Hydroids (Cnidaria, Hydrozoa) from the Vema and Valdivia seamounts (SE Atlantic) Author Gil, Marta FFF187EB-84CE-4A54-9A01-4E4326B5CD26 Vigo - Centro de Investigación Mariña, Facultade de Ciencias do Mar, Universidade de Vigo, Spain. & Instituto Español de Oceanografía, Centro Oceanográfico de Vigo, Spain. martag@uvigo.es Author Ramil, Fran 67BAF0B6-E4D5-4A2D-8C03-D2D40D522196 Vigo - Centro de Investigación Mariña, Facultade de Ciencias do Mar, Universidade de Vigo, Spain. framil@uvigo.es text European Journal of Taxonomy 2021 2021-07-07 758 49 96 http://dx.doi.org/10.5852/ejt.2021.758.1425 journal article 5506 10.5852/ejt.2021.758.1425 604af154-8d8e-4fa4-8492-44181607a659 2118-9773 5088125 7CA6D8AC-2312-47F9-8C17-528B94E4C8A7 Monostaechoides providentiae ( Jarvis, 1922 ) gen. et comb. nov. Figs 5–6 , 7A–B ; Table 11 Plumularia providentiae Jarvis, 1922: 347–348 , pl. 26 fig. 21. Antennella quadriaurita – Millard 1966: 492–493 . — Calder 1997: 27–29 , fig. 6 (not Antennella quadriaurita Ritchie, 1909 ). Material examined SOUTH ATLANTIC OCEAN • 3 colonies , 19–23 mm high, on sponge (1 with gonothecae); Vema Seamount , stn PT4; 31°39′43″–31°38′10″ S, 8°22′37″–8°23′42″ E; 50–108 m depth ; 31 Jan. 2015 ; SEAFO-2015 leg.; SEAFO-2015-40063 , LZM-UV slide R. 576 • 4 colonies , 5–7 mm high (1 colony, growing on algae, with gonothecae); Vema Seamount , stn BT5; 31°37′16″–31°36′58″ S, 8°22′37″– 8°23′06″ E; 71–94 m depth ; 31 Jan. 2015 ; SEAFO-2015 leg.; SEAFO-2015-40227 , SEAFO-2015-40497 , SEAFO-2015-40768 , LZM-UV slide R. 581 . Description Hydrorhiza composed of a cluster of perisarcal tubes covered by a sponge growing on old gorgonian axis. In some cases, isolated hydrocladia are born directly on the hydrorhiza but, in most cases, several monosiphonic primary hydrocladia arise in tufts from a short, polysiphonic axis composed by several entangled stolons protruding from the sponge. The basal part of the primary hydrocladium is composed of one to five internodes separated by straight nodes, provided with a variable number of scattered nematothecae separated from the remainder of hydrocladium by an oblique node. This part is formed by a regular succession of hydrothecate and ahydrothecate internodes, delimited by alternating oblique and straight nodes; hydrothecate internodes with proximally oblique and distally straight nodes; ahydrothecate internodes with a reversed position of nodes ( Figs 5E , 6C , 7B ). Almost all primary hydrocladia carry lateral ramifications randomly disposed, always originating from their posterior side. In most cases, the subsidiary hydrocladia arise from the distal end of ahydrothecate internodes, just on the back side of the oblique nodes within the heteromerous part of the colony ( Fig. 6A ); occasionally, some ramifications are found on the basal part of primary hydrocladia ( Figs 5F–G , 7A ). All subsidiary hydrocladia (i.e., of the second, third and even fourth order) are born on small apophyses and are composed of a basal ahydrothecate internode of varied length carrying between one and four nematothecae ( Figs 6A, D , 7A ), followed by a regular succession of hydrothecate and ahydrothecate internodes with the same structure as the primary hydrocladia. Usually, all subsidiary hydrocladia originating from the same hydrocladium are directed to the same side in a linear succession, but irregularities also occur. Hydrothecate internodes with one hydrotheca and five nematothecae: one mesial inferior and two pairs of laterals. Hydrotheca cup-shaped, widening towards rim; adcauline wall adnate for about half its length; abcauline wall straight; hydrothecal rim circular, even and slightly everted. Mesial nematothecae not reaching hydrothecal base. Two pairs of lateral nematothecae; first pair borne on well-developed apophyses adpressed to the hydrothecal wall, and as long as the nematothecae proper, the latter reaching the hydrothecal rim; second pair small, inserted on bases of apophyses ( Fig. 5D ). Ahydrothecate internodes usually with two frontal nematothecae in a row, although the number may vary between one and three. All nematothecae bithalamic, movable and conical, with adcauline wall of distal chamber scooped. Colonies monoecious; gonothecae of both sexes found on same hydrocladia, arising from below the hydrothecal bases, just above the mesial nematothecae ( Figs 6A–B , 7B ). Male gonotheca small, sackshaped, with small and circular aperture located at the rounded top, basal part slightly curved and carrying one nematotheca, and narrowing into a short pedicel composed of one