Errinopora Fisher, 1931

Cairns, Stephen D. & Lindner, Alberto, 2011, A Revision of the Stylasteridae (Cnidaria, Hydrozoa, Filifera) from Alaska and Adjacent Waters, ZooKeys 158, pp. 1-88 : 8-12

Genus Errinopora Fisher, 1931

Errinopora Fisher, 1931: 397; 1938: 536.- Boschma 1956: F102; 1957: 57.- Cairns 1983a: 123; 1983b: 462. - Lindner 2005: 79-88.

Protoerrina Broch, 1935: 59; 1936: 99-100.

Diagnosis.

(emended from Lindner 2005): Colonies uniplanar to slightly bushy; branches round, elliptical, or lamellar in cross section, often robust with blunt tips. Coenosteal texture reticulate-spinose (with wide slits resulting in a spongy texture) or reticulate-granular; exterior surface of dactylopore spines usually inconspicuously longitudinally ridged; coenosteum orange, pink, and white. One species, Errinopora cestoporina , bears numerous perforated mounds on surface. Dactylopores dimorphic, the most common, termed the primary dactylopore spine, is U-shaped and usually robust (thick-walled), occurring randomly, in pseudocyclosystems, or often laterally fusing to form rows or taller terraces that flank rows of gastropores. When dactylopore spines flank both sides of a gastropore row and their dactylotomes are directed toward the gastropores it is termed bilateral or distichoporine; if only one row of spines flank a row of gastropores, then unilateral. If isolated, dactylotomes usually abcauline in orientation. Much smaller flush dactylopores, termed secondary dactylopores, which lack dactylostyles, commonly scattered over coenosteum of many species. Dactylostyles usually well developed, easily seen from external view. Secondary dactylopores much smaller, flush with coenosteum, and lack styles. Gastropores also dimorphic, the primary gastropores being circular in outline, flush with coenosteum (having no lip), and arranged in irregular vertical rows, short horizontal rows, or randomly. Tabulae and ring palisades absent. Gastrostyles lanceolate, covered with longitudinal or oblique, spiny ridges. Smaller secondary gastropores much smaller, having only a small gastrostyle or none at all. Female ampullae superficial hemispheres, often without an obvious efferent pore. Male ampullae usually smaller hemispheres and spongy.

Discussion.

The ten species in this genus are differentiated and compared in both a dichotomous key (see below) and tabular key (Table 1); six of them occur exclusively in the Aleutian Islands. Another species was tentatively assigned to this genus by Cairns (1983b), Errinopora lobata (Nielsen, 1919), a Paleocene fossil from Denmark. This species was re-examined by Bernecker and Weidlich (1990, 2005), based on subsequently collected non-type material from the Faske Formation in Denmark. They noted that whereas the dactylopore spines were typical of Errina or Errinopora , the spines did not contain dactylostyles, and thus resembled Errina more than Errinopora . We have examined the holotype of Labiopora lobata Nielsen, 1919 (GM1782), which is a uniplanar colony 10.2 cm tall and 8.0 cm wide, with branches about 0.5 cm in diameter embedded within a Dendrophyllia matrix. The colony has pores, or broken bulges, of three sizes: small and elongate (75-110 µm in width), medium and round to somewhat quadratic (0.3-0.53 mm wide), and large, round or somewhat triangular (up to 1.7 mm). The former are quite shallow and probably the result of a reticulate coenosteal surface, whereas the medium-sized pores are deep and possibly represent the gastropores, one of which has a cyclosystem-like structure 1.9 mm in diameter. The largest pores appear to be ruptured ampullae. None of them, however, resemble dactylopore spines like those reported by Nielsen (1919) or Bernecker and Weidlich (1990, 2005), suggesting that the species reported by the latter authors is neither Errina nor Errinopora . Likewise, the lack of dactylopore spines in the type of Labiopora lobata precludes it from being Errinopora , and thus we currently suggest an incertae sedis placement of this species until further analysis.

