Sertularella eleganta, Watson, 2016

Watson, Jeanette E., 2016, Two new species and a new record of hydroids (hydrozoa: hydroidolina) from Port Phillip, Australia, Memoirs of Museum Victoria 75, pp. 1-5 : 1-2

Sertularella eleganta sp. nov.

Figure 1A-F

Material examined. NMV F228240 , holotype, colony initially 5% formalin preserved later transferred to alcohol; fertile colony on rock in crevice 1m deep, coll: J.E.Watson, 22/3/2016. NMV F228241 , microslide malinol mounted, from holotype colony .

Description. Hydrorhiza comprised of narrow stolonal tubes reptant on concrete surface. Colony without definite main stem, branching from base, branches monosiphonic except proximally where some are lightly fascicled from upward-growing stolons which become primary branches. Branches straight, secondary branches given off irregularly from primaries below a hydrotheca at an angle of c. 45°. Branch internodes variable in length, an indistinct oblique node at junction of adnate and free hydrothecal adcauline wall, marked by an indentation and narrowing of perisarc. Proximal internode of secondary branch cylindrical, long to first hydrotheca.

Hydrothecae alternate, tubular, widely separated along branches, set at an angle of 40-50° to internodal axis, walls smooth, narrowing from base to margin. Hydrotheca widest at junction of adnate and free adcauline wall, adnate adcauline wall almost parallel to internodal axis, free adcauline wall slightly concave to straight, ratio of length of adnate to free adcauline wall 1:2, abcauline wall weakly convex to straight. Floor of hydrotheca short, transverse to internode with a small central foramen. Margin delicate with four equidistant cusps with shallow embayments between and four large thin internal submarginal cusps of similar shape and size below margin. Operculum of four very thin flaps. Hydranth too decomposed for description.

Gonothecae borne abundantly along lower to mid sections of branches, inserted singly on a short unsegmented pedicel opposite a hydrotheca, facing obliquely upwards. Body of mature gonotheca elongate oval, variable in length with three to five broad corrugations, obscure proximally becoming more prominent distally, surmounted by a long narrow neck above distalmost deep corrugation, with four equidistant very long, sharp, often inwardly curved apical spines. Gonophores female, some extruded from gonotheca as acrocysts.

Perisarc moderately thin throughout. Colour in life pale yellowish-grey, stolons pale brown.

Remarks. The colony was growing in a sheltered crevice between concrete jetty footings in an oceanic strong currentflow habitat. The delicate flexuous perisarc suggests a deep water species. Many hydrothecae are infested with one or two large crustacean eggs.

The nearest congeners of Sertularella eleganta are Sertularella robusta Coughtrey 1876 and Sertularella natalensis Millard, 1968 . Sertularella . robusta is a very common southern Australian species occurring in the same habitat as Sertularella eleganta in Port Phillip. While similar to S. robusta the hydrothecae of that species are sometimes faintly rugose, and the gonothecae is more ridged and terminal spines are shorter. Colony morphology of S. natalensis differs from S. eleganta in the ratio of fixed:free wall and in striations on the hydrothecae. Although Sertularella is a genus with many species, no others have the same morphological, hydrothecal and gonothecal characters as Sertularella eleganta .

Etymology. The species name refers to the elegantly branched colony.