Lineus flavescens species complex
Many of the undescribed species we’ve uncovered in the NE Pacific are cryptic species complexes which are currently lumped under the same name. One example is the species complex consisting of four species, including one described species – Lineus flavescens. Lineus flavescens is a species known from central CA to OR, and we have found the adults intertidally near Coos Bay, OR. Another species which we find frequently as adults is an undescribed species, which we call Lineus sp. "red". The remaining two species in this complex have so far only been found as larvae. The larvae of these four species are indistinguishable: a relatively small episphere, relatively large round lappets and lobes, juvenile occupies a large fraction of the episphere, has two large eyes and lacks caudal cirrus.
The larval morphotype is characterized by a relatively small episphere, and juvenile with two large eyes and without caudal cirrus
Lineus flavescens larva collected November 2013 (left) and newly metamorphosed juvenile (right), collected as a larva in February 2013. Scale bars 100 µm.
Lineus flavescens
Observed in Coos Bay: Jan, Feb, Apr, July, Aug, Oct-Dec
These larvae exhibit the typical pilidium morphology. They are shaped like a hat with earflaps and sometimes the episphere can be proportionally smaller than the lateral lappets. There is often a faint orange hue along the ciliated band in these larvae and the developing juvenile has two eyes which are either red or black. They are common in the plankton and easy to rear to metamorphosis on a diet of Rhodomonas lens. The larva of Lineus flavescens was the first that we identified with DNA sequence data in 2008 (Maslakova 2010b).
Oocytes of L. flavescens obtained in April 2013 (left) and wild-caught larvae collected in January 2013 (middle) and October 2012 (right). Note the orange hue near the larval ciliated band (middle). Scale bars 100 µm.
Lineus sp. "1" larva collected in February at different focal planes. Left focal plane shows ciliated band and right, the juvenile. Scale bar 100 µm.
Young larva of Lineus sp. 1 and metamorphosed juvenile (right), both collected as larvae in February. Scale bars 100 µm.
orphan larvae: Lineus sp. 1
Sequence Data: 16S, COI
Observed in Coos Bay: February
These larvae belong to an undescribed Lineid species, which we currently only find as larvae in the plankton and have yet to find as adults. Although the larvae are difficult to differentiate from L. flavescens, DNA sequence data strongly suggests that these larvae represent another species (6.6 and 12.9 % divergence for 16S and COI, respectively. You'll note that the eyes of the metamorphosed juvenile (above right) appear fused, however this is seen in other closely related species and does not appear to be a distinguishing character.
Larva of another Lineus sp. 2 which was collected in October 2012, two focal planes are shown to emphasize pigment along ciliated band (left) and fully competent juvenile worm (right). Scale 100 µm.
orphan larvae: Lineus sp. 2
Sequence Data: 16S, COI
Observed in Coos Bay: Aug, Oct
This is the larva of another undescribed lineid species, which we currently only find as larvae in the plankton and have yet to find as adults. Although the larvae are difficult to differentiate from L. flavescens, DNA sequence data strongly suggests that these larvae represent another species (14.2 and 18.3 % divergence for 16S and COI, respectively).
Wild-caught pilidium larva of Lineus sp. "red" which was collected in a plankton sample in January 2013. Scale 100 µm.
Lineus sp. "red"
Sequence Data: 16S, COI
Observed in Coos Bay: Jan, Feb
These are the larvae of a common and undescribed species in the NE Pacific, to which we refer as Lineus sp. “red”. Adults are found in intertidal sand and mudflats and the larvae have been found in the plankton in January. Ripe adults were collected in February and the development of this species followed.
These larvae exhibit the typical pilidium morphology and are virtually indistinguishable from the larvae that belong to the Lineus flavescens species complex.
Development of this species is described by Hiebert and Maslakova (2015):
Larval Development of Two N. E. Pacific Pilidiophoran Nemerteans (Heteronemertea; Lineidae). Biological Bulletin 229:3, 265-275
Lineid sp. "red" development from fertilization on 14 February to metamorphosis on 18 May 2012. Scale 100 µm.
The development of Lineus sp. “red” was followed from artificially fertilized gametes in February 2012 and is shown above (Hiebert and Maslakova, in prep). When dissected oocytes are 90 µm in diameter and sperm are of primitive morphology. Early cleaving stages take place roughly once per hour (e.g. two polar bodies present at 2 hr, upper left) and the development proceeds as in other pilidium larvae (e.g. Maslakova 2010a). The later development proceeded more slowly than in other pilidia which may be due to their reproductive season and associated cooler water temperatures. Juvenile discs fused at 26 days, juvenile eyes become apparent at 64 days and metamorphosis occurs at 90 days.