrinus barrandii, MCZ 113420   Sketch of Calceocrinus in feeding and resting positions
MCZ 106419: Syntype, 22mm long crown
 
MCZ 113420: Syntype, 31mm long
 
Click for diagram illustrating unusual living positions

<<Return to top
Cincinnaticrinus varibrachialus Warn and Strimple, 1977

Heterocrinus heterodactylus Hall, 1866. Warn and Strimple, 1977, p. 41; Webster, 1986, p. 96.
Heterocrinus difficilis (Ulrich, Ms). Ruedemann, 1925, p. 70 (nomen nudum); Bassler and Moodey, 1943, p. 505; Warn and Strimple, 1977, p. 42; Webster, 1986, p. 96.
Heterocrinus tenuis Billings, 1857, p. 273; Billings, 1859, p. 50, Pl. 4, figs. 6a-6b; Bassler and Moodey, 1943, p. 506; Wilson, 1946, p. 32; Warn, 1973, p. 11, Pl. 1, fig. 1; Webster, 1973, p. 148; Warn and Strimple, 1977, p. 43; Webster, 1977, p. 96; Webster 1986, p. 96.
Ottawacrinus tenuis Jaekel, 1918, p. 85, fig. 79; Bassler and Moodey, 1943, p. 506.
Cincinnaticrinus varibrachialus Warn and Strimple, 1977, p. 41, pls. 3-5; figs. 8, 9 no. 2, 11, 13; Webster, 1986, p. 96; Kallmeyer and Donovan, 1998, p. 31, fig. 6, no. A.

Description and Occurrence: Disparida Cincinnaticrinidae. Ubiquitous at many localities in the Trenton Group. Cup conical with wide base; smooth or slightly nodose plates. Arms nonpinnulate, uniserial; branching isotomously on primibrachs; higher branches with bilateral heterotomy, proximal ramule on interray side; adults with up to 80 branches. Primibrachs typically 3 or 4; higher branches generally separated by 3 to 5 plates. Column with some prominent nodose plates, round to rounded sub-pentagonal outline; some columnals pentameric in proximal and middle stem; distal stem fully pentameric. “Lichenocrinid” type holdfast with round to lobate margins.

Ecology: Specimens are found attached to a wide range of hard objects including bryozoans, brachiopods, clams, cephalopods, trilobites, and pebbles as seen in one of the digital photographs. The stem length of juveniles ranges from 41 mm to 124 mm. Complete adults are not known but the longest preserved stem segment from the Trenton is 235 mm long so the mature columns were obviously somewhat longer. D. L. Meyer (2004, personal communication) has noted a specimen consisting of a crown and an incomplete stem with a length of 500 mm from the Kope Formation of the Cincinnati, Ohio region. The food grooves of juveniles and adults range from 0.185 mm to 0.215 mm in width so that the animals ate medium sized food particles. One preserved specimen suggests that the filtration net was held in a planar or parabolic fan.

 

Cincinnaticrinus varibrachialus, MCZ 136869   Cincinnaticrinus varibrachialus, MCZ 136870   Cincinnaticrinus varibrachialus, MCZ 136876
Young specimen. MCZ 136869: 15mm long
 
Young specimen. MCZ 136870: 10.5mm long (complete stem not shown)
 
Middle sized specimen. MCZ 136876: 11mm long
                                 
Cincinnaticrinus varibrachialus holdfasts, MCZ 114060   Cincinnaticrinus varibrachialus, MCZ 136892   Cincinnaticrinus Diagram
(tentatively placed in C. varibrachialus) MCZ 114060: middle stem and holdfast 12mm long
 
Complete young specimen missing only a small portion of stem. MCZ136892: 53mm long
 
Diagram showing branching

<<Return to top
Dendrocrinus sp. probably D. gregarius Billings, 1859

Dendrocrinus gregarius Billings, 1857, p. 265; Billings 1859a, p. 36, Pl. 3, figs. 1a-1c; Shumard, 1868, p. 365; Bigsby, 1868, p. 19; Miller, S. A., 1889, p. 238; Bassler, 1915, p. 396; Bassler and Moodey, 1943, p. 414; Wilson, 1946, p. 37, pl. 6, fig. 4; Webster, 1973, p. 103.

