Raxifabia oligopora n. sp.

(Fig. 6, A–E)

Material examined. Holotype: SMF 15005, SO 205 Stn 61, 13.174° N – 3.194° N, 118.106° W – 118.0953° W, Equatorial East Pacific, 3996–4007 m, collected 16 May 2010. Bleached.

Etymology. From the Greek oligo, few and poros, pore, alluding to the number of pores in comparison to the two most similar species.

Description. Colony form not known; only a single stem in the collection, 2.7 mm long and up to 0.4 mm wide (Fig. 6, A–B). Zooids alternating, bilaterally flattened, stem lenticular in cross-section. Lateral suture forming a zigzag line from avicularium to avicularium (Fig. 6, C). Median suture lightly carinate, sinuous (Fig. 6, B). A row of 11–16 pores along the periphery and additional tiny pores at median suture and irregularly distributed on frontal surface (Fig. 6, B, D). At proximolateral end are large areolar pores (Fig. 6, D). Orifice round, no rim. A pair of transversely D-shaped avicularia mid-distal to orifice, separated from each other only by a suture, facing almost frontally, pertaining to distal zooid (Fig. 6, B, E); rim of each avicularium continuous with lateral peristomial rim; no mandibular pivots. Fertile zooids not present.

Measurements.

Zooid length 544–598 µm, σ = 41 µm, N = 5; width 202–224 µm, σ = 16 µm, N = 5

Orifice length 92–94 µm, σ = 1, N = 5; width 91–102 µm, σ = 5 µm, N = 5

Avicularium length 34–40 µm, σ = 2 µm, N = 5; width 32–38 µm, σ = 2 µm, N = 5.

Remarks. This species closely resembles Raxifabia rara Gordon, 1993 . Differences include: Raxifabia oligopora n. sp. is larger and a row of pores is adjacent to the median suture; in particular, the shape of the contact line with neighbouring zooids forms parallel bands transverse to the growth direction around the branch in R. rara, whereas in the new species the suture forms a zigzag-line between the avicularia. Another difference is the shape of the orifice, which is round and rimless in R. oligopora, in contrast to a V-shaped proximal rim in R. rara .

Raxifabia porosa Gordon, 1993 differs in its more numerous pores having a different distribution pattern, and the oral avicularia are located distolateral to the orifice and face distolaterally. The position of the avicularia in R. oligopora is also one of the most conspicuous differences from most other species of Raxiafabia, including Raxifabia gemella (Harmer, 1957), Raxifabia longicaulis (Harmer, 1957), Raxifabia laevis (Busk, 1884), Raxifabia minuta (Busk, 1884) and R. vafra . In all these species avicularia have a distolateral position and are thus not in contact, whereas those in R. oligopora are distally positioned and are in direct contact with each other.

The new species differs significantly from the type species of the genus, R. vafra, in the shape of the orifice, which is much more elongated and shows distinct condyles. In Raxifabia tunicata Gordon, 1988, the triangular avicularian cystids are in contact, but only at one corner, and the mandible has a distolateral orientation, resulting in a very different appearance compared to R. oligopora .

Species of this genus mainly occur in Pacific waters at great depth, being reported from off the Philippines (Busk 1884), Indonesia (Harmer 1957) and New Zealand (Gordon 1988). Only R. minuta has been reported from the Northern Atlantic (Busk 1884).