Species within Errinopora are unique with the Stylasteridae in having both dimorphic gastro- and dactylopores, a condition first noted by Fisher (1938) for three Alaskan species but interpreted exclusively as secondary dactylopores. Careful examination of longitudinal sections of several of these pores reveal that they contain not dactylostyles, but rather small gastrostyles. This implies that most species of Errinopora (all but Errinopora fisheri and Errinopora cestoporina Cairns, 1983, see Table 1) have two types of gastrozooids (feeding polyps), a unique case for stylasterids but previously reported for the hydractiniids Stylactaria conchicola (see Namikawa et al. 1992). Secondary gastropores differ from primary gastropores in being narrower and deeper, and in having only a minute or no gastrostyle. All but one species ( Errinopora fisheri , see Table 1) also have dimorphic dactylopores: a large type surrounded by a prominent horseshoe-shaped spine, and smaller, flush pores only 40-110 µm in diameter, which do not have dactylostyles and are termed secondary dactylopores.

In comparison to other stylasterid genera, Errinopora is most similar to Gyropora Boschma, 1960, whose only species, Gyropora africana Boschma, 1960, has dactylopore spines and gastropores coordinated in pore rows, as in some species of Errinopora . Errinopora is also similar to Errina Gray, 1835 and Errinopsis Broch, 1935, whose species may also have thick-walled dactylopore spines. None of these genera, however, include species with dactylostyles, as in Errinopora . Among genera with species having dactylostyles, only species of Errinopora , Inferiolabiata Broch, 1951, and Paraerrina Broch, 1942 lack a coordination of gastropores and dactylopores in well-developed cyclosystems (whereas species of Stenohelia Kent, 1870, Stylantheca Fisher, 1931, Stylaster Gray, 1831 and Calyptopora Boschma, 1968 do have both dactylostyles and well-developed cyclosystems). Inferiolabiata differs from Errinopora in many characters, in particular by having thin-walled dactylopore spines (instead of thick-walled) that are markedly truncated at the tip (instead of rounded), whereas Paraerrina Broch, 1942 differs in having delicate dactylostyles (instead of robust) and either flush or only slightly raised dactylopore spines-instead of tall and robust (Cairns 1984, 1991). Errinopora is also one of the few stylasterid genera with species having calcitic, rather than aragonitic, colonies ( Thompson and Chow 1955, Lowenstam 1964, Cairns and Macintrye 1992). The only other stylasterid genera with species known to have mostly calcitic colonies are Errinopsis , Errina , and one species of Stylaster - Stylaster verrillii (Dall, 1884) (see Cairns and Macintrye 1992). Within Errinopora , only Errinopora cestoporina , known solely from the Subantarctic Region, is known to have coralla formed by precipitation of aragonite. This result confirms the more general observation of the prevalence of calcitic stylasterids in the North Pacific ( Cairns and Macintrye 1992), possibly related to the shallower depth of the Aragonite Saturation Horizon (ASH) in the Region (Guinotte et al. 2006).

In an attempt to investigate phylogenetic relationships, 37 partial mitochondrial rDNA 16S sequences were obtained for the six species of Errinopora from the Aleutian Islands, including the holotypes of Errinopora dichotoma , Errinopora disticha , Errinopora fisheri and Errinopora undulata . Based on Lindner et al. (2008) included Errinopora nanneca (specimen USNM1027820) and Errinopora zarhyncha Fisher, 1938 (specimen USNM1071915), and shows that these species diverged only about 4 million years ago. Moreover, the same study shows that Cyclohelia lamellata Cairns, 1991 and Distichopora borealis Fisher, 1938, two sympatric Alaskan stylasterids that are also clearly distinguishable with marked morphological differences (see above), may have diverged as recently as 1 million years ago. These results indicate that part of stylasterid species diversity in Alaska may have diverged only within the past 1-4 million years and, at least for Errinopora , the results presented herein show that despite the marked morphological differences, some species are not recovered as reciprocally monophyletic lineages ( Baum and Shaw 1995, Avise 2000) using mitochondrial rDNA 16S.

Type species.

Errina pourtalesii Dall, 1884, by original designation.

Distribution.

North Pacific: Aleutian Islands, Kurile Islands, Sea of Okhotsk, Sea of Japan, off California. Subantarctic: off Tierra del Fuego, 40-658 m.

Key to the Recent species of Errinopora (bold face = occurs off Alaska)