Fig. 38.—Culeolus wyville-thomsoni, Herdman. A, from left side (half-nat. size); B, part of branchial sac. At, Atrial aperture; Br, branchial aperture; br.f, branchial fold; i.l, internal bar; sp, spicules; tr, transverse vessel. (After Herdman.)
Sub-Fam. 3. Bolteninae.—More than eight folds in branchial sac; tentacles compound; body pedunculated (Fig. 38, A). The chief genera are—Boltenia, Savigny, with the branchial aperture four-lobed, and the stigmata normal; and Culeolus, Herdman (Fig. 38), with branchial aperture having less than four lobes, and the stigmata absent or modified (Fig. 38, B), the branchial sac showing a wide mesh-work of vessels stiffened by branched calcareous spicules. Culeolus is a deep-sea genus discovered by the "Challenger" expedition; eight or nine species are now known from various parts of the world, ranging in depth from 630 to 2425 fathoms. Most of the species are from the Pacific; only one from the North Atlantic. The curiously curved type of spicule found in the branchial sac and other organs is shown at Fig. 50, C (p. 87).
Amongst the Cynthiidae are found most varied conditions of the reproductive organs. The gonads are sometimes on both, sometimes on only one side of the body, sometimes in one or several branched masses, and sometimes distributed as a large number of minute "polycarps" over the inner surface of the mantle.
Fig. 39.—Various Cynthiidae. A, two forms of Styelopsis grossularia, Van Ben.; B, Forbesella tessellata, Forb.; C, Polycarpa aurata, Q. and G.; D, Styela clava, Herdman; E, Polycarpa tinctor, Q. and G.; F, Cynthia formosa, Herdman; G, Polycarpa comata, Alder; H, Polycarpa pedata, Herdman; I, Pelonaia corrugata, Forb. and Goods. (After Herdman.)
The family Cynthiidae is the largest section of the Simple Ascidians. The species range from the size of a pea to that of a large cocoa-nut. They are for the most part opaque, and often richly coloured—reds, yellows and rich browns predominating—and so look very different to the grey gelatinous Ascidiidae, and to the sand-encrusted Molgulidae. They extend from between tide-marks (Styelopsis grossularia), down to the abysses (Styela bythia and S. squamosa at 2600 fathoms). Some genera (Styela and the closely related Dendrodoa), extend far into Arctic seas, but many allied forms (Styela and Polycarpa) are also found in the tropics.
Fig. 40.—Three simple Ascidians with vascular adhering processes from the test (nat. size). A, Ascidiella aspersa, O. F. Müller; B, Ciona intestinalis, Linn.; C, Molgula oculata, Forb.
Fig. 41.—Branchial sacs of Molgulidae showing curved stigmata. A, Ascopera gigantea, Herdman; B, Molgula pyriformis, Herdman; C, Eugyra kerguelenensis, Herdman.