Subphylum Asterozoa
 
               
                                   
 

ASTEROIDEA- Descriptions by F. H. C. Hotchkiss

OPHIUROIDEA- Descriptions by F. H. C. Hotchkiss

 

         
   
-Species Descriptions-
 
   
ASTEROIDEA - Descriptions by F. H. C. Hotchkiss
 

   
Macroporaster matutinus (Hall, 1847)

Asterias matutina Hall, 1847, p. 91, pl. 29, figs. 5a, 5b.
Coelaster matutina (Hall, 1847). d’Orbigny, 1850, p. 22.
Palasterina rigidus Billings [part], 1857, p. 291; Bolton, 1960, p. 91.
Petraster rigidus (Billings, 1857). Billings [part], 1858, p. 79, pl. 10, fig. 3b [not fig. 3a].
Asteracanthion matutina (Hall, 1847). Dujardin & Hupé, 1862, p. 342.
Palaeaster matutina (Hall, 1847). Hall, 1866, p. 3, p. 14, plate 9, fig. 2.
Palaeaster matutinus (Hall, 1847). White, 1896, p. 92; Whitfield, 1898, p. 24.
Hudsonaster matutinus (Hall, 1847). Schuchert, 1915, p. 57, pl. 2, fig. 2, pl. 3, fig. 2, pl. 5, fig. 1, pl. 5, fig. 2; Wilson, 1946, p. 42; Bolton, 1960, p. 91.
Macroporaster matutinus (Hall, 1847). Raymond, 1921, p. 167; Delo, 1934, p. 248; Spencer & Wright [part], 1966, p. U51 [but not fig. 48.1 = M. nylanderi]; Branstrattor, 1975, p. 62, pl. 1, fig. 2, pl. 1, fig. 3; Titus, 1986, p. 823; Blake, 1990, p. 352, fig. 3A-3C.
Protopalaeaster matutinus (Hall). Spencer, 1950, pp. 398, 405-406.

Description: Hudsonasteridae. Five arms. Small size. Approximate measurements of the three specimens MCZ 108055, MCZ 146701, and MCZ 146702: primary radius (R) from center of disk to arm tip, minor radius (r) from center of disk to interradial edge of disk, and width (w) of arm at base: R/r/w 7 mm/3 mm/2.5 mm (oral view); 13 mm/4.5 mm/5 mm (oral view); and 9 mm/3.5 mm/3.3 mm (aboral view). Heavily plated aborally and in the oral interbrachial area. The upper surfaces of the rays have five columns of ossicles. The carinals in the center are bounded on either side by the superomarginals, outside of which are the inferomarginals which border the rays. There are no accessory plates between the columns of ossicles. Spaces between carinal and superomarginal ossicles are implied papular openings (Branstrattor, 1975). The ossicles of adjoining superomarginal and inferomarginal columns alternate with each other. The upper surface of the disk has prominent radial and interradial plates that form a circlet. Highly prominent on the ventral surface is a single axillary marginal plate that fills the interbrachial arc. On the under surface of the ray the inferomarginal column borders the ambulacral ossicles. Adambulacrals are about one and one-half to two times as numerous as inferomarginals. The ambulacral groove is quite widely open in these specimens but is fairly closed in others (Blake 1990:fig. 3A). Biserial podial basins are prominent on each arm. The podial basins are floored by overlapping flanges of two consecutive ambulacral plates. The adambulacral ossicles are aligned one-for-one with the ambulacral ossicles. Notches at the junction of ambulacral and adjacent adambulacral columns may have housed podial ampullae; the notches are bounded by skeleton and do not reach the interior of the arm (Blake, 1990). All ossicles except the ambulacrals carried spines articulated upon spine-base pustules.

