Han et al.—Olivooides-like tube aperture in carinachitids
carinachitids reflects competition for ecological tiering among a varied benthos. In contrast to the reduced vestigial peridermal theca of cubopolyps and most scyphistomae, the thickening of the tube wall in carinachitids, and coeval tubular fossils (anabaritiids, hyolithelminths), indicate an adaptive strategy focusing on defense against predators such as cycloneuralians (e.g., Liu et al., 2014a; Zhang et al., 2015). Interestingly, sus- pension feeding by the hypostome rather than normal elongate tentacles with nematocysts has also been observed in extant polyps of Eudendrium (Hydrozoa) (Puce et al., 2002), in which the mucous-lined gastroderm plays a major role in capturing food particles such as zooplankton. Such behavior correlates with high concentrations of food particles and intense water movement, a scenario that seems compatible with the marine shelf environment favored by Cambrian small shelly fossils (Yin et al., 1999; Steiner et al., 2004, 2007). The asynchronous displacement of the ribs in Carinachites
spinatus indicates that the flexible tube aperturemay have opened to a greater extent in this taxon than in olivooids. Relative to the radius of the tube, both the width and height of the ribs on Emeiconularia amplicanalis are smaller than in E.
trigemme.This fact indicates that the oral lobes of E. amplicanalis could only partially cover the tube aperture, thus allowing continual contact of the soft body with the ambient environment. Presumably, retractile tentacles in E. amplicanalis,ifpresent,could protrude beyond the tube opening, thus enabling limited predatorial behavior.
Comparisons
Carinachitids versus coronate polyps.—Carinachitid tubes resemble the chitinous periderm of coronate scyphozoans (i.e., Stephanoscyphus), which are sheathed in a cone-shaped tube showing well-developed longitudinal folds and horizontal annulations (Chapman, 1966; Werner, 1966, 1973). However, differences between them are also evident. In particular, Stephanoscyphus may be either solitary or colonial. The periderm of colonial forms is irregularly branched (Jarms, 1991), in some cases with a tube-in-tube structure (Werner, 1966, fig. 13). By contrast, carinachitid tubes are exclusively solitary. Second, whereas Stephanoscyphus has an operculum that is separate from the tube, the tube aperture and lappets of carinachitids constitute a continuous extension of the rest of the tube. Third, the scyphozoan periderm, including the peridermal teeth or cusps inside the tube of Stephanoscyphus, is secreted by ectoderm of the lateral body wall. By contrast, the external layer of the carinachitid tube, except for the apex, was generated by epithelium of the oral part, and neither teeth nor cusps are present within the carinachitid tube. Fourth, Stephanoscyphus tubes are more or less circular in transverse cross section and uniform in thickness; by contrast, carinachitid tubes are polygonal and exhibit distinct faces and corner sulci. Fifth, an operculum with triangular cusps is absent in Stephanoscyphus (Werner, 1966), while oral lobes or lappets are a consistent diagnostic feature of the tube of carinachitids and co-occurring olivooids. Finally, strobilation, a characteristic of Stephanoscyphus, has not been observed in carinachitids. In short, these comparisons suggest that carinachitids may only be distantly related to extant scyphozoans.
Comparison among carinachitids, olivooids, hexangulaconulariids, and conulariids.—Prior to conducting a cladistic analysis of relationships among extant and fossil taxa within Medusozoa, morphological comparisons among olivooids, carinachitids, hex- angulaconulariids, and Paleozoic conulariids are necessary. As noted previously (He, 1987), the similarities among the skeletons of olivooids, carinachitids, hexangulaconulariids, and Paleozoic con- ulariids are striking (Table 1). They include: (1) possession of a superficially cone-shaped tube that almost completely enveloped the soft tissue (Qian and Bengtson, 1989; Sendino et al., 2011); (2) tube with serially repeated transverse and longitudinalwrinkles (Qian and Bengtson, 1989) representing periodic growth by oral addition (Brood, 1995); (3) fine, regularly spaced longitudinal striations, ~5–10µm in width, as one of typical features of Olivooides tubes
(e.g., Yue and Bengtson, 1999, fig. 2D; Steiner et al., 2014, fig. 12.13, 12.14), are present also on the corner surface of
Carinachites tetrasulcatus (e.g., Conway Morris and Chen, 1992, fig. 9.15, 9.16); (4) tube tapered in the apertural region (Qian and Bengtson, 1989), where the tube aperture is folded inward (e.g., Brood, 1995; Steiner et al., 2014); (5) all tubes exhibit distinct apical and abapical regions (Fig. 1.8) (Van Iten et al., 2010), although the carinachitid apex is unknown yet; and (6) radial symmetry, a characteristic that is a link to the medusozoans, is well represented by all four families. Apart from the mentioned similarities, additional specific
similarities between carinachitids and olivooids are remarkable: (1) The cone-shaped tubes of these two taxa exhibit similar variation in the pattern of radial symmetry. Both of them exhibit rare pentaradial symmetry and dominant tetraradial symmetry. However, triradial symmetry is not known in olivooids. (2) The
9
Comparison with extant hydrothecae.—Extant, colonial thecate hydranths begin and complete their development within a small, capsule-like hydrotheca. The hydrotheca in some species, for example Sertulariella quadrata Nutting, 1900a, is square in transverse cross section and exhibits dense transverse striations or longitudinal folds (i.e., S. rugosa (Linnaeus, 1758)) similar to those of carinachitid tubes (Nutting, 1900a). The oral end of the hydrotheca has a protective operculum with or without a set of triangular, plate-like teeth or converging cusps capable of opening and closing (Crowell, 1991). Many species of Sertu- lariella, for example S. quadrata, S. rugosa, and S. peculiaris (Leloup, 1935 in Galea, 2008), have an operculum with four triangular cusps (Nutting, 1900a; Chapman, 1966; Galea, 2008) that are somewhat similar to the lobes of Carinachites spinatus. Symplectoscyphus (Millard, 1975) and S. rathbuni (Nutting, 1900a) have three teeth similar to those of Emeiconularia (assuming our reconstruction is correct). Notably, the chitinous hydrotheca and operculum are secreted by glandular cells of the epidermis of the hydranth, especially the hypostome (Berrill, 1949), thus supporting the previously inferred oral formation of carinachitid tubes. In rare cases, the apertural teeth of the hydrothecae are folded inward as in solitary carinachitid tubes (Nutting, 1900b, pl. 14, fig. 6). Major differences between hydrothecae and carinachitids include: (1) the colonial habit of hydrothecae; (2) the absence of triangular cusps in the lateral walls of hydrothecae; and (3) the teeth in hydrothecae, which are sheet-like, with a free adaxial end, and thus are quite different from those of carinachitids.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124
