Glyptometra lateralis, from Okeanos Explorer.

Belongs within: Tropiometracea.

Forgotten feather stars
Published 19 January 2009
The Atlantic charitometrid Crinometra brevipinna. Photo by John E. Miller.

Despite including the vast majority of modern species (and the best-studied of modern species), the feather stars (the order Comatulida) are in fact somewhat odd creatures within the main scope of crinoid historical diversity. The main point of oddness, of course, is their massively reduced stem (other strange features, which they share with other living crinoids, include the reduction of plating on the adoral side of the animal). When they first settle down from their free-swimming larval stage, feather stars are attached to the substrate by a stalk as in more typical crinoids, but before they reach maturity they once again break free. Technically, however, adult feather stars are not completely stemless—the proximalmost part of the stem is retained and becomes expanded and fused with the infrabasals (the lowermost ring of plates in the main body of the crinoid) to form the large basal plate known as the centrodorsal (Breimer 1978a—it may seem odd to have something called the “centrodorsal” on the underside of the animal but the thing is that, compared to other living echinoderms, crinoids are upside-down). The centrodorsal is the point of attachment for the cirri, tendril-like outgrowths of the underside. The cirri are used by the feather star for moving about, like something out of a Japanese cartoon.

Not that they necessarily do much moving about. Though feather stars are capable of a surprising amount of motility when the mood takes them (some even using their arms to become active swimmers), the mood does not often take them. Like their permanently attached ancestors, feather stars are still filter feeders, a lifestyle that is best achieved in a sedentary manner. Crinoids will only move if the local conditions become unfavourable, and then only as far as they must to find a more suitable location. Once there, they will fix themselves onto any available piece of substrate—Austin Clark provided a brief but disturbing description of the consequences of comatulids being denied a suitable attachment site (quoted in Breimer, 1978b):

If a dozen specimens of Antedon were thrown at night into a large basin of water and were left without any means of attachment they were all found dead in the morning, conglomerated at the bottom of the basin, clinging to each other with their cirri and having their arms intertwined in such a manner as to suggest the idea that they had died of the asphyxia produced by overcrowding after exhausting themselves in efforts to find suitable attachment…

Chondrometra robusta, a charitometrid from around the Philippines and Indonesia, with distinctly large cirri compared to other members of the family. Figure from Clark (1950).

The majority of studies on modern comatulids seem to relate to two families, the Antedonidae and Comasteridae—particularly the former. The Charitometridae, in contrast, have been much more neglected. As far as I can tell, they seem to have been pretty much untouched since being monographed in 1950 by Austin Clark who recognised 32 species divided between eight genera, distributed pretty much world-wide but with the main centre of diversity in the Pacific (only a single genus, Crinometra, seems to have made it into the Atlantic*). Clark distinguished the Charitometridae from related families by the presence of distinct covering plates at the bases of the pinnules (the side-branches of the arms), by the lack of differentiation between pinnules at the bases and more distally on the arms, and by the relatively undifferentiated cirri. In general, Clark regarded the Charitometridae as a more generalised form than the closely related Thalassometridae, though of course in those pre-cladistic days its a little difficult to know exactly what he meant by this—whether or not he was actually saying that the charitometrids were ancestral to the thalassometrids, or whether he was just making a comparison.

*Clark recognised only a single species in this genus, Crinometra brevipinna, but a large number of varieties within that genus. Whether some of those varieties might be recognised as species were the genus to be revised, I couldn’t say.

This lack of specialisation is perhaps part of the reason for the lack of study of charitometrids. Clark (1950) writes at length about the difficulties of distinguishing taxa within the family and one gets the distinct impression that he was not particularly satisfied even with the system he himself ended up using. Even more of a factor, probably, is that charitometrids seem to be mostly inhabitants of deeper waters—Clark gives a depth range of 55–2194 metres. The ecology of the group, not surprisingly, seems to be completely untouched. We know that they’re down there but we don’t really know what they’re doing with their time.

