Corbulella extenuata, Dick & Tilbrook & Mawatari, 2006

Dick, Matthew H., Tilbrook, Kevin J. & Mawatari, Shunsuke F., 2006, Diversity and taxonomy of rocky-intertidal Bryozoa on the Island of Hawaii, USA, Journal of Natural History 40 (38 - 40), pp. 2197-2257 : 2207-2209

Corbulella extenuata new species

( Figure 4A–D )

Type material

Holotype: NHM 2006.7.21.5, specimen HI-61, bleached, coated for SEM; Kapa’a Beach Park, Island of Hawaii; 1 March 2005; M. H. Dick, collector; intertidal, 0.15 m low tide.

Etymology

The species name derives from the Latin extenuata (weak, slight), referring to the reduced ovicell.

Measurements ZL, 0.48–0.60 (0.558¡0.0425). ZW, 0.38–0.45 (0.405¡0.028). OpL, 0.30–0.38

(0.335¡0.023). OpW, 0.23–0.25 (0.241¡0.010).

Description

Colony unilaminar, encrusting, sheet-like, tan in colour. Zooids distinct, well separated by deep grooves; in bleached specimens, small lacunae evident between broad zones of interzooidal connection. Several zooids show complete regeneration of a new zooid within the opesia of another, and in one case, two successive such regenerations. Gymnocyst ( Figure 4A, B ) smooth, sloping, visible around the zooid, extensive proximally, narrower laterally. Mural rim sharp, crenulate; cryptocyst a well-developed, sloping, coarsely granulated band inside mural rim, narrower distally than proximally. Around mural rim, 7– 14 well-developed tubular spines ( Figure 4A ), the distal two pairs in the vicinity of the orifice thicker than the rest, with the distal pair erect and the second pair tilted toward midline; the other, more proximal spines thinner, often tilted over opesia, but not meeting in midline. Opesia ( Figure 4B ) oval, widest near middle or proximally. Ovicell vestigial, comprising a small cap ( Figure 4B ); both the mural rim and opesial margin are transversely straight at the distal end of the zooid, with the crenulated mural rim traversing the proximofrontal surface of the cap. What appears to be an interzooidal avicularium ( Figure 4C ) is present, comprising about one-quarter the area of an autozooid, without pivotal constrictions or hinge bar, without spines, the rostrum tapering and twisted distally. Zooids interconnect by triporous septulae ( Figure 4D ).

Remarks

Only a single, small colony of quality useful for SEM observation was found. This species resembles Corbulella corbula ( Hincks, 1880) , which was reported from the Hawaiian Islands as Pyrulella corbula ( Soule et al. 1988) . However, that species has a narrower cryptocyst not continuing around the distal rim of the opesia; longer spines often meeting in the midline, with a pair lateral to the orifice sometimes greatly elongated; a conspicuously developed ovicell; and vicarious avicularia around the same size as autozooids. In having a reduced, cap-like ovicell, Corbulella extenuata is similar to Crassimarginatella spatulifera Harmer, 1926 ( Corbulella and Crassimarginatella were formerly considered subgenera within Crassimarginatella ; see Gordon 1984; Tilbrook 2001). However, the latter species lacks spines and has vicarious avicularia larger than the autozooids. Crassimarginatella corniculata Tilbrook, 2001 has the ovicell even further reduced, evident only as a slightly raised distal margin on endozooidally brooding zooids.

Distribution

Kapa’a Beach on the Island of Hawaii is the only known locality.

Figures

Figure 4. Corbulella extenuata n. sp., holotype (NHM 2006.7.21.5): (A) autozooid, unbleached; (B) marginal zooids, bleached; note cap-like reduced ovicells; (C) autozooids and interzooidal avicularium (centre), bleached; (D) lateral wall of marginal autozooid showing septula, bleached. (B–D) are from same colony as (A), after bleaching. Scale bars: 500 Mm (A, C, D); 400 Mm (B).