Ecology: The heavy skeleton may have imposed a limit on the body size by limiting the number of respiratory papulae (Branstrattor, 1975). A suggested ecology has been inferred from the skeletal mechanics by Blake (1990). Like modern asteroids, Macroporaster must have been subject to inversion by wave action or other external forces, and must have been able to right itself, which involves considerable twisting of the arms and disk. Accordingly, despite its massive and inflexible appearance, Macroporaster must have had both facultative flexibility and rigidity. Depressions on the sides of ossicles are interpreted as attachment areas for tissues linking the ossicles to each other. The ossicles are rather closely articulated which facilitates rigidity. The connective tissues could rigidly lock the marginal frame while still allowing the oral ossicles to move rather freely within the central portion of the disk during feeding. The axillary provided both support for overall body structure and contributed to the operation of the mouth frame. “Macroporaster is suggested to have selected an area of rich organic content, then locked the marginal frame and raked the sediment surface with the tube feet, concentrating organic materials such as epibenthic algal or bacterial films. Organic material was passed toward the mouth and shoveled through the mouth frame with a back-and-forth pumping action of the oral and axillary ossicles” (Blake 1990:354).

Notes: The type specimen of Hall (1847) “is from the thin shelly layers at Trenton Falls about midway of the rock.” MCZ No. 108055, 146701, 146702 are from Rathbone Brook, near Newport, Herkimer County, NY. MCZ 108056 is from Deerfield, Oneida County, NY. Spencer (1950) suggested that Macroporaster should lapse into the synonymy of Protopalaeaster, but this was not followed by Spencer & Wright (1966) or later authors.

 

 
    Macroporaster matutinus, MCZ 108055, MCZ 146701, and MCZ 146702    
   
MCZ 108055, 146701, 146702: Hypotypes, largest is 25mm wide
   

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Salteraster medusa (Hudson, 1916)

Urasterella pulchella (Billings, 1857). Raymond, 1912, p. 106, pl. 6, fig. 1; Schuchert [part], 1915, p. 178, pl. 28, fig. 4, pl. 30, fig. 5; Delo, 1934, p. 248.
Urasterella medusa Hudson, 1916, p. 121, pl. 1-6; Spencer, 1918, p. 135, p. 146, pl. 8 fig. 4, 7; Delo 1934, p. 248; Hotchkiss, Prokop & Petr, 1999, p. 190.

