Charles Messing's Crinoid Pages: Symbols and Abbreviations

Though not often necessary, basal ossicles are abbreviated B (plural: BB) and radials R (plural: RR). Columnals may be abbreviated C, beginning with the first adjacent to the crown (C1), and with series separated by a dash, e.g., C12‒109.

As noted on the Morphology / Crown and calyx / Arms and ray page, brachitaxes (or division series) are series of 2 to 20 brachials between branch points, either following a radial and including the first ossicle at which the ray branches (axillary or axil) or following an axil and including the next. In the system widely used for stalked crinoids (particularly Isocrinida), each brachial is indicated by Br followed by an Arabic number indicating its place in the sequence from proximal to distal. Specific ossicles in brachitaxes are preceded by a Roman numeral beginning with the most proximal, e.g., IIBr3 is the third ossicle in the second brachitaxis. An appended ax (for axil) indicates an entire brachitaxis, e.g., IIIBr6ax is the third brachitaxis composed of 6 ossicles, the last of which is an axil. For unbranched arms following the final axil, e.g., Br5 is the fifth ossicle of an undivided arm (Roux et al., 2002; Mironov, 2019).

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In feather stars, Br indicates an entire brachitaxis, e.g., IIIBr4 is a third brachitaxis composed of four ossicles. Most older literature (e.g., A. H. Clark, 1931, 1941, 1947, 1950; A. M. Clark, 1972; Messing 1995) used a subscript to distinguish individual ossicles from entire brachitaxes, e.g., IIIBr₄ for the fourth ossicle in the third brachitaxis. To reduce possible confusion, I began using br for individual ossicles (e.g., Messing, 1997; Messing, et al., 2000), e.g., IIIbr₄ for the fourth ossicle of the third brachitaxis and br₃ for the third brachial of the undivided arm. However, the combination of br AND subscript is not necessary, and I have begun omitting the subscript for individual ossicles, e.g., IIIbr4 and br3 for the preceding examples (Messing, 2020). In one variation that attempted to more clearly reflected ossicle homologies, I (Messing, 2013) treated the entire series of brachials of the undivided arms arising from a primibrach series (IBr) as secundibrachial ossicles, abbreviated as IIbr₁, IIbr₂, etc. (rather than br₁, br₂), a practice characteristic of the fossil crinoid literature (e.g., Hagdorn and Campbell, 1993). A newer variation identifies axils, e.g., Iax2 (or Iax₂) identifies the second ossicle of the first brachitaxis (primibrachial series) as an axil. Brs or Brr (or brr) may be used as plurals, e.g., brr3 through 6, or brr3‒6.

NOTE: The explanation of feather star brachitaxis abbreviations in Hess (2011, p. 11) attributed to me (in Messing, 1997) incorrectly indicates an entire brachitaxis using lower case br, i.e., Ibr2 (rather than IBr2) for the entire primibrach series and omits the subscript for individual ossicles, i.e., IIIbr4 (instead of IIIbr₄) for the fourth ossicle of the third brachitaxis. It only took me nine years to notice that—a bit too late to fix it.

The great majority of living crinoids (including stalked crinoids) with ten or more arms, that is, five rays that branch at least once, have two ossicles in the first brachitaxis (IBr2). So, to orient yourself, the radial is the second ossicle counting from the first axil toward the ray base. Exceptions are the stalked genera Metacrinus and Saracrinus, which have more ossicles in the first division series.

Ossicles of the first and second brachitaxes are often referred to as primibrachs (or primibrachials) and secundibrachs, with those of the third and fourth series more rarely called tertibrachs and tetrabrachs. Much of the 19th-century literature referred to these as costals, distichals, palmars and post-palmars (Carpenter, 1888).

References

A plus sign (+) indicates a non-muscular articulation between two brachials. Unfortunately, three different non-muscular brachial articulations exist: syzygy, synostosis and transverse synarthry. In feather star rays, non-muscular articulations with flat facets are generally syzygies (usually visible externally as a perforated line), while, in stalked crinoids, synostoses are most frequent (visible externally as a thin line with no ligament between adjacent ossicles). Both are typically indicated by +. So, in feather stars, IIBr4(3+4) is a second brachitaxis of four ossicles with the third and fourth joined by non-muscular articulation; br9+10 refers to the ninth and tenth brachials united by syzygy (Messing, 1997) (or Br₉₊₁₀ in older literature). A transverse synarthry has sometimes been identified by a 1-em dash (—), although now only rarely, e.g., IIBr4(1—2, 3+4) for a secundibrachial series of four ossicles with brr1 and 2 joined by transverse synarthry and brr3 and 4 by syzygy (Gislén, 1934; Messing, 1995; Messing, et al., 2000).

