Thalamoporella karesansui, Dick & Grischenko, 2016

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 (3 - 4), pp. 141-266 : 156-161

Thalamoporella karesansui sp. nov.

( Figure 4 (a–e))

Etymology

The specific name is a noun in apposition (Japanese karesansui: Zen rock garden), referring to the raked-sand appearance of the granulated floor of the avicularian rostrum.

Material examined

Holotype: NSMT-Te 1060 ( SES-43 ), bleached, on SEM stub . Paratypes: NSMT-Te 1061, dried specimen, SES site; NSMT-Te 1062, seven dried specimens, SES site; NHMUK 2016.5 . 13.7, SES-Thal1, bleached, on SEM stub; NHMUK 2016.5 .13.8–11, four dried specimens, SES site.

Measurements

AzL, 0.63–0.80 (0.702 ± 0.051); AzW, 0.38–0.46 (0.423 ± 0.025) (n = 20, 1). OrL, 0.16–0.21 (0.188 ± 0.012); OrW, 0.18–0.22 (0.200 ± 0.012) (n = 20, 1). OvL, 0.47; OvW, 0.60 (average values, n = 2). AvL, 0.74–0.86 (0.795 ± 0.040); AvW, 0.25–0.34 (0.278 ± 0.025) (n = 15, 1). Calliper H, 0.024 –0.030 (0.026 ± 0.003); calliper W, 0.046 –0.054 (0.049 ± 0.003); calliper H/ W ratio, 0.44–0.65 (0.547 ± 0.081) (n = 7, 1). Compass lengths in several discrete size ranges: 0.069 –0.094 (n = 5); 0.144 –0.163 (n = 4); 0.193 –0.209 (n = 3); 0.364 (n = 1).

Description

Colony forming a unilaminar, encrusting sheet; irregular in outline, up to several centimetres in extent; tightly adhering to substratum; dried specimens pale yellowish-tan. Zooids distinct ( Figure 4 (a, b)). Cryptocyst finely granulated; area proximal to opesiules flat and perforated with 20–40 small, circular, evenly spaced, often occluded pseudopores. Mural rim narrow, beaded, raised around entire margin of cryptocyst proximal to orifice. Opesiules large; oval or irregular; one often larger than other; zone between opesiules somewhat sunken. Basal insertions ( Figure 4 (c)) usually paired, but asymmetrical, of different shape and size between the two sides, consisting of two hooks, or one hook and one bar; usually closed distally by looping back to reconnect with lateral wall. Orifice ( Figure 4 (a, b)) usually broader than long, with broad sinus between bracket-like hinge articulations; proximal margin of sinus straight or slightly convex; orifice broadly D-shaped distal to articulations. Avicularia ( Figure 4 (a, b)) fairly common, longer than autozooids (ratio of average AvL to average ZL, 1.14; ratio of AvL to length of sibling zooid, 0.95–1.26, average 1.12); cryptocyst broad, flat, entirely granulated. Rostral opening narrow, elongate, occupying more than half the total length of avicularium. Mandibular articulations conspicuous, sharp, bracket-like, at proximal edge of broad, smooth, nearly semicircular, medially directed flange on each side. Mandibular part of rostrum spatulate distal to flanges; sides parallel or tapering proximomedially towards flanges; rounded-truncate distally; floor below mandible wide, flat, evenly granulated. Mandible (not shown) narrow in region between central flanges, spatulate distally; margin thin, smooth, lacking denticles. Avicularium-associated torsion mild and variable; many avicularium-sibling pairs show no torsion, but some appear to show slight torsion of avicularium, sibling zooid, or both; adjacent zooids not torqued. Spicules ( Figure 4 (d)) include small C-shaped callipers rather uniform in size, and several sizes of slightly angled compasses (see Measurements). Ovicell ( Figure 4 (a)) hyperstomial; ooecium bivalved, broader than long, smooth, with median suture; distal arch of opening rounded or acute. Zooids interconnect ( Figure 4 (e)) via group of uniporous septula in central third of distal wall and one elliptical multiporous septulum in each distolateral wall.