Description and Occurrence: Cladida Dendrocrinidae. Rare in the Trenton Group with only a single specimen found at the Walcott-Rust Quarry. Conical cup with smooth plates. Arms nonpinnulate, uniserial; arms branching isotomously on primibrachs and secundibrachs.

Ecology: Not known, the specimen is not complete enough to provide any useful data.


Dendrocrinus sp., MCZ 113642
MCZ 113642: 20mm long

<<Return to top
Ectenocrinus simplex (Hall, 1847)

Heterocrinus simplex Hall, 1847, p. 280, pl. 76, figs. 2a-2; d’Orbigny, 1850, p. 24; Billings, 1857, p. 271; Hall, 1866, pl. 1, figs. 11-12. Owen in Shumard, 1866, p. 377; Shumard, 1868, p. 377; Bigsby, 1868, p. 20; Hall, 1872a, pl. 5, figs. 11-12; Hall, 1872b, pl. 5, figs. 11-12; Hall, 1873, p. 7, pl. 1, figs. 4a-4c, 5a-5b, 6a-6b; Quenstedt, 1885, p. 945, pl. 75, figs. 14, 16; Miller, S. A., 1889, p. 252; Dyche, 1892, p. 130; Grabau and Shimer, 1910, p. 502, fig. 1814; Bassler, 1915, p. 471; Bassler, 1938, p. 91; Bassler and Moodey, 1943, p. 443.
Heterocrinites simplex (Hall, 1847). Troost, 1850a, p. 61; Troost, 1850b, p. 419.
Ectenocrinus (Heterocrinus) simplex (Hall, 1847). Wachsmuth and Springer, 1889b, p. 379; Bassler, 1915, p. 471.
Ectenocrinus simplex (Hall, 1847). Miller, S. A., 1889, p. 242, fig. 296; Cumings, 1908, p. 720, pl. 4, figs. 10-10a; Bassler, 1915, p. 471; McFarlan, 1917, p. 68, pl. 9, fig. 21; Miller, A. M., 1919, pl. 22, fig. 3; Ulrich in Foerste, 1924, p. 94, fig. 11; Ruedemann, 1925, p. 69; Butts, C., 1941, p. 114, pl. 96, figs. 24-25; Bassler and Moodey, 1943, p. 443; Moore and Laudon, 1943b, p. 130, pl. 1, fig. 5; Moore and Laudon 1944, p. 145, pls. 52, fig. 7, pl. 53, fig. 8; Moore, 1962b, p. 31, pl. 1, fig. 2a, fig. 3, no. 2a; Jillson, 1963, p. 4, fig. 2; Webster, 1973, p. 119; Warn, 1975, p. 437, fig. 3; Warn and Strimple, 1977, p. 84, pls. 12-13, 14, figs. 1-7, 9-10, fig. 20; Moore and Lane in Moore and Teichert, 1978, p. T522, fig. 322, nos. 1a-1e; Smith, A. B., 1985, p. 170, pl. 7.4.15; Webster, 1986, p. 134; Brower, 1988, p. 919, fig. 2, no. 1; Webster, 1988, p. 80; Titus, 1989, p. 90, figs. 4.24-4.25, 5.9-5.10; Brower, 1992b, p. 979, figs. 8-11, 13; Webster, 1993, p. 53; Ausich, 1996b, p. 244, fig. 17-3, nos. 9-10; Brower, 1997, p. 442, figs. 1, 2, 8.
Ectenocrinus canadensis (Billings, 1857). Miller, S. A., 1889, p. 242; Wood, E., 1909, p. 22, pl. 4, fig. 10; Bassler, 1915, p. 471; Bassler and Moodey, 1943, p. 442; Wilson, A. E., 1946, p. 32, pl. 6, fig. 8; Moore, 1962b, p. 31, fig. 3, nos. 2b-2c; Webster, 1973, p. 119; Brower, 1992b, p. 979.
Heterocrinus canadensis Billings, 1857a, p. 273; Billings, 1859a, p. 48, pl. 4, figs. 5a-5d; Shumard, 1868, p. 377; Bigsby, 1868, p. 20, 196; Miller, S. A., 1889, p. 252; Bassler, 1915, p. 471; Bassler and Moodey, 1943, p. 442.
Ectenocrinus grandis (Meek, 1873). Miller, S. A., 1889, p. 242, fig. 295; Foerste, 1914, p. 124, pl. 1, figs. 8a-8d; Bassler, 1915, p. 471; McFarlan, 1917, p. 69, pl. 9, fig. 22; Miller, A. M., 1919, pl. 22, fig. 2; Bassler and Moodey, 1943, p. 442; Moore, 1962b, p. 24, pl. 1, figs. 2b-2c; Webster, 1973, p. 119; Moore and Lane in Moore and Teichert, 1978, p. T522, fig. 322, nos. 1f-1g; Webster, 1986, p. 134; Brower, 1992b, p. 979.
Heterocrinus simplex var. grandis Meek, 1873a, p. 9, pl. 1, figs. 6-7; Miller, S. A., 1889, p. 252; Grabau and Shimer, 1910, p. 502, fig. 1814; Bassler, 1915, p. 471; Bassler and Moodey, 1943, p. 442.
Ectenocrinus raymondi Slocom, 1924, p. 337, pl. 29, figs. 5-9; Thomas and Ladd, 1926, p. 14, pl. 2, fig. 2; Bassler and Moodey, 1943, p. 442; Brower, 1992b, p. 979.
Decadactylocrinites planus Owen, 1843, p. 1 (nomen nudum); Bassler, 1938, p. 84.

