Escharoides jacksoni ( Waters, 1900 )

Kuklinski, Piotr, Taylor, Paul D. & Denisenko, Nina, 2007, Arctic cheilostome bryozoan species of the genus Escharoides, Journal of Natural History 41 (1 - 4), pp. 219-228 : 223-226

Escharoides jacksoni ( Waters, 1900)

( Figures 3 , 4 )

Smittina jacksoni Waters 1900, p 87 , Plate 12, Figure 18.

Mucronella coccinea ( Abildgaard, 1806) : Bidenkap 1897, p 624, Plate 25, Figures 5 , 6.

Escharoides jacksoni var. rostrata Kluge 1946, p 201 , Figure 6; Kluge 1962, p 569, Figure 402; Kluge 1975, p 693, Figure 402.

Escharoides jacksoni: Kluge 1962, p 568 , Figure 401; Kluge 1975, p 692, Figure 401; Powell 1968, p 2294, Plate 5, Figure B; Bille-Hansen 1962, p 33.

Type material examined

Holotype: MM 4307 , 77 ° 559N, 55 ° 109E, collected during Jackson-Harmsworth Expedition, 7 October 1897, Waters Collection.

Other material examined

NHM 2006.07.31.2, Laptev Sea, 74 ° 30.09N, 137 ° 05.09E, Transdrift 1 project, Stn 48, 18 August 1993, 22 m depth, dredge, coll. Schmid ; ZI 30/2945, East Siberian Sea, Stn 25, 23 August 1937, ‘‘ Sadko’ ’, det. Kluge, coll. Gorbunov ; ZI 50/354, NE Polar Basin, Stn 73, 1948, det. Petrovskaya; ZI 7, Fram Straight , Stn 43, 1901, ‘‘ Zaria’ ’, det. Kluge, coll . R.P.E.; ZI 10, Laptev Sea, in front of Pronchischev Bay, Stn 34, ‘‘ Sibiriakov’ ’, trawl, 14 September 1933, det. Kluge, coll. Gorbunov ; ZI 15, Kara Sea, O-b Ruskij– Dickson Bay, Stn 40, ‘‘ Sibiriakov’ ’, trawl, 27 August 1933, det. Kluge, coll. Gorbunov ; ZI 65/50534, Chukchi Sea, depth 39 m, Stn 17, 13 August 2004, ‘‘ Prof. Khromov’ ’, coll. Sirenko, Gagaev, Denisenko Collection ; CMN 2006-0013 , southwestern Baffin Island , 69 ° 55.79N, 80 ° 199W, Stn 820, depth 73 m, 28 August 1956, Powell Collection ; CMN 2006-0014 , Cornwallis Island , 72 ° 44.19N, 94 ° 069W, Stn 62-2014, depth 35 m, 25 July 1962, Powell Collection ; CMN 2006-0015 , Nunavut, Frozen Strait, 65 ° 329N, 84 ° 529W, Stn 61-39, depth 38–42 m, 27 August 1961, Powell Collection ; CMN 2006-0016 , Creswell Bay , 72 ° 46.59N, 94 ° 15.59W, Stn 62-2052, depth 59–62 m, 11 August 1962, Powell Collection .

Description

Colony forming a thick unilaminar crust ( Figure 3A ). Ancestrula ( Figure 3D ) tatiform, oval, with narrow cryptocyst, broad proximal gymnocyst, and 11 spines.

Autozooids irregular in shape, separated by deep grooves, large, 0.88–1.33 mm long (mean 1.02 mm, n 520) by 0.58–0.88 mm wide (mean 0.69 mm, n 520). Frontal shield finely granular, bordered by a single or double row of small, round areolae. Orifice suborbicular; distal border with a broad, smooth, suboral shelf; proximal edge developed as a thick, projecting peristome, sometimes with one or two thickened lateral denticles around proximal inner margin ( Figures 3B , 4B ), and often with a median notch on the rim. Denticles striated when present. Oral spines short, usually numbering four, the outer two fused with the peristome, only two visible in ovicellate zooids. Avicularia typically paired at distolateral corners of autozooids, sometimes single or absent, large, 0.22–0.32 mm long (mean 0.27 mm, n 520) by 0.13–0.20 mm wide (mean 0.15 mm, n 520), directed laterally, rostrum long, tapering distally, rarely hooked at tip; avicularian chamber well developed, pores often present at the base and rarely on chamber itself; mandible elongate-triangular, crossbar calcified.

