Eusynstyela ordinata ( Monniot C. 1983 )

Monniot, Françoise, 2018, Ascidians collected during the Madibenthos expedition in Martinique: 2. Stolidobranchia, Styelidae, Zootaxa 4410 (2), pp. 291-318 : 293-294

Eusynstyela ordinata ( Monniot C. 1983)

Figs 1–2 .

Stations : AB 62; AB 157; AB 159; AB 169; AB 197; AB 301; AB 400; AD 224; AD 257; AR 100; AR 101; AR 116; AS 96. ( MNHN S1 EUS 51).

Described from Guadeloupe E. ordinata is now recorded in Martinique. Either isolated or in colonies the zooids are strongly attached on hard substrates as dead corals, shells or other ascidians. They have a deep red tunic and the colour remains but darker in formalin ( Fig 1A ). The zooid shape resembles “fried eggs” as the thick dorsal tunic of the body expands laterally and become a thin sheet spread on the support, colourless and firmly stuck to the irregularities of the substrate and difficult to remove without damage. The siphons are well apart with 6 lobes slightly protruding and luminescent internal pigment. The tunic lining the siphons has a honeycomb structure. The body wall is dorsally opaque, red on the siphons and yellowish or brown elsewhere. On the ventral side the body wall is colourless, transparent and very thin ( Fig. 1B ). No musculature could be seen. The oral tentacles are in two orders of size ( Fig. 2A ). The prepharyngeal space is wide without papillae. The dorsal tubercle opens in a simple hole. The branchial sac has 4 high folds on each side ( Fig. 2C ), the number of longitudinal vessels being variable according to the zooid size and sexual maturity. The gut is located posteriorly in the body and occupies a small part of the atrial cavity ( Fig. 1B ). The stomach is oval with about 10 longitudinal folds and has a round caecum. The intestinal loop is short, closed. Numerous endocarps are distributed on the whole internal layer of the body wall. The gonads are absent in most specimens. When present they form irregular but long lines on each body side at some distance from the endostyle. When immature they protrude at the internal side of the body wall, but when mature the polycarps are each embedded in a closed pouch of the body wall and only the gonoducts open into the atrial cavity. The polycarps are round with 2 testis lobes tightly applied on the small ovary ( Fig. 2B ). There is no thick ventral bundle of the body wall between or along the gonad lines as can be found in the genus Seriocarpa .

The specimens collected from Martinique have all characters as described and figured for E. ordinata by Monniot C. (1983) from Guadeloupe. This species has not been recorded elsewhere and is certainly endemic in the Caribbean area.

The systematic attribution to the genus Eusynstyela instead of Seriocarpa ( Diehl 1969) was already discussed in Monniot C. (1983) (who initially listed it as a subspecies of Polyandrocarpa but later ( Monniot C. 1991) elevated it to genus level). Both Seriocarpa and Eusynstyela have the same anatomy and only differ by the presence in Seriocarpa of a thickening of the tunic in a bulge containing the gonads. E. ordinata differs from E. tincta to which it is closely allied by the tunic structure and colour and by the gut with an elongated stomach. E. tincta may also have the polycarps invaginated into the body wall (Van Name 1945).

Figures

FIGURE 1. Eusynstyela ordinata. A, colony, scale bar = 1cm. B, ventral side of a zooid.

FIGURE2. Eusynstyela ordinata stained.A, oral siphon,scale bar = 1mm. B, polycarps, scalebar 0.5mm. C, branchial tissue.