Description: Five arms. The disk lacks interbrachial development. The width of the base of the arms determines the size of the mouth-disk region. The arms are fairly long, gently tapering and flexible. Arms rounded in section (MCZ 108087). Approximate measurements of primary radius (R), minor radius (r) and width (w) of arm at base: R/r/w 28 mm/3.3 mm/4 mm [MCZ 108067] and 27 mm/3.5 mm/4.5 mm [MCZ 108069]. The dorsolateral and aboral plating of the arms is continuous onto the aboral disk. The plating is a dense array of subequal paxillae, each with well-formed base, shaft and spine tuft [the spine tuft and shaft are lost in weathering]. At the margins of the disk and rays the paxillar shaft is about twice as tall as the thickness of the paxillar base. The central portion of the disk is not sunken and has plates similar to the plates of the disk perimeter and the arm bases (MCZ 108069), or is sunken and with less evident plating than the arm bases (MCZ 108067), or is sunken and like a calcareous mat (MCZ 146700). The madreporite is aboral, interradial, between the perimeter and the center of the disk, and has typical furrows (MCZ 146700), but is not evident in most specimens. The carinal row of paxillar plates is not prominent or distinct from the other rows of aboral arm plates. The carinal paxillae, paxillar shaft and spine tuft are well shown in MCZ 146704. On each side of the ray, lateral to the carinals are four rows of dorsolateral plates that are arranged in a close-fitting diamond pattern which produces diagonal rows of plates on the sides of the ray. Between the lowermost dorsolateral plates and the adambulacral plates is a single row of marginal plates labeled inframarginals or inferomarginals by Schuchert (1915:pl. 30 fig. 5), Hudson (1916:129) and Spencer (1918:126). Ten marginals are adjacent to 14 adambulacrals (MCZ 108070). The marginals are paxillar; the paxillar base is longer (radially) than tall (dorsally). The marginals extend to the tip of the ray. In oral view there is no visible interbrachial arc of disk (MCZ 108068). No axillary plates are seen externally (in oral view), but they are seen internally as part of the mouth frame (weathering of the aboral surface exposes an aboral view of the mouth frame in MCZ 108087). In oral view only the ambulacral groove bordered by the adambulacral plates is visible (MCZ 108068): The ambulacral groove is very deep. The mouth angle plates are small triangular pieces not wider than the adambulacrals. The ambulacrals are deep in the groove and most are concealed by matrix. One arm has a distortion that shallows the groove and puts the ventral surface of the ambulacrals into view (MCZ 108068). The ambulacrals are closely packed with no spaces between them perradially. The ambulacrals have a proximal lobe that overlies the adjacent proximal ambulacral, and an abradial lobe that points toward a lobe or stem on the adambulacrals. A view of the inside of the ambulacral furrow made possible by a perradial split in the arm clearly shows abradial pockets between the ambulacrals and the adambulacrals (MCZ 108071, arm tip of the smaller specimen). These pockets almost certainly housed ampullae (Blake & Guensburg, 1988:Fig. 5A). The adambulacrals have furrow spines that are long and stout, ventral spines that are like short broad papillae bridging between successive adambulacrals, and ventral and abradial spines in double or triple rows (MCZ 108068). The adambulacrals margin the ambulacral groove which is in places widely open and in places closed to a miniscule gap by the adambulacrals. The adambulacrals imbricate adorally with substantial space between successive plates, or they imbricate distally and are close-fitting with no space between them. The distal face of each adambulacral has a large interadambulacral muscle depression. The abradial surfaces of the adambulacrals form the ventrolateral margin of the ray and displace upward the single row of marginal plates. The ambulacral plates overlie the adambulacral plates (MCZ 146704). The ambulacrals and adambulacrals are stout, tightly packed together, and fill the interior of the arm. The first three adambulacrals are beneath single ambulacrals; the ninth and more distal adambulacrals are lodged beneath two ambulacrals; between is a region of transition (MCZ 146704). In the holotype (MCZ 108087) nearly all the plates of the abactinal skeleton are weathered away, exposing the dorsal aspect of the ambulacral plates and the dorsal aspect of the mouth frame which Hudson called a ‘peristomial ring’. Key features of U. medusa noted by Hudson (1916:121, also plates 1, 2) that are unique to this internal view are: “Peristomial ring heavy. Axillary inframarginal prominent, its long axis parallel with the ring. First floor plates (peristomial) with radial diameters equal to the sum of those of the three following floor plates.” “The first floor plates make a radial (‘ambulacral’) jaw.” The axillary plates and the large ambulacral mouth plates are not visible externally in oral view. Comparison of the present state of the holotype with Hudson’s photographs (1916:plates 1, 2) shows that the internal axillary and some other parts of the fossil are missing. The space that was occuppied by the missing axillary is floored by the two triangular mouth angle plates, which explains why the axillary is not seen in oral view. The space for the axillary lines up with the row of paxillar marginals. Hudson’s photographs (1916: plates 1,2) are stereo-pairs and show the paxillar marginals abutting the internal axillary. The dorsal aspect of the ambulacral plates shows an absence of podial openings between the ambulacrals. The ambulacrals near to the mouth frame are oppositely placed, but the arrangement in the arms is for the greater part an alternate one (Hudson, 1916:127). The ambulacrals (in aboral view) are obtusely pointed at the perradial ends where they fit together closely (Raymond, 1912:105). This gives the ambulacrals a keeled convex angular shape and a zigzag median line of junction between the two columns of ambulacrals.

