Generalized Carinoma larva in lateral view with single intra-epidermal eye anterior to the mouth.
Carinoma spp.
Larvae of the genus Carinoma are recognizable by their single intra-epidermal eye which is ventral and usually just anterior to the mouth (Norenburg and Stricker 2002; Maslakova et al. 2004a, b). Lateral cirri in the anterior body region have also been observed in Carinoma larvae (C. tremaphoros, Norenburg and Stricker 2002). The early development of Carinoma tremaphorus has been described (Maslakova et al. 2004a, 2004b). Carinoma mutabilis is the only Carinoma species reported between central CA to OR. However, we have found that there are actually five species on the southern OR coast alone, all species who's larvae we've collected and identified.
The four larval types of Carinoma species collected in southern OR. The larvae of Carinoma mutabilis, C. hamanako, C. sp. "5" are all species-specific. However, the larvae of C. sp. "yellowback" and C. sp. "white" are difficult to differentiate, but are both orange in color (right). All larva described below. Scale bars 100 µm.
Carinoma mutabilis larva collected in February 2013 in lateral view (left) and dorsal view (middle and right). Note mid-ventral eye and mouth (left) and lateral cirri that are both stiff and flapping (right). Scale bar 100 µm.
Months collected: Feb
Carinoma mutabilis
Sequence Data: 16S, COI
The larvae of Carinoma mutabilis have a small triangular eye. As is true for other Carinoma larvae (e.g. C. tremaphoros, Norenburg and Stricker 2002), C. mutabilis larvae have several lateral cirri in the anterior region of the body. The cirri are not bilaterally symmetrical and some are stiff and extend outward while others flutter like flames (above right). The larval anterior is rather blunt and possess a small cirrus (an apical tuft?) and the posterior tapers, terminating with an inconspicuous posterior cirrus. The larvae are distinct from other Carinoma larvae by their deep blue body color, which can be most prominent in anterior and posterior regions. The size of palaeonemertean larvae varies considerably as they are known to feed and grow in the plankton. In Charleston, OR, C. mutabilis larvae we collected in February 2013 were approximately 500–650 µm in length. In Friday Harbor, WA ripe adults were collected between Jan and Feb 2007 (Bartolomaeus et al. 2014) and Coe reported sexually mature individuals in Aug (California and Puget Sound, 1901; 1905), but we have yet to observe ripe adult C. mutabilis on the southern OR coast.
Larva of Carinoma hamanako collected October 2013 in lateral (left) dorsal (middle) and ventral (right) view. Scale bar 100 µm.
Months collected: Feb, May, July, Oct
Carinoma hamanako
Sequence Data: 16S, COI
This is an example of a larva found in plankton samples from southern OR that likely belongs to a species described from another geographic region and was previously unknown to the NE Pacific. Carinoma hamanako is a species described from Lake Hamana on the Pacific coast of Honshu, Japan in 2011 (Kajihara et al. 2011). Although, we have yet to find the adults along the NE Pacific coast, we have found larvae in the plankton, which we believe are the larvae of C. hamanako.
The larvae are easily recognizable as Carinoma larvae, with large and round mid-ventral eye. But, these larvae are distinct from other Carinoma larvae in possessing two prominent transverse bands of color, one near the mouth and the other in the posterior body region. They also have a patch of darker color at the mid anterior most region and a cirrus at the larval posterior. We have collected one young C. hamanako larva, which did not yet possess bands. Instead, the specimen had an eye and distinct, long lateral cirri in the body region anterior to the mouth. Advanced larvae have a large mouth and proboscis and tend to rotate between the coverslip and microscope slide such that the mouth is down.