Description and Occurrence: Disparida Homocrinidae. Ectenocrinus simplex and Cincinnatirinus varibrachialus are by far the most common crinoids in the Trenton Group and they are almost invariably collected together. Cup broadly conical with smooth plates. Arms nonpinnulate, uniserial; two primibrachs; primiaxillary gives rise to two “main arms” (secundibrachs) which consist of large proximal plates that taper distally; alternate “main arm” plates bear unbranched and thin ramules on opposite sides of the “main arms” with the proximal ramule in the interray position; adults with up to 260 arm branches. When the “main arms” are closed, the ramules are enclosed and hidden below the “main arms.” Column trimeric, round; some stem plates nodose; axial canal fully pentagonal. Holdfast is “lichenocrinid” type. Holdfasts of E. simplex and C. varibrachialus can be separated by the presence of trimeric as opposed to pentameric columnals. E. simplex differs from its ancestor E. triangulus Titus, 1989 in the Denley and Sugar River Limestones by its round stem and completely pentagonal axial canal. The ancestral axial canal varies from triangular to partly pentagonal in which two of the points are shorter than the other three and the stem is triangular to subround.

Ecology: Like C. varibrachialus, the lichenocrinid holdfast of E. simplex is attached to a wide range of hard objects. Complete specimens of E. simplex are not known but adults in the Trenton Group have attached incomplete stem segments ranging from 320 mm to 450 mm long, so the animals were located well above the seafloor. The available data suggest that on average, E. simplex lived at somewhat higher elevations than did C. varibrachialus in the Trenton oceans; nevertheless, the two taxa must have overlapped considerably with respect to distance above the seafloor. The filtration net of E. simplex was roughly conical in contrast to the more planar one seen in C. varibrachialus. The food grooves of juveniles and adults of E. simplex are 0.0947 and 0.16 mm wide, respectively, so that most of the food particles taken were slightly smaller than those utilized by C. varibrachialus. As with the elevations above the seafloor, the food particle sizes also intergrade with 32.5% and 75.1% overlap between the juveniles and adults of the two species, respectively. Clearly, E. simplex and C. varibrachialus would have competed if resources were limited in terms of food and/or space. When the arms are tightly closed, the soft parts and ramules are protected inside of relatively stout plates. This is interpreted as an adaptation to predators. The presence of regenerated arms in E. simplex and C. varibrachialus suggests that predation, perhaps by cephalopods and trilobites as well as other organisms, was moderately common in the Trenton seas.

