Parasmittina soulesi Scholz and Cusi, 1991

Dick, Matthew H. & Grischenko, Andrei V., 2016, Rocky-intertidal cheilostome bryozoans from the vicinity of the Sesoko Biological Station, west-central Okinawa, Japan, Journal of Natural History 51, pp. 141-266 : 191-194

Parasmittina soulesi Scholz and Cusi, 1991

( Figure 16 )

Parasmittina soulesi Scholz and Cusi, 1991, p. 416 , pl. 5, figs 1 – 4.

? Pleurocodonellina soulesi: Tilbrook 2006, p. 172 , pl. 37A, B.

Material examined

NSMT-Te 1097 ( SES- 13), bleached, on SEM stub (with Celleporaria triangula ); NSMT-Te 1102, bleached, dried specimen, SES site; NHMUK 2016.5.13.39, bleached, dried specimen, SES site.

Measurements

AzL, 0.42 – 0.66 (0.517 ± 0.056); AzW, 0.28 – 0.40 (0.311 ± 0.033) (n = 20, 1). OrL, 0.10; OrW, 0.12 (n = 1). SecOrL (including sinus), 0.11 – 0.15 (0.127 ± 0.007); SecOrW, 0.10 – 0.12 (0.107 ± 0.006) (n = 20, 1). OvL, 0.13 – 0.16 (0.15 ± 0.015); OvW, 0.18 – 0.25 (0.22 ± 0.033) (n = 4, 1). Largest colony observed 9 mm across.

Description

Colony circular or irregular, forming a unilaminar, encrusting sheet; light tan to very light chestnut in colour when dried. Zooids distinct, outlined by suture and marginal pores. Frontal wall slightly convex, weakly dimpled in young, marginal zooids ( Figure 16 (a)), nearly flat and more strongly dimpled with age; around 10 small, circular to oval areolae along each lateral margin. Primary orifice ( Figure 16 (a, b)) immersed, difficult to observe; proximal margin more or less straight, formed by large, blunt, medially directed condyles; each condyle with band of minute denticles extending from tip to nearly halfway to lateral margin. Lyrula quite variable, ranging from minute denticle in sinus between condyles ( Figure 16 (a)), to narrow, tapering, non-alate projection bisecting sinus, reaching level of tips of condyles ( Figure 16 (b)). Peristome low to moderately tall, slightly asymmetrical, with secondary sinus variably developed; often bearing one or two low flanges or pointed projections on each side. Marginal zooids with two spines ( Figure 16 (a)) distal to orifice. Frontal avicularia ( Figure 16 (a – c)) single (77%) or paired (23%) (n = 82, 1) proximolateral to orifice, sometimes lacking. Rostrum elevated from frontal surface in young zooids ( Figure 16 (a)), but less so in secondarily calcified older zooids ( Figure 16 (c)); tilted slightly laterally to one side; narrow, elongate, rounded distally. Rostral margins smooth. Medial to each avicularium is small pseudopore; young, marginal zooids have tiny pseudopore in each side of the avicularian chamber. No giant avicularia observed. Ovicell ( Figure 16 (c)) subimmersed. Ooecium broader than long; covered with and surrounded by secondary calcification originating from maternal and distal zooids, same texture as frontal wall; with around eight conspicuous pseudopores in a crescent around the top periphery; proximal margin raised as crescentic lip forming distal part of peristome. Zooids interconnect by uniporous septula, up to six in each distolateral wall and up to six in the distal wall. One ancestrular complex observed ( Figure 16 (d)); ancestrula (mostly obscured by surrounding zooids) appears to have a very broad lyrula; surrounded by triplet of small zooids distally and distolaterally, and pair of larger zooids proximolaterally.

Remarks

While Scholz and Cusi (1991, p. 417) noted in the original description of P. soulesi from the Philippines that ‘ a lyrula is lacking ’, the low median projection responsible for the bifoliate sinus in their specimen can be interpreted as a reduced lyrula. This character is variable in our specimens: zooids can lack the central projection altogether (giving a deep, basally broad sinus) or have a low median denticle (giving a bifoliate sinus) ( Figure 16 (a)), or bear a long, tapering, terminally truncate tooth, essentially a lyrula ( Figure 16 (b)). Our specimens further differ from the Philippine specimen in having fewer, larger pseudopores around the distal margin of the ooecium (around eight, compared to 14 – 20), and in lacking the conspicuous rows of heavy denticles on the condyles. Specimens that Tilbrook (2006) reported as Pleurocodonellina soulesi from the Solomon Islands differ from Philippine and Okinawan material in having two or three distal spines; much larger areolae; raised zooidal margins; hypertrophied spatulate avicularia; and small denticles at the tips of the condyles.

Soule and Soule (1973) erected the genus Pleurocodonellina for Parasmittina -like species lacking a lyrula, designating Pleurocodonellina lahainae Soule and Soule, 1973 as the type species. The original generic description included a round primary aperture with a wide, curving sinus between lateral condyles; no median denticle (i.e. no lyrula); a single (rarely paired), acute, non-median frontal avicularium; and a subimmersed ovicell with a crescent of small pseudopores. Soule and Soule (1973) discussed some additional species that might go into Pleurocodonellina , the best known of which was Smittina signata Waters, 1889 , which has a narrow, U-shaped orificial sinus and a broad crescent of 60 – 70 small pseudopores in the ectooecium. We note that while the original description did not mention oral spines, and Soule et al. (1995) reiterated that Pleurocodonellina lacks oral spines, marginal zooids in the original illustrations ( Soule and Soule 1973) of P. lahainae , the type species, each have a single distal spine scar. Ryland and Hayward (1992, p. 273) addressed this issue by amending the generic diagnosis for Pleurocodonellina to include distal oral spines.

The only character separating Pleurocodonellina from Parasmittina appears to be lack of a lyrula in the former and presence in the latter. The two genera overlap considerably in the number and distribution of ooecial pseudopores, another character putatively distinguishing between them. Thus, while Tilbrook (2006) transferred Parasmittina soulesi to Pleurocodonellina , we have retained it in Parasmittina by virtue of its small but variable lyrula. In some zooids in our specimens, the lyrula is about the size of that typically present in some other species in Parasmittina , such as P. trunculata Tilbrook, 2006 .

Soule et al. (1995, p. 219) argued that lack of a lyrula should prohibit placement of Pleurocodonellina in Smittinidae : ‘ Placing alyrulate species in Smittinidae is... an oxymoron, although they may belong to the same superfamily ’. Parasmittina soulesi is intermediate between Pleurocodonellina and Parasmittina , with some zooids in our specimens having a simple orificial sinus (as in Pleurocodonellina ) and others having a well-developed lyrula (as in Parasmittina ). One interpretation of this variation is that P. soulesi is a Parasmittina species undergoing evolutionary loss of the lyrula – and this leads to further speculation that Pleurocodonellina may prove to be an alyrulate lineage embedded within Parasmittina .

Occurrence

We found a total of four colonies, at the SES and REEF sites. This species was previously known only from the Philippines and the Solomon Islands.

Figures

Figure 16. Parasmittina soulesi Scholz and Cusi, NSMT-Te 1097: (a) marginal autozooids, showing alyrulate orifice (bottom centre) and orifice with weakly developed lyrula (right); (b) orifice with welldeveloped lyrula; (c) ovicelled autozooids; (d) periancestrular zooids (one distal, two distolateral,and two proximolateral; ancestrula obscured, but very broad lyrula evident. All panels are scanning electron microscopic images of bleached specimen. Scale bars: a = 300 µm; b = 100 µm; c, d = 250 µm.