Sertularella peculiaris ( Leloup, 1935 )

Galea, Horia R., 2008, On a collection of shallow-water hydroids (Cnidaria: Hydrozoa) from Guadeloupe and Les Saintes, French Lesser Antilles, Zootaxa 1878, pp. 1-54 : 31-34

Sertularella peculiaris ( Leloup, 1935)

(fig. 6A–E, table 12)

Thyroscyphus intermedius f. peculiaris Leloup, 1935: 33 , figs 15–17.

not Thyroscyphus intermedius Congdon, 1907: 482 , figs 33–36 [= Symmetroscyphus intermedius ( Congdon, 1907) ]. Sertularella peculiaris Leloup, 1974: 34 , footnote 1.

Sertularella parvula — Vervoort, 1968: 46, fig. 22.—? Vervoort, 1972: 131, fig. 41B–C. not Calamphora parvula Allman, 1888: 29 , pl. 10 figs 3, 3A.

Sertularella conica — Calder, 1983: 11, fig. 4.— Calder, 1991d: 99, fig. 52.— Migotto, 1996: 67, fig. 12J–K. not Sertularella conica Allman, 1877: 21 , pl. 15 figs 6–7.

Material examined. Stn. 2: 22.01.2008 —several small, fertile colonies, on algae; 26.01.2008 —several sterile colonies, on algae. Stn. 3: 01.04.2008 —several small, sterile colonies with both stolonal and erect growth forms, on concretions and algae. Stn. 7: 25.03.2008 —several small, sterile colonies, on Dictyota sp. and other algae; 27.03.2008 —several colonies, with both stolonal and erect growth forms, some with gonothecae, on Halimeda sp. and other algae ( MHNG INVE 60981).

Type locality. Bonaire Island, Netherlands Antilles, Caribbean Sea [Leloup’s (1935) station 27].

Description. Colonies mostly stolonal, occasionally bearing a few erect, sparingly branched stems. Stolonal form with both hydrothecae and gonothecae arising at more or less regular intervals from linear hydrorhiza creeping on algae. Hydrothecae borne on short, slightly undulated pedicels, both separated by a relatively thick diaphragm (the hydrothecal base). Erect form slender, geniculate, with stems of up to 13 hydrothecae. Side branches arising below stem hydrothecae, the latter becoming axillar. Internodes of variable length, delimited by nearly imperceptible oblique nodes; perisarc slightly undulated to smooth. Hydrothecae alternate; bilaterally symmetrical in both stolonal and erect forms; flask-shaped, adnate for one third or less their length; widest basally, narrowing towards aperture, margin flaring; walls provided with 6–8 transverse ridges completely encircling the theca. Margin rhomboidal with rounded corners; with 4 triangular, pointed cusps separated by 4 shallow, rounded embayments. Operculum composed of 4 triangular flaps forming a shallow roof. Five large, conspicuous, intrathecal cusps present just below the aperture: one abcauline, 2 latero-abcauline, and 2 latero-adcauline; easily seen through the hydrothecal wall, exact position best visible in apical view of aperture; cusps protruding at about one third inside lumen of hydrotheca. Gonotheca (male=female?) arising from stolon via short pedicel; elongated-ovoid, with 7–8 transverse ridges; a short neck below aperture, the latter surrounded by 3–4 small, rounded, apical projections.

Remarks. The present material is identical in every respect with that described and figured by Leloup (1935) as Thyroscyphus intermedius f. peculiaris from Bonaire Island, southern Caribbean. Later on, Leloup (1974) recognized important differences with Congdon’s (1907) species (presently known as Symmetroscyphus intermedius ), and gave his specimens the new name Sertularella peculiaris .

Sertularella peculiaris shares some features with S. robusta Coughtrey, 1876 , as follows: 1) colonies with both stolonal and erect growth forms; 2) stems always monosiphonic; 3) hydrothecae flask-shaped, with slightly swollen basal part, narrowing distally, rim slightly everted; walls provided with a number of external ribs; several internal projections of perisarc below aperture; 4) gonothecae elongated-ovoid; walls with a number of external folds; aperture encircled by projections of perisarc.