Systematics of Charitometridae
<==Charitometridae [Charitometrinae]
    |--Crinometra Clark 1909WR78
    |    `--*C. brevipinna (Pourtalès 1868)WR78 (see below for synonymy)
    |--Chlorometra Clark 1909 [incl. Diodontometra Gislén 1922]WR78
    |    `--*C. garettiana (Clark 1907)WR78 (see below for synonymy)
    |--Charitometra Clark 1907WR78
    |    |--*C. incisa (Carpenter 1888) [=Antedon incisa]WR78
    |    `--C. basicurva (Carpenter 1884) [=Antedon basicurva]C50
    |--Poecilometra Clark 1907WR78
    |    |--*P. acoela (Carpenter 1888) [=Antedon acoela]WR78
    |    `--P. scalaris (Clark 1907) [=Antedon scalaris]C50
    |--Chondrometra Clark 1916WR78
    |    |--*C. robusta (Clark 1911) [=Chlorometra robusta]WR78
    |    |--C. aculeata (Carpenter 1888) [=Antedon aculeata, Charitometra aculeata, Chlorometra aculeata]C50
    |    `--C. rugosa Clark 1918 [=Chlorometra rugosa Clarke & Wheeler 1915 (n. n.)]C50
    |--Strotometra Clark 1909WR78
    |    |--*S. hepburniana (Clark 1907) [=Antedon hepburniana, Charitometra hepburniana]C50
    |    |--S. ornatissimus Clark 1912 [=S. ornatissimns (l. c.)]C50
    |    |--S. parvipinna (Carpenter 1888) [=Antedon parvipinna, Charitometra parvipinna]C50
    |    `--S. priamus Clark 1912C50
    |--Monachometra Clark 1916 [=Monachomera (l. c.); incl. Perissometra Clark 1916]WR78
    |    |--*M. fragilis (Clark 1912) [=Pachylometra fragilis]WR78
    |    |--M. flexilis (Carpenter 1888)C50 (see below for synonymy)
    |    |--M. patula (Carpenter 1888) [=Antedon patula, Charitometra patula, Pachylometra patula, Perissometra patula]C50
    |    `--M. robusta (Carpenter 1888) (see below for synonymy)C50
    `--Glyptometra Clark 1909WR78 (see below for synonymy)
         |--*G. tuberosa (Carpenter 1888)WR78 [=Antedon tuberosaWR78, Charitometra tuberosaC50]
         |--G. angusticalyx (Carpenter 1884) (see below for synonymy)C50
         |--G. crassa (Clark 1912) [=Pachylometra crassa, Perissometra crassa; incl. Pe. gorgonia Clark 1918]C50
         |--G. distincta (Carpenter 1888)C50 (see below for synonymy)
         |--G. inaequalis (Carpenter 1888) (see below for synonymy)C50
         |--G. invenusta (Clark 1909) [=Pachylometra invenusta, Perissometra invenusta]C50
         |--G. investigatoris (Clark 1909)WR78 (see below for synonymy)
         |--G. lata (Clark 1907) [=Antedon lata, Charitometra lata, Perissometra lata]C50
         |--G. lateralis (Clark 1908)C50 [=Charitometra lateralisC50, *Calyptometra lateralisC50]
         |--G. levigata (Clark 1909) [=Pachylometra levigata, P. laevigata]C50
         |--G. macilenta (Clark 1909) [=Pachylometra macilenta, Perissometra macilenta; incl. Pe. occidentalis Clark 1929]C50
         |--G. sclateri (Bell 1905) [=Antedon sclateri, Charitometra sclateri, Pachylometra sclateri]C50
         |--G. septentrionalis (Clark 1911) [=Pachylometra septentrionalis, Crossometra septentrionalis]C50
         |--G. sparksi (John 1937) [=Perissometra sparksi]C50
         `--G. timorensis Clark 1912 [=Perissometra timorensis]C50

*Chlorometra garettiana (Clark 1907)WR78 [=Antedon garettianaWR78, Charitometra garettianaC50; incl. *Diodontometra bocki Gislén 1922WR78, C50]