Remarks

This species is allied with Thalamoporella tubifera Levinsen, 1909 , on the basis of having large zooid size (average ZL, 0.70 mm); the orifice with a rather deep, widely arcuate margin proximal to the opercular articulations; torsion weak or lacking in avicularia, sibling and adjacent zooids; spatulate avicularia not greatly shorter or longer than autozooids; and spicules in the form of small, C-shaped callipers and compasses of varying length. After describing variation in nominal T. tubifera throughout its range, Soule et al. (1992, p. 61) noted, ‘There are some subtle differences within the tubifera complex which could lead to separation of this species into distinct populations, if not separate taxa, as for example the French Polynesia specimens’, and again (p. 64), ‘It seems probable that this widespread and very common species may in fact consist of several closely related taxa’. Unfortunately, proceeding as though variation across the distributional range of nominal T. tubifera were intraspecific rather than at least in part interspecific, Soule et al. (1992) presented some distinct measurements for the holotype, but otherwise gave ranges of measurements and average values across all populations, which makes comparisons among the populations they treated impossible.

The type locality of T. tubifera Levinsen is Papua New Guinea. Levinsen (1909) indicated the range of zooid length as 0.53–0.73 mm, somewhat smaller than in our material; in the type material, the avicularian rostrum is vase- or lyre-shaped, with very little granulation on the rostral floor beneath the mandible ( Levinsen 1909, pl. 4a, fig. 2 (a); see also Soule et al. 1992, fig. 86). Soule et al. (1992, p. 61) noted that zooids and avicularia in the holotype are the smallest among all populations: ‘On the basis of size alone, the type of T. tubifera lies entirely outside the range of any of the specimens’ (from numerous populations across the distributional range of the nominal species). The AvL/ZL ratio in the holotype of T. tubifera is 1.00, while the range across all nominal T. tubifera populations is 0.85–1.18, with an overall average of 1.01 ( Soule et al. 1992). The ratio in T. karesansui (1.12–1.14) is larger than in the holotype of T. tubifera , and close to the high end of the range across all nominal T. tubifera populations. According to Soule et al. (1992), species or populations in the T. tubifera complex usually have basal insertions in the form of two widely open hooks. In T. karesansui , some zooids have open hooks (or a hook and a bar), but most zooids have each insertion closed distally by a lateral extension that loops back to meet the lateral wall.

If the Okinawa specimens and the type material for T. tubifera from Papua New Guinea were the only material available from the T. tubifera complex, there would be no hesitation in describing the Okinawa population as a different species from T. tubifera , and this is the approach we have taken. The status of other populations will have to be evaluated on a case-by-case basis.

Several other Indo-West Pacific species ( Soule et al. 1992) have large, spatulate avicularia like T. karesansui , but differ in colony form, zooid size, avicularium size and shape, degree of torquing, form of the basal insertions or other characters; here we will mention two additional encrusting species as an example of the sorts of differences involved. Thalamoporella granulata Levinsen, 1909 sensu lato has the avicularia considerably longer than zooids (AvL/ZL, 1.19–1.34) ( Soule et al. 1992); both the avicularium and sibling zooid are strongly torqued; opesiule insertions are paired open hooks, or one hook and a bar; and strongly bent (120°) compasses are present. Thalamoporalla granulata (sensu lato) is distributed from Lombok, Indonesia eastward to Tonga and ranges in latitude from the equator to about 20°S, with some questionable records from the Philippines and Taiwan ( Soule et al. 1992). Thalamoporella sibogae Soule et al., 1992 , has smaller zooids (average ZL, 0.54 mm) and proportionally longer avicularia (the AvL/ ZL ratio reaches 1.25); the avicularium is straight, but both the sibling and adjacent nonsibling zooids are torqued; and the avicularian mandible has unique chitinous teeth on the margin. Thalamoporella sibogae has been reported as far north as the Korean Peninsula (~ 33°N) ( Seo 2005).

