Lytocarpia myriophylum ( Linnaeus, 1758 )

Peña Cantero, Álvaro L. & Horton, Tammy, 2017, Benthic hydroids (Cnidaria, Hydrozoa) from bathyal and abyssal depths of the Northeast Atlantic held in the modern Discovery Collections, Zootaxa 4347 (1), pp. 1-30 : 16-20

Lytocarpia myriophylum ( Linnaeus, 1758)

( Fig. 7 )

Lytocarpia myriophylum— Ansín Agís et al., 2001: 88 –99, figs 40–45 (synonymy).

Material examined. 10108#1, two delicate stems up to 40 mm high, no corbulae; 51401#1, a colony with four stems up to 170 mm high, no corbulae; 52026#1, fourteen stems up to 145 mm high, no corbulae.

Description. Stems almost completely polysiphonic, unbranched, up to 170 mm high. Rhizoidal hydrorhiza consisting of a dense mass of fine stolons. Stem divided into large parts by very oblique nodes. Cauline main tube with strong septae. Stem provided with alternate short apophyses giving rise to hydrocladia. Each apophysis with two basal nematothecae ( Fig. 7B ). Stem with one or two nematothecae between apophyses.

Hydrocladia unbranched and alternately arranged in two planes (angle up to 90°). Hydrocladial internodes with strong septae ( Fig. 7C–D ). Each internode with a hydrotheca and three sessile nematothecae ( Fig. 7C–E ): one mesial nematotheca adnate to abcauline hydrothecal wall, and two lateral ones slightly surpassing hydrothecal rim. Hydrotheca cup-shaped ( Fig. 7C–D ), elongate, but highly variable in height. Adcauline wall adnate, with basal part curved inwards giving rise to an internal septum. Abcauline wall straight or slightly convex. Rim of hydrothecal aperture with five pairs of lateral of cusps and one strongly developed and wide, abcauline cusp, slightly directed inwards ( Fig. 7F ).

Measurements (in µm). Hydrothecae: height 480–890; diameter at aperture 250–300, distance from axil of mesial nematotheca to end of abcauline cusp 330–850.

Remarks. See Ramil & Vervoort (1992) and Ansín Agís et al. (2001) for a much wider description and an extensive discussion on the species.

The material from Stn 10108#1 allows us to put in evidence the basal structure of the stem, as it consists of two delicate stems 40 and 20 mm high. The latter is completely monosiphonic and the former has a single accompanying tube at its basal part. Both have an undivided basal part with eight or nine frontal nematothecae, followed by a rhomboid prosegment with one nematotheca ( Fig. 7A ). Then the stems have the hydrocladia, resting on the alternating cauline apophyses. There is a single nematotheca between them.

Ecology and distribution. This is a eurybathic species, collected at depths from 5 and 1800 m ( Ansín Agís et al. 2001); present material between 210 and 1390 m.

Widely distributed in the Atlantic (Vervoort 2006). See Ansín Agís et al. (2001) for a comprehensive revision of the Atlantic records. Present material from the Rockall Trough and Porcupine Seabight.

Figures

FIGURE 7. Lytocarpia myriophylum (Linnaeus, 1758): A, rhomboid prosegment with nematotheca; B, hydrocladial apophysis and nematothecae; C, fragment of hydrocladium showing hydrothecal arrangement; D – E, hydrothecae; F, distal part of hydrotheca showing cusps of hydrothecal aperture. Scale bars: 200 µm (A, C, E), 100 µm (B, D, F).