Juvenile and early growth stage of Salteraster medusa

Juvenile of Salteraster medusa [MCZ No. 108072]: The specimen is somewhat free of matrix and looks like a minute example of the larger specimens of S. medusa. The animal is folded ventrally near the perimeter of the disk, bringing one arm beneath the disk. As a result, only the abactinal surface of the disk and rays, and a bit of the lateral surface of the rays is visible. Overall size approximately 11 mm. Approximate measurements of R/r: 7.5 mm/2 mm. The folding of the specimen indicates some flexibility. The folding prevents a geometrical determination of the center of the disk. Only the disk perimeter and arm bases have knobs on the plates. There is a ‘largest knob' near the presumed center of the disk, perhaps implying a central plate. The arms and the disk perimeter do not have unequivocally differentiated carinal plates. Rows of plates can be discerned, but otherwise the arrangement of the plates is not very clear. The plate boundaries are not clear; the high points of the plates have the greatest definition. There is a hint of a chevron arrangement, a hint of a diamond pattern. In one ray, three adjacent abactinal rows of plates appear to go to the tip of the ray. These are interpreted as a central row of carinals and adjacent rows of superomarginals. There is no row of plates between the carinals and the superomarginals. A ray on the fold axis shows a row of plates on its lower lateral surface that have greater distinctness and are more widely spaced than other plates. These are taken to be the inferomarginal plates, and beneath them can be seen a few faint adambulacrals. It is evident from the visibility of the adambulacrals in this lateral view of the ray that the adambulacrals form the lower lateral margin of the ray.

Notes: Prior catalog numbers for this specimen are MCZ No. 36 and MCZ No. 461. This specimen was remarked on by Schuchert (1915:178-179, MCZ No. 36) as “the smallest specimen seen,” a “very young example,” and as having the arrangement of the disk plates “plainly preserved.” In the present study the arrangement of the central disk plates was not discernable.

Early growth stage attributed by hypothesis to Salteraster medusa [MCZ No. 108066]: The specimen is free of matrix and can be viewed from both sides. The short rays have blunt, rounded tips. Approximate measurements of R/r/w: 2.3 mm/1.4 mm/1.6 mm. The aboral surface has many small plates, but the exact plating arrangement is indistinct due to lack of differentiation. The center of the disk is a depressed area approximately 0.6 mm diameter, bordered by five primary radial plates. Probably there are primary interradials between and slightly distal to the primary radials. An abactinal madreporite is presumed present but was not detected. A row of carinal plates is present. An inconspicuous row of plates on each side of the carinals was discerned. The plates of these rows are of about the same size as the carinal plates. The location of each row can be described as being between the carinals and the ambitals (pertaining to edge of body). Probably there is an inconspicuous terminal plate. In oral view: The ambulacral groove is open, but the ambulacral plates are indistinct. The interradial mouth angle plates are triangular, paired, and in line with the adambulacrals of the rays. There are six adambulacrals between the mouth angle plates and the indistinct presumed terminal plate; the distal sixth plate is notably smallest. The adambulacrals do not margin the ray. Indistinct plating adjacent to the adambulacrals forms the ambitus and interbrachial arc. If there is an axillary plate, it is indistinct and not detected. An important question is whether the ambitals seen in actinal view and the ambitals seen in abactinal view are the same or different plates. In the present study they are interpreted as being the same plates seen both from above and from below. If that is a correct assessment, then the ambital plates are inferomarginal plates, and the plates between the carinals and the ambitals are superomarginal plates. 

Notes: Prior catalog numbers for this specimen are MCZ No. 27 and MCZ No. 465. A label with prior number MCZ No. 465 states “Young of Urasterella pulchella ,” “C. Schuchert ident.,” but this specimen was not included in the materials of U. pulchella listed by Schuchert (1915:178). In this study, Schuchert's unpublished identification as U. pulchella is used as a working hypothesis, except that the Trenton Falls “ U. pulchella ” material is reidentified as Salteraster medusa . Identification as a urasterellid early growth stage is supported by the undifferentiated appearance of the plates of the dorsal surface [not the stout plates of the ‘hudsonasterid' look], the lack of visible axillary plates on the oral surface, and especially that the adambulacral plates dominate as the most prominent plates of the oral surface. On the other hand, the general aspect is quite different from the juvenile specimen MCZ No. 108072 described above. Accordingly, attribution of this early growth stage specimen to S. medusa is uncertain because the associated specimens do not form a connected growth-series. This specimen is an important addition to the meager number of early growth stage specimens of Paleozoic stelleroids (Spencer 1916:figs. 35, 49, Blake 1990).