 

Ectenocrinus simplex, MCZ 111108   Ectenocrinus simplex, MCZ 113621   Ectenocrinus simplex, MCZ 133422
Young specimen. MCZ 111108: 20mm wide crown
 
MCZ 113621: 31mm long
 
MCZ 133422: 71mm long
             
      Ectenocrinus simplex, MCZ 113598 Ectenocrinus simplex, MCZ 133431          
     
MCZ 113598: 34.5mm long
(tentatively placed in E. simplex) MCZ 133431: right stem and holdfast 10.5mm long
         

<<Return to top
Embyrocrinus problematicus Hudson, 1917

Embyrocrinus problematicus Hudson, 1917, p. 162, fig. 1,2; Bassler, 1938, p. 93; Bassler and Moodey, 1943, p. 445; Lane and Moore in Moore and Teichert, 1978, p. T596.

Description and Occurrence: Cladida Dendrocrinidae. Rare in the Trenton Group and is only known from a single specimen found at Walcott-Rust Quarry. Cup only 1.8 mm high, conical with smooth plates; four or five infrabasals, five basals, and five radials with narrow arm facets. Arms only represented by unbranched primibrachs. Columnals thin. The small size and construction of the cup indicates that this form is a juvenile dendrocrinid. It is probably a synonym of a previously described species and could be conspecific with the crinoid listed as Dendrocrinus sp. probably D. gregarius.

Ecology: Not known.

 

        Embryocrinus problematicus, MCZ 144889                  
     

MCZ 144889: Holotype, 7mm long

 

   
      Sketch of Embryocrinus problematicus    
     

Provisional sketch showing plates on E. problematicus

   

<<Return to top

Iocrinus trentonensis Walcott, 1884

Iocrinus trentonensis Walcott, 1883, p. 4, pl. 17, fig. 7-8 (adv. pub.); Walcott, 1884, p. 210, pls. 17-18; Miller, S. A., 1889, p. 257; Bassler, 1915, p. 668; Bassler and Moodey, 1943, p. 525.

Description and Occurrence: Disparida Iocrinidae. Common in the Trenton Group. I. trentonensis mainly occurs in monospecific associations but one specimen has been observed with Ectenocrinus simplex. Aboral cup conical, low and wide; plates covered with heavy ridges, sometimes with small rugose or pimple-like ornamentation. Arms uniserial, nonpinnulate; branching isotomously at various levels; generally 4 or 5 primibrachs; 5 to 7 secundibrachs; tertibrachs more variable, ranging from 6 to 16 plates; brachs commonly with distal flanges; adults with 40 to 50 branches. Tall anal sac is prominent in many specimens, covered with vertical and horizontal ridges; main anal sac plates short and wide, arranged in vertical columns or series of plates; small arched covering plates roof over areas between main anal series plates in the same column; construction of anal sac unique for Ordovician crinoids. Column pentagonal with some nodose plates. I. trentonensis is closely related to I. subcrassus from the Upper Ordovician in and around Cincinnati, Ohio. According to Walcott (1884), the Trenton crinoid is easily distinguished by its smaller size and less robust appearance. Adults of I. trentonensis are consistently smaller that those of I. subcrassus.

Ecology: Species of Iocrinus where the stem is known have a rather loose distal coil, which was presumably wrapped around some object on the seafloor or it may have formed an open coil directly on the substrate. One small specimen with a cup height of about 3.3 mm shows an attached incomplete stem segment that is about 120 mm long so the animal must have been at least that high above the seafloor. The wide food grooves (approximately 0.49 mm) and large covering plates denote that I. trentonensis caught relatively large food items with its big and widely spaced tubefeet. Several specimens are preserved with the arms spread, which demonstrates that I. trentonensis maintained a planar or parabolic filtration net. Iocrinids are generally thought to be relatively primitive disparids, but the anal sac is both specialized and unique which implies that I. trentonensis and related species are more derived than generally visualized.

 

   
Iocrinus trentonensis, MCZ 106417   Iocrinus trentonensis, MCZ 113625   Iocrinus trentonensis, MCZ 145300
MCZ 106417: Syntype, 65mm long
 
MCZ 113625
 
MCZ 145300

<<Return to top

Merocrinus corroboratus Walcott, 1884

Merocrinus corroboratus Walcott, 1883. p. 4 (adv. pub.); Walcott, 1884, p. 210, pl. 17, fig. 6; Miller, 1889, p. 262; Bassler, 1915, p. 800; Bassler and Moodey, 1943, p. 562; Moore and Laudon, 1944, p. 155, pl. 53, fig. 17; Webster, 1973, p. 174.

