(Figure 2)
Material. Holotype: CANADA: British Columbia. 54 ˚ 13 ’00”N, 132 ˚09’00”W, 29.iv. 1961, 98.8 meters, coll. D.B. Quayle, hydrocauli on hydroid hydrocaulus fragment, without gonothecae, ROMIZ B 4051. Paratypes: CANADA: British Columbia. Esperanza Inlet, 27. vii. 1934, hydrocaulus fragments, without gonothecae, ROMIZ B 4052; CANADA: British Columbia. Swan Hill Locality, 54 ˚07’00”N, 131 ˚ 36 ’00”W, 21. iv. 1961,16.5 meters, fragment of hydrocaulus, without gonothecae, coll. D.B. Quayle, ROMIZ B 4053. Other material: CANADA: British Columbia. 1 mile east of Cape Ball, east coast of Graham Island, Queen Charlotte Islands, 8.vii. 1960, hydrocaulus fragment, without gonothecae, ROMIZ B 4054. CANADA: British Columbia. No location data, 7. iv. 1961, coll. D.B. Quayle, young colony on Sertularia similis Clark, 1876 with primary hydrothecae arising from hydrorhiza, hydrothecae showing incipient internodes, without gonothecae, ROMIZ B 4055.
Reported distribution. Only known from British Columbia, off Vancouver Island.
Description. Colony upright, colony arising from creeping stolon. Internodes of hydrocaulus geniculate, each with a single hydrotheca; nodes indistinct or absent in young colonies. Perisarc rigid, yellowish-brown, ringed at nodes, thickened throughout. Hydrothecae alternate, without septa, tumid, barrel-shaped, widest medially, somewhat tapering basally, with 3–5 transverse rings, varying from sharp ribs to rounded ribs; up to 1 / 3 of hydrotheca adnate on adcauline side, abcauline side free, up to 1 / 3 longer than adnate side. Abcauline and adcauline walls distinctly ribbed. Adnate portion of hydrotheca straight, curving at hydrothecal base. Hydrothecae very constricted distally, smooth, appearing neck-like, frequently strongly contracted into downward curve towards abcauline side. Hydrothecal margin with 4 prominent cusps, operculum slightly flaring, opercular flaps extend and meet well-beyond margin of opening forming pyramidal structure. Intrathecal (submarginal) cusps large, plate-like, three or sometimes four in number, with two behind lateral marginal cusps and one or two behind abcauline marginal cusps. Gonothecae not found.
Differential diagnosis. This species somewhat resembles Sertularella robusta Coughtrey, 1876 (not S. robusta Clark, 1877); however, there are marked morphological differences in the hydrocladia and hydrothecae, as well as significant differences in size (Table 1). The internodes of Sertularella cervicula sp. nov. (1520–3600 mm) are four to five times longer than those in S. robusta, and the hydrothecae are also at least three times the reported dimensions of S. robusta elsewhere (Hirohito 1995; Ralph 1961; Vervoort 1972; Vervoort & Vasseur 1977; Vervoort & Watson 2003). While this material agrees with descriptions of S. robusta by Vervoort & Vasseur (1977) and Hirohito (1995) in possessing transverse hydrothecal rings and variable number of intrathecal cusps, in S. robust a the most common number of transverse hydrothecal rings is 5–6 whereas in this species the most common number is 3–4. The overall general outline of the hydrothecae of this species also distinguishes it from its congener; it is characterized by a well-marked constriction and tendency of the distal end of the hydrothecae to curve forward towards the abcauline side. Although a slight tendency of the hydrothecae to bend forward have been observed in some hydrothecae in S. robusta (Vervoort & Vasseur 1977), this is an exception in S. robusta; Vervoort & Watson (2003) suggested that these may have resulted from regeneration after damage. In S. cervicula, this character is observed in incipient colonies and is considered taxonomically significant. The marked forward hydrothecal bend also distinguishes S. cervicula from S. simplex (Hutton, 1873) and S. integra Allman, 1876.
Etymology. The species name is derived from the Latin cervicula (small neck), referring to very constricted, neck-like distal part of the hydrotheca.