Two important differences allow the separation of both species, as follows: 1) the hydrothecae of S. peculiaris possess 5 conspicuous, internal projections of perisarc below the aperture, whilst only 3 (one abcauline and two lateral) are normally found in S. robusta ; 2) the gonothecal opening of the former possesses 3 or 4 small, rounded perisarcal projections, whilst the latter has 4 prominent spines. The number of external ribs on both hydrotheca and gonotheca of S. robusta is a variable character (see Galea, 2007) and has no taxonomic value.

A hydroid strikingly resembling S. peculiaris was described by Vervoort (1968) under Sertularella parvula ( Allman, 1888) . His material originated from St. Thomas ( British Virgin Islands, northeastern Caribbean) and was rather scarce, but fortunately contained three hydrothecae and a gonotheca, all arising directly from the stolon. Vervoort (1968) found his material in perfect agreement with that of Leloup (1935) but, however, synonymized it with Allman’s species, most probably due to its stolonal condition.

Later on, Vervoort (1972) described a similar hydroid with stolonal habit from the Strait of Magellan. Though considering his material as being conspecific with Leloup’s (1935) hydroid, he assigned it again to Allman’s species. Because the South-American material was sterile and had hydrothecae with variably developed internal projections of perisarc ( Vervoort 1972), it is here thought to be different from the Caribbean specimens. Vervoort’s hydroid might be a variant of S. robusta , a hydroid abundantly found along the coast of southern Chile ( Galea 2007); it was present on the same substrate, Symplectoscyphus subdichotomus ( Kirchenpauer, 1884) as the material described by Galea (2007). However, in possessing 5 internal hydrothecal cusps, instead of 3, it does not match the current concept of S. robusta .

Although Calamphora parvula Allman (1888) may superficially resemble the material studied by Vervoort (1968, 1972), there are some arguments supporting their separation: 1) both the hydrothecae and gonothecae of C. parvula have a greater number (10–12) of closely-set, “annular ridges” (see Allman 1888, p. 29 and pl. 10 fig. 3A) than Vervoort’s specimens; 2) no internal perisarcal projections have been described in the hydrothecae of C. parvula , although this feature may not have been considered as of any taxonomical importance by Allman; 3) the gonotheca of C. parvula has 4 large, prominent marginal projections of perisarc around its aperture; 4) Allman’s species originated from the Bass Strait, Australia, a quite remote locality compared with that from which Vervoort’s material was found. Therefore, I consider at least Vervoort’s (1968) material as being conspecific with S. peculiaris .

Additionally, the present specimens of S. peculiaris from Guadeloupe very much resemble the hydroids from Bermuda and Brazil described by Calder (1991d) and Migotto (1996), respectively, under Sertularella conica Allman, 1877 . The hydrothecae of both specimens exhibit the characteristic 5 large, intrathecal cusps below the rim of hydrotheca. Moreover, the general shapes and dimensions of both hydrotheca and gonotheca fit those observed in S. peculiaris (see table 12).

TABLE 12. Measurements of Sertularella peculiaris ( Leloup, 1935) , in µm. (1)The dimensions given by Leloup (1935) are obviously erroneous and should be read as given below. (2)Dimensions calculated from fig. 12J. (3)The length of the abcauline wall is here considered as an approximation of the height of hydrotheca.

The description of S. conica given by Allman (1877) is very succinct and was based on sterile material. The main typical features of his species are: the long stem internodes; the flask-shaped hydrothecae, narrowing from base to margin; the rather straight free adcauline wall, with several slightly-marked folds on its surface. There is no mention of the presence of internal cusps below the hydrothecal aperture. Therefore, the features listed above are very insufficient to allow a positive identification of the species. Sertularella conica shares, for example, more morphological similarities with the trophosome of S. unituba ( Calder, 1991d) than with the specimens described by Calder (1991d) and Migotto (1996) under Allman’s species. Sertularella conica should be regarded as an unrecognizable species, pending the discovery of additional, fertile material from the type locality. In my opinion, both Calder’s and Migotto’s specimens undoubtely belong to S. pecu-