internode. Female gonotheca Fig. 5. Monostaechoides providentiae ( Jarvis, 1922 ) gen. et comb. nov. , stn PT4. A–C . Three distinct colonies showing their distinctive ramification. D . Detail of hydrotheca, frontal view. E . Detail of hydrocladia with hydrothecae, lateral view. F–G . Details of the basal part of several hydrocladia. Fig. 6. Monostaechoides providentiae ( Jarvis, 1922 ) gen. et comb. nov. , stn PT4. A . Part of colony with hydrocladia, and male and female gonothecae. B . Detail of hydrocladia with hydrothecae and two female gonothecae, lateral view. C . Part of hydrocladia, lateral view. D . Portion of hydrocladia with two consecutives ramifications. Fig. 7. A–B . Monostaechoides providentiae ( Jarvis, 1922 ) gen. et comb. nov. A . Stn PT4, detail of basal part of hydrocladia. B . Stn BT5, part of hydrocladium with hydrothecae and a male gonotheca. C–D . Monotheca bergstadi sp. nov. C . Hydrocladia ramified and with gonothecae. D . Detail of hydrotheca, lateral view. Table 11. Measurements of Monostaechoides providentiae ( Jarvis, 1922 ) , in µm.
SEAFO-2015 Stn PT4 Antennella quadriaurita ( Calder, 1997 )
Length hydrothecate internodes 400–470 294–820
length ahydrothecate internodes 300–370 168–503
diameter at node 60–80 –
Hydrotheca, length abcauline wall 200–260 163–256
length free part adcauline wall 120–170 –
diameter at rim 210–260 140–168
Male gonotheca, length 415–475 –
max diameter 140–180 –
length pedicel 50–60 –
Female gonothecae, length 630–750 515
max. diameter 270–390 195
length pedicel 90–160 80
pear-shaped, rather curved, with a distal, slightly tilted, circular aperture, closed by lid; basally provided with two nematothecae and narrowing into a two-segmented pedicel. Variability In some hydrocladia, the regeneration processes when ahydrothecate internodes are damaged result in two ahydrothecate internodes, each one with one or two nematothecae, between two consecutive hydrothecate internodes. We have also observed a subsidiary hydrocladium originating from the back side of a hydrothecate internode ( Fig. 6D ), but this type of ramification is exceptional and probably related to regeneration processes. Remarks Our material agrees with the main features described by Jarvis (1922) as Plumularia providentiae . In both cases the colonies are ramified, with the subsidiary hydrocladia originating from the back side of a true axis (or hydrocladia) shifted on to one side, but that does not adopt the shape of a scorpioid sympodium. Moreover, the morphology of hydrothecae and the number and arrangement of the nematothecae are also similar. The main difference is found in the presence, in our colonies, of subsidiary hydrocladia originating from the basal part of some primary hydrocladia; however, this is an occasional feature and not the norm. Moreover, Jarvis (1922) described P. providentiae with homomerously segmented hydrocladia, but in our colonies the segmentation is heteromerous. Nevertheless, the existence of intermediate ahydrothecate internodes is clearly visible only in subsidiary and younger hydrocladia. In older parts of the colony, and mainly in primary hydrocladia, the perisarc of the wall is thick, masking the heteromerous segmentation. In our opinion, these differences do not justify the description of a new species and, therefore, we identify our material as Monostaechoides providentiae ( Jarvis, 1922 ) gen. et comb. nov. In addition, the material described from the Vema Seamount by Millard (1966) as Antennella quadriaurita ( Ritchie, 1909 ) , with hydrocladia clustered together basally and ramified following the same pattern as our colonies, also belongs to this species. Colonies found in Bermuda with a similar morphology and with the same ramification pattern were described by Calder (1997) as A. quadriaurita (see Calder 1997: 28 , fig. 6a). That material, excluded from A. quadriaurita by Galea & Ferry (2015) , is also included here in M. providentiae gen. et comb. nov. Differences between M. providentiae gen. et comb. nov. and M. bertoti gen. et comb. nov. were discussed by Galea & Ferry (2015) , and refer to the ramification pattern, with hydrocladia more or less alternately arranged in M. bertoti gen. et comb. nov. , and a different number of nematothecae on both cauline and cladial internodes. Distribution This species has been reported from Providence Atoll, the Seychelles ( Jarvis 1922 , as Plumularia providentiae ), Vema Seamount ( Millard 1966 ; Berrisford 1969 , both as A. quadriaurita ) and Bermuda ( Calder 1997 , as A. quadriaurita ) in depths from 42 to 85 m .