Colliculoamphora gabgabensis Lobban, 2015

Lobban, Christopher S., 2015, Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis), Micronesica 2015 (2), pp. 1-49 : 4-5

Colliculoamphora gabgabensis Lobban , n. sp. Figs 33–40

EUNOTIALES Silva : Eunotiaceae Kützing

Samples: GU44K-6; GU44I-1, GU44Z-15, GU44W-10, GU44U-1B, GU44AK-6, GU66F-4, GU66F-8

Dimensions: Length 6.4–11 µm, width 2.8–4.2 µm, striae 25–27 in 10 µm in the middle, denser around the apices.

Diagnosis: Differing from other Colliculoamphora species in the smaller size, finer striae, and markedly concave dorsal margin; dorsal striae interrupted by longitudinal hyaline area.

Holotype: GU44AK-6, slide 958, Fig. 33. Deposited at California Academy of Sciences ( CAS), accession # 627425, slide # 223041.

Paratypes: A specimen ( Fig. 35) is marked on GU44I-1, slide 494, CAS accession # 627427, slide # 220343, in addition to the holotype of Lauderia excentrica , and the specimen in Fig. 29 from GU44Z-15 is on a stub deposited at CAS, accession # 627385.

Type locality: GabGab reef, Apra Harbor Guam, 13°26′ 33.63′′ N 144° 38′ 34.25′′ E, associated with filamentous algal turf in a farmer-fish territory, collected by C. Lobban & M. Schefter, 5 Nov. 2011 .

Etymology: named for the type location, which in turn is a Chamorro name for the coral tree ( Erythrina variegata L.).

Description: Valves linear, asymmetrical about the apical plane, dorsal margin curved, more or less strongly concave, ventral margin slightly bent. Raphe visible on the valve face at each pole but lying mostly on the mantle ( Figs 36, 37). Striae on the dorsal side interrupted by an irregular, apparently depressed hyaline area ( Figs 36, 37); striae parallel on the proximal side of this area, but on the distal side parallel only in the middle, becoming radiate around the poles, where they also become denser from the interpolation of additional short striae along the margin ( Figs 37, 38). Single row of more closely-spaced pores on the ventral side of the raphe ( Fig. 38). Copulae areolate ( Fig. 40). Valve surface smooth, not colliculated (i.e., lacking small elevations).

Comments: Present in low numbers in several samples and probably overlooked in others. Colliculoamphora was established by Williams & Reid (2006) for two species formerly placed in Amphora . They noted the similarity to Eunotia , from the way the raphe hooks off the valve face onto the mantle, and placed it in Eunotiaceae . Williams & Reid (2009) gave a comprehensive list of the ten known species of Colliculoamphora , noted the paucity of material for all species, and rationalized the description of new species on such data as they had, an argument I applaud. Most species have straight or convex dorsal margins but three have concave dorsal margins. Of the latter, C. palawanensis G. Reid & D.M. Williams ( Williams & Reid 2009, figs 15, 17–21) most closely resembles our species, in having a central hyaline area the length of the valve and the closest shape, but it is larger (14–17 x 4–5 µm) and the striae coarser (18–19 in 10 µm). Indeed, our species is smaller and the striae denser than any in Williams & Reid’s (2009) list. No external SEM was given for C. palawanensis .