A label with prior number MCZ No. 27 has the identification Stenaster salteri [= S. obtusus ] and is annotated “The smallest known fossil starfish” and “Schuchert”. The identification is crossed out as incorrect but is interesting because Shimer & Shrock (1944:211) included New York in their list of occurrences of S. salteri . A search of the literature did not confirm a New York record (Hotchkiss 1976:10), but it is not unreasonable that S. obtusus could be an undiscovered member of the Trenton Limestone, Trenton Falls , NY , fauna.

Ecology: The massive closely abutted ambulacral and adambulacral ossicles that alternated and interlocked in compression are highly suggestive of an asteroid that often is in a rigid state. At the same time, the rays could flex and twist as evidenced by the layout of the fossils. If overturned, the animal must have been able to right itself, indicating capability of interossicular displacement. The significance of the massive peristomial frame, with its large odontophore [internal axillary], to the interpretation of the ecology of this species is not yet understood. The size of S. medusa would permit it to gather prey smaller than itself such as diminutive mollusks, bryozoan twigs, etc., using its tube feet. The limited space inside the disk and arms suggests that no large items were ingested. It could have been a deposit feeder on epibenthic film. The starfish needed to move in order to obtain food. The ambulacrals had limited cross-furrow movement, but the adambulacrals were highly movable and could open up the ambulacral groove to expose the lateral cups for tube feet. Optimal foraging behavior is an important aspect of their feeding biology (Lawrence 1987:43). [Other references: Blake & Guensberg (1993) on Stibaraster; Jangoux (1982)]

Notes: The Walcott-Rust specimens identified as Urasterella pulchella by Schuchert (1915) and Delo (1934) are reidentified here as Urasterella medusa Hudson. Urasterella medusa is transferred to the genus Salteraster.

Hotchkiss et al. (1999:190) discussed the feature of alternating ambulacral plates (which in an asteroid should be opposite), with a perradial keel that makes a zigzag median suture. They suggested that the ambulacrals of this species are so solid-block-like and sutured together that the placement of the ambulacrals as either opposite or alternate is no longer an important constraint. They suggested that perhaps the shape of the sutures is determined in response to mechanical forces, and suggested comparison with the plates in regular echinoids that have convex outlines and zigzag sutures between columns of plates. They suggested that the convex angular sutures of this species are secondarily evolved and may be a useful taxonomic character.

 

   
Salteraster medusa, MCZ 108072   Salteraster medusa, MCZ 108087 Salteraster medusa, MCZ 108069
MCZ 108072: Hypotype 10.5mm wide
 
MCZ 108087: Holotype, 37mm wide
MCZ 108069: Hypotype, 44.5mm wide
                                   
Salteraster medusa, MCZ 108066   Salteraster medusa, MCZ 108067   Salteraster medusa, MCZ 108068
MCZ 108066: Hypotype, 3mm wide
 
MCZ 108067: Hypotype, 45mm wide
 

MCZ 108068: Hypotype, 31.5mm wide

                                   
Salteraster medusa, MCZ 146703   Salteraster medusa, MCZ 108070   Salteraster medusa, MCZ 108071
MCZ 146703: 26mm long
 
MCZ 108070: Hypotype, 47.5mm wide
 
MCZ108071: Hypotype 27mm long
                                   
          Salteraster medusa, MCZ 146700                  
         
MCZ 146700: 12.5mm wide
                 

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OPHIUROIDEA - Description by F. H. C. Hotchkiss
   

   
Protasteridae n. sp.

Alepidaster? n. sp. Schuchert, 1915, p. 230; Delo, 1934, p. 248.
cf. Protasterina sp. Hotchkiss, 1970, p. 73.

Description: MCZ No. 108075: The specimen is in oral view. Measurements: R at least 19 mm; arm width with open ambulacral groove ca. 2.5 mm. Three of five mouth angle plates are exposed; the mouth frame is in the closed position so that the oral slits are small. In three arms seen in oral view, the ambulacral groove is widely exposed. The groove is very shallow as the laterals do not form a gutter. The ambulacrals alternate. The median suture is nearly straight. The lateral plates are thin, lacking a heavy vertical ridge; they have a thin ventral edge and a thin distal edge on which distally directed spines articulate. The side arm plates overlap by about 50% of their length. The spines of the distal edge are slender and overlap the spines of the next segment by about 20% of length or less. At least four distal spines. Indistinct leaf-like groove spines are recognized by comparison with MCZ 108076. The gap for ventral longitudinal muscles is about 40% of the segment interval.

