Polysertularella polyseriata, Antsulevich, Alexander, 2011

Antsulevich, Alexander, 2011, Polysertularella polyseriata, a new genus and species of hydroid (Hydrozoa; Leptothecata; Sertulariidae) from the Sea of Okhotsk, Zootaxa 3107, pp. 59-64 : 60-63

Polysertularella polyseriata sp. nov.

Figs. 1–4

Material. One mature and fertile colony. Holotype: R.V. “Akademik Oparin”, Pacific Ocean, eastern part of the Sea of Okhotsk near middle part of Kuril Islands, coordinates 47о22’N; 152o10’E, collected 1 July 1988 by Eugeny Gruzov, Zool. Inst. of Russian Acad. Sci., St. Petersburg ( ZI RAS); bottom trawl, depth 146 m. Specimen No 11211 in the systematic collection of Department of Porifera & Cnidaria of ZI RAS.

Description. Colony erect, tree-like, irregularly branched, 7.5 cm high ( Fig. 1). Primary common stolon (or primary stem?) consisting of thick tubes, root-like, unplaited at base of common stolon. Tubes anastomosing and densely braided on stolon and sometimes even on proximal parts of secondary stems and (or) primary branches. Bases of secondary stems separated from common stolon by several thick annulations. Hydrocaulus differing from branches only in having thicker perisarc; hydrothecae arranged in eight longitudinal rows on hydrocaulus. Branches bifurcate dichotomously several (up to five) times. Lower branches of older orders (1st and 2nd) more thickened, hydrothecae again arranged in eight rows. Towards distal regions of colony, branches of next orders becoming slightly thinner and with hydrothecae arranged in six and in five rows ( Fig. 2). At tips of distal branches, hydrothecae may occur in four cross-wise rows. Hydrothecal rows very close to one other, but along a given row hydrothecae widely separated, with distance between adjacent ones usually exceeding hydrothecal length. Hydrothecae of three adjacent rows arranged as in “chess cells” (as in many other sertulariids with multi-serial hydrothecae), allowing neighbouring hydranths space for feeding. Hydrothecae normally about 3/4 adnate, distal part always free. Hydrothecae from proximal and distal parts of colony may be slightly unequal in shape; in distal regions of branchlets, hydrothecae may be less adnate – about 2/3. Perisarc of hydrothecae thick, especially on abcauline wall; abcauline wall almost straight to slightly concave, then slightly curved in opposite direction (toward the branch) just below the rim so that entire abcauline wall has very gentle S -shape profile; “distal” hydrothecae usually somewhat more curved than “proximal” ones. Hydrothecal aperture forming an angle of about 45o with branch axis in “distal” hydrothecae, but may be nearly at right angles in “proximal” ones. Hydrothecal aperture square, with rounded corners; rim with four short, equal cusps separated by shallow embayments. The operculum consists of four equal triangular valves, flattened and almost in one plane rather than pyramidal as in most species of Sertularella . The hydranth has 12–16 filiform tentacles; abcauline caecum present ( Figs. 2, 3 ).

Gonothecae on lowest part of shoots only, at base of secondary stems just above annulations; arising in opposite pairs from apertures of tubular hydrotheca-like processes on two sides of stem; equal pairs of gonothecae found only on two shoots of colony. Gonothecae oval, with 6-7 well developed sharp transverse corrugations; distal end with short, thin neck; top of neck with or without apical widening in shape of trumpet; apical spines absent ( Fig. 4 ).

Dimensions (mm): stolon tube diameter 0.21–0.35. Hydrotheca: abcauline wall 0.42–0.56; free part of adcauline wall (in hydrothecae from proximal and medial regions of colony) 0.07–0.08; same for hydrothecae on distal region of colony or branches 0.11–0.15; aperture width 0.20–0.22. Gonotheca: height 2.17–2.31; maximal width 1.47–1.61.

Distribution. The species is known only from the type locality.

Notes. Hydroids of Polysertularella polyseriata demonstrate that multi-serial arrangement of hydrothecae exists amongst sertulariids having opercula with four valves, as well as in those having a different opercular shape. Convergent evolution is thus evident within this family, and the arrangement increases the number of feeding hydranths on a colony. It is likely that other hydroids with multi-serial rows of hydranths exist in Sertulariidae . The arrangement of hydrothecae and hydranths in the form of “chess cells” minimizes overlapping of feeding areas and makes colonial prey capture more effective.

The specific name “ polyseriata ”, an adjective agreeing in gender with the feminine generic name Polysertularella , reflects the main morphological character of the colony structure – multi-serial arrangement of hydrothecae.

I am endebted to Dr. Evgeny Gruzov, a famous Russian investigator of polar oceans and my first teacher of marine biology. This work was undertaken without any financial support.

Figures

FIGURE 3. Polysertularella polyseriata sp. nov. Hydrotheca (2 of the 4 valves shown opened).

FIGURE 4. Polysertularella polyseriata sp. nov. Basic part of the stem with hydrothecae and a pair of gonothecae.