Microporella umbonata Chowdhury & Martino & Lee & Windecker & Craig 2024

Microporella umbonata (Hincks, 1883) Fig. 10, Table 2 Microporella ciliata form umbonata Hincks, 1883: 444, pl. 17 fig. 1. Material examined USA • 1 colony of 30 zooids, two ovicellate, on rock; California, Greenwood; 39°7′45.0582″ N, 123°43′9.192″ W; 22 Jun. 2020; I.A. Chowdhury and H. Lee leg.; SBMNH 704779 • 1 colony of 40 zooids, six ovicellate, on rock; California, Palmer′s Point, Trinidad; 41°7′51.6″ N, 124°9′49.32″ W; 9 Dec. 2019; I.A. Chowdhury and H. Lee leg.; NHMO H1940. Description Colony encrusting, multiserial, unilaminar, forming subcircular patches, typically inhabiting rocks of various sizes; three distal pore chamber windows evident in zooids at colony growing edge. Autozooids hexagonal, rectangular or irregularly polygonal, ZL = 574–859 µm (689±78 µm, N = 11), ZW = 411–616 µm (522±66 µm, N = 13), mean L/W = 1.32; boundaries marked by grooves. Frontal shield convex centrally due to umbonate process; smaller umbo on each side lateral to orifice; smooth to finely granular, with numerous (38–55) circular pseudopores, D = 7–14 µm; marginal areolae distinguishable from pseudopores because elliptical and slightly larger (ca 20 µm) (Fig. 10A). Primary orifice transversely D-shaped, OL = 104–131 µm (117±8 µm, N = 13), OW = 142–169 µm (155±9 µm, N = 13), mean OL/OW = 0.75, mean ZL/OL = 5.89; hinge-line smooth, with minute triangular condyles at some distance from corners, slightly concave between condyles (Fig. 10A–B); oral spines absent. Ascopore small, depressed relative to adjacent frontal shield, unusually close to orifice, much less than ascopore width from proximal margin, outlined by rim of gymnocystal calcification continuous with the one encircling the orifice; ascopore opening 35–38 µm in diameter, transversely C-shaped, with distal projection and outer margin radially denticulate (Fig. 10B). Avicularium mostly absent, sometimes single, AvL = 88–94 µm (91±4 µm, N = 2), AvW = 37–51 µm (44±10 µm, N = 2), mean AvL/AvW = 2.10; located laterally in distal half of zooid, proximolateral to ascopore, more or less lateral to frontal umbo; crossbar complete; rostrum triangular, truncated, directed distolaterally, rostrum tip only slightly raised (Fig. 9B). Mandible not observed. Ovicell globose, wider than long, OvL = 208–257 µm (233±34 µm, N = 2), OvW = 372–384 µm (378±9 µm, N = 2), mean OvL/OvW = 0.63; continuous with frontal shield of next distal zooid, obscuring distal margin of maternal orifice; calcification finely granular, completely and evenly covered with minute, circular pseudopores, 6–13 µm in maximum dimension (Fig. 10A–B). Ancestrula not observed. Remarks Microporella umbonata can be distinguished from M. umboniformis Soule, Soule & Chaney, 1995 (Fig. 11) by several consistent morphological differences. Microporella umbonata consistently lacks oral spines (Figs 10A, 12A), while M. umboniformis has 5–6 robust spines observed in both mature zooids at the colony centre and young zooids at the colony margin (Fig. 11A–B, E–F). Microporella umbonata consistently display a small umbo on each side lateral to the orifice (Figs 10A, 12A). In M. umboniformis, the development of two lateral umbones may occur exclusively in ovicellate zooids, resulting from the thickening of the proximalmost pair of oral spines as illustrated by Soule et al. (1995: pl. 54a). However, it’s noteworthy that we did not observe this particular feature in the holotype, where the two proximalmost pair of spines in ovicellate zooids where simply retained in their original state (Fig. 11G–H). This observation suggests the possibility that the figured specimen in Soule et al. (1995: pl. 54a) might not be the holotype. Additionally, the adventitious avicularium in M. umbonata is either single or frequently absent (Figs 10A–B, 12A–B). On the other hand, M. umboniformis consistently exhibits avicularia, which are more commonly single, though they also frequently occur in pairs (Fig. 11A–B, E). The ascopore in M. umbonata is unusually close to the proximal margin of the orifice, sometimes in direct contact, and enclosed by the same smooth gymnocystal calcification rim surrounding the orifice (Figs 10B, 12B–C), while in M. umboniformis it is clearly separated from the proximal margin of the orifice at a distance of about one ascopore width (Fig. 11C–D). Soule et al. (1995: 21) delineate key characteristics to differentiate between the two species, emphasizing the presence of a “frontal wall with large pores” in M. umbonata and a “frontal wall with small pores” in M. umboniformis. Our specimens (Fig. 10) and the specimen of M. umbonata from Departure Bay, Canada (Fig. 12), used for comparative analysis, show no discernible difference in pseudopore size [D = 7–14 µm (9.75±2.1 µm, N = 20) and D = 6–14 µm (9.3±2.2 µm, N = 20) in M. umbonata from California and Canada, respectively] when contrasted with the holotype of M. umboniformis [D = 7–15 µm (9.8±2.1 µm, N = 20)]. Notably, it is in the holotype of M. umboniformis that we observed larger pseudopores in some zooids (see Fig. 11E–F), seemingly attributable to the absence of the external layer of calcification. The sole difference is in their arrangement of pseudopores, which form radiating lines in our specimens and the specimen from Departure Bay, consistent with Hincks’ (1883) description, as opposed to the scattered distribution observed in M. umboniformis. Soule et al. (1995) synonymized Osburn’s records of M. umbonata with their newly described species M. umboniformis, but it remains unclear whether they re-examined Osburn’s specimens. In their paragraph on distribution, they referred to Osburn’s records as “probably the new species”, a statement that introduced some uncertainties. Nevertheless, Osburn (1952: 378) described “4 to 6 small oral spines which are evanescent” but he did not illustrate them (see Osburn 1952: pl. 44 fig. 4), suggesting the possibility that he might have been dealing with both species. The shape and size of ovicell in M. umbonata vary among zooids, even within the same colony (Fig. 10A), likely influenced by the extent of secondary calcification. Distribution and ecology Microporella umbonata has been recorded along the eastern Pacific coast, with previous records from the Queen Charlotte Islands, British Columbia, Canada (Hincks 1883). Osburn’s records of M. umbonata, though uncertain, originated from San Pedro Island, Santa Cruz Island and Dillon Beach in California, and Puget Sound, Washington, USA, from the intertidal zone down to a depth of 102 m (Osburn 1952; Soule et al. 1995). Colonies from this study were found in Greenwood and Palmer’s Point, Trinidad, California, USA, both encrusting rocks.

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