Probathylepadidae

Family Probathylepadidae fam. nov.

Diagnosis. Capitulum with 30 plates, including 8 primary plates (rostrum, carina, paired scuta, terga and latera) and 2 distinct whorls of supplementary imbricating plates, each whorl with 11 plates. Peduncle smooth, shorter than capitulum, without scales. Cirrus II shorter than remaining cirri, anterior ramus shorter, thicker than posterior ramus, posterior ramus long, fine; basal part of cirrus VI without caudal appendage.

Remarks. Although only a single specimen was collected, it is reasonably recognizable as a new family due to its obvious morphological differences from other known scalpelliforms. Probathylepadidae fam. nov. is similar to other recent scalpelliform families, such as the Calanticidae Zevina, 1978 and the Lithotryidae Gruvel, 1905, but its naked peduncle and its capitulum with two whorls of 22 supplementary imbricating plates easily distinguishes it. Although Smilium zancleanum (Seguenza, 1876) also has a peduncle without scales, its capitulum bears 10 primary plates and supplementary imbricating plates are lacking (Zevina 1981). The scalpelliform family Eolepadidae is only found in hydrothermal vent areas. The new family differs from the Eolepadidae by the capitulum having imbricating supplementary plates and the naked peduncle; by the anterior ramus of cirrus II being thicker and shorter than the posterior ramus; and each of the intermediate segments of cirri III–VI having 2–3 pairs setae only; and by the lack of caudal appendages associated with the basal part of cirrus VI (Newman 1979; Jones 1993; Buckeridge 2000, 2009; Southward & Jones 2003; Yamaguchi et al. 2004; Southward 2005).

The new specimen occurred at a hydrothermal vent together with the sessile Neoverruca intermedia Sha & Ren, 2015, a primitive living member of the suborder Verrucomorpha of the order Sessilia. Some characters of the new family are similar to Neoverruca Schumacher, 1817. For example, the inner surface of the scutum has a longitudinal ridge, and there are similarities of the soft body, mouth, cirri, etc. The new family is also similar to another member of the Sessilia, the primitive living Neobrachylepas relica Newman & Yamaguchi, 1995, of the suborder Brachylepadomorph (Newman & Yamaguchi, 1995). For example, the capitulum bears paired scuta, terga and latera, a single rostrum and carina plus whorls of small imbricating supplementary plates, and there are similarities of the soft body, mouth, morphology of cirri I and II, etc.

The relationship between the new family and the Verrucomorpha and the Brachylepadomorpha appears to be very close and thus the systematic position and evolutionary position of the new family may have important significance (Newman & Yamaguchi 1995). However, phylogenetic relationships between major lineages of the Thoracica can only be further discussed when additional specimens of the new family are found and evidence from their molecular analysis considered.

Etymology. The name of the new family: Pro from the Latin prefix for former and bathy referring to deep waters, in combination with Lepas.