NOTE: Hess (2011) used a dash to identify non-muscular articulations in a list of symbols, i.e., IIBr3–4, in a list of symbols for crinoid morphology but I cannot find that he applied it in descriptions in the text.

The sequence of articulations in a stalked crinoid arm, or brachial formula, is often of diagnostic importance. The ossicles joined by a synostosis are typically treated as a brachial pair, noted by a + sign, whereas a brachial with a muscular articulation on both ends is called a free brachial and lacks a symbol. So, a series of brachials from br1 through br6 with synostoses between brr1 and 2 and between brr5 and 6, and with muscular synarthries between brr2 and 3, 3 and 4, and 4 and 5, would have the formula 1+2 3 4 5+6 (sometimes with the free brachials in red) (Roux & Lambert, 2011), or 1+2,3,4,5+6 (Mironov, 2008). In a variation on this, Mironov (2008) gave the number of consecutive brachials with muscular articulations between two non-muscular articulations, e.g., a portion of an arm with the formula 6+5 consists of 11 brachials with a non-muscular articulation dividing the series into two groups of 6 and 5 brachials, with 5 and 4 consecutive muscular articulations in the first and second series, respectively. So, he represented a brachial formula of 1+2,3+4,5,6,7,8 as 1+2+5. For feather stars, descriptions of the middle and distal undivided arms just give the intersyzygial interval—the number of muscular articulations between syzygies, e.g., 3 or 4-16.

References

Feather star cirri often require detailed description. The total number of cirri on an individual is given as a Roman numeral followed by the number of cirrals per cirrus as an Arabic numeral. Species descriptions typically give a range for both, e.g., XVII-XXVII, 15-29. Individual cirrals are indicated by c followed by an Arabic numeral (or subscript in older literature) counting from the base of the cirrus (e.g., c3, c17).

P indicates a pinnule. Arabic numbers and lower-case letters indicate successive exterior and interior pinnules, respectively (e.g., P1, P2, Pa, Pb). The interior side of an arm or brachitaxis is that side closest to the extrapolated median axis of the preceding axil. In older literature, the numbers are subscripts (e.g., P₂, P_b) (A. H. Clark, 1931; Messing, 1997). In most feather star species, br2 bears exterior P1, br4 bears interior Pa (rather than br3, because most feather stars have br3+4 united by syzygy; the proximal ossicle of a pair joined by non-muscular articulation (syzygy, synostosis, or synarthry) never bears a pinnule); br5 bears exterior P2; br6 bears Pb, and so on. Brachitaxes of three or four ossicles bear an exterior pinnule on the first or second ossicle, respectively, indicated by a Roman numeral corresponding to the brachitaxis (e.g., PII (or P_II in older literature) on IIbr2). However, in many stalked crinoids and a few feather stars, pinnules first appear further out along the arm. In feather stars, the first pinnule that appears is sometimes identified as if all pinnules were present, e.g., P2 on br5 (Messing, 1984). However, the first pinnule may be called P1 regardless of its brachial, e.g., P1 on the inner side of Br9 (Mironov, 2008), which obscures homology. The location of pinnules in a brachial series are sometimes indicates by a bar above or below the numeral that indicates a brachial, e.g., 1+2, 3, 4+5, 6+7 (Gislén, 1924; A. M. Clark, 1973).

Some papers specify pinnulars, the individual segments of a pinnule, as either Pn (Mironov, 2008) or p (Eléaume, et al., 2012), e.g., Pn1 or p1 as the first pinnular of a pinnule. As a more condensed alternative, I have used a parenthetical subscript to identify particular pinnulars (numbered from the pinnule base) of specific pinnules, e.g., P3₍₂₎ refers to the second pinnular of the third pinnule (Messing, 2020). 

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