Ovicell ( Figures 3B , 4B ) hyperstomial, globular, finely granular, slightly longer than broad, large, 0.35–0.46 mm long (mean 0.40 mm, n 520) by 0.37–0.44 mm wide (mean 0.41 mm, n 520); pseudopores scattered over distal part, bordered by a single or double series of small, round areolae.

Distribution

An Arctic, circumpolar species recorded from the Greenland, Barents, Kara, Laptev, East Siberian, and Chukchi Seas; and the Canadian Arctic ( Kluge 1975; current account).

Remarks

Bille-Hansen (1962) and Hayward and Ryland (1999) synonymized Escharoides bidenkapi ( Kluge, 1946) with E. jacksoni ( Waters, 1900) . However, their analyses were based on small sample sizes, and the synonymy is not supported by a more detailed comparison. Our broader investigation using SEM permits us to distinguish E. bidenkapi ( Figure 2 ) and E. jacksoni ( Figures 3 , 4 ) as separate species. Both species have a similar peristome shape, but there is large variation both among colonies and within colonies of Escharoides in this character. However, a few skeletal morphological characters do allow us to distinguish these two species with confidence. In general, the peristome of E. bidnekapi is much more complex than that of E. jacksoni . In E. jacksoni the peristome is never produced into three prominent denticles (cf. Figure 2C ). On average, autozooids of E. bidenkapi are smaller than those of E. jacksoni , as are the avicularia. Also, in the majority of cases, avicularia of E. bidenkapi are directed distolaterally, whereas those of E. jacksoni are typically directed laterally. The frontal shield texture of E. bidenkapi is polygonal, whereas that of E. jacksoni is finely granulated, although in early astogeny E. jacksoni also has frontal shields with a polygonal texture (see Figures 2D , 3D ). A very stable character of skeletal morphology among the specimens studied is the structure of the distal edge of the suboral shelf. In E. bidenkapi this is crenulated, whereas in E. jacksoni it is always smooth. Escharoides jacksoni has more bulbous avicularian chambers, which are better demarcated from the autozooidal frontal shield than in E. bidenkapi .

Escharoides bidenkapi and E. jacksoni overlap in geographical distribution but whereas E. jacksoni is circumpolar in distribution, E. bidenkapi does not occur in some parts of the Arctic (e.g. Canadian Arctic, Chukchi Sea). In our study material, we found one instance of the two species growing together on the same substratum ( Figure 5 ). The adjacent colonies show the distinctive characters mentioned above for the two species, which cannot be ecophenotypic as the colonies are juxtaposed. This specimen therefore supports the assertion that E. bidenkapi and E. jacksoni are two separate species.

According to Kluge (1946), E. jacksoni var. rostrata ( Figure 4 ) exhibits an atypical peristome shape (‘‘strongly raised forward and narrows toward the end’’). However, the majority of skeletal characters (frontal shield, avicularian size and shape, smooth-edged suboral shelf) allow us to subsume this taxon into E. jacksoni (Waters) .

Figures

Figure 2. Escharoides bidenkapi (Kluge, 1946), bleached. (A) Colony showing autozooids and ovicellate zooids (lectotype: ZI 30/2945); (B) ovicellate zooid with two lateral avicularia (ZI 36/5223); (C) orifice of autozooid with two lateral avicularia and characteristic suboral shelf with distal crenulation (ZI 38/5468); (D) ancestrula and surrounding zooids (ZI 38/5468). Scale bars: 100 mm (A, C); 200 mm (B, D).

Figure 3. Escharoides jacksoni (Waters, 1900), bleached. (A) Colony showing autozooids and ovicellate zooids (NHM 2006.07.31.2); (B) autozooid lacking avicularia and ovicellate zooid with paired lateral avicularia (ZI 50/ 354); (C) orifice of autozooid with characteristic plain suboral shelf (NHM 2006.07.31.2); (D) ancestrula and surrounding zooids (ZI 50/354). Scale bars: 1 mm (A); 100 mm (B, C); 200 mm (D).

Figure 4. Escharoides jacksoni (Waters, 1900), material formerly placed in Escharoides jacksoni var. rostrata (Kluge, 1946) (ZI 1/2364), bleached. (A) Colony encrusting a stem showing autozooids and ovicellate zooids; (B) ovicellate zooid with paired lateral avicularium; (C) autozooid with one lateral avicularia; (D) orifice of autozooid with characteristic plain suboral shelf. Scale bars: 200 mm (A); 100 mm (B, C, D).

Figure 5. Escharoides bidenkapi (Kluge, 1946) (black arrow) growing on a colony of Escharoides jacksoni (Waters, 1900) (white arrows) (ZI 1), bleached.