Occurrence

This species, presently known only from Okinawa, was abundant at SES and uncommon at REEF ( Table 1). Thalamoporella tubifera (sensu lato) has a broad Indo-West Pacific distribution, ranging from the Maldive Islands in the Indian Ocean eastward to French Polynesia, and as far north as Taiwan (22°N; Gluhak et al. 2007) .

Suborder NEOCHEILOSTOMINA d’ Hondt, 1985 Superfamily CALLOPOROIDEA Norman, 1903a Family CALLOPORIDAE Norman, 1903a

Genus Crassimarginatella Canu, 1900

Crassimarginatella eremitica sp. nov.

( Figure 5)

Etymology

The specific name is an adjective (Latin eremiticus: reclusive, solitary), referring to our finding only a single small colony.

Material examined

Holotype: NSMT-Te 1063 (REEF-9), bleached, on SEM stub.

Measurements

AzL, 0.48–0.55 (0.516 ± 0.023); AzW, 0.38–0.43 (0.404 ± 0.016), OpL, 0.38–0.44 (0.409 ± 0.018); OpW, 0.26–0.34 (0.304 ± 0.019) (n = 15, 1). One colony, 5.3 × 3.0 mm.

Description

Colony ( Figure 5 (a)) forming a unilaminar, encrusting sheet; dried specimen light orange. Zooids ( Figure 5 (b, c)) delineated by deep groove; gymnocyst moderately wide proximally and/or laterally. Opesia elliptical to irregularly oval, surrounded by narrow, raised mural rim. Cryptocyst ( Figure 5 (d)) narrow, nearly vertical, smooth around inner margin, serrated around mural rim, except in vicinity of orifice. Non-reproductive zooids in zone of astogenetic change bear two pairs of short, blunt, erect orificial spines, and four to eight short, tapering, acute, slightly or markedly curved opesial spines. Most zooids in zone of astogenetic repetition have single pair of thick, distolateral orificial spines and two to four opesial spines. All spines non-articulated, hollow, arising from gymnocyst. Vestigial ooecium ( Figure 5 (d, e)) is formed by next-distal autozooid as a visor-like structure around distal end of zooid; pointed, with pseudopore at tip. Vestigial ooecium is indicative of embryonic incubation in a brood sac immersed in distal part of maternal zooid. Colony precocious; most zooids more than two generations away from ancestrula bear ooecium. Zooids interconnect by uniporous septula, one in transverse wall and one or two in each distolateral wall, leading to large, more-or-less tubular interzooidal chambers. Basal walls calcified. Ancestrula ( Figure 5 (f)) partly obscured in our specimen due to substratum irregularity; tatiform, 0.25 mm wide, with two pairs short, straight orificial spines at distal end and at least one curved spine more proximally; surrounded by six periancestrular zooids.

Remarks

The generic assignment of this species is unclear. Gordon (1984) subdivided Crassimarginatella Canu, 1900 into three subgenera: Corbulella , for species having vicarious avicularia with opesial spines and a serrated rostral rim, and a prominent ovicell with a single broad fenestra; Crassimarginatella , for species in which the vicarious avicularia lack spines and serration, and the ovicell is either prominent and unifenestrate, or small and cap-like; and Valdemunitella , for species having a bifenestrate ovicell. Tilbrook et al. (2001) raised all three subgenera to the rank of genus.

This species clearly bears vestigial ooecia, making it difficult to place in Corbulella . Crassimarginatella is a better fit because the generic diagnosis permits small, cap-like ooecia ( Gordon 1984), and the genus now contains some species having prominent, well-developed ooecia and others with vestigial ooecia ( Ostrovsky et al. 2009). Our specimen lacks vicarious avicularia, and it is unknown whether they occur in this species. Crassimarginatella eremitica shares with Cr. extenuata (next description) a moderately wide, somewhat irregular gymnocyst; relatively few spines scattered irregularly around the opesia; and zooids loosely connected by tube-like interzooidal chambers. With its short, fang-like opesial spines and vestigial ooecium with a median pseudopore, C. eremitica differs from any previously described species in either Corbulella or Crassimarginatella .

Occurrence

We found a single small colony at the REEF site, the only known locality.