Description and Occurrence: Cladida Merocrinidae. Rare in the Trenton Group. Aboral cup low and wide with smooth plates. Arms nonpinnulate, uniserial; arms slender, branching isotomously; primibrachs 6 or 7; secundibrachs 9 or 10; tertibrachs 10 or 11. Anal sac long, straight, slender and arm-like. Column round with short and smooth columnals; stem with little taper. M. corroboratus is basically the same as M. typus except for smaller size and more slender cup and arms. These differences could well be ontogenetic and later study may indicate that the two crinoids are conspecific.

Ecology: See Merocrinus typus.

 

Merocrinus corroboratus, MCZ 106416 Isotomous branching diagram      
MCZ 106416: Holotype, 48mm long
Diagram of isotomous branching
     

<<Return to top

Merocrinus retractilis (Walcott, 1884)

Dendrocrinus retractilis Walcott, 1883 (adv. pub.); Walcott, 1884, p. 211, pl. 17, fig. 4; Miller, 1889, p. 239; Bassler, 1915, p. 397; Bassler and Moodey, 1943, p. 415.

Description and Occurrence: Cladida, Merocrinidae. Represented only by the holotype found at Walcott-Rust Quarry. Aboral cup low and wide; plates smooth. Arms nonpinnulate, uniserial; arms branch isotomously on primibrachs; higher branches follow bilateral heterotomy with the proximal unbranched ramule located in the interray position; primibrachs 5; secundibrachs 8 or 9; tertibrachs 10 or 11; quartibrachs 9 or 10. Anal tube long, slender, coiled in a loose spiral, which is unique. Column round with thin and smooth columnals; stem with little taper. M. retractilis can be separated from the other Trenton merocrinids by its heterotomous arm branching and spiral anal tube.

Ecology: See Merocrinus typus.

 

Merocrinus retractilis, MCZ 106418 Merocrinus Diagram      
MCZ 106418: Holotype, 73mm long
Diagram showing heterotomous branching
     

<<Return to top

Merocrinus typus Walcott, 1884

Merocrinus typus Walcott, 1883, p. 2 (adv. pub.); Walcott, 1884, p. 208, pl. 17, fig. 5; Miller, S. A., 1889, p. 262; Bassler, 1915, p. 801; Bassler, 1938, p. 132. Bassler and Moodey, 1943, p. 562; Moore and Laudon, 1943b, p. 132, pl. 3, fig. 3; Moore and Laudon, 1944, p. 155, pl. 53, fig. 16; Webster, 1973, p. 173; Moore and Lane in Moore and Teichert, 1978, p. T627, fig. 409, no. 3a; Webster, 1986, p. 203.

Description and Occurrence: Cladida Merocrinidae. Rare in the Trenton Group. Merocrinids at several Trenton localities occur in beds with Cincinnaticrinus varibrachialus and Ectenocrinus simplex. Same features as M. corroboratus except for larger size, comparatively wider cup, and more massive arms. As noted above, M. corroboratus may be a growth variant of and a junior synonym of M. typus.

Ecology: Complete stems and holdfasts are not known for any of the Trenton merocrinids so elevation above the seafloor is uncertain. Specimens from the Kope Formation of the Cincinnati, Ohio area have stems that are at least moderately long, and Meyer et al. (2002) reported an incomplete merocrinid stem segment with a length of 600 mm. The food grooves and covering plates are not preserved. However, the distal arms are all thin which is consistent with mainly feeding on small food particles.

 

      Merocrinus typus, MCZ 106415                  
     
MCZ 106415: Holotype, 24.5mm long
                 

<<Return to top

Pycnocrinus argutus (Walcott, 1884)

Glyptocrinus argutus Walcott, 1883, p. 1 (adv. pub.); Walcott, 1884, p. 1, pl. 17, fig. 9; Miller, 1889, p. 248; Bassler, 1915, p. 1184; Bassler and Moodey, 1943, p. 684.
?Stelidiocrinus argutus (Walcott, 1883). Wachsmuth and Springer, 1897, p. 280, pl. 24, fig. 6; Bassler and Moodey, 1943, p. 684.
Stelidiocrinus argutus (Walcott, 1883). Bassler, 1915, p. 1184; Bassler and Moodey, 1943, p. 684.

