Atelecrinus

Messing, Charles G., 2013, A revision of the genus Atelecrinus PH Carpenter (Echinodermata: Crinoidea), Zootaxa 3681 (1), pp. 1-43 : 5-8

Atelecrinus PH Carpenter, 1881

Atelecrinus PH Carpenter 1881:16 –18; 1882:488–489; 1888:68–70.— Hartlaub 1912:480 –481.—AH Clark 1918:262, 266– 267.— Clark and Clark 1967:817 –819.—AM Clark 1970:49.

Diagnosis. Atelecrinidae with centrodorsal hollow and thin-walled, closely joined to basal ring; central cavity diameter>0.6 of basal diameter; adoral rim of centrodorsal with five shallow interradial depressions ( Figure 3 a). Cirrus sockets in 10 columns with moderately (Figure 2a) to strongly developed (Figure 2b) aborally-projecting lateral fulcral tubercles, triangular in side view; cirri tapering to a point with no opposing spine, of up to 40 segments, 65 mm long. Externally visible portion of each basal flat or slightly arched, weakly or moderately swollen interradially, with lateral portions parallel-sided or tapering, and ends contiguous midradially; sometimes reduced, triangular and separated midradially. Aboral surface of basals with featureless, central depression ( Figure 3 b) and with adorally curved and distally expanded pair of interior projections. Radial cavity with delicate aboral calcareous deposit. Most proximal pinnule usually on IIbr17.

Type species. Atelecrinus balanoides PH Carpenter, 1881.

Other included species. Atelecrinus helgae AH Clark, 1913.

Remarks. Unlike Paratelecrinus and (most) Adelatelecrinus , described below, Atelecrinus has a tight suture between centrodorsal and basal ring, and shallow interradial depressions rather than deep, ring-shaped pits on the adoral rim of the centrodorsal ( Messing 2003). Although these deep pits are usually associated with an interradial, ligament-filled, externally visible gap or slit between centrodorsal and basals, a few Adelatelecrinus sulcatus specimens also exhibit the tight suture of Atelecrinus ; the presence of the deep pits therefore cannot be uniformly recognized without dissociation. A few Ad. sulcatus specimens also share with Atelecrinus comparatively weaker cirrus socket fulcral tubercles, and a dissociated specimen of At. balanoides and one of Ad. sulcatus both have a cluster of irregular calcareous needles forming a thin, delicate plug at the aboral end of the radial cavity not yet seen in other atelecrinids.

Centrodorsal Basals

Rοughly quadrate

. anomalus 1.4 - 10 3 Nοne Τhick∶Heptagοnal Nοne Nοne excavatiοn

……continued on the next page Cirri Radial Ibr1 Iax2 (axil)

Taxon Opposing spine Profile angle Lateral margins Shape Lateral margin. balanoides - <90º Parallel Rhοmbic Smοοth

AM Clark (1977) attributed a post-pentacrinoid juvenile (centrodorsal basal diameter 0.6 mm) collected by R/ V Atlantis II off Argentina to Atelecrinus sp. based on its complete basal ring, very attenuated cirri, and lack of pinnules proximal to IIbr14. This identification may not be correct. Remodeling of the basals into a rosette takes place after stem loss in some other comatulids, e.g., Antedon bifida (Pennant, 1777) (WB Carpenter 1866). Similarly attenuated cirrus segments occur in other deep-water comatulids, e.g., Bathymetra , Thaumatometra ( Clark and Clark 1967) , although the latter have an opposing spine not present in the Atlantis specimen. The initial pinnule appears at a similar distance along the arm (IIbr12) in Antedon serrata AH Clark, 1908b (as Compsometra serrata in Mortensen 1920). In addition, the proximal syzygies lie at 3+4 and 9+10, as in Antedonidae , rather than 3+4, 6+7, 9+10, as in Atelecrinidae . AM Clark (1977) also attributed three pentacrinoid postlarvae to Atelecrinus sp. based on the similarity of their aboral cups to that in the juvenile (one was collected at the same station). However, the constricted base of the basal ring and the raised median belt on the more distal figured columnals (her fig. 5b) are characteristic of many Hyocrinidae , which retain the stalk (e.g., Roux & Pawson 1999, Roux 2002, Roux et al. 2002). Nevertheless, these pentacrinoids may be comatulids; little enough is known about postlarvae in any deep-sea crinoids.

Figures

FIGURE 3. Adoral view of centrodorsal cavity of (a) Atelecrinus balanoides PH Carpenter showing shallow interradial depressions, and (c) Paratelecrinus orthotriremis n. sp. showing interradial buttresses and deep pits. Aboral view of basal ring of (b) At. balanoides, showing central, shallow, flat depression on each basal, and (d) P. orthotriremis showing central spoonshaped fossa on each basal. Arrows indicate suture of basal with radial ossicle. R = radial ossicle. Scale bars (a – d) 0.5 mm.