*Crinometra brevipinna (Pourtalès 1868)WR78 [=Comatula brevipinnaWR78, Antedon brevipinnaC50, Charitometra brevipinnaC50, Pachylometra brevipinnaC50; incl. Crinometra brevipinna var. angusta Clark 1950C50, Antedon angusticalyx Hartlaub 1912 non Carpenter 1884C50, Cr. concinna Clark 1909C50, Cr. brevipinna var. concinnaC50, Antedon brevipinna var. coronata Hartlaub 1912C50, Cr. brevipinna var. coronataC50, An. brevipinna var. decora Hartlaub 1912C50, An. brevipinna var. diadema Hartlaub 1912 non Clark 1907C50, Crinometra brevipinna var. diademaC50, An. brevipinna var. elegans Hartlaub 1912C50, Cr. gemmata Clark 1909C50, Cr. brevipinna var. gemmataC50, Antedon brevipinna var. gracilis Hartlaub 1912 nec Solanocrinus gracilis Walther 1886 nec Antedon gracilis Carpenter 1888C50, Cr. brevipinna var. gracilisC50, An. granulifera Pourtalès 1878C50, Actinometra granuliferaC50, Charitometra granuliferaC50, Crinometra brevipinna var. granuliferaC50, Antedon brevipinna var. granulosa Hartlaub 1912C50, Cr. brevipinna var. granulosaC50, Charitometra imbricata Clark 1908C50, Crinometra imbricataC50, Pachylometra imbricataC50, Cr. insculpta Clark 1909C50, Cr. brevipinna var. insculptaC50, Antedon brevipinna var. laevis Hartlaub 1912 non Carpenter 1888C50, Cr. brevipinna var. laevisC50, Cr. margaritacea Clark 1909C50, Cr. brevipinna var. margaritaceaC50, Cr. mortenseni Clark 1921C50, Antedon brevipinna var. ornata Hartlaub 1912C50, Cr. brevipinna var. ornataC50, An. pourtalesii Carpenter 1888C50, An. brevipinna var. pourtalesiC50, Charitometra pourtalesiC50, Crinometra brevipinna var. pourtalesiC50, Cr. brevipinna var. pulchella Clark 1950C50, Antedon brevipinna var. pulchra Hartlaub 1912 non Crinometra pulchra Clark 1909C50, Cr. pulchra Clark 1909C50, Cr. brevipinna var. pulchraC50, An. brevipinna var. spinosa Hartlaub 1912C50, Cr. brevipinna var. spinosac50, Cr. transversa Gislén 1933C50, Cr. brevipinna var. transversaC50, Antedon brevipinna var. tuberosa Hartlaub 1912 non Carpenter 1888C50, Cr. brevipinna var. tuberosaC50]

Glyptometra Clark 1909WR78 [=Glytometra (l. c.)C50; incl. Calyptometra Clark 1916WR78, Crossometra Clark 1916WR78, Pachylometra Clark 1909WR78]

Glyptometra angusticalyx (Carpenter 1884) [=Antedon angusticalyx, Charitometra angusticalyx, Pachylometra angusticalyx, Perissometra angusticalyx]C50

Glyptometra distincta (Carpenter 1888)C50 [=Antedon distinctaC50, Charitometra distinctaC50, Crossometra distinctaC50, *Pachylometra distinctaWr78; incl. Pa. selene Clark 1911C50, Glyptometra selenaB78, Perissometra seleneC50, Charitometra smithi Clark 1908C50, Pachylometra smithiC50]

Glyptometra inaequalis (Carpenter 1888) [=Antedon inaequalis, A. inequalis (l. c.), Charitometra inaequalis, Pachylometra inaequalis]C50

Glyptometra investigatoris (Clark 1909)WR78 [=Pachylometra investigatorisWR78, *Crossometra investigatorisWR78; incl. P. helius Clark 1912C50, C. heliusC50, P. luna Clark 1911C50]

Monachometra flexilis (Carpenter 1888)C50 [=Antedon flexilisC50, Charitometra flexilisC50, Pachylometra flexilisC50, *Perissometra flexilisWR78]

Monachometra robusta (Carpenter 1888) [=Antedon robusta, Charitometra robusta, Pachylometra robusta, Perissometra robusta]C50

*Type species of generic name indicated


[B78] Breimer, A. 1978a. General morphology: recent crinoids. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 1 pp. T9–T58. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

Breimer, A. 1978b. Ecology of recent crinoids. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 1 pp. T316–T330. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[C50] Clark, A. H. 1950. A monograph of the existing crinoids. Vol. 1. The comatulids. Part 4c. Superfamily Tropiometrida (the families Thalassometridae and Charitometridae). Bulletin of the United States National Museum 82 vol. 1 (4c): 1–383.

[WR78] Wienberg Rasmussen, H. 1978. Articulata. In: Moore, R. C., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt T. Echinodermata 2. Crinoidea vol. 3 pp. T813–T927. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

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