MCZ No. 108076: Oral view. Disk diameter at least 5.5 mm (not fully exposed); R at least 15 mm; width of ray at edge of disk approximately 2 mm. Oral interradial areas show indistinct plating. The half-jaws on each side of an oral slit are composed of a mouth angle plate and two oral frame plates [possibly a single plate has weathered to look like two plates]. The oral slits end abruptly where the ambulacral groove begins. The proximal ambulacral plates are small, half the length of the succeeding ambulacrals. In one arm the ambulacral groove is widely open and the laterals do not form a gutter; the ambulacral plates actually stand proud of the lateral plates. The double row of ambulacral plates of each ray alternate across a fairly straight but slightly sinuous perradial suture. The ambulacrals are only approximately boot-shaped because the leg and the foot of the boot are about equidimensional. The cups for the tube feet are formed by both the ambulacral boot and the adjoining lateral plate. The ventral edge of the lateral plates is thin and carries three or four broad leaf-like groove spines. When the groove spines are splayed outward the cups for the tube feet are fully exposed. When splayed inward the cups for the tube feet are completely covered. The distal edge of the laterals is thin and carries at least three needle-like spines that do not quite overlap the spines of the next segment. Successive lateral plates do not notably overlap, and they lack a heavy vertical ridge.

MCZ No. 108077: The specimen shows the aboral side of a disk with the arm bases almost entirely missing. Disk diameter ca. 8 mm. The aboral integument is partly worn away to reveal the mouthframe and arm bases (inside the disk) in apical view. The disk integument is a thin granular calcareous mat that does not show discrete plating centrally, but there is a hint of discrete plating in the aboral interradial areas. Discrete plating is suggested also by spines lying in the aboral interradial areas. The half-jaws are quite long and slender; the oral gape is large; the oral slits are capacious. Proximal ambulacrals within the disk are beveled to accommodate the overriding action of the ossicles of the mouth frame during opening of the mouth aperture. 

Ecology: The protasterid ophiuroid Strataster devonicus (Devonian Silica Shale) was reconstructed with “flat scapula-shaped” groove spines because such spines were found loose on the bedding plane in close proximity with the holotype (Kesling 1972:12 and text-fig. 3). The Trenton Falls ophiuroids serve to definitely place leaf-shaped groove spines on a protasterid ophiuroid. Kesling & Chilman (1975:169 and plate 50) remark that the shale at the S. devonicus locality “contains millions of these little flat spatula-shaped spines” and that “The species appears to have been ideally suited to rake through the bottom debris with these large spines along its oral surface.” The unrelated ophiuroid Furcaster (belonging the to suborder Zeugophiurina with ambulacrals in pairs) also has leaf-shaped groove spines, illustrating parallel evolution. This complicates the identification of isolated spines of this type. Many such spines identified as Furcaster are beautifully illustrated by Boczarowski (2001). 

Notes: In this study the specimens are identified only to family level. The unique leaf-like groove spines in MCZ 108075 and 108076 mark this as an undescribed species. Specimen MCZ 108077 is presumed to be the same taxon by association. These specimens are under study by Alexander Glass as part of a larger study of Protasterina and of this family (personal communication April 2004). Schuchert (1915) thought that these specimens represented a new species of Alepidaster but they were reidentified as cf. Protasterina by Hotchkiss (1970). Alepidaster was considered a subjective junior synonym of Taeniaster by Hotchkiss (1970).

 

   
Alepidaster? n. sp., MCZ 108077   Alepidaster? n. sp., MCZ 108076   Alepidaster? n. sp., MCZ 108075
MCZ 108077: Syntype, 8mm wide
 
MCZ 108076: Syntype, 21mm wide
 
MCZ108075: Syntype, 25mm wide

                                   
       
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