Hincksella pusilla (Ritchie, 1910)

Castro Mendonça, Luana M., Parisotto Guimarães, Carmen R. & Haddad, Maria A., 2022, Taxonomy and diversity of hydroids (Cnidaria: Hydrozoa) of Sergipe, Northeast Brazil, Zoologia (e 21032) 39, pp. 1-65 : 29-30

Hincksella pusilla (Ritchie, 1910)

Fig. 14C–D

Synonyms available from: Galea (2010).

Sertularella cylindrica var. pusilla Ritchie, 1910: 817 , pl. 77, fig. 9. Hincksella cylindrica . – Galea, 2010: 20, figs 5N-P (synonymy)

(not Sertularella cylindrica Bale, 1888: 765 , pl. 16, fig. 7.

Description: Colonies erect, up to 10.4 mm high, arising from a creeping hydrorhiza. Stem monosiphonic, unbranched, divided into internodes by slightly oblique nodes. The first internode ahydrothecate, with an indistinct node, separates it from the others. Remaining internodes with hydrothecae. Hydrothecae tubular, 0.36–0.47 mm high, 0.11–0.18 mm wide at the margin, arising from the distal portion of the internodes, adnate to the internode for about one-third of its length, free portion curved slightly to outside. Adcaulinar hydrothecal wall slightly convex and abcaulinar straight, except the base. Margin smooth, aperture rounded, without operculum.

Material examined: PCS – two infertile colonies from the rainy season. CZUFS CNI-00038.

Stations: PCS – 4, 5, 12.

Bottom: sand.

Distributon: Brazil – Alagoas (Maximiliano M. Maronna unpub. data), Bahia ( Grohmann et al. 2003), Rio de Janeiro ( Miranda et al. 2015), and Santa Catarina ( Bouzon et al. 2012). World distribution – circumglobal with records from Atlantic, Pacific, and Indian Oceans ( Calder 1991).

Taxonomic remarks: Galea and Ferry (2015) present a discussion in respect to the distinction between Hincksella cylindrica var. pusilla and H. cylindrica sensu Preker and Lawn (2010) , both distinguished by the proportion of hydrothecae attached to the stem, the first having from 1/3 to 1/4 of their length attached and the second at least half of its length. The authors also mentioned that those differences could be enough to raise the variety pusilla to species status. Even if H. pusilla is not already recognized as valid in WoRMS (2022), the morphology found in specimens from Sergipe matches the description and illustrations of H. cylindrica var. pusilla presented by Vervoort (1959, p. 245-247, figures 18, 19a), Millard (1975, p. 232-234, figure 76B-E), and Galea and Ferry (2015, p. 236, figure 6H, I).

Remarks: Found colonizing algae, Bryozoa, and the hydroids Sertularelloides cylindritheca , and Thyroscyphus marginatus .

Synthecium tubithecum ( Allman, 1877) Fig. 14E–G

Synonyms available from: Galea (2010).

Sertularia tubitheca Allman, 1877: 24 , pl. 16, fig. 5, 6.

Synthecium tubithecum Vannucci, 1950: 86 , pl. 1, fig. 4, Vannucci, 1951b: 83, Maÿal, 1983: 5, fig. 1, 2.

Description: Colonies erect, up to 2.4 cm high, arising from a creeping hydrorhiza. Stem monosiphonic, straight, divided into internodes of variable length, separated by indistinct nodes. Cauline internodes with either a pair of opposite/subopposite hydrothecae or a pair of distal opposite apophysis, each supporting a hydrocladium. Hydrocladium of variable height (6.2–9.2 mm high), arising from the stem at angles of 111–120.6°, unbranched, divided into internodes by transverse nodes, sometimes not visible. Each internode of hydrocladium with a pair of opposite or subopposite hydrothecae. Pairs of hydrothecae of stem and hydrocladium are similar, never touching each other in the inferior or superior region. Hydrothecae tubular, 0.53–0.66 mm high, 0.18–0.24 mm wide, adnate to the stem for more than half of their length, curving abruptly to the exterior in the distal free portion. Adcaulinar hydrothecal wall straight in the adnate portion and convex in the free one, abcaulinar wall slightly convex in the basal portion and concave in the distal one. Hydrothecal margin smooth, generally with renovations, aperture round, without operculum. Male and female colonies found; male gonotheca arising from inside the hydrothecae in the stem and female ones from the stem and the hydrocladia. Male gonothecae elongated, 1.04–1.31 mm high, 0.52–0.58 mm wide, in the form of a cocoon, generally larger in the medial portion, arising from the pedicel inserted in the hydrothecae, perisarc waved in both laterals or waved in the external wall and smooth in the internal one. Female gonothecae small, 0.6–0.79 mm high, 0.64–0.76 mm wide, sac-shaped, wider in the median portion, perisarc with several transverse ribs crossing all their length. The majority of the male and female gonothecae were empty in the material; however, few females had a single egg in the interior. Nematocysts macrobasic mastigophores discharged (34.7–38.1 × 8.4–10.3 µm) in the coenosarc of stem, hydrothecae, hydrocladium, and gonotheca (male and female).

Material examined: PCS – abundant colonies with and without gonothecae (male and female) from the dry and rainy seasons. CZUFS CNI-00145; CNI-00146; CNI-00147.

Stations: PCS – 4, 5, 9, 11, 12, 15, 16, 18.

Bottom: sand, and mud.

Distribution: Brazil – Pernambuco ( Maÿal 1983), Espírito Santo ( Vannucci 1950), and Rio de Janeiro ( Vannucci 1951b, Grohman et al. 2003, Shimabukuro 2007, Miranda et al. 2015). World distribution – widely distributed at Western and Eastern Atlantic ( Calder 1991).

Remarks: A few stems were found attached to substrates, including algae, Bryozoa, and Sertularelloides cylindritheca . Zooxanthellae were found on the stem, hydrocladium, hydrothecae, and gonangia.

Figures

Figure 14. (A-B) Hincksella formosa: (A) general view of a stem showing several hydrocladia with hydrothecae; (B) detail of the stem with a gonotheca (red arrow); (C-D) Hincksella pusilla: (C) general view of the distal part of a stem with hydrothecae; (D) detail of an intersegment with a hydrotheca; (E-G) Synthecium tubithecum: (E) general view of a stem showing stem and hydrothecae; (F) detail of a stem with a pair of hydrothecae bearing two male gonothecae; (G) detail of the stem with a pair of hydrothecae bearing two female gonothecae.