Uncertain Identity
As mentioned in our methods section, matching larvae to adults using DNA sequence data is usually relatively straightforward because the sequences match so closely. In fact, unless mentioned otherwise all larvae identified with sequence data on this website show sequence divergences of <1% from their corresponding adults (for both 16S and COI gene regions). The larvae of C. hamanako shown here exhibit a sequence divergence of 1.7% and 8.7% from adult sequences for C. hamanako, for the 16S and COI gene regions, respectively. Although, this remains under the average interspecific sequence divergence for congeneric nemertean species (3–5% for 16S, Mahon et al. 20; Meyer and Paulay 2005; Hiebert and Maslakova, unpublished and 19.6% for COI, Kvist et al. 2014), it remains higher than we typically see for species level larval identification. We frequently find these larvae in the plankton and we are confident that the adults live nearby, but their species level identity is currently uncertain. Whether these are the larvae of C. hamanako or another closely related Carinoma species remains to be seen.
Larva of Carinoma hamanako collected in July 2013. Dorsal view, note proboscis at anterior and posterior cirrus, lateral view where single intra-epidermal eye is present anterior to mouth and ventral view where eye is in focus (left to right). Scale 100µm.
The larva of the fifth Carinoma species found in southern OR collected March 2013. Larval anterior and posterior are pointed and coiled proboscis is visible in dorsal view (left), mid-ventral eye is small (middle) and lateral cirri are not stiff (right). Scale bar 100 µm.
Months collected: March
Carinoma sp. 5
Sequence Data: 16S, COI
We have found or observed the adults of all locally collected Carinoma larvae – except this one. This is an example of a larva which belongs to yet another Carinoma species, but this one we have yet to find as a benthic adult. Our 16S and COI phylogenies both situate this larva nested within the genus Carinoma and it exhibits characteristics of Carinoma larvae.
We have encountered just one larva of this species,, which has a small mid-ventral eye, is brown in color and rather pointed at anterior and posterior ends. This specimen has lateral cirri, as is common for larvae of this genus. They are situated equatorially and anterior to the mouth and are quite long (as seen in Carinoma sp. “white” and “yellow back”, below) and we detected two cirri on the left side (above right). The larval posterior has a distinct yet small cirrus and this specimen was equipped with a very developed and coiled proboscis (above left).
The similar larvae of Carinoma sp. "yellowback" (left) and C. sp. "white" (right). Scale 100 µm.
Carinoma sp. "white" and "yellowback"
There are two different species of Carinoma that produce larvae with distinctive orange color, both species are awaiting formal description, Carinoma sp. "yellowback" and Carinoma sp. "white". Interestingly, the adults exhibit species-specific characters, but the larvae are (thus far) indistinguishable. The sequence divergence between these two species is 16.5% (16S) and 17.4% (COI).
Larva of Carinoma sp. "white" collected in February 2013, note long ventral and dorsal cirri anterior to mouth (left) and large eye, mouth and proboscis anterior to mouth in lateral view (right). Scale bars 100 µm.
Months collected: Feb
Carinoma sp. "white"
Sequence Data: 16S, COI
This is an example of a larva that belongs to a currently undescribed species which we find as adults intertidally in Charleston, OR, near the OIMB and to which we refer as Carinoma sp. “white”. As the name suggests, this species exhibits relatively simple adult morphology and a pale color. The larvae, on the other hand, are recognizable by their bright orange color and are, so far, unrecognizable from Carinoma sp. “yellow back”. Their mid-ventral eye is rather large and rounded. Besides the orange body color, the mid-anterior most region is additionally orange in color and rather bulbous in proportion to the rest of the body. The larvae have anterior lateral cirri, one pair exists dorsally and ventrally across from one another and are quite long (above left). Most individuals we encountered in February had very large mouths and advanced proboscis development. The posterior end tapers in all individuals and is marked with a small cirrus (above right).
Larvae of Carinoma sp. "yellowback" collected in March 2013 (left two images) and very long 'juvenile' collected in a plankton sample in October 2014 (right two images). Scale bars 100 µm.
Months collected: March, Oct
Carinoma sp. "yellowback"
Sequence Data: 16S, COI
The larva of Carinoma sp. "yellowback" are also distinctly orange in color. We have found the larva of this species in plankton samples from March 2013 and October 2014. In October, we collected a large specimen that was actively swimming in the plankton, suggesting it had not yet settled into a benthic and juvenile existence. This long larva (1.5 cm in length) was orange in color with characteristic Carinoma eye.