Description and Occurrence: Camerata Glyptocrinidae. Rare in the Trenton Group. Crown small with maximum height of roughly 12 mm. Aboral cup with rounded sides; cup plates smooth to slightly swollen; median-ray ridges present; distal plates fixed into cup vary from primibrachs to proximal secundibrachs. Arms uniserial, with juvenile appearance, pinnulate; pinnules relatively short, stout and widely separated; arms branching on primibrach 2 and on secundibrachs well above the cup. Stem round to weakly pentagonal with some nodose plates. End of stem coiled.

Ecology: Two distal stem configurations may be present in P. argutus. The illustrated specimen exhibits a loose distal coil that either lay directly on the seafloor or was wrapped around a soft object on the seabed and the cup of this individual would have been at about the 14 mm elevation. Some of the stems that are tightly wrapped around the columns of other crinoids may also belong to P. argutus. The elevations of these animals would have depended on where the host stem was located. The food grooves have not been seen but the pinnules only range from about 0.1 mm to 0.2 mm wide which would restrict the species to small food items.

 

      Pycnocrinus argutus, MCZ 113640 Pycnocrinus Diagram          
     
MCZ 113640: 25.5mm long
Diagram showing arm branching
         
            Pycnocrinus reconstruction (from W. I. Ausich, 1999)                      
           
Reconstruction of a Pycnocrinus species showing it attached to a bryozoan from W. I. Ausich, 1999
                     

<<Return to top
   

Rhaphanocrinus subnodosus (Walcott, 1883)

Glyptocrinus? subnodosus Walcott, 1883, p. 208 (adv. pub.); Walcott, 1884, p. 208, pl. 17, fig. 3; Miller, 1889, p. 248; Bassler, 1915, p. 1106; Bassler, 1938, p. 164; Bassler and Moodey, 1943, p. 661.
Rhaphanocrinus subnodosus (Walcott, 1883). Wachsmuth and Springer, 1885, p. 98 (320); Miller, 1889, p. 277; Wachsmuth and Springer, 1897, p. 259, pl. 11, fig. 2; Bassler, 1915, p. 1106; Bassler and Moodey, 1943, p. 661; Ubaghs in Moore and Teichert, 1978, p. T418, Fig. 228, no. 1a; Webster, 1986, p. 276.

Description and Occurrence: Camerata Archaeocrinidae. Common at some localities in the Trenton Group. Like Iocrinus trentonensis, R. subnodosus is mainly collected in monospecific associations. A single arm fragment is on a small slab with Ectenocrinus simplex. Aboral cup low and wide with rounded sides and numerous plates; cup plates with prominent median-ray and stellate ridges; moderate sized basal concavity with infrabasals and parts of basals; first interradials followed by two or three plates, many plates in higher ranges; numerous interbrachs between secundibrachs of same ray; secundibrachs form distal fixed brachs. Tegmen constructed of small irregular plates; small anal tube present. Arms uniserial, pinnulate, with numerous short and wide brachs; 10 unbranched arms present; pinnules long, slender and closely spaced. Stem round with some nodose plates. The most common fossils are cups and arm fragments.

Ecology: The stem length and elevation above the seafloor are not known. The food grooves are narrow (width 0.14 mm) and the covering plates are very fine which denotes that the animals subsisted on small food particles. Judging from the available material, the arms were quite flexible despite the fact that the arm articulations are purely ligamental as in other Ordovician crinoids. The dense filtration net with its close spaced pinnules and many small tube feet was probably parabolic like that of many living isocrinids.

 

   
      Rhaphanocrinus subnodosus, MCZ 113448                  
     

MCZ 113448: 130.5mm long

                 

           

Click here for more images of Echinoderms

 

                 
<<Return to top
   
 
Contact Curatorial Associate
© 